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J^eference  Hibrarp 


Digitized  by  the  Internet  Arciiive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/handbookofphysio1908kirk 


HALLIBURTON'S 
HANDBOOK   OF   PHYSIOLOGY 


KIRKES'    HAND-BOOK    OF    PHYSIOLOGY 


HAND-BOOK 


OF 


PHYSIOLOGY 


By    W.    D.    HALLIBURTON,    M.D. 

LL.D.,   F.R.C.P.,  F.R.S. 

PROFESSOR     OF     PHYSIOLOGY,     KING'S     COLLEGE,     LONDON. 


TWENTY-FIRST    EDITION 
WITH    NEARLY    SEVEN    HUNDRED    ILLUSTRATIONS 

INCLUDING    SOME    COLOURED    PLATES 


PHILADELPHIA  : 

P.    BLAKISTON'S    SON,    &    CO. 

1012    WALNUT    STREET 

1908 

[PrhUed  in  Great  Britain] 


PREFACE 

The  rapid  progress  Physiology  has  made  within  the  last  few  years 
has  necessitated  somewhat  extensive  alterations  in  the  present 
edition.  The  chapters  dealing  with  the  proteins,  blood  coagulation, 
digestion,  absorption,  respiration,  kidney  function,  and  metabolism 
are  almost  entirely  new.  I  am  much  indebted  to  Mr  J.  Barcroft, 
M.A.,  of  King's  College,  Cambridge,  for  his  valued  help  in  re-writing 
many  portions  of  the  book,  especially  those  relating  to  gaseous 
metabolism.  I  have  also  again  to  thank  Dr  C.  S.  Myers,  M.A., 
Professor  of  Psychology  at  King's  College,  London,  for  assistance  in 
revising  the  account  given  of  the  special  senses,  and  to  Professor 
Arthur  Eobinson,  of  the  University  of  Birmingham,  for  similar  help 
in  connection  with  the  subjects  of  generation  and  development.  A 
good  many  new  illustrations  have  been  introduced,  room  having 
been  made  for  them  by  the  omission  of  some  of  the  old  ones.  Some 
of  the  new  tracings  shown  I  owe  to  the  kindness  of  Professor  Sher- 
rington, P.Pi.S.,  of  the  University  of  Liverpool.  Without  the  kind 
co-operation  of  so  many  friends,  it  would  have  been  impossible  for 
me  to  have  brought  out  such  a  complete  revision  of  the  book  within 
the  short  space  of  time  that  has  elapsed  since  the  last  edition  was 
published.  In  spite  of  the  introduction  of  so  much  new  material, 
the  bulk  of  the  volume  has  not  been  materially  increased,  extensive 
excisions  of  what  has  now  become  antiquated  having  also  been  carried 
out.  In  bringing  the  book  up  to  date,  I  have  endeavoured  to 
remember  that  the  main  object  of  the  work  is  to  supply  students 
with  an  elementary  text-book,  although  at  the  same  time  my  aim 
has  been  to  make  it  as  complete  as  possible. 


W.  D.  HALLIBUKTON. 


King's  College,  London . 
1907. 


CONTENTS 


CHAPTER    I 


I\TKODUCTORY 


Definition  of  the  Science  of  Physiology 

Physiological  Methods 

The  Organs,  Tissues,  and  Cells  of  the  Body 

Animal  and  Vegetable  Cells  . 

The  Signs  of  Life 


PAGE 
1 

1 
3 

4 


CHAPTER    II 


The  Animal  Cell 

Protoplasm 

Nucleus 

Attraction  Sphere 

Protoplasmic  Movement 

Cell  Division    . 

The  Ovum       . 


10 
12 
12 
16 
20 


CHAPTER   III 


Epitheliuji             ..... 

22 

Classification  of  Epithelium   . 

22 

Pavement  EpitheUum 

22 

Cubical,  Spheroidal,  and  Columnar  Epithehum 

25 

CUiated  Epithelium    .... 

27 

CUiary  Motion            .... 

29 

Transitional  Epithelium 

30 

Stratified  Epithelium  .... 

31 

Nutrition  of  Epithelium 

33 

Chemistry  of  Epithehum 

33 

VIU 


CONTENTS 


CHAPTER    IV 


PAGE 

The  Connective  Tissies  ..... 

35 

Areolar  Tissue            ..... 

36 

Fibrous  Tissue            ..... 

41 

Elastic  Tissue ....... 

43 

Adipose  Tissue            ..... 

43 

Retiform  Tissue          ..... 

46 

Adenoid  or  Lymphoid  Tissue 

47 

Basement  Membranes            .... 

47 

Jelly-like  Connective  Tissue  .... 

48 

CHAPTER   V 

The  Connective  Tissues — continued       ......         49 

Cartilage          ...... 

49 

Bone    ....... 

54 

Ossification      .             .            . 

59 

Teeth  .            .            .            . 

64 

The  Blood 

76 

CHAPTER   VI 


Muscular  Tissue  . 
Voluntary  Muscle 
Red  Muscles  . 
Cardiac  Muscle 
Plain  Muscle  . 
Development  of  Muscular  Fibres 


78 
79 

87 
87 

87 


Nerve 

Structure  of  Nerves    • 
Terminations  of  Nerves 
Development  of  Nerves 


CHAPTER    VII 


90 
90 
95 
96 


CHAPTER   VIII 


IllUITAlilLITV    AND    CONTRACTILITY 


99 


CHAPTER    IX 

Contraction  of  Muscle — Summary 


105 


CONTENTS 


IX 


CHAPTER    X 

ClIANllK    IN'     l''oit.M    IN    A    MlSCLi;    WHEN'    11'    CoMKAC  IS 

Instruments  used 

Simple  Muscle  Curve. 

The  Muscle- Wave 

KfTect  of  two  Successive  Stimuli 

Effect  of  more  than  two  Stimuli 

Tetanus 

Voluntary  Tetanus     . 


PAOK 

107 
107 
116 

118 
119 
120 
121 
121 


CHAPTER   XI 

Ektensibilitv,   Elasticitv,   and  Work  of  Muscle 


125 


CHAPTER  Xn 

The  Electiucal  Phexojiena  of  Muscle 


133 


CHAPTER   XIII 

Thermal  and  Chemical  Changes  in  Muscle  , 
Fatigue  ..... 

Rigor  ]\Iortis   .  .  .  .  • 

Chemical  Composition  of  Muscle 


147 
150 
153 
154 


CHAPTER  XIV 


Comparison  of  Voluntary  and  Involuntary  Muscle 


158 


CHAPTER   XV 


Physiology  of  Nerve 

Classification  of  Nerves 
Investigation  of  Nerve  Functions 
Degeneration  of  Nerve 
Regeneration  of  Nerve 
Roots  of  the  Spinal  Nerves   . 
Changes  in  Nerve  during  Activity 
Velocity  of  a  Nerve  Impulse. 
Direction  of  a  Nerve  Impulse 
Crossing  of  Nerves 
Chemistry  of  Nervous  Tissues 


161 
161 
164 
164 
166 
168 
171 
172 
173 
178 
175 


CHAPTER   XVI 


Electrotonus 


179 


a    2 


CONTENTS 


CHAPTER    XVII 

Nerve  Centres     ...... 

Structure  of  Nerve-Cells         .... 

The  Significance  of  Nissl's  Granules 

Classification  of  Nerve-Cells  according  to  their  Function 

The  Law  of  Axipetal  Conduction 


PAOE 

190 

192 

200. 

203 

204 


CHAPTER   XVIII 


The  Circulatory  Svste3I 
The  Heart 

Course  of  the  Circulation 
Structure  of  Arteries  , 
Structure  of  ^'eins 
Structure  of  CapUlaries 
Structure  of  Lymphatic  Vessels 


206 
206 
213 
214 
216 
219 
221 


CHAPTER   XIX 

The  Circulation  of  the  Blood 


226 


CHAPTER   XX 


Physiology  of  the  Heart 
The  Cardiac  Cycle 
Action  of  the  Valves  of  the  Heart 
Sounds  of  the  Heart  . 
Coronary  Arteries 
Cardiographs  . 
Intracardiac  Pressiu-e 
Frequency  of  the  Heart's  Action 
Work  of  the  Heart 
Innervation  of  the  Heart 
The  Excised  Heart 


231 

231 
233 
234 
237 
237 
240 
244 
244 
247 
252 


CHAPTER   XXI 


The  Circulation  in  the  Blood-vessels 
Use  of  the  Elasticity  of  the  Vessels 
Blood-pressure 

Velocity  of  the  Blood-flow     . 
The  Time  of  a  Complete  Circulation 
The  Pulse 
The  Capillary  Flow 
The  Venous  Flow 
The  Vaso-motor  Nervous  System 
Plethysmography 
Pathological  Conditions 
Local  Peculiarities  of  the  Circulation 


259 
261 
263 
278 
2S5 
287 
293 
295 
297 
307 
310 
311 


CONTENTS 


xi 


CHAPTER   XXII 


LVJII'II    ANO    Lv.MlMIATIC    GlAVDS 

Composition  of  Lymph 
Lymphatic  Glands 
Lymph  Flow   . 
Relation  of  Lymph  and  Blood 
Formation  of  Lymph  . 
Osmotic  Phenomena  . 


PAOB 

314 
314 
315 
317 
318 
318 
321 


CHAPTER   XXIII 


The  Ductless  Glands 
Spleen 

Haemolymph  Glands 
Thynms 
Thyroid 
Parathyroids    . 
Supra-renal  Capsules 
Pituitary  Body 
Pineal  Gland   . 
Coccygeal  and  Carotid  Glands 


328 
329 
333 
334 
335 
337 
338 
341 
341 
342 


CHAPTER  XXIV 

Respihation  .... 

Respiratory  Apparatus 
Respiratory  Mechanism 
The  Respiratory  Centre 
The  Nervous  Cause  of  Respiration   . 
The  Chemical  Cause  of  Respiration  . 
Special  Respiratory  Acts 
Effect  of  Respiration  on  the  Circulation 
Asphyxia  .... 

Effects  of  Foreign  Gases,  and  Alterations  of  Pressure 
Chemistry  of  Respiration 
External  Respiration  . 
Gases  of  the  Blood     . 
Tension  of  Gases  in  Fluids    . 
Tissue  Respiration 
Ventilation      .... 


CHAPTER   XXV 


The  Chemical  Composition  of 
Carbohydrates 
Fats      . 
Proteins 

Protein-hydrolysis 
Ferments 


BODV 


343 

343 
351 
359 
360 
362 
364 
366 
370 
373 
374 
374 
377 
380 
384 
389 


390 
390 
397 
399 
414 
415 


Xll 


CONTENTS 


CHAPTER   XXVI 


The  Blood  .... 

Coagulation  of  the  Blood 
The  Plasma  and  Serum 
The  Blood-Corpuscles 
Development  of  the  Blood-Corpuscles 
Chemistry  of  the  Blood-Corpuscles    . 
Haemoglobin  .... 
Immunity        .... 


PACK 

419 
421 
426 
429 
J3fi 
439 
440 
451 


The  Alimentauy  Canal 


CHAPTER   XXVII 


CHAPTER    XXVIII 


Food 

Dietaries 

Milk    . 

The  Mammary 


Glands 


Meat    . 
Flour   . 
Bread  . 
Cooking  of  Food 
Accessories  to  Food 


470 
470 
472 
475 
476 
477 
478 
479 
479 
480 


CHAPTER   XXIX 


Secreting  Glands 

Electrical  Variations  in  Glands 


481 
484 


CHAPTER   XXX 


Saliva         ..... 
The  Sahvary  Glands  . 
Secretory  Nerves  of  Salivary  Glands 
The  SaUva       .... 


485 
485 
487 
490 


CHAPTER   XXXI 


The  Gastric  Juice 
Composition    . 

Innervation  of  the  Gastric  Glands 
Action  of  Gastric  Juice 


493 

495 
496 
498 


CONTENTS 


Xlll 


CHAPTER   XXXII 


DiGKsiioy  IS  THE  Intkstines 
The  Pancreas 

Composition  and  Action  of  Pancreatic  Juic 
The  so-called  Peripheral  ReHex  Secretion  of 
The  Succus  P'ntericus 
Bacterial  Action 
Leucine  and  Tyrosine 
Extirpation  of  the  Pancreas   . 


. 

502 

. 

502 

e            .             .             . 

503 

f  the  Pancreas 

505 

507 

510 

.       511 

,             , 

.       511 

CHAPTER   XXXIII 


HE    LiVEK                     ...... 

.       513 

Functions         ...... 

.       518 

Bile 

.       518 

Glycogenic  Function  of  the  Liver      . 

524 

Diabetes           ...... 

.       526 

Nerves  of  the  Liver     ..... 

.       528 

CHAPTER   XXXIV 


The  Absori'tiok  of  Food 


529 


CHAPTER   XXXV 


The  Mechanical  Processes  of  Digestion 
Mastication 
Deglutition 

Movements  of  the  Stomach 
Vomiting 
Movements  of  the  Intestines 


535 
535 
536 
538 
540 
541 


CHAPTER    XXXVI 


The  Urinary  Apparatus 
Functions  of  the  Kidneys 
The  Nerves  of  the  Kidney 
The  Kidney  Oncometer 
Activity  of  Renal  Epithelium 
Activity  of  Glomeruli 
The  Work  done  by  the  Kidney 
Extirpation  of  the  Kidneys    . 
Passage  of  Urine  into  the  Bladder 
Micturition 


545 
553 
553 
554 
555 
557 
559 
560 
561 
561 


XIV 


CONTENTS 


CHAPTER   XXXVII 


The  Urine 


Urea    . 

Ammonia 

Creatinine 

Uric  Acid 

Hippuric  Acid 

Inorganic  Constituents  of  Urine 

Urinary  Deposits 

Pathological  Urine     . 


PAQK 

563 
564 
570 
570 
571 
574 
575 
578 
581 


CHAPTER   XXXVIII 
The  Skin  and  Its  Appendages  .... 


585 


CHAPTER   XXXIX 


Geneuai.  Metaholism       ..... 

.       594 

Balance  in  Health     .              .... 

.595 

Metabolism  of  Carbohydrates 

.       596 

Metabolism  of  Fat     ..... 

.       598 

Metabolism  of  Protein            .... 

.       602 

Inanition  or  Starvation          .... 

.       607 

CHAPTER   XL 


Animal  Heat 


609 


CHAPTER   XLI 

The  Central  Nervous  System  . 


618 


CHAPTER   XLII 
Structure  or  the  Spinal  Cord 


620 


CHAPTER   XLIII 


The  Brain 


634 


CHAPTER   XLIV 

Structure  of  the  Bulh,  Pons,  and  Mid-Brain 
The  Cranial  Nerves     .... 


638 
652 


CONTENTS 


XV 


CHAPTER   XLV 
Structure  of  the  Cereueixum  . 


659 


CHAPTER    XLVl 


Structure  of  the  Cerebrum 
Histology  of  the  Cortex 
The  Convolutions 


CHAPTER   XLVII 


Functions  of  the  Si'inal  Corii  . 

The  Cord  as  an  Organ  of  Conduction 

Reflex  Action  of  the  Cord 

Reflex  Action  in  Man 

The  Principle  of  the  Common  Path 

Reaction  Time 

Spinal  Visceral  Reflexes 


CHAPTER   XLVni 


663 
667 
673 


678 
678 
680 
682 
686 
689 
690 


Functions  of  the  Cerebrum       ...... 

692 

Removal  of  the  Cerebrum      ...... 

692 

Localisation  of  Cerebral  Functions    ..... 

693 

Function  and  MyeUnation      ...... 

705 

Association  Fibres  and  Centres          .             .             .            • 

707 

Electrical  Variation    ....... 

711 

Sleep    .....•••• 

711 

CHAPTER   XLIX 

Functions  of  the  Cerebellum  ...... 

,       716 

The  Semicircular  Canals         ...... 

719 

CHAPTER   L 

Comi'arative  Physiology  of  the  Brain 

CHAPTER    LI 


Sensation 


CHAPTER    LH 


Cutaneous  Sensations 
Tactile  End-Organs    . 
Locahsation  of  Tactile  Sensations 
Varieties  of  Cutaneous  Sensations 
The  Motorial  Sense     . 


724 


728 


733 
733 
737 
739 
742 


XVI 


CONTENTS 


CHAPTER    LIII 


Taste  and  Smell 
Taste   . 
SraeU   . 


PAGE 

743 
743 
748 


CHAPTER   LIV 


Hearing 

Anatomy  of  the  Ear   . 
Physiology  of  Hearing 


CHAPTER   LV 


Voice  and  Speech 

Anatomy  of  the  Larynx 

Movements  of  the  Vocal  Cords 

The  Voice 

Speech 

Defects  of  Speech 


752 
752 

759 


764 
764 
770 

771 
773 

774 


CHAPTER   LVI 


The  Eye  and  Vision 

TheEyebaU    .... 

The  Eye  as  an  Optical  Instrument    . 

Accommodation 

Defects  in  the  Optical  Apparatus 

Functions  of  the  Iris  . 

Functions  of  the  Retina 

The  Ophthalmoscope 

The  Perimeter 

Visual  Sensations  and  Colour  Vision 

Changes  in  the  Retina  during  Activity 

Positions  of  the  Eyeballs 

Nervous  Paths  in  the  Optic  Nerves  . 

Visual  Judgments 


CHAPTER   LVIJ 


Trophic  Nerves 


776 
777 
788 
792 
796 
799 
801 
804 
806 
808 
813 
816 
819 
820 


824 


CHAPTER    LVin 


The  REPnoDi'criVE  (Jugans 
Male  Organs   . 
Female  Organs 


827 
828 
832 


CONTENTS 


xvn 


CHAPTER    LIX 

Develop.mext 
The  Ovtim 

Maturation  of  the  Ovum 
Impregnation 
Segmentation 

The  Decidua  and  the  Foetal  Membranes 
Development  of  tlie  Ka-tal  Appendages  and  Membranes 
Development  of  the  Framework  of  the  Body 
Development  of  the  Vascular  System 
Development  of  the  Nervous  System 
Development  of  the  Alimentary  Canal 
Development  of  the  Respiratory  Apparatus 
Development  of  the  Genito-urinary  Apparatus 


PAOB 

838 
838 
839 
841 
842 
847 
850 
856 
861 
871 
879 
882 


INDEX 


891 


FAHRENHEIT 

and 

CENTIGRADE 

SCALES. 


F. 

500° 
401 
S92 
388 
874 
856 
347 
8SS 
S29 
820 
811 
802 
284 
275 
266 
248 
239 
230 
212 
203 
194 
176 
167 
140 
122 
113 
105 
104 
100 


98-5 
95 


C. 

260' 
205 
200 
195 
190 
180 
175 
170 
165 
160 
155 
150 
140 
135 
130 
120 
115 
110 
100 

95 

90 

80 

75 

60 

50 

45 

40-54 

40 

37-8 


To    convert     de- 
grees  F.    into   de- 


grees C, 
32,  and 
by  j. 


subtract 
multiply 


To  convert  de- 
grees C.  into  de- 
grees F.,  multiply 
by  f ,  and  add  32°. 


MEASUREMENTS. 

FRENCH  INTO  ENGLISH. 


LENGTH. 


1  metre  "| 

10  d^cimi'tres   I 

100  centimetres  f  ,„_  ,  „„_j  .„  j  q.  i„  \ 
1000  millimetres  I  (°'  ^  yard  and  3J  In.) 


=   39-37  English 
inches 


1  decimetre    |      ^  3.937  j^^j^g^ 
ijrmStresJ    (---ly^-'=^-)- 


1  centimrtre  ) 
10  millinirtres  / 
1  millimrtre 


=  -3937  or  about 
(nearly  f  inch). 
=  nearly  ^\,  inch. 


Or, 

One  MteTRE  =  39-37079  inches. 

(It  is  the  ten-millionth  part  of  a  quarter 
of  the  meridian  of  the  earth.) 


1  Decimetre 
1  Centimetre 
1  Millimetre 
Decametre 
Hectometre 
Kilometre 
One  inch      = 
One  foot     = 
One  yard     = 
One  mile     = 


4  in. 
,<f  in. 

=     A  in. 

=     32-80  feet. 

=     109-.36  yds. 

=     0-62  mile. 
2-539  Centimetres. 
3-047  Decimetres. 
0-91  of  a  Metre. 
1-60  Kilometre. 


WEIGHT. 

(One  gramme  is  the  weight  of  a  cubic 
centimetre  of  water  at  i'  C.  at  Pari.s.) 

1  gramme  ^ 

10  decigrammes    I      =   15-432349  grs. 
100  centigrammes  j       (or  nearly  15A). 
1000  milligrammes  J 


1  decigramme    ^ 

10  centigrammes  - 

100  milligrammes  j 


=  rather  more 
than  I3  grain. 


1  centigramme   1 
10  decigrammes    | 


=  rather  more 
than  A  grain. 


1  milligramme 


=  rather  more 
than  .,^n  grain. 


Or, 


1  Decagramme  =  2  dr.  34  gr. 

1  Hectogrm.      =  3i  oz.  (Avoir.) 

1  Kilogrm.         =  2  lb.  3  oz.  2  dr.  (Avoir.) 


A  grain  equals  about  1-16  gram., 

a  Troy  oz.  about  31  grams., 

a  lb.  Avoirdupois  about  A  Kilogrm., 

and  1  cvft.  about  50  Kilogrnis. 


CAPACITY. 
1,000  cubic  decimitres    1=1  cubic 
1,000,000  cubic  centimetres  f     m^tre. 


}  = 


1  cubic  decim«?tre 

1  litre. 
1000  cubic  centimetres 

Or, 
One  Litre  =  1  pt.  15  oz.  1  dr.  40. 

(For  simplicity,  Litre  is  used  to  signify 

1  cubic  decimetre,  a  little  less  than  1 

English  quart.) 

Decilitre  (100  c.c.)  =  3J  oz. 

Centilitre  (10  c.c.)  =  2|  dr. 

Millilitre  (1  c.c.)  =  17  m. 

Decalitre  =  2J  gals. 

Hectolitre  =  22  gals. 

Kilolitre  (cubic  metre)   =  27i  bushels. 
A  cubic  inch  =  16-38  c.c. ;  a  cubic  foot 

=28*315  cubic  dec,  and  a  gallon  = 

454  litres. 


CONVERSION    SCALE. 

To  convert  Grammes  to  Ounces  avoir- 
dupois, multiply  by  20  and  divide  by  567. 

To  convert  Kilogrammes  to  Pounds, 
multiply  by  1000  and  divide  by  454. 

To  convert  Litres  to  Gallons,  mul- 
tiply by  22  and  divide  by  100. 

To  convert  Litres  to  Pints,  multiply 
by  88  and  divide  by  50. 

To  convert  Millimetres  to  Inches, 
multiply  by  10  and  divide  by  254. 

To  convert  Mi:TREs  to  Yards,  multi- 
ply by  70  and  divide  by  64. 


SURFACE   MEASUREMENT. 

1  square  metre  =  about  1550  sq.  inches 
(or  10,000  sq.  centimetres,  or  10-75  sq.  ft.) 
1  sq.  inch  =  about  6-4  sq.  centimetres. 
1  sq.  foot    =      „      930    ,,  „ 


ENERGY   MEASURE. 
1  kilogrammetre  =  about  7-24  ft.  pounds. 
1  foot  pound         =     „      -1381  kgm. 
1  foot  ton  =     >i      310  kgms. 


HEAT    EQUIVALENT. 
1  kilocalorie  =  424  kilogrammetres. 


ENGLISH    MEASURES. 

Apothecaries  Weight.  |  Avoirdupois  Weight. 

7000  grains     =     1  lb. 
Or, 


437-5  grains 


1  oz. 


16 

drams 

= 

1  oz. 

16 

oz. 

= 

1  lb. 

28  lbs. 

= 

1  quarter. 

4 

quarters 

= 

1  cwt. 

20 

cwt. 

= 

1  ton. 

Measure  of  1  decimetre,  or  10  centimStres,  or  100  millimetres. 


10 


HANDBOOK  OF  PHYSIOLOGY 


CHAPTEE    I 

INTKODUCTORY 

Biology  is  the  science  that  treats  of  living  things,  and  it  is  divided 
into  two  main  branches,  which  are  called  respectively  Morphology 
and  Physiology.  Morphology  is  the  part  of  the  science  that  deals 
with  the  form  or  structure  of  living  things,  and  with  the  problems 
of  their  origin  and  distribution.  Physiology ,  on  the  other  hand, 
treats  of  their  functions,  that  is,  the  manner  in  which  their  individual 
parts  carry  out  the  processes  of  life.  To  take  an  instance :  the  eye 
and  the  liver  are  two  familiar  examples  of  what  are  called  organs ; 
the  anatomist  studies  the  structure  of  these  organs,  their  shape,  their 
size,  the  tissues  of  which  they  are  composed,  their  position  in  the 
body,  and  the  variations  in  their  structure  met  with  in  different 
parts  of  the  animal  kingdom.  The  physiologist  studies  their  uses, 
and  seeks  to  explain  how  the  eye  fulfils  the  function  of  vision,  and 
how  the  liver  forms  bile,  and  ministers  to  the  needs  of  the  body  in 
other  ways. 

Each  of  these  two  great  branches  of  biological  science  can  be 
further  subdivided  according  as  to  whether  it  deals  with  the  animal 
or  the  vegetable  kingdom;  thus  we  get  vegetable  physiology  and 
animal  physiology.  Human  Physiology  is  a  large  and  important 
branch  of  animal  physiology,  and  to  the  student  of  medicine  is 
obviously  the  portion  of  the  science  that  should  interest  him  most. 
In  order  to  understand  morbid  or  pathological  processes  it  is  neces- 
sary that  the  normal  or  physiological  functions  should  be  learnt  first. 
Physiology  is  not  a  study  which  can  be  put  aside  and  forgotten  when 
a  certain  examination  has  been  passed ;  it  has  a  most  direct  and 
intimate  bearing  in  its  application  to  the  scientific  and  successful 
investigation  of  disease.  It  will  be  my  endeavour  throughout  the 
subsequent  pages  of  this  book  to  point  out  from  time  to  time  the 
practical  relationships  between  physiology  and  pathology. 


2  INTRODUCTOKY  [CH.  I. 

Human  physiology  will  be  our  chief  theme,  but  it  is  not  a  portion 
of  the  great  science  that  can  be  studied  independently  of  its  other 
portions.  Thus,  many  of  the  experiments  upon  which  our  knowledge 
of  human  physiology  rests  have  been  performed  principally  on  certain 
of  the  lower  animals.  In  order  to  obtain  a  wide  view  of  vital  pro- 
cesses it  will  be  occasionally  necessary  to  go  still  further  afield,  and 
call  the  science  of  vegetable  physiology  to  our  assistance. 

The  study  of  physiology  must  go  hand  in  hand  with  the  study  of 
anatomy.  It  is  impossible  to  understand  how  the  body  or  any  part 
of  the  body  acts  unless  we  know  accurately  the  structure  of  the 
organs  under  consideration.  This  is  especially  true  for  that  portion 
of  anatomy  which  is  called  Microscopic  Anatomy  or  Histology. 
Indeed,  so  close  is  the  relationship  between  minute  structure  and 
function  that  in  this  country  it  is  usual  for  the  teacher  of 
physiology  to  be  also  the  teacher  of  histology.  Another  branch 
of  anatomy,  namely.  Embryology,  or  the  process  of  growth  from 
the  ovum,  falls  also  to  some  extent  within  the  province  of  the 
physiologist. 

But  physiology  is  not  only  intimately  related  in  this  way  to  its 
sister  science  anatomy,  but  the  sciences  of  chemistry  and  physics 
must  also  be  considered.  Indeed,  physiology  has  been  sometimes 
defined  as  the  application  of  the  laws  of  chemistry  and  physics  to 
life.  That  is  to  say,  the  same  laws  that  regulate  the  behaviour  of 
the  mineral  or  inorganic  world  are  also  to  be  found  operating  in  the 
region  of  organic  beings.  If  we  wish  for  an  example  of  this  we  may 
again  go  to  the  eye ;  the  branch  of  physics  called  optics  teaches  us, 
among  other  things,  the  manner  in  which  images  of  objects  are  pro- 
duced by  lenses;  these  same  laws  regulate  the  formation  of  the 
images  of  external  objects  upon  the  sensitive  layer  of  the  back  of  the 
eye  by  the  series  of  lenses  in  the  front  of  that  organ.  An  example 
of  the  application  of  chemical  laws  to  living  processes  is  seen  in 
digestion ;  the  food  contains  certain  chemical  substances  which  are 
acted  on  in  a  chemical  way  by  the  various  digestive  juices  in  order  to 
render  them  of  service  to  the  organism. 

The  question  arises,  however,  is  there  anything  else  ?  Are  there 
any  other  laws  than  those  of  physics  and  chemistry  to  be  reckoned 
with  ?  Is  there,  for  instance,  such  a  thing  as  "  vital  force  "  ?  It 
may  be  frankly  admitted  that  physiologists  at  present  are  not  able  to 
explain  all  vital  phenomena  by  the  laws  of  the  physical  world ;  but 
as  knowledge  increases  it  is  more  and  more  abundantly  shown  that 
the  supposition  of  any  special  or  vital  force  is  unnecessary ;  and  it 
should  be  distinctly  recognised  that  when,  in  future  pages,  it  is 
necessary  to  allude  to  vital  action,  it  is  not  because  we  believe  in  any 
specific  vital  energy,  but  merely  because  the  phrase  is  a  convenient 
one  for  expressing  something  that  we  do  not  fully  understand,  some- 


CH.  I.]  INTRODUCTORY  3 

thing  tliat  cannot  at  present  be  brought  into  line  with  the  physical 
and  chemical  forces  that  operate  in  the  inorganic  world. 

But  just  as  there  is  no  hard-and-fast  line  between  physiology  and 
its  allies  pathology,  anatomy,  physics,  and  chemistry,  so  also  there  is 
no  absolute  separation  between  its  three  great  divisions;  physical, 
chemical,  and  so-called  vital  processes  have  to  be  considered  together. 

Physiology  is  a  comparatively  young  science.  Though  Harvey 
more  than  three  hundred  years  ago  laid  the  foundation  of  our  science 
by  his  discovery  of  the  circulation  of  the  blood,  it  is  only  during  the 
last  half-century  that  active  growth  has  occurred.  The  reasons  for 
this  recent  progress  come  under  two  headings :  those  relating  to 
observation  and  those  relating  to  experiment. 

The  method  of  observation  consists  in  accurately  noting  things 
as  they  occur  in  nature ;  in  other  words,  the  knowledge  of  anatomy 
must  be  accurate  before  correct  deductions  as  to  function  are  possible. 
The  instrument  by  which  such  correct  observations  can  be  made  is, 
'par  excellence,,  from  the  physiologist's  standpoint,  the  microscope,  and 
it  is  the  extended  use  of  the  microscope,  and  the  knowledge  of  minute 
anatomy  resulting  from  that  use,  which  has  formed  one  of  the  greatest 
stimuli  to  the  successful  progress  of  physiology  during  the  last  sixty 
years. 

But  important  as  observation  is,  it  is  not  the  most  important 
method;  the  method  of  experiment  is  still  more  essential.  This 
consists,  not  in  being  content  with  mere  reasonings  from  structures  or 
occurrences  seen  in  nature,  but  in  producing  artificially  changed 
relationships  between  the  structures,  and  thus  causing  new  combina- 
tions that  if  one  had  waited  for  Nature  herself  to  produce  might  have 
been  waited  for  indefinitely.  Anatomy  is  important,  but  mere 
anatomy  has  often  led  people  astray  when  they  have  tried  to  reason 
how  an  organ  works  from  its  structure  only.  Experiment  is  much 
more  important ;  that  is,  one  tests  one's  theories  by  seeing  whether 
the  occurrences  actually  take  place  as  one  supposes ;  and  thus  the 
deductions  are  confirmed  or  corrected.  It  is  the  universal  use  of  this 
method  that  has  made  physiology  what  it  is.  Instead  of  sitting  down 
and  trying  to  reason  out  how  the  living  machine  works,  physiologists 
have  actually  tried  the  experiment,  and  so  learnt  much  more  than 
could  possibly  have  been  gained  by  mere  cogitation.  Many  experi- 
ments involve  the  use  of  living  animals,  but  the  discovery  of  anaes- 
thetics, which  renders  such  experiments  painless,  has  got  rid  of  any 
objection  to  experiments  on  the  score  of  pain. 

We  must  next  proceed  to  an  examination  of  the  general  structure 
of  the  body,  and  an  explanation  of  some  of  the  technical  terms  which 
will  frequently  be  used  hereafter. 

The  adult  body  consists  of  a  great  number  of  different  parts;  and 
each  part  has  its  own  special  work  to  do.     Such  parts  of  the  body  are 


INTRODUCTORY 


[CH.  I. 


called  organs.  Each  organ  does  not  only  its  own  special  work,  but 
acts  in  harmony  with  other  organs.  This  relationship  between  the 
organs  enables  us  to  group  them  together  into  what  are  termed 
systems.  Thus,  we  have  the  circulatory  system,  that  is,  the  group  of 
organs  (heart,  arteries,  veins,  etc.)  concerned  in  the  circulation  of  the 
blood ;  the  respiratory  system,  that  is,  the  group  of  organs  (air 
passages,  lungs,  etc.)  concerned  in  the  act  of  breathing ;  the  digestive 
system,  which  deals  with  the  digestion  of  food ;  the  excretory  system, 
with  the  getting  rid  of  waste  products;  the  miiscular  system,  vfith. 
movement;  and  the  skeletal  system,  with  the  support  of  the  softer 
parts  of  the  body.  Over  and  above  all  these  is  the  nervous  system 
(brain,  spinal  cord,  nerves),  the  great  master  system  of  the  body 
which  presides  over,  controls,  and  regulates  the  functions  of  the 
other  systems. 

If  we  proceed  still  further  on  our  anatomical  analysis,  and  take 
any  organ,  we  see  that  it  consists  of  various  textures,  or,  as  they  are 
called,  elementary  tissues.  Just  as  one's  garments  are  made  up  of 
textures  (cloth,  lining,  buttons,  etc.),  so  each  organ  is  composed  of 
corresponding  tissues.  The  elementary  tissues  come  under  the 
followinij;  four  headings: — 


1.  Epithelial  tissues. 

2.  Connective  tissues. 


3.  Muscular  tissues. 

4.  Nervous  tissues. 


Protoplasm. 


Each  of  these  is  again  divisible  into  sub-groups. 

Suppose  we  continue  our  anatomical  analysis  still  further,  we  find 
that  the  individual  tissues  are  built  up  of 
structures  which  lequire  the  microscope  for 
their  accurate  study.  Just  as  the  textures 
of  a  garment  are  made  up  of  threads  of 
various  kinds,  so  also  in  many  of  the  animal 
tissues  we  find  threads  or  fibres,  as  they  are 
called.  But  more  important  than  the  threads 
are  little  masses  of  living  material.  Just  as 
the  wall  of  a  house  is  made  up  of  bricks 
united  by  cement,  so  the  body  walls  are  built 
of  extremely  minute  living  bricks,  united 
together  by  different  amounts  of  cementing 
material.  Each  one  of  these  living  units  is 
called  a  cell. 

Some  of  the  tissues  already  enumerated 
consist  of  cells  with  only  very  little  cement 
material  binding  them  together;  this,  for 
instance,  is  seen  in  the  epithelial  tissues; 
but  in  other  tissues,  particularly  the  connective  tissues  which  are 
not  so  eminently  living  as  the  rest,  the  amount  of  cement  or  inter- 


CeU-wall. 


Fig.  1. — Vegetable  cells. 


CH.  I.] 


INTRODUCTORY 


5 


cellular  material  is  much  greater,  and  in  this  it  is  that  the  fibres 
are  developed  that  confer  the  necessary  strength  upon  these  binding 
tissues. 

If,  instead  of  going  to  the  adult  animal,  we  look  at  the  animal 
in  its  earliest  stage  of  development,  the  ovum,  we  find  that  it  con- 
sists of  a  single  little  mass  of  living  material,  a  single  cell.  As 
development  progresses  it  becomes  an  adherent  mass  of  cells.  In  the 
later  stages  of  development  various  tissues  become  differentiated 
from  each  other  by  the  cells  becoming  grouped  in  different  ways,  by 
alterations  in  the  shape  of  the  cells,  by  deposition  of  intercellular 
matter  between  the  cells,  and  by  chemical  changes  in  the  living 
matter  of  the  cells  themselves.  Thus  in  some  situations  the  cells  are 
grouped  into  the  various  epithelial  linings ;  in  others  the  cells  become 
elongated  and  form  muscular  fibres ;  and  in  others,  as  in  the  con- 
nective tissues,  there  is  a  preponderating  amount  of  intercellular 
material  which  may  become  permeated  with  fibres,  or  be  the  seat  of 
the  deposition  of  calcareous  salts,  as  in  bone.  Instances  of  chemical 
changes  in  the  cells  themselves  are  seen  on  the  surface  of  the  body 
where  the  superficial  layers  of  the  epidermis 
become  horny ;  in  the  mucous  glands,  where 
they  become  filled  with  mucin,  and  in  adipose 
tissue,  where  they  become  charged  with  fat. 

The  term  cell  was  first  used  by  botanists ; 
in  the  popular  sense  of  the  word  a  cell  is  a 
space  surrounded  by  a  wall,  as  the  cell  of  a 
prison,  or  the  cell  of  a  honeycomb.  In  the 
vegetable  cell  there  is  a  wall  made  of  the 
starch-like  material  called  cellulose,  within 
this  is  the  living  matter,  and  a  number  of 
large  spaces  or  vacuoles  filled  with  a  watery 
fluid.  The  use  of  the  term  cell  by  botanists 
was  therefore  completely  justified. 

But  the  animal  cell  is  different;  as  a  rule, 
it  has  no  cell- wall,  and  vacuoles  are  not 
conspicuous.  It  is  just  a  little  naked  lump  of  living  material. 
This  living  material  is  jelly-like  in  consistency,  possessing  the  power 
of  movement,  and  the  name  protoplasm  has  been  bestowed  on  it. 

Somewhere  in  the  protoplasm  of  all  cells,  generally  near  the  middle 
in  animal  cells,  is  a  roundish  structure  of  more  solid  consistency  than 
the  rest  of  the  protoplasm,  called  the  nucleus. 

An  animal  cell  may  therefore  be  defined  as  a  mass  of  protoplasm 
containing  a  nucleus. 

The  simplest  animals,  like  the  amoebae,  consist  of  one  cell  only ; 
the  simplest  plants,  like  bacteria,  torulse,  etc.,  consist  of  one  cell  only. 

Such  organisms  are  called  unicellular.     In  the  progress  of  their 


Fio.  2.— Animal  cell  consisting 
of  protoplasm  containing  a 
nucleus. 


6  INTRODUCTORY  [CH.  1. 

life  history  the  cell  divides  into  two ;  and  the  two  new  cells  separate 
and  become  independent  organisms,  to  repeat  the  process  later  on. 

In  the  case  of  the  higher  animals  and  plants,  they  are  always  uni- 
cellular to  start  with,  but  on  dividing  and  subdividing  the  resulting 


@©0         V5 


Fig.  3. — Amnebae  ;  unicellular  animals 


Fig.  4.— Cells  of  the  yeast 
plant  in  process  of  bud- 
ding ;  unicellular  plants. 


cells  stick  together  and  subsequently  become  differentiated  and  altered 
in  the  manner  already  indicated.  In  spite  of  these  changes,  the 
variety  of  which  produces  the  great  complexity  of  the  adult  organism, 
there  are  certain  cells  which  still  retain  their  primitive  structure; 
notable  among  these  are  the  white  corpuscles  of  the  blood. 


Fig.  5. — Human  colourless  blood-corpuscle,  showing  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.    (Scholield.) 

It  would  appear  at  first  sight  an  easy  problem  to  distinguish 
between  a  living  thing,  and  one  which  is  not  li\ang.  The  principal 
signs  of  life  are  the  following : — 

1.  Irritability ;  that  is  the  property  of  responding  by  some  change 
under  the  influence  of  an  external  agent  or  stimulus.  The  most  obvious 
of  these  changes  is  movement  (amoeboid  movement,  ciliary  movement, 
muscular  movement,  etc.). 

2.  Power  of  assimilation,  that  is,  ability  to  convert  into  protoplasm 
the  nutrient  material  or  food  which  is  ingested. 

3.  Power  of  growth ;  this  is  a  natural  consequence  of  the  power 
of  assimilation. 

4.  Power  of  reproduction ;  this  is  a  variety  of  growth. 

5.  Power  to  excrete ;  to  give  out  waste  materials,  the  products  of 
other  activities. 

It  should,  however,  be  recognised  that  certain  of  these  five  char- 
acteristics may  be  absent  or  latent,  and  yet  the  object  may  be  living. 
For  instance,  power  of  movement  is  absent  in  many  vegetable  struc- 
tures ;  certain  seeds  and  spores  can  be  dried  and  kept  for  many  years 
in  an  apparently  dead  condition,  and  yet  will  sprout  and  grow  when 
placed  in  appropriate  surroundings. 


CH.  I.]  INTRODUCTORY  7 

Of  all  the  signs  of  life,  those  numbered  2  and  5  in  the  foregoing 
table  are  the  most  essential.  Living  material  is  in  a  continual  state 
of  unstable  chemical  equilibrium,  building  itself  up  on  the  one  hand, 
breaking  down  on  the  other ;  the  term  used  for  the  sum  total  of  these 
intra-molecular  rearrangements  is  metabolism.  The  chemical  sub- 
stances in  the  protoplasm  which  are  the  most  important  from  this 
point  of  view  are  the  complex  nitrogenous  compounds  called  Proteins. 
So  far  as  is  at  present  known,  protein  material  is  never  absent  from 
living  substance,  and  is  never  present  in  any  thing  else  but  that 
which  is  alive  or  has  been  formed  by  the  agency  of  living  cells.  It 
may  therefore  be  stated  that  Protein  Metabolism  is  the  most  essential 
characteristic  of  vitality. 

The  proteins  or  albuminous  substances  have  received  different  names  at 
different  times,  and  the  nomenclature  has  thus  given  rise  to  confusion.  They  have 
been  very  generally  called  proteids  in  English  books,  but  the  term  protein  which 
I  have  decided  to  adopt  appears  likely  to  meet  with  general  acceptance. 


CHAPTER   ir 


THE    A  N  I  .M  A  L    C  E  L  L 


Ax  animal  cell  is  usually  of  microscopic  dimensions,  in  the  human 
body  varying  from  -j,Vjj  to  tjoVtt  of  ^i^  ii^ch  in  diameter. 
It  consists  of — 

1.  Protoplasm.     This  makes  up  the  main  substance  of  the  cell. 

2.  Nuclev^:   a  vesicular  body  within  the  protoplasm,  generally 
situated  near  the  centre  of  the  cell. 

3.  Centrosome  and  attraction  sphere :  these  are  contained  within 
the  protoplasm,  near  the  nucleus. 

These  three  portions  demand  separate  study. 


Protoplasm. 

Until  recent  years,  protoplasm  was  supposed  to  be  a  homogeneous 
material  entirely  destitute  of  structure,  though  generally  containing 
minute  granules  of  solid  consistency,  or  globules  (vacuoles)  containing 
a  watery  fluid. 

It  has,  however,  now  been  shown  with  high  powers  of  the  micro- 
scope that  in  many  cells  the  protoplasm  consists  of  two  parts,  a  fine 


-<A.)  A  colourless  blood-corpuscle  showing  the  iutra-cellular  network,  and  two  nuclei  with  intra- 
nuclear network. 
(b.)  Coloured  blood-corpnscle  of  newt  showing  the  intra-cellular  network  of  fibrils.    Also  oval 
nucleus  composed  of  limiting  membrane  and  fine  intra-nuclear  network  of  fibrils       •  ""^ 
(Klein  and  Xoble  Smith.) 


X  800. 


network  of  fibrillte  in  which  the  more  fluid  and  apparently  structure- 
less portion  of  the  protoplasm  is  contained.     (See  figs.  2  and  6.) 


CH.  II.]  PROTOPLASM  9 

The  network  or  spongework  is  called  the  reticulum  or  spongio- 
plasm,  and  the  more  fluid  portion  in  its  meshes  the  enchylema  or 
hyaloplasm. 

Ill  order  to  study  the  microscopic  structure  of  such  transparent  objects  as 
cells,  it  is  necessary  to  have  recourse  to  various  methods  of  fixing  and  stain- 
ing. When  one  sees  certain  appearances  after  such  treatment  of  the  cells,  the 
question  arises  whether  they  may  not  be  due  to  the  action  of  the  reagents 
employed.  Appearances  which  are  undoubtedly  produced  artificially  in  this  way 
are  generally  spoken  of  as  artifacts.  The  network  just  described  is  regarded  by 
some  observers  as  an  artifact,  but  it  is  impossible  at  present  to  state  this  posi- 
tively. Hardy,  in  i:)arti(ular,  has  shown  that  a  film  of  any  colloidal  substance 
like  gelatin  will,  when  it  sets,  present  the  appearance  of  a  network,  and  he 
regards  it  as  probable  that  the  network  seen  in  cells  may  be  due  to  a  similar 
setting  or  coagulation  of  the  protoplasm  which  occurs  either  when  the  cell 
dies,  or  is  fixed  by  hardening  reagents.  Biitschli  regards  the  spongioplasm  as 
the  optical  effect  of  a  honeycomb  or  froth-like  structure.  There  are  numerous 
other  views. 

The  granules  in  protoplasm  are  partly  thickened  portions  of  the 
spongioplasm,  but  in  addition  to  this  there  appear  to  be  free 
granules,  some  fatty  in  nature  (staining  black  with  osmic  acid), 
some  composed  of  the  substance  called  glycogen  or  animal  starch 
(staining  reddish-brown  with  iodine),  and  sometimes  in  a  few 
unicellular  animals  they  consist  of  inorganic  (calcareous)  matter. 
But  by  far  the  most  constant  and  abundant  of  the  granules  are  like 
the  main  substance  of  the  protoplasm,  protein  or  albuminous  in 
composition.  In  all  probability  the  protein  granules  are  actual 
constituents  of  the  protoplasm.  Substances  stored  within  the  proto- 
plasm, such  as  pigment  granules,  fat  globules,  fluid  in  vacuoles,  and 
glycogen,  are  spoken  of  as  cell-contents  or  paraplasm. 

The  chemical  structure  of  protoplasm  can  only  be  investigated 
after  the  protoplasm  has  been  killed.  The  substances  it  yields  are 
(1)  Water;  protoplasm  is  semifluid,  and  at  least  three-quarters  of 
its  weight,  often  more,  are  due  to  water.  (2)  Proteins.  These  are 
the  most  constant  and  abundant  of  the  solids.  A  protein  or 
albuminous  substance  consists  of  carbon,  hydrogen,  nitrogen,  oxygen, 
with  sulphur  and  phosphorus  in  small  quantities  only.  In  nuclein,  a 
protein-like  substance  found  in  the  nuclei  of  cells,  phosphorus  is 
more  abundant.  The  protein  obtained  in  greatest  abundance  in  the 
cell  protoplasm  is  called  a  nucleo-protein ;  that  is  to  say,  it  is  a 
compound  containing  varying  amounts  of  this  material  nuclein  with 
protein.  White  of  egg  is  a  familiar  instance  of  an  albuminous 
substance  or  protein,  and  the  fact  (which  is  also  familiar)  that  this 
sets  into  a  solid  on  boiling  will  serve  as  a  reminder  that  the  greater 
number  of  the  proteins  foimd  in  nature  have  a  similar  tendency  to 
coagulate  under  the  influence  of  heat  and  other  agencies.  (3) 
Various  other  substances  occur  in  smaller  proportions,  the  most  con- 
stant of    which    are  lecithin,    a   phosphorised    fat;   cholesterin,  a 


10 


THE   ANIMAL   CELL 


[CH.  n. 


monatomic  alcohol ;  and  inorganic  salts,  especially  phosphates  and 
chlorides  of  calcium,  sodium,  and  potassium. 

The  large  quantity  of  water  present  should  be  particularly  noted ; 
the  student  when  first  shown  diagrams  of  the  reticulum  in  proto- 
plasm is  apt  to  imagine  that  it  consists  of  a  firm  solid,  like  a  system 
of  wires  pervading  a  jelly.  The  reticulum  is  only  sKghtly  more  solid 
than  the  hyaloplasm. 

The  Nucleus. 

In  form  the  nucleus  is  generally  round  or  oval,  but  it  may  have 
in  some  cases  an  irregular  shape,  and  in  other  cases  there  may  be 
more  than  one  nucleus  in  a  cell. 

The  nucleus  exercises  a  controlling  influence  over  the  nutrition 
and  subdivision  of  the  cell ;  any  portion  of  a  cell  cut  off  from  the 
nucleus  undergoes  degenerative  changes. 

A  nucleus  consists  of  four  parts — 

1.  The  nuclear  membrane,  which  encloses  it. 

2.  A  network  of  fibres  in  appearance  like  the  spongioplasm  of  the 

protoplasm  but  on  a  larger  scale ;  that  is  to  say,  the  threads 
of  which  it  is  composed  are  much  coarser  and  much  more 
readily  seen.  The  name  chromoplasm  has  been  given  to 
this  network. 

3.  The   nuclear  sap   or  matrix,  a   more   fluid  and   homogeneous 

substance  which  occupies  the  interstices  of  the  spongework 
of  chromoplasm. 

4.  Nucleoli ;  these  are  of  two  principal  varieties ;  some  are  knots 

or  thickened  portions  of  the  network  (pseudo-nucleoli),  and 
others,  the  true  nucleoli,  float  freely  in  the  nuclear  sap. 
These  four   parts   of  the    nucleus   are  represented   in  the  next 
diagram. 


Node  of  network 


Node  of  network- 


--'-  Nuclear  membrane. 
-Nucleolus. 
Nuclear  matrix. 
'}  ' Nuclear  network. 


Fig.  7.— The  resting  nucleus— diagrammatic.    (Waldeyer.) 

The  next  figure  (fig.  8)  gives  a  view  of  the  nucleus,  according  to 
the  researches  of  Eabl.  He  considers  that  the  fibres  of  the  network 
may  be  divided  into  thick  fibres  which  he  terms  primary,  and  thinner 
connecting  branches  which  he  terms  secondary  (shown  only  on  the 


CH.  II.] 


THE  NUCLEUS 


11 


;'.'■■/. 


8. — Diagram  of  nucleus  sliowiuK  tlie 
arrangement  of  cliief  chromatic  filaments. 
Viewed  from  the  side,  the  polar  end  being 
uppermost,  p.c.f.,  primary  chromatic  fjla- 
meuts;  «.,  nucleolus  ;  re.  o.m.,  node  of  mesh- 
work.    (Rabl.) 


right-hand  side  of  the  figure).     This  observer  also  supposes  that  the 
primary  fibres  have  the  looped  arrangement  depicted  in  the  diagram. 

In  the  investigation  of  microscopic  objects,  a  histologist  is  nearly 
always  obliged  to  use  staining  agents ;  the  extremely  thin  objects  he 
examines  are  so  transparent  that,  without  such  stains,  much  of  the 
structure  would  be  invisible.  If 
such  dyes  as  haematoxylin  or 
safranin  are  employed,  it  is  the 
nucleus  which  becomes  most  deeply 
stained,  and  thus  stands  out  on  the 
lighter  background  of  the  proto- 
plasm. 

But  the  whole  nucleus  does  not 
stain  equally  deeply;  it  is  the 
chromoplasmic  filaments  and  the 
nucleoli  which  have  most  affinity 
for  the  stain,  while  the  nuclear  sap 
is  comparatively  unaffected.  Hence  the  terms  chromatin  and  achro- 
matin  originally  introduced  by  Fleming.  The  membrane,  the  net- 
work, and  the  nucleoli  are  composed  of  chromatic  substance  or 
chromatin ;  it  is  so  called  not  because  it  has  any  colour  in  the 
natural  state,  but  because  it  has  an  affinity  for  colours  artificially 
added  to  it.  For  a  corresponding  reason,  achromatin  or  achro- 
matic substance  is  the  name  given  to  the  substances 
which  make  up  the  nuclear  sap. 

Balbiani  showed  that  the  chromoplasmic  filaments  are 
apparently  transversely  marked  into  alternate  dark  and  light 
bands  ;  this  is  due  to  the  existence  of  minute  highly  refracting 
particles  imbedded  in  regular  series  in  a  clear  homogeneous 
and  unstainable  matrix  (see  fig.  9).  The  term  chromatin  should 
properly  be  restricted  to  these  particles.  These  particles  have 
special  affinity  for  basic  dyes  like  methyl  green,  and  safranin. 

Coming  next  to  the  chemical  composition  of  the 
nucleus,  it  is  found  to  consist  principally  of  protein 
and  protein-like  substances.  The  nuclei  of  cells 
may  be  obtained  by  subjecting  the  cells  to  the 
action  of  artificial  gastric  juice;  the  protoplasm  is 
nearly  entirely  dissolved,  but  the  nuclei  resist  the 
solvent  action  of  the  juice.  No  doubt  the  nuclei  contain  several 
chemical  compounds,  but  the  only  one  of  which  we  have  any  accu- 
rate knowledge  has  been  termed  nuclein,  and  this  is  identical  with 
the  substance  called  chromatin  by  histologists.  It  is  soluble  in 
alkalis,  but  precipitated  by  acids;  it  is  different  from  a  simple  protein, 
as  it  contains  in  addition  to  carbon,  nitrogen,  oxygen,  hydrogen,  and 
sulphur,  an  enormous  quantity  (7  to  8  per  cent,  or  even  more)  of 
phosphorus  in  its  molecule.    In  many  cases  nucleins  contain  iron  also. 


Fio.  9. —  Part  of  a 
chromoplasmic  fila- 
ment, greatly  magni- 
fied.   (Camoy.) 


12 


THE   ANIMAL   CELL 


[CH.  n. 


The  Attraction  Sphere. 

Eecent  research  has  shown  that,  in  addition  to  the  nucleus  and 
protoplasm,  most  if  not  all  living  cells  contain  another  structure ;  it 
consists  of  a  minute  particle  called  a  "  centrosome"  which  has  an 
attractive  influence  on  protoplasmic  fibrils  and  granules  in  its 
neighbourhood,  the  whole  appearance  produced  being  called  an 
attraction  sphere  (fig.  10). 


Fig.  10.— a  cell  (white  blood-cor- 
puscle) showing  its  attraction 
sphere.  In  this,  as  in  most 
cases,  the  attraction  sphere  lies 
near  the  nucleus.    (Schafer.) 


.  11. — Ovum  of  the  worm  Ascaris, 
showing  a  twin  attraction  sphere. 
Tlie  nucleus  with  its  contorted 
filament  of  chromoplasm  is  repre- 
sented, but  the  protoplasm  of 
the  cell  is  not  filled  in.  (v. 
Beneden.) 


It  is  most  prominent  in  cells  which  are  dividing  or  about  to 
divide.  The  centrosome,  and  then  the  attraction  sphere,  become 
double  (fig.  11).  In  all  probability  the  centrosome  gives  the  primary 
impulse  to  cell-division.  Some  cells,  like  the  giant  cells  of  red 
marrow,  contain  numerous  centrosomes. 


Protoplasmic  Movement. 

A  cell  possesses  the  power  of  breathing,  that  is,  taking  in  oxygen  ; 
of  nutrition,  of  building  itself  up  from  food  materials ;  and  of  excre- 
tion, or  the  getting  rid  of  waste  material.  But  the  most  obvious 
physiological  characteristic  of  most  cells  is  their  power  of  move- 
ment. 

When  an  amoeba  is  observed  with  a  high  power  of  the  micro- 
scope, it  is  found  to  consist  of  an  irregular  mass  of  protoplasm  con- 
taining one  or  more  nuclei,  the  protoplasm  itself  being  more  or  less 
granular  and  vacuolated.  If  watched  for  a  minute  or  two,  an 
irregular  projection  is  seen  to  be  gradually  thrust  out  from  the  main 
body  and  retracted;  a  second  mass  is  then  protruded  in  another 
direction,  and  gradually  the  whole  protoplasmic  substance  is,  as  it 


CH.  II.] 


PROTOPLASMIC    MOVEMENT 


13 


were,  drawn   into   it.     The   Amoeba   thus  comes   to   occupy  a  new 
position,  and  when  this  is  repeated  several  times  we  have  locomotion 
in  a  definite  direction,  together   with  a  continual  change  of   form. 
These  movements,  when  observed  in  other 
cells,  such   as   the   colourless   blood-cor- 
puscles of  higher  animals  (fig.  13),  in  the 
branched   corneal  cells   of   the  frog  and 
elsewhere,    are   hence    termed    amceboid. 
The    projections    which    are    alternately 
protruded  and  retracted  are  called  pseudo- 
podia. 

A  streaming  movement  is  not  infre- 
quently  seen   in   certain   of   the   protozoa,  in  which   the  mass  of 
protoplasm  extends  long  and  fine  processes,  themselves  very  little 
movable,  but  upon  the  surface  of  which  freely-moving  or  stream- 
ing granules  are  seen.     A  gliding  movement  has  also  been  noticed 


Flo.  12. — Amcebse. 


FiQ.  13.— Human  colourless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  warm  stage.    (Schofield.) 

in  certain  animal  cells  ;  the  motile  part  of  the  cell  is  composed  of 
protoplasm  bounding  a  central  and  more  compact  mass ;  by  means 
of  the  free  movement  of  this  layer,  the  cell  may  be  observed  to 
move  along. 

In  vegetable  cells  the  protoplasmic  movement  can  be  well  seen 


Fio.  14. — (a.)  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  with  granular  protoplasm 
enclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli. 
(b.)  Older  cells  from  same  plant,  showing  distinct  cellulose-waU  and  vacuolation  of  proto- 
plasm. 

in  the  hairs  of  the  stinging-nettle  and  Tradescantia  and  the  cells  of 
Vallisneria  and  Chara ;  it  is  marked  by  the  movement  of  the  granules 
nearly  always  imbedded  in  it.  For  example,  if  part  of  a  hair  of 
Tradescantia  (fig.  15)  be  viewed  under  a  high  magnifying  power, 


14 


THE   ANIMAL   CELL 


[CH.  n. 


.  lo. — Cell  of  Tradescantia  drawn  at  suc- 
cessive intervals  of  two  minutes. — The  cell- 
contents  consist  of  a  central  mass  connected 
by  many  irregular  processes  to  a  jieriplieral 
film,  the  whole  forming  a  vacuolated  mass 
of  protoplasm,  which  is  continually  changing 
its  shape.    (Schofield.) 


streams  of  protoplasm  containing  crowds  of  granules  hurrying  along, 
like  the  foot-passengers  in  a  busy  street,  are  seen  flowing  steadily  in 
definite  directions,  some  coursing 
round  the  film  which  lines  the 
interior  of  the  cell-wall,  and  others 
flowing  towards  or  away  from  the 
irregular  mass  in  the  centre  of  the 
cell-cavity.  Many  of  these  streams 
of  protoplasm  run  together  into 
larger  ones  and  are  lost  in  the 
central  mass,  and  thus  ceaseless 
variations  of  form  are  produced. 
The  movement  of  the  protoplasmic 
granules  to  or  from  the  peri- 
phery is  sometimes  called  vege- 
table circulation,  whereas  the 
movement  of  the  protoplasm  round  the  interior  of  the  cell  is  called 
rotation. 

The  first  account  of  the  movement  of  protoplasm  was  given  by 
Eosel  in  1755,  as  occurring  in  a  small 
Proteus,  probably  a  large  freshwater 
amoeba.  His  description  was  followed 
twenty  years  later  by  Corti's  demonstra- 
tion of  the  rotation  of  the  cell  sap  in 
Characeae,  and  in  the  earlier  part  of  last 
century  by  Meyer  in  Vallisneria,  1827, 
and  by  Eobert  Brown,  1831,  in  "  Staminal 
Hairs  of  Tradescantia."  Then  came  Du- 
jardin's  description  of  the  granular  stream- 
ing in  the  pseudopodia  of  Rhizopods; 
movements  in  other  animal  cells  were 
described  somewhat  later  (Planarian  eggs, 
V.  Siebold,  1841 ;  colourless  blood-cor- 
puscles, Wharton  Jones,  1846). 

There  is  no  doubt  that  the  proto- 
plasmic movement  is  essentially  the  same 
thing  in  both  animal  and  vegetable  cells. 
But  in  vegetable  cells  the  cell-wall  obliges 
the  movement  to  occur  in  the  interior, 
while  in  the  naked  animal  cells  the  move- 
ment results  in  an  external  change  of 
form. 

Although  the  movements  of  amoeboid  cells  may  be  loosely  de- 
scribed as  spontaneous,  yet  they  are  produced  and  increased  under 
the  action  of  external  agencies  which  excite  them,  and  which  are 


Fio.  16. — Cells  from  the  staminal 
hairs  of  Tradescantia.  A,  fresh 
in  water ;  B,  the  same  cell  after 
slight  electrical  stimulation ; 
a,  h,  region  of  stimulation; 
c,  d,  clumps  and  knobs  of  con- 
tracted protoplasm.    (Klihne.) 


en.  II.]  IRRITABILITY    OF    PROTOPLAS.M  15 

therefore  called  stimuli,  and  if  the  movement  has  ceased  for  the  time, 
as  is  the  case  if  the  temperature  is  lowered  beyond  a  certain  point, 
movement  may  be  set  up  by  raising  the  temperature.  Again,  contact 
with  foreign  bodies,  gentle  pressure,  certain  salts,  and  electricity, 
produce  or  increase  the  movement  in  the  amoeba.  The  protoplasm 
is,  therefore,  sensitive  or  irritable  to  stimuli,  and  shows  its  irritability 
by  movement  or  contraction  of  its  mass. 

The  effects  of  some  of  these  stimuli  may  be  thus  further 
detailed  :— 

a.  Changes  of  temperature. — Moderate  heat  acts  as  a  stimulant : 
the  movement  stops  when  the  temperature  is  lowered  near  the 
freezing-point  or  raised  above  40°  C.  (104°  F.) ;  between  these  two 
points  the  movements  increase  in  activity ;  the  optimum  temperature 
is  about  37  to  38  C.  Though  cold  stops  the  movement  of  proto- 
plasm, exposure  to  a  temperature  even  below  0'  C.  does  not  prevent 
its  reappearance  if  the  temperature  is  raised;  on  the  other  hand, 
prolonged  exposure  to  a  temperature  of  42'' -45°  C.  altogether  kills  the 
protoplasm  and  causes  it  to  enter  into  a  condition  of  coagulation  or 
heat  rigor.  We  have  already  seen  that  proteins,  the  most  abundant 
constituents  of  protoplasm,  are  coagulated  by  heat. 

h.  Chemical  stimuli. — Distilled  water  first  stimulates  then  stops 
amoeboid  movement,  for  by  imbibition  it  causes  great  swelling  and 
finally  bursting  of  the  cells.  In  some  cases,  however  (myxomycetes), 
protoplasm  can  be  almost  entirely  dried  up,  but  remains  capable  of 
renewing  its  movement  when  again  moistened.  Dilute  salt  solution 
and  very  dilute  alkalis  stimulate  the  movements  temporarily.  Acids 
or  strong  alkalis  permanently  stop  the  movements  :  ether,  chloroform, 
veratrine  and  quinine  also  stop  it  for  a  time. 

Movement  is  suspended  in  an  atmosphere  of  hydrogen  or  carbonic 
acid,  and  resumed  on  the  admission  of  air  or  oxygen ;  complete  with- 
drawal of  oxygen  will  after  a  time  kill  protoplasm. 

c.  Electrical. — Weak  currents  stimulate  the  /<^^-^^- 

movement,   while    strong    currents    cause    the  ^^^^^>i?^ 

cells  to  assume  a  spherical  form  and  to  become  ^-^    y-'^-T^f 

motionless.  r  '  -.iv:-v-:SX'V':*i'V  1 

The  amoeboid  movements  of  the  colourless      ;    -^^y^^^^^/i^^  ^ 
corpuscles   of   the  blood  may  be   readily  seen      ^^Jy   ^^-^^^^' 
when  a  drop  of  blood  from  the  finger  is  mixed     fig.  n.-An  Amceboid  cor- 
with   salt   solution,   and  examined  on  a  warm         by'fniunteneous*  aS 
stage  with  the  microscope.     If  a  pseudopodium         cation  of  steam,  show- 

„°  -,        .      ^  ■,  iii'i  '"o    the    appearance   of 

01  such  a  corpuscle  is   observed  under  a  high         the  pseudopodia.  (After 

•  ,         -ii     1  .  •    j_      J!    1         1       1  Schafer,  "  Qnain's  Ana- 

power,  it  Will  be  seen  to  consist  or  hyaloplasm,         tomy."j 

which  has  flowed  out  of  its  spongy  home,  the 

reticulum.     Later,  however,  a  portion  of  the  reticular  part  of   the 

protoplasm  may  enter  the  pseudopodium.     The  cells  may  be  fixed 


16  THK   ANIMAL   CELL  [CH.  IL 

by  a  jet  of  steam  allowed  to  play  fur  a  moment  on  the  surface 
of  the  cover  ^lass.  The  next  figure  illustrates  one  fixed  in  this 
way. 

The  essential  act  in  the  protrusion  of  a  pseudopodium  is  the 
flowing  of  the  hyaloplasm  out  of  the  spongioplasm ;  the  retraction 
of  the  pseudopodium  is  a  return  of  the  hyaloplasm  to  the  spongio- 
plasm. The  spongioplasm  has  an  irregular  arrangement  with  open- 
ings in  all  directions,  so  that  the  contractility  of  undifferentiated  cells 
may  exhibit  itself  towards  any  point  of  the  compass. 

The  relation  of  cells  to  various  forms  of  stimulus  has  been  recently  very 
extensively  studied.  Various  forms  of  unicellular  organisms  have  been  used  in 
these  experiments,  and  the  stimuli  employed  have  been  chemical,  thermal,  light, 
electric  currents,  and  so  forth.  If  the  cell  moves  towards  the  source  of  attraction, 
the  term  positive  ta.cis  is  employed  ;  if  it  is  repelled,  nf(i((tive  (a.ris.  The  words, 
chemo-taxis,  thermo-taxis,  photo-taxis,  galvano-taxis,  etc.,  indicate  the  kind  of 
stimulus  investigated. 

Cell  Division. 

A  cell  multiplies  by  dividing  into  two;  each  remains  awhile 
in  the  resting  or,  more  correctly,  non-dividing  condition,  but 
later  it  grows  and  subdivides,  and  the  process  may  be  repeated 
indefinitely. 

The  supreme  importance  of  the  cell,  the  growth  of  the  body  from 
cells,  and  the  fact  that  cells  are  the  living  units  of  the  organism, 
were  first  established  in  the  vegetable  world  by  Schleiden,  and 
extended  to  the  animal  kingdom  by  Theodor  Schwann.  The  ideas 
of  physiologists  depending  on  this  idea  are  grouped  together  as 
cellular  physiology,  which  under  the  guidance  of  Virchow  was  ex- 
tended to  pathology  also :  Virchow  expressed  the  doctrine  now  so 
familiar  as  to  be  almost  a  truism  in  the  terse  phrase  omnis  cellula  e 
cellula  (every  cell  from  a  cell). 

The  division  of  a  cell  is  preceded  by  division  of  its  nucleus. 
Nuclear  division  may  be  either  (1)  simple  or  direct,  which  consists  in 
the  simple  exact  division  of  the  nucleus  into  two  equal  parts  by  con- 
striction in  the  centre,  which  may  have  been  preceded  by  division  of 
the  nucleoli ;  or  (2)  indirect,  which  consists  in  a  series  of  changes 
which  goes  on  in  the  arrangement  of  the  nuclear  reticulum,  resulting 
in  the  exact  division  of  the  chromatic  fibres  into  two  parts,  which 
form  the  chromoplasm  of  the  daughter  nuclei. 

The  changes  in  the  nucleus  during  indirect  division  constitute 
karyokinesis  (Kupvov,  a  kernel),  or  mitosis  {fxlro?,  a  thread),  and 
direct  division  is  called  amitotic  or  akinetic  (^'/i-z/o-i?,  movement).  It 
is  now  believed  that  the  mitotic  nuclear  division  is  all  but,  though 
not  quite,  universal.  Somewhat  different  accounts  of  the  stages  of 
the  nuclear  division  have  been  given  by  different  authorities,  accord- 
ing to  the  kind  of   cell  in  which    the  nuclear  changes   have  been 


CH.  II.] 


CELL   DIVISION 


17 


studied.     The  following  figure  (fig.  18)  shows  some  of    the  typical 
stages  of  karyokinesis  as  observed  by  Klein : — 


Fig.  is.— Karyokinesis.  a,  or<linary  nucleus  of  a  columnar  epithelial  cell ;  b,  c,  the  same  nucleus  In 
the  stage  of  convohition  ;  d,  the  wreath  or  rosette  form  ;  e,  the  aster,  or  single  star;  r,  a  nuclear 
spindle  from  the  Descemet's  endothelium  of  the  frog's  cornea ;  g,  h,  i,  diaster;  k,  two  daughter 
nuclei.    (Klein.) 

The  process  may  be  divided  into  the  following  stages : — 
1.  The  non-dividing  nucleus  (fig.  19.) 


Node  of  network 


Node  of  network 


--»-  Nuclear  membrane. 

—  Nucleolus. 

— -Nuclear  matrix. 
Nuclear  network. 


Fig.  19.— The  resting  nucleus.    (Waldeyer.) 

2.  The  spirem  or  skein  stage :  the  nucleoli  dissolve,  the  secondary 
fibres  disappear,  and  the  primary  loops  running  from  polar  to  anti- 
polar  regions  remain  (figs.  8,  20).  In 
some  cells  there  is  at  first  one  long, 
much  twisted  thread,  which  subse- 
quently breaks  up  into  segments.  The 
loops  are  called  chromosomes. 

3.  Each  loop  becomes  less  convo- 
luted and  splits  longitudinally  into  two 
sister  threads,  and  the  achromatic 
spindle  appears  (fig.  21,  a  and  b). 

4.  The  equatorial  stage;  monaster. 
The  nucleus  has  now  two  poles,  those 
of  the  spindle ;  and  at  each  pole  there  is  a  polar  corpuscle  or  centro 

B 


Fig.  20. — Early  condition  of  the  skein 
stage  viewed  at  the  polar  end.  I.  c.f., 
looped  chromatic  filament,  i./.,  irre- 
gular filament.    (Rabl.) 


18 


THE   ANIMAL   CELL 


[CH.  IL 


some.     The  division  of  the  cehtrosorae  of  the  original  cell,  and  then 
of  the  attraction  sphere  into  two,  usually  precedes  the  commence- 


Achromatic  spindle 


Fio  21  -Later  condition  of  the  skein  stace  in  karyokinesis.  a.  The  thicker  primary  fabres  or  chromo- 
wmes  become  less  convoluted  and  the  achromatic  spindle  appears,  b.  The  chromosomes  split  into 
two  and  the  achromatic  spindle  becomes  longitudinal.     (Waldeyer.) 

ment  of  changes  in  the  nucleus ;  the  two  attraction  spheres  become 
prominent  in  cell  division,  and  the 


Pole  of  spindle. 


Outer  granular 
zone. 


-  Split  fibres. 


Inner  clear  zone. 


'- Polar  corpuscle. 


-Monaster  stage  of  karyokinesis. 
(^Yaldeyer.) 


connecting  achromatic  spindle  is 

probably  also  formed  from  them 

or  from  the  achromatic  material 

of  the  nucleus. 

At    this    stage    the    nuclear 

membrane  is  lost,  and  thus  cell 

protoplasm      and     nuclear     sap 

become    continuous;   the   proto- 
plasm   immediately   around   the 

nucleus  is  clear;  outside  this  is 

a   granular   zone,   and   here   the 

granules    are    arranged    radially 

from  the  polar  corpuscles.     The 

star-like  arrangement  of  these  granules  is  much  better  marked  in 
Polar  circle  embryouic    cells,   indeed    the 

lines  present  very  much  the 
appearance  of  fibrils  (see  fig. 
23). 

The  V-shaped  chromosomes 
sink  to  the  equator  of  the 
spindle,  and  arrange  them- 
selves so  as  to  project  hori- 
zontally from  it. 

In  cells  which  are  the  re- 
sult of  the  sexual  process, 
the  number  of  chromosomes  is 
always  even,  an  equal  number 
being  contributed  by  each  sex. 
The  number  of  chromo- 
somes varies  with  the  species 
from  four  to  twenty-four ;  in  man  the  number  is  sixteen. 


B/IeduUary 


Spindle 


Atirnctio 
sphere 


Pole-body 


Antipodal  zone 


Fig.  23.— Ovum  of  the  worm  Ascaris  in  process  of  divi- 
sion. The  attraction  spheres  are  at  opposite  ends 
of  the  ovum  ;  at  the  equator  of  the  spindle  which 
unites  them,  four  chromosomes  are  seen.  The  proto- 
plasm of  the  ovum,  except  in  the  equatorial  zone  of 
the  cell,  is  arran.i,'ed  in  lines  radiating  from  the  centre 
(centrosome)  of  the  attraction  sphere.     (Waldeyer.) 


CH.  II.] 


KARYOKINESIS 


19 


5.  The  stage  of  mctakinesis.  The  sister  threads  separate,  one  set 
going  towards  one  pole,  and  the  other  to  the  other  pole  of  the  spindle 
(fig.  24)  :  these  form  the  two  daughter  nuclei.  The  chromosomes  are 
probably  pulled  into  their  new  position  by  the  contraction  of  the 
spindle  fibres  attached  to  them. 

6.  Each  daughter  nucleus  goes  backwards  through  the  same  series 


^^.1T^ 


Fine  uniting 
filaments. 


Fio.  24.— Metakinesis.     a.  Early  stage,     b.  Later  stage,     c.  Latest  stage— fonnatiou  of  diaster.     it.  and 
c.  show  how  the  sister  threads  disentangle  themselves  from  one  another.     (Waldeyer.) 

of  changes ;  the  diaster  or  double  star  is  followed  by  the  dispirem  or 
double  skein,  until  at  last  two  resting  nuclei  are  obtained  (fig.  25). 

A  new  membrane  forms  around  each  daughter  nucleus,  the  spindle 
atrophies,  and  the  attraction  sphere  becomes  less  prominent.  The 
division  of  the  cell  protoplasm  into  two  parts  around  the  two  nuclei 
begins  in  the  diaster  stage,  and  is  complete  in  the  stage  represented 
in  fig.  25. 


Remains  of  spindle. 


Line  of  separation  of  the 

two  cells. 
Antipole     of     daughter 

nucleus. 


~--.^  Lighter  substance  of  the 
..--"*     nucleus. 


Cell  protoplasm. 

Hilus. 


Fig.  25. — Final  stages  of  karyokinesis.     In  the  lower  daughter  nucleus  the  changes  are  still  more 
advanced  than  in  the  upper.    (Waldeyer.) 


The  karyokinetic  process  has  been  watched  in  all  its  stages  by 
more  than  one  observer.  The  time  occupied  varies  from  half  an  hour 
to  three  hours;  the  details,  however,  must  be  studied  in  hardened 
and  appropriately  stained  specimens.  They  are  most  readily  seen 
in  cells  with  large  nuclei,  such  as  occur  in  the  epidermis  of 
amphibians. 

The  process  varies  a  good  deal  in  different  animal  and  vegetable 


20 


THE   AJN'IMAL    CELL 


[CH.  II. 


cells ;  such  as  in  the  number  of 
importance  of  the  different  stages 
to  give  an  account  of  a  t}"pical  case, 
in  a  tabular  way  as  follows  (from  " 

NirnvoRK  OR  REncruM   . 


Skeis  or  Spirem 
Cleavage  .... 

Star  or  Monaster    . 

DlVERGEXCE   OR    MeTAKINESIS 

DornLE    SlAU    ()]{    DiA-l'EH 


DOLBLE    SkEIV    or    DiSPIREJI 

NEnvoHK  or  Rmrct'LVM    . 


chromosomes,  and    the  relative 
All  attempted  here  has   been 
The  phases  may  be  summarised 
Quain's  Anatomy  ") : — 

Resting    condition    of    mother    nucleus 

(fig.  19). 
Close  skein  of  fine  convoluted  filaments 

(fig.  20). 
Open  skein  of  thicker  filaments.    Spindle 

appears  (fig.  21  a). 
Movement   of    V-shaped    chromosomes 

to  middle  of  nucleus,  and  each   splits 

into  two  sister  threads  (fig.  21  b). 
Stellate  arrangement  of  V  filaments  at 

equator  of  spindle  (fig.  22). 
Separation  of  cleft  filaments  and  move- 
ment along  fibres  of  spindle  (fig.  24  a 

and  b). 
Conveyance  of  V  filaments  towards  poles 

of  sjjindle  (fig.  24  c). 
Open  skein  in  daughter  nuclei. 
Close  skein  in  daughter  nuclei  (fig.  25). 
Resting   condition    of    daughter    nuclei 

(fig.  25). 


The  Ovum. 

The  ovary  is  an  organ  which  produces  ova. 

An  ovum  is  a  simple  animal  cell ;  its  parts  are  seen  in  the  next 
diagram. 

It  is  enclosed  in  a  membrane  called  the  zona  pellucida  or  vitelline 
membrane.     The  body  of  the  cell  is  composed  of  protoplasm  loaded 


-Nucleus  or  geniiiiial  vesicle. 

\ Xucleoliis  or  germinal  spot. 

..space   left   by  retraction  of 
protoplasm. 

_  Protoplasm  containing  yolk 
spherules. 


-Vitelline  membrane. 


Fig.  26. Kepresentation  of  a  human  o\Tim.     (Cadiat.) 

with  granules  of  food  material,  called  the  yolk  or  vitellus.  The 
nucleus  and  nucleolus  are  sometimes  still  called  by  their  old  names, 
germinal  vesicle  and  germinal  spot  respectively.  The  attraction  sphere 
is  not  shown  in  the  diagram. 

The  formation  of  ova  will  form  the  subject  of  a  chapter  later  on, 


CII.  II.] 


THE   OVUM 


21 


but  it  is  convenient  here  at  the  outset  to  state  briefly  one  or  two 
facts,  and  introduce  to  the  student  a  few  terms  which  we  shall  have 
to  employ  frequently  in  the  intervening  chapters. 

The  ovum  first  discharges  from  its  interior  a  portion  of  its 
nucleus,  which  forms  two  little  globules  upon  it  called  the  polar 
globules. 

Fertilisation  then  occurs ;  that  is  to  say,  the  head  or  nucleus  of 
a  male  cell  called  a  spermatozoon  penetrates  into  the  ovum,  and 
becomes  fused  with  the  remains  of  the  female  nucleus. 

Cell  division  or  segmentation  then  begins,  and  the  early  stages 
are  represented  in  the  next  figure. 

Fluid  discharged  from  the  cells  accumulates  within  the  interior 
of  the  mulberry  mass  seen  in  fig.  27  d,  and  later,  if  a  section  is  cut 
through  it,  the  cells  will  be  found  arranged  in  three  layers. 

The  outermost  layer  is  called  the  epiblast. 

The  middle  layer  is  called  the  mesoblast. 

The  innermost  layer  is  called  the  hypoblast. 

From  these  three  layers  the  growth  of  the  rest  of  the  body  occurs, 


Fig.  27. — Diagram  of  an  ovum  (a)  imdergoing  segmentation.  In  (6)  it  has  divided  into  two,  in  (c)  into 
four;  and  in  (d)  the  process  has  resulted  in  the  production  of  the  so-called  "mulberry-mass." 
(Fray.) 

nutritive  material  being  derived  from  the  mother  in  mammals  by 
means  of  an  organ  called  the  placenta. 

The  epiblast,  the  outermost  layer  of  the  embryo,  forms  the  epi- 
dermis, the  outermost  layer  of  the  adult.  It  also  forms  the  nervous 
system. 

The  hypoblast,  the  innermost  layer  of  the  embryo,  forms  the 
lining  epithelium  of  the  alimentary  (except  that  of  the  mouth  and 
anus  which  are  involutions  from  the  epiblast)  and  respiratory  tracts, 
that  is,  the  innermost  layer  of  the  adult.  It  also  forms  the  cellular 
elements  in  the  large  digestive  glands,  such  as  the  liver  and  pancreas, 
which  are  originally,  like  the  lungs,  outgrowths  from  the  primitive 
digestive  tube. 

The  mesoblast  forms  the  remainder,  that  is,  the  great  bulk  of  the 
body,  including  the  muscular,  osseous,  and  other  connective  tissues ; 
the  circulatory  and  urino-genital  systems. 


CHAPTEK  III 

EPITHELIUM 

The  elementary  tissues  of  which  the  organs  of  the  body  are  built 
up  may  be  arranged  into  four  groups  :  epithelial,  connective,  muscular, 
and  nervous.  The  first  of  these,  the  epithelial  tissues,  follows 
naturally  on  a  study  of  the  animal  cell,  as  an  epithelium  may  be 
defined  as  a  tissue  composed  entirely  of  cells  united  by  a  minimal 
amount  of  cementing  material.  As  a  rule,  an  epithelium  is  spread 
out  as  a  membrane  covering  a  surface  or  lining  the  cavity  of  a  hollow 
organ. 

These  epithelia  may  be  grouped  into  two  great  classes,  each  of 
which  may  be  again  subdivided  according  to  the  shape  and  arrange- 
ment of  the  cells  of  which  it  is  composed.  The  following  table  gives 
the  principal  varieties  : — 

ClASS  1. — Simple  epithelium;  that  is,  an  epithelium  consisting 
of  one  layer  of  cells  only.     Its  subgroups  are  as  follows : — 

a.  Pavement  epithelium. 

b.  Cubical  and  columnar  epithelium. 

c.  Ciliated  epithelium. 

Class  2. — Compound  epithelium;  that  is,  an  epithelium  consist- 
ing of  more  than  one  layer  of  cells.     Its  subgroups  are  as  follows : — 

a.  Transitional  epithelium. 

b.  Stratified  epithelium. 

This  classification  does  not  include  the  more  specialised  forms  of 
epithelium  found  in  secreting  glands,  or  in  the  sense  organs,  nor 
structures  like  hair,  and  enamel  of  tooth,  which  are  epithelial  in 
origin.     These  will  be  considered  in  their  proper  place  later  on. 

Pavement  Epithelivun. 

This  consists  of  a  layer  of  thin  cells,  arranged  like  flat  pavement- 
stones  accurately  fitting  together  and  united  by  a  small  amount  of 
cementing  material.  The  structure  of  the  cells  and  their  outlines 
may  be  best  demonstrated  in  the  following  way : — 

A  portion  of  the  fresh  tissue  is  taken  and  immersed  for  a  few 


CII.  ITT.] 


PAVEMENT    EPITIIETJUM 


23 


minutes  in  a  1  per  cent,  solution  of  nitrate  oi'  silver;  it  is  taken  out, 
washed  with  distilled  water,  and  cxi)osed  in  water  or  spirit  to  sun- 
light.    The  silver  forms  a  compound  with  the  cement,  which  in  the 


---i-'. 


v<  S 

<  V 


Fio.  28. — From  a  section  of  the  lung  of  a  cat,  stained  witli  silver  nitrate.  N.  Alveoli  or  air-cells, 
lined  with  large  flat,  nucleated  cells,  with  some  smaller  polyhedral  nucleated  cells.  (Klein  and 
Noble  Smith.) 

light  is  decomposed  or  reduced,  leading  to  a  fine  deposit  of  silver, 
showing  as  black  or  brown  lines  between  the  cells,  and  accurately 
defining  their  outlines.  The  preparation  may  then  be  immersed  in 
some  stain  like  logwood  to  bring  out  the  nuclei,  and  finally  mounted 
in  the  usual  wav. 


Fig.   29. — Abdominal  surface  of  central  tendon  of  the  diaphragm  of  rabbit,   showing  the   general 
polygonal  shape  of  the  endothelial  cells  ;  each  cell  is  nucleated,     x  300.    (Klein.) 

Fig.  28  shows  the  appearance  presented  in  a  preparation  of  lung. 
In  the  alveoli  or  air-sacs  of  the  lung,  pavement  epithelium  of  a  typical 
kind  is  found  forming  a  linincr  membrane. 


24 


EPITHELIUM 


[CH.  III. 


Endothelium. — Epithelium  of  similar  appearance  is  found  lining 
the  interior  of  the  whole  of  the  vascular  system,  heart,  arteries,  capil- 


FiG.  30.— Peritoneal  surface  of  a  portion  of  the  septum  of  the  great  lymph-sac  of  a  frog.    The  stomata, 
some  of  which  are  open,  some  collapsed,  are  well  shown,     x  160.    (Klein.) 

laries,  veins,  and  lymphatics,  and  in  the  adjuncts  of  the  circulatory 

system  called  the  serous  membranes  (pericardium,  peritoneum,  etc.). 

This  epithelium  is  formed  from  the  middle  layer  of  the  embryo, 


Fig.  31.— a  portion  of  the  great  omentum  of  dog,  which  shows,  amongst  the  flat  endothelium  of  the 
surface,  smaU  and  large  groups  of  germinating  endothelium,  between  which  are  many  stomata. 
X  300.    (Klein.) 

the  mesoblast;  most  other  epithelium  is  derived  either  from  epiblast  or 
hypoblast.     Hence  it  has  received  a  distinct  name,  viz.:  endothelium. 


en.  III.] 


COLUMNAR   EPITHKLIUM 


2f) 


The  general  appearance  presented  by  endothelium  in  serous  mem- 
branes is  shown  in  figs.  29,  30,  and  31 ;  in  blood-vessels  in  fig.  32. 

The   stomata   seen    in   some   of   the       

drawings  are  minute  openings  sur- 
rounded by  more  darkly  staining  cells, 
which  lead  from  serous  cavities  into 
lymphatic  vessels. 

Cubical,  Spheroidal,  and  Columnar 
Epithelium. 

In  these  forms  of  epithelium,  the 
cells  are  not  flat,  but  are  thick ;  if  they 
approximate  cubes  or  spheres  in  shape, 
the  epithelium  is  called  cubical  or 
spheroidal  respectively.  Polyhedral  epi- 
thelium is  found  in  the  alveoli  of  secret- 
ing glands,  such  as  the  salivary  glands, 
liver,  and  pancreas  (see  figs.  33  and  34), 
and  will  be  discussed  at  length  in  con- 
nection with  those  organs.  Cubical  epi- 
thelium is  found  in  the  alveoli  of  the 
thyroid  (see  fig.  35),  in  the  tubules  of 
the  testis,  and  in  the  ducts  of  some 
glands. 

In  columnar  epithelium  the  cells  are 
tall,  and  form  a  kind  of  palisade  or  rows 
of  columns.  It  is  found  lining  the  in- 
terior of  the  stomach  and  intestines,  and 
the  ducts  of  the  majority  of  secreting 
glands;  it  forms  also  the  layer  on  the 
outer  surface  of  the  ovary. 

In  the  intestinal  epithelium  each  cell  has  a  distinct  brightly 
refracting  and  striated  border.  Fig.  36  shows  two  isolated  cells  of 
this  kind. 

The  nucleus  with  its  usual  network  and  the  vacuolated  condition 
of  the  protoplasm  are  very  well  seen.  The  attached  border  is  narrower 
than  the  free  edge.  Amoeboid  lymph  cells  are  found  in  the  spaces 
that  must  necessarily  be  left  when  cells  of  such  a  shape  cover  a 
surface.  Fig.  37  shows  a  row  of  columnar  cells  from  the  rabbit's 
intestine. 

The  next  figure  (fig.  38)  shows  the  arrangement  of  these  cells  on 
the  surface  of  a  villus,  one  of  the  numerous  little  projections  found 
in  the  small  intestine. 

The  gaps  seen  there  are  due  to  the  formation  of  what  are  called 
goblet  cells.     In  some  of  the  columnar  cells,  a  formation  of  granules 


Fio.  32.-  Surface  view  of  an  artery  from 
the  mesentery  of  a  frog,  ensheathed 
in  a  peri-vascular  lympliatic  vessel, 
o,  The  artery,  with  its  circular 
muscular  coat  (media)  indicated  by 
broad  transverse  markings,  with 
an  indication  of  the  adveutitia  out- 
side. I,  Lymphatic  vessel ;  its  wall 
is  a  simple  endothelial  membrane. 
(Klein  and  Noble  Smith.) 


2G 


EPITHELIUM 


[ni.  III. 


occurs  which  consist  of  a  substance  called  mucigen ;  these  run 
together,  and  are  discharged  from  the  cell  as  a  brightly  refracting 
globule  of  mucin,  leaving  the  cell  with  open  mouth  like  a  goblet,  the 


Fig.  33.— Glandular  epithelium.  Small  lobule  of  a 
mucous  gland  of  the  tongue,  showing  nucleated 
glandular  cells.      -■  200.     (V.  D.  Harris.) 


Flo.  34. — A  small  piece  of  the  liver  of 
the  horse.     (Cadiat.) 


nucleus  being  surrounded  by  the  remains  of  the  prot02:)lasm  in  its 
narrow  stem  (see  fig.  39). 

This  transformation  is   a  normal  process    continually  going  on 


Fig.  35.— Section  of  human  thyroid;  the  few  vesicles  shown  are  lined  by  cubical  epithelium,  and 
contain  a  colloid  material.     (After  Schlifer.) 

throughout  life,  the  discharged  mucin  contributing  to  form  mucus. 
The  cells  themselves  may  recover  their  original  shape  after  discharge, 
and  repeat  the  process  later  on. 


CII.  III.] 


CILIATED    EPITHELIUM 


27 


Ciliated  Epithelium. 

The  cells  of  ciliated  epithelium  are  generally  of  columnar  shape 
(fig.  40),  but  they  may  occasionally  be  spheroidal  (fig.  41). 


,,tr.j 


Kit;.  30. — Columnar  epithelium  cells  of  the  rabbit's 
intestine.  The  cells  have  been  isolated  after 
maceration  in  very  weak  chromic  acid.  The 
cells  are  much  vacuolated,  ami  one  of  them 
has  a  fat  globule  near  its  attached  end.  The 
striated  border  (str.)  is  well  seen,  and  the 
bright  disc  separating  it  from  the  cell  proto- 
plasm, n,  nucleus  with  intranuclear  net- 
work, a,  a  thiimed-out  winglike  projection 
of  the  cell  which  probably  fitted  between  two 
.adjacent  cells.    (Schafer.) 


Fig,  ?S.— Vertical  section  of  an  intestinal  villus 
of  a  cat.  a,  the  striated  border  of  the  epi- 
thelium ;  h,  columnar  epithelium ;  c,  goblet 
cells  ;  d,  central  lymph-vessel ;  e,  unstriped 
muscular  fibres ;  /,  adenoid  stroma  of  the 
villus  in  which  are  contained  lymph-cor- 
puscles.   (Klein.) 


Fig.  37. — A  row  of  colunmar  cells  from  the 
rabbit's  intestine.  Smaller  cells  are  seen 
between  the  epithelium  cells ;  these  are 
lymph-corpuscles.    (Schafer.) 


FiQ.  39.— Goblet  cells.    (Klein.) 


Fig.  40. — Ciliated  epithelium  from  the  human 
trachea,  a,  large  fully-formed  cell ;  b, 
shorter  cell ;  c,  developing  cells  with  more 
than  one  nucleus.     (Cadiat.) 


Fig.  41. — Spheroidal  ciliated 
cells  from  the  mouth  of 
the  frog.  X  SOO  diame- 
ters.   (Sharpey.) 


28 


EPrrHEUITM 


[cH.  ni. 


trachea,  a,  layer  of  longitadinally  arranged 
elastic  fibres ;  h,  basement  membrane ;  e, 
deepest  cells,  circalar  in  fDrm;  d,  inter- 
mediate elongatMl  cells;  e,  outermost  layer 
of  cells  folly  developed  and  bearing  cilia- 
X  350.    (Kolliker.) 


Each  cell  is  sm-mounted  by  a  bunch  of  fine  tapering  filaments. 

They  were  originally  called  cilia  because  of  their  resemblance  in  shape 

to  eyelashes.  They  differ  from 
eyelashes  in  being  extremely 
small,  and  in  not  being  stiff; 
they  are  in  fact  composed  of  pro- 
toplasm. During  life  these  move 
to  and  fro,  and  so  produce  a  cur- 
rent of  fluid  over  the  surface  they 
cover.  Like  columnar  cells,  they 
may  form  goblet  cells  and  dis- 
charge mucin. 

In  the  larger 
ciliated  cells,  it 
will  be  seen  that 
the  border  on 
which  the  ciHa 
are  set  is  bright, 

and  composed  of  little  knobs,  to  each  of  which  a 

cilium  is  attached ;  in  some  cases  the  knobs  are 

prolonged  into  the  cell  protoplasm  as  filaments 

or  rootlets  (fig.  43).     According  to  some  observers 

these  rootlets  are  outgrowths  from  the  multiplied 

centrosome  of  the  cell 

The   bunch   of    cilia  is  homologous  with   the 

striated  border  of  columnar  cells. 

Ciliated  epithelium   is  found   in   the  human 

body,  '1)  lining  the  air  passages,  but  not  in  the 

alveoli  of  the  lungs ;  these  are  lined  by  pavement 

epithelium ;  (2)  in  the  Fallopian  tubes  and  upper 

part  of  the  uterus ;  (3)  in  the  ducts  of  the  t-estis 

known  as  the  vasa  efferentia  and  coni  vasculosi ; 

here  the  cilia  are  the  longest  found  in  the  body ; 

(4)  in  the  ventricles  of   the    brain  and    central 

canal  of  the  spinal  cord ;  (5)  the  tail  of  a  sperma- 
tozoon may  also  be  regarded  as  a  long  cilium. 
In   other   animals   cilia   are   found   in   other 

parts;  for  instance,  in  the  frog  the  mouth   and 

gullet  are  Lined  by  ciliated  cells ;  in  the  tadpole, 

the  whole  surface  of  the  body  and  especially  the 

gills  are  covered  with  cilia 

brates  one  finds  many  protozoa  completely  covered 

with  cilia ;  in  many  embryos  the  cilia  are  arranged 

in  definite  bands  round  the  body ;  in  the  rotifers  or  wheel  animal- 
cules, a  ring  of  cilia  round  the  mouth  gives  the  name  to  this  par- 


Amons  the  inverte-  F'<^-  43.-<^tedoeUfr«im 

"  the  utestme  of  «  mol- 

Insc.    (Engelmann.) 


CH.  III.]  CILIARY   MOTION  29 

ticular  group.     The  gills  of   many  animals  are  covered  with  cilia; 
and  the  cells  of  the  kidney  tubules  in  some  animals  are  ciliated. 

Ciliary  Motion. 

Ciliary  motion  reminds  one  of  amoeboid  movement,  but  it  is  much 
more  rapid,  and  more  orderly.  It  consists  of  a  rhythmical  movement 
of  the  cilia,  a  bending  over,  followed  by  a  lessening  of  the  curvature, 
repeated  with  great  frequency. 

When  living  ciliated  epithelium,  e.g.,  from  the  gill  of  a  mussel,  or 
from  the  mouth  of  the  frog,  is  examined  under  the  microscope  in  a 
drop  of  075  per  cent,  solution  of  common  salt  {normal  saline  solution), 
the  cilia  are  seen  to  be  in  constant  rapid  motion,  each  cilium  being 
fixed  at  one  end,  and  swinging  or  lashing  to  and  fro.  The  general 
impression  given  to  the  eye  of  the  observer  is  very  similar  to  that 
produced  by  waves  in  a  field  of  corn,  or  swiftly  running  and  rippling 
water,  and  the  result  of  their  movement  is  to  produce  a  continuous 
current  in  a  definite  direction,  and  this  direction  is  the  same  on  the 
same  surface,  being  usually  in  the  case  of  a  cavity  towards  the 
external  orifice. 

There  is  not  only  rhythmicality  in  the  movement  of  a  single 
cilium,  but  each  acts  in  harmony  with  its  fellows  in  the  same  cell, 
and  on  neighbouring  cells. 

The  uses  of  cilia  can  from  the  above  be  almost  guessed ;  in  the 
respiratory  passages  they  create  a  current  of  mucus  with  entangled 
dust  towards  the  throat;  in  the  Fallopian  tube  or  oviduct  they  assist 
the  ovum  on  its  way  to  the  uterus ;  in  the  gullet  of  the  frog  they  act 
downwards  and  assist  swallowing ;  in  the  ciliated  protozoa  they  are 
locomotive  organs.  Over  the  gills  of  marine  animals  they  keep  up  a 
fresh  supply  of  water,  and  in  the  case  of  the  rotifers,  which  are  fixed 
animals,  the  current  of  water  brings  food  to  the  mouth. 

Ciliary  motion  is  independent  of  the  will,  and  of  the  influence 
of  the  nervous  system.  It  may  continue  for  several  hours  after 
death  or  removal  from  the  body,  provided  the  portion  of  tissue  under 
examination  be  kept  moist.  Its  independence  of  the  nervous  system 
is  shown  also  in  its  occurrence  in  the  lowest  invertebrate  animals, 
which  are  unprovided  with  anything  analogous  to  a  nervous  system. 
The  vapour  of  ether  or  chloroform  and  carbon  dioxide  arrest  the 
motion,  but  it  is  renewed  on  the  discontinuance  of  the  application. 
The  movement  ceases  when  the  cilia  are  deprived  of  oxygen,  although 
it  may  continue  for  a  time  in  the  absence  of  free  oxygen,  but  is 
revived  on  the  admission  of  this  gas.  The  contact  of  various  sub- 
stances, e.g.,  bile,  strong  acids,  and  alkalis,  will  stop  the  motion 
altogether;  but  this  depends  on  destruction  of  the  delicate  substance 
of  which  the  cilia  are  composed.    Temperatures  above  45'  C.  and  near 


30  EPITHELIUM  [CH.  III. 

0"  C.  stop  the  movement,  whereas  moderate  heat  and  dilute  alkalis 
are  favourable  to  the  action,  and  revive  the  movement  after  tempoi'ary 
cessation.  The  exact  explanation  of  ciliary  movement  is  not  known ; 
whatever  may  be  the  exact  cause,  the  movement  must  depend  upon 
some  changes  going  on  in  the  cell  to  which  the  cilia  are  attached,  as 
when  the  latter  are  cut  off  from  the  cell  the  movement  ceases,  and 
when  severed  so  that  a  portion  of  the  cilia  are  left  attached  to  the 
cell,  the  attached  and  not  the  severed  portions  continue  the  move- 
ment. It  has  been  suggested  by  Engelmann  that  the  contractile  part  ^ 
of  the  protoplasm  is  only  on  the  concave  side  of  a  curved  cilium,  and 
that  when  this  contracts  that  the  cilium  is  brought  downwards ; 
where  relaxation  occurs,  the  cilium  rebounds  by  the  elastic  recoil  of 
the  convex  border. 

Schafer  has  suggested  that  the  flow  of  hyaloplasm  backwards  and 
forwards  will  explain  ciliary  as  it  will  amceboid  movement.  In  an 
amoeboid  cell,  the  spongioplasm  is  irregular  in  arrangement,  hence  an 
outflow  of  hyaloplasm  from  it  can  occur  in  any  direction.  But  in 
the  curved  projection  called  a  cilium,  the  hyaloplasm  can  obviously 
flow  in  only  one  direction  into  the  cilium  and  back  again.  The  flow 
of  hyaloplasm  into  the  cilium  will  raise  the  pressure  there  and  cause 
it  to  straighten  ;  a  movement  in  the  reverse  direction  will  cause  the 
cilium  to  curve. 

The  action  of  dilute  alkalis  and  acids  on  cilia  is  interesting. 
Dilute  acids  stop  ciliary  motion ;  and  cilia,  if  allowed  to  act  in  salt 
solution  for  a  time,  get  more  and  more  languid,  and  finally  cease 
acting;  in  popular  language  they  become  fatigued.  Now  we  shall 
find  in  muscle  that  fatigue  is  largely  due  to  the  accumulation  of  the 
acid  products  of  muscular  activity ;  remove  the  sarco-lactic  acid  and 
fatigue  passes  off.  It  is  probalDle  that  the  same  occurs  in  other 
contractile  tissues ;  the  cilia  gradually  stop,  due  to  acid  products  of 
their  activity  collecting  around  them;  when  these  are  neutralised 
with  dilute  alkali  the  cilia  resume  activity. 

Transitional  Epithelium. 

This  term  has  been  applied  to  cells  which  are  neither  arranged 
in  a  single  layer,  as  is  the  case  with  simple  epithelium,  nor  yet  in 
many  superimposed  strata,  as  in  stratified  epithelium;  in  other 
words,  it  is  employed  when  epithelial  cells  are  found  in  two,  three,  or 
four  superimposed  layers. 

The  upper  layer  may  be  either  columnar,  ciliated,  or  squamous. 
When  the  upper  layer  is  columnar  or  ciliated  the  second  layer  con- 
sists of  smaller  cells  fitted  into  the  inequalities  of  the  cells  above 
them,  as  in  the  trachea  (fig.  42). 

The  epithelium  which  is  met  with  lining  the  urinary  bladder  and 


en.  III.] 


STRATIFIED    EPITHELIUM 


31 


ureters  is,  however,  the  transitional  far  excellence.  In  this  variety 
there  are  two  or  three  layers  of  cells,  the  upper  being  more  or  less 
flattened  according  to  the  full  or  collapsed  condition  of  the  organ, 
their  under  surface  being  marked  with  one  or  more  depressions,  into 
which  the  heads  of  the  next  layer  of  club-shaped  cells  fit.  Between 
the  lower  and  narrower  parts  of  the  second  row  o^  cells  are  fixed  the 


Fig.  44. — Eijithelium  of  the  bladder,  a,  one 
of  tlie  cells  of  the  first  row ;  h,  a  cell  of 
the  second  row  ;  c,  cells  in  situ,  of  first, 
second,  and  deepest  layers.  (( )bersteiner.) 


Fi<;.  45.— Transitional  epithelial  cells 
from  a  scraping  of  the  mucous 
membrane  of  the  bladder  of  the 
rabbit.    (V.  D.  Harris.) 


irregular  cells  which  constitute  the  third  row;  sometimes  a  fourth 
row  is  present  (fig.  44).  If  a  scraping  of  the  mucous  membrane  of 
the  bladder  is  teased,  and  examined  under  the  microscope,  all  these 
forms  may  be  made  out  (fig.  45).  Each  cell  contains  a  large  nucleus, 
and  the  larger  and  superficial  cells  often  possess  two. 


Stratified  Epithelium. 

The  term  stratified  epithelium  is  employed  when  the  cells  forming 
the  epithelium  are  arranged  in  a  considerable  number  of  super- 
imposed layers.  The  shape  and  size  of  the  cells  of  the  different 
layers,  as  well  as  the  number  of  the 
layers,  vary  in  different  situations ;  but 
the  superficial  cells  are,  as  a  rule,  of  the 
squamous,  or  scaly  variety,  and  the 
deepest  of  the  columnar  form. 

The  cells  of  the  intermediate  layers 
are  of  different  shapes,  but  those  of  the 
middle  layers  are  more  or  less  rounded. 
The  superficial  cells  are  broad  and  over- 
lap by  their  edges  (fig.  46).  Their  chemical  composition  is  different 
from  that  of  the  underlying  cells,  as  they  contain  keratin,  and  are 
therefore  horny  in  character. 

The  really  cellular  nature  of  even  the  dry  and  shrivelled  scales 
cast  off  from  the  surface  of   the  epidermis  can  be   proved  by  the 


Fig.  46.— Epithelium  scales  from  their 
side  of  the  mouth,     x  260.    (Henle.) 


32 


EPITHELIUM 


[CH.  III. 


application  of  caustic  potash,  which  rapidly  causes  them  to  swell 
and  assume  their  original  form.  Their  nuclei,  however,  have 
disappeared. 

The  squamous  cells  exist  in  the  greatest  number  of  layers  in  the 
epidermis   or  superficial  part  of   the   skin;   the  most  superficial   of 


Fig.  47. Vertical  section  of  the  stratified  epithelium  of  the  rabbit's  cornea,    a,  anterior  epithelium, 

showing  the  different  shapes  of  the  cells  at  various  depths  from  the  free  surface  ;  b,  a  portion  of  the 
substance  of  cornea.    (Klein.) 

these  are  being  continually  removed  by  friction,  and  new  cells  from 
below  supply  the  place  of  those  cast  off. 

In  many  of  the  deeper  layers  in  the  mouth  and  skin  the  outline 
of  the  cells  is  very  irregular,  in  consequence  of  processes  passing 
from  cell  to  cell  across  these  intervals. 

Such  cells  (fig.  48)  are  termed  "  ridge  and  furrow,"  "  cogged  "  or 
"prickle"  cells.  These  "prickles"  are  prolongations  of  the  intra- 
cellular network  which  run  across  from  cell  to  cell,  thus  joining  them 

together,  the  interstices  being  filled  by 
lymph  and  transparent  inter-cellular 
cement  substance.  When  this  increases 
in  quantity  in  inflammation  the  cells 
are  pushed  further  apart,  and  the  con- 
necting fibrils  or  "  prickles "  are  elon- 
gated and  therefore  more  clearly  visible. 


This  connection  of  cell  to  cell  is  sometimes 
spoken  of  as  conf.inuitij  of  protoplasm  ;  the  same 
occurs  in  involuntary  muscular  tissue.  It  is 
very  marked  in  the  tissues  of  many  plants. 


Fig.  48. — Jagged  cells  from  the  middle 
layers  of  stratified  epithelium,  from  a 
vertical  section  of  the  gum  of  a  new- 
bom  infant.    (Klein.) 


The  columnar  cells  of  the  deepest 
layer  are  distinctly  nucleated;  they 
multiply  rapidly  by  division ;  and  as  new  cells  are  formed  beneath, 
they  press  the  older  cells  forwards  to  be  in  turn  pressed  forwards 
themselves  towards  the  surface,  gradually  becoming  flatter  in  shape 
and  horny  in  composition  until  they  are  cast  off  from  the  surface. 

Stratified  epithelium  is  found  in  the  following  situations: — (1) 
Forming  the  epidermis,  covering  the  whole  of  the  external  surface  of 
the  body;  (2)  Covering  the  mucous  membrane  of  the  nasal  orifice, 


CH.  III.]  CHEMISTRY   OF    EPITHELIUM  33 

tongue,  mouth,  pharynx,  and  oesophagus ;  (3)  As  the  conjunctival 
epithelium,  covering  the  cornea ;  (4)  Lining  the  vagina  and  the 
vaginal  part  of  tlie  cervix  uteri. 

Nutrition  of  Epithelium. 

Epithelium  has  no  blood-vessels ;  it  is  nourished  by  lymph. 
When  the  blood  is  circulating  through  the  thin-walled  small  blood- 
vessels in  the  tissues  beneath  the  epithelium,  some  of  its  fluid  con- 
stituents escape.  This  fluid  is  called  lyviph ;  it  penetrates  to  all 
parts  of  the  cellular  elements  of  tissues  and  nourishes  them.  In  the 
thicker  varieties  of  epithelium,  the  presence  of  the  irregular  minute 
channels  between  the  prickle  cells  (fig.  48)  enables  the  lymph  to  soak 
more  readily  between  the  cells  than  it  would  otherwise  be  able  to  do. 
Epithelium  is  also  destitute  of  nerves  as  a  rule.  But  in  stratified 
epithelium,  particularly  that  covering  the  cornea  at  the  front  of  the 
eye  and  in  the  deeper  layers  of  the  epidermis,  a  plexus  of  nerve 
fibrils  is  found. 

Chemistry  of  Epithelium. 

There  is  not  much  to  add  to  what  has  been  already  stated  con- 
cerning cells ;  protoplasm  and  nucleus  have  the  same  chemical  com- 
position as  has  been  already  described  in  Chapter  II.  Two  new 
substances  have,  however,  been  mentioned  in  the  foregoing  chapter — 
namely,  mucin  and  keratin. 

Mucin. — This  is  a  widely  distributed  substance  occurring  in 
epithelial  cells  or  shed  out  by  them  (see  goblet  cells,  fig.  39).  It  also 
forms  the  chief  constituent  of  the  cementing  substance  between 
epithelial  cells.  We  shall  again  meet  with  it  in  the  intercellular 
substance  of  the  connective  tissues.  The  mucin  obtained  from 
different  sources  varies  somewhat  in  composition  and  reactions,  but 
they  all  agree  in  the  following  points : — 

(a)  Physical  character :  viscid  and  tenacious. 

(b)  Precipitability  from  solutions  by  acetic  acid.     They  all  dis- 

solve in  dilute  alkalis,  like  lime-water. 

(c)  They  are   all   compounds   of   protein,   with   a   carbohydrate 

material;  by  treatment  with  mineral  acid  this  is  hydrated 
into  a  reducing  but  non-fermentable  sugar-like  substance. 
The  substance  mucin,  when  it  is  formed  within  cells  (goblet  cells, 
cells  of  mucous  glands),  is  preceded  in  the  cells  by  granules  of  a 
substance  which  is  not  mucin,  but  is  readily  changed  into  mucin. 
This  precursor,  or  mother-substance  of  mucin,  is  called  mucigen  or 
mucinogen. 

Keratin,  or  horny  material,  is  the  substance  found  in  the  surface 
layers  of  the  epidermis,  in  hairs,  nails,  hoofs,  and  horns.     It  is  very 

C 


34  EPITHELIUM  [CH,  III. 

insoluble,  and   chiefly   differs   from  other  proteins  in  its  high  per- 
centage of  sulphur. 

The  silver  nitrate  reaxtion  of  cementi'nrj  suhstrxnce.  7  he  principal 
chemical  reaction  which  is  employed  by  hi.stologists  for  demonstrat- 
ing the  cement  or  intercellular  substance  which  binds  epithelial  cells 
together  was  formerly  supposed  to  be  due  to  the  formation  of  a 
silver-protein  compound  which  was  reduced  by  sunlight.  Macallum 
has  conclusively  shown  that  this  is  not  the  case,  but  that  it  is  an 
inorganic  reaction.  Cementing  material  is  especially  rich  in  chlorides 
(mainly  sodium  chloride);  the  addition  of  silver  nitrate  leads  to  the 
formation  of  silver  chloride,  and  it  is  this  which  is  reduced  by  light. 
The  silver  reaction  obtained  in  other  tissues  is  similarly  explained : 
in  fact  silver  nitrate  is  a  micro-chemical  reagent  for  detecting  the 
localities  in  the  body  where  chlorides  occur.  According  to  Mac- 
allum the  nuclei  of  all  cells  are  entirely  free  from  chlorides. 


CHAPTER  IV 

THE   CONNECTIVE   TISSUES 


The  connective  tissues  are  the  following 


1.  Areolar  tissue. 

2.  Fibrous  tissue. 

3.  Elastic  tissue. 

4.  Adipose  tissue. 

5.  Eetiform  and  lymphoid  tissues. 

6.  Jelly-like  tissue. 

7.  Cartilage. 

8.  Bone  and  dentine. 

9.  Blood. 

At  first  sight  these  numerous  tissues  appear  to  form  a  very 
heterogeneous  group,  including  the  most  solid  tissues  of  the  body 
(bone,  dentine)  and  the  most  fluid  (blood). 

But  on  examining  a  little  more  deeply,  one  finds  that  the  group- 
ing of  these  apparently  different  tissues  together  depends  on  a  number 
of  valid  reasons,  which  may  be  briefly  stated  as  follows : — 

1.  They  all  resemble  each  other  in  origin.     All  are  formed  from 

the  mesoblast,  the  middle  layer  of  the  embryo. 

2.  They  resemble  each  other  structurally;   that   is   to   say,  the 

cellular   element   is   at  a   minimum,  and   the   intercellular 
material  at  a  maximum. 

3.  They  resemble  each  other  functionally ;  they  form  the  skeleton, 

and  act  as  binding,  supporting,  or  connecting  tissues  to  the 

softer  and  more  vital  tissues. 
An  apology  is  sometimes  made  for  calling  the  blood  a  tissue, 
because  one's  preconceived  idea  of  a  tissue  or  texture  is  that  it  must 
be  something  of  a  solid  nature.  But  all  the  tissues  contain  water. 
Muscular  tissue  contains,  for  instance,  at  least  three-quarters  of  its 
weight  as  water.  Blood,  after  all,  is  not  much  more  liquid  than 
muscle.  Blood,  moreover,  contains  cellular  elements  analogous  to  the 
cells  of  other  tissues,  but  separated  by  large  quantities  of  a  fluid 
intercellular  material  called  blood-plasma. 

35 


36 


THE   CONNECTIVE   TISSUES 


[CH.  IV. 


Blood  is  also  mesoblastic,  and  thus  the  two  first  characteristics  of 
a  connective  tissue  are  present.  It  does  not  fulfil  the  third  condition 
by  contributing  to  the  support  of  the  body  as  part  of  the  skeleton, 
but  it  does  so  in  another  sense,  and  serves  to  support  the  body  by 
conveying  nutriment  to  all  parts. 

Areolar  Tissue. 

This  is  a  very  typical  connective  tissue.  It  has  a  wide  distribu- 
tion, and  constitutes  the  subcutaneous,  subserous,  and  submucous 
tissues.  It  forms  sheaths  (fasciae)  for  muscles,  nerves,  blood-vessels, 
glands,  and  internal  organs,  binding  them  in  position  and  penetra- 
ting into  their  interior,  supports  and  connects  their  individual  parts. 

If  one  takes  a  little  of  the  subcutaneous  tissue  from  an  animal, 
and  stretches  it  out  on  a  glass  slide,  it  appears  to  the  naked  eye  like 
a  soft,  fleecy  network  of  fine  white  fibres,  with  here  and  there  wider 
fibres  joining  it.     It  is,  moreover,  elastic. 

But  in  order  to  make  out  its  structure  accurately,  it  is  necessary 
to  examine  the  thinnest  portions  of  the  film  with  the  microscope,  and 


Fig.  49.— Bundles  of  the  white  fibres  of  areolar  tissue  partly  unravelled.     (After  Sharpey.) 

the  action  of  staining  and  other  reagents  may  then  be  also  studied. 
By  such  means  it  is  seen  that  this  typical  connective  tissue  consists 
of  four  different  kinds  of  material,  or,  as  they  may  be  termed,  histo- 
logical elements.     They  are : — 

(a)  Cells,  or  connective-tissue  corpuscles. 

(b)  A   homogeneous  matrix,  ground   substance,  or  intercellular 

material. 


(c)  White  fibres 

(d)  ^  "" 


v¥  muo  1     , .    „,        v  These  are  deposited  in  the  matrix. 

Yellow  or  elastic  fibres  )  ^ 


CH.  rv.] 


AREOLAR   TISSUI? 


37 


In  considering  these  four  histological  elements  we  may  first  take 
the  fibres,  because  they  are  the  most  obvious  and  abundant  of  the 
structures  observable. 

The  white  fihres.  These  are  exquisitely  fine  fibres  collected  into 
bundles  which  have  a  wavy  outline.  The  bundles  run  in  different 
directions,  forming  an  irregular  network,  the  meshes  between  which 
are  called  areolce ;  hence  the  name  areolar.  The  individual  fibres 
never  branch  or  join  other  fibres,  but  they  may  pass  from  one  bundle 
to  another. 

On  treatment  with  dilute  acetic  acid  they  become  swollen  and  in- 
distinct, leaving  the  other  structures  mixed  with  them  more  apparent. 


Fio.  50. — Elastic  fibres  of  areolar 
tissue.    (After  Schafer.) 


Fig.  51. — A  white  bundle 
swollen  by  acetic 
acid.    (Toldt.) 


They  are  composed  of  the  chemical  substance  called  collagen.  On 
boiling  they  yield  gelatin;  some  chemists  regard  collagen  as  the 
anhydride  of  gelatin;  but  whether  this  is  so  or  not,  the  gelatin  is 
undoubtedly  derived  from  the  collagen.  Gelatin  is  a  protein  though 
it  has  certain  characters  which  distinguish  it  from  most  members  of 
the  large  protein  family.  Its  most  characteristic  property  is  its 
power  of  jellying  or  gelatinising ;  that  is,  it  is  soluble  in  hot  water, 
but  on  cooling  the  solution  it  sets  into  a  jelly. 

The  yellow  or  elastic  fibres.  These  are  seen  readily  after  the  white 
fibres  are  rendered  almost  invisible  by  treatment  with  dilute  acetic 


38 


THE   CONNECTIYE   TISSUES 


[CH. 


IV. 


acid,  or  after  staining  with  such  dyes  as  magenta  and  orcein,  for  which 
elastic  fibres  have  a  great  affinity.     They  are  bigger  than  the  white 


Fig.  52.— Horizontal  preparation  of  the  cornea  of 
frog,  stained  with  gold  chloride ;  showing  the 
network  of  branched  corneal  corpuscles.  The 
ground  substance  is  completely  colourless. 
X  400.    (Klein.) 


Fig.  53. — Ramified  pigment- 
cells,  from  the  tissue  of 
the  choroid  coat  of  the 
eye.  x  350.  o,  Cell  with 
pigment ;  b,  colourle.ss 
fusifonn  cells.  (KoUi- 
ker.) 


fibres,  have  a  distinct  outline,  and  a  straight  course ;  they  run  singly, 
branch,  and  join  neighbouring  fibres  (fig.  50). 

The  material  of  which  the  elastic  fibres  are  composed  is   called 

^^^^fl  -,,.  elastin,    another    somewhat    exceptional 

^^BBC,     .'^ij^  protein.     It  is  unaltered,  as  we  have  seen, 

^^^F       ^^  by  dilute  acid.     It  also  resists  the  action 

of  very  strong  acid,  and  is  not  affected  by 

boiling  water. 

The  bundles  of  white  fibres  which  have 
Vjji^      W^^^^^Stti     ^®®^   swollen   out   by  dilute  acetic  acid 
ity^    /"^P'^HHPw       sometimes    exhibit    constrictions    as    in 
^Sj(^^^>^'*;^to5>        %•  51.     These  are  due  to  elastic  fibres  or 
'  --**^         ^      "         cell  processes  encircling  them  and   pre- 
venting the  swelling  at  those  points. 

Connective-tissue  corpuscles.  These  are 
the  cells  of  connective  tissue :  several 
varieties  may  be  made  out,  especially 
after  a  preparation  has  been  stained. 

1.  Flattened  cells,  branched,  and  often 
united  by  their  processes,  as  in 
the  cornea. 

2.  Flattened  cells,  unbranched,  and 
joined  edge  to  edge  like  the  cells  of  an  epithelium ;  these  are 
well  seen  in  the  sheath  of  a  tendon. 

Plasma  cells  of  Waldeyer,  varying  greatly  in  size  and  form, 
but  not  flattened.     The  protoplasm  is  much  vacuolated. 


.  54. — Flat,  pigmented,  branched 
connective-tissue  cells  from  the 
sheath  of  a  large  blood-vessel  of 
the  frog's  mesentery ;  the  pigment 
is  not  distributed  uniformly 
throughout  the  substance  of  the 
larger  cell,  consequently  some 
parts  of  it  look  blacker  than  others 
(uncontracted  state).  In  the  two 
smaller  cells  most  of  the  pigment 
is  withdrawn  into  the  ceU-body,  so 
that  they  appear  smaller,  blacker, 
and  less  branched,  x  350.  (Klein 
and  Noble  Smith.) 


CH.  IV.] 


CONNECTIVE-TISSUE   CORPUSCLES 


39 


4.  Granule  cells  ("  mast "  cells  of  Ehrlich) :  like  plasma  cells,  but 

containing  albuminous  granules  (stainable  by  basic  aniline 
dyes)  instead  of  vacuoles. 

5.  Wander  cells :    white  blood-corpuscles  which  have  emigrated 

from  the  nei(?hbouring  blood-vessels. 

6.  Pigment  cells:  these  are  seen  in  the  subcutaneous  tissues  of 

many  animals,  e.g.,  the  frog,  and  in  the  choroid  coat  of  the 
eyeball. 
Fig.  55  shows  a  highly  magnified  view  of  a  small  piece  of  sub- 


FiG.  55. — Areolar  tissue.  The  white  fibres  are  seen  in  wavy  bundles ;  the  elastic  fibres  fonii  an  open 
network,  p,  p.  Plasma  cells ;  g,  granule  cell ;  c,  c,  lamellar  cells ;  /,  fibrillated  cell.  (After 
Schcifer.) 

cutaneous  tissue,  and  illustrates  the  irregular  way  in  which  the  fibres 
and  cells  are  intermixed. 

The  ground-substance.  This  may  be  represented  in  fig.  55  by  the 
white  background  of  the  paper. 

It  may  be  readily  demonstrated  in  a  silver  nitrate  preparation ; 
for  the  intercellular  material  has  the  same  property  of  reducing  silver 
salts  in  the  sunlight  that  the  cement-material  of  epithelium  has  (see 
p.  34).  It  becomes  in  consequence  dark  brown,  with  the  exception 
of  the  spaces  occupied  by  the  corpuscles. 

The  spaces  intercommunicate  like  the  cells,  and  being  consider- 
ably larger  than  the  cells  form  a  ramifying  network  of  irregular 
channels,  which  were  first  termed  by  v.  Recklinghausen  the  Saft 
Kandlchen,  or  little  juice  canals.     Areolar  tissue  is   certainly  pro- 


40 


THE   CONNECTIVE  TISSUES 


[CH.  IV. 


vided  with  blood-vessels,  but  the  tissue  elements  are,  as  in  all  tissues, 

provided  with  nutriment  by  the 
exudation  from  the  blood  called 
lymph.  The  Saft  Kandlchen  en- 
able the  lymph  to  penetrate  to 
every  part  of  the  areolar  tissue. 

Development  of  Areolar 
Tissue. 

The  mesoblastic  cells  in  those 
parts  where  the  tissue  is  to  be 
formed  become  branched  and 
fusiform. 

These  ultimately  become  the 
connective-tissue  corpuscles,  and 
they  get  more  and  more  widely  separated  by  intercellular  material, 


Fjo.  56. — Ground-substance  of  connective  tissue, 
stained  by  silver  nitrate.  The  cell  spaces  are 
left  white.    (After  SchUfer.) 


Pio.  57. — Portion  of  submucous  tissue  of  gravid  uterus  of  sow.    a,  Branched  cells,  more  or  less  spindle- 
shaped  ;  h,  bundles  of  connective  tissue.    (Klein.) 

partly  shed  out  by  the  cells  themselves,  partly  shed  out  from  the 


Fio.  58.— Jelly  of  Wharton,    r.  Ramified  cells  intercommunicating  by  their  branches ;   I,  a  row  of 
lymph-cells  ;  /,  fibres  developing  in  the  ground-substance.    (Ranvier.) 

neighbouring    blood-vessels.      This    becomes    the  ground-substance. 


CH.  IV.] 


FIBROUS   TISSUE 


41 


The  fibres  are  subsequently  deposited  in  this  matrix.  At  one  time 
it  was  believed  that  the  cells  themselves  became  elongated  and 
converted  into  fibres.  No 
doubt  the  cells  do  exercise 
a  controlling  influence  on 
fibre  -  formation  in  their 
neighbourhood,  but  it  is 
certain  that  they  never 
become  fibres.  The  forma- 
tion of  fibres  is  intercel- 
lular. Some  of  the  fibres 
formed  are  of  the  white, 
others  of  the  yellow  variety. 
In  the  case  of  the  elastic 
fibres,  rows  of  granules  of 
elastin  are  first  deposited ; 
these  joining  together  in 
single  or  multiple  rows  form 
the  long  fibres :  traces  of  this  are  seen  in  transverse  markings  occa 
sionally  noticeable  in  the  larger  elastic  fibres. 


Kio.  59. — Development  of  elastic  tissue  by  deposition  of 
fine  granules,  g,  Fibres  being  formed  by  rows  of 
elastic  granules ;  P,  platelike  expansion  of  elastic 
substance  formed  by  tlie  fusion  of  elastic  granules. 
(Ranvier.) 


Fibrous  Tissue. 

This  is  a  kind  of  connective  tissue  in  which  the  white  fibres  pre- 
dominate ;  it  is  found  in  tendons  and  ligaments,  in  the  periosteum, 

dura  mater,  true  skin,  the  sclerotic 
coat  of  the  eye,  and  in  the  thicker 
fasciae  and  aponeuroses  of  muscle. 

The  tissue  is  one  of  great 
strength;  this  is  conferred  upon 
it  by  the  arrangement  of  the  fibres, 
the  bundles  of  which  run  parallel, 
union  here,  as  elsewhere,  giving 
strength.  The  fibres  of  the  same 
bundle  now  and  then  intersect  each 
other.  The  cells  in  tendons  (fig. 
61)  are  forced  to  take  up  a  similar 
orderly  arrangement,  and  are  ar- 
ranged in  long  chains  in  the  ground- 
substance  separating  the  bundles  of 
fibres,  and  are  more  or  less  regu- 
larly quadrilateral  with  large  round 
nuclei  containing  nucleoli,  which  are  generally  placed  so  as  to  be  nearly 
contiguous  in  two  cells.  Each  of  these  cells  consists  of  a  thick  body, 
from  which  processes  pass  in  various  directions  into,  and  partially  fill 


•  Fig. 


60. — Fibrous  tissue  of  tendon,  consisting 
mainly  of  white  fibres.    (Strieker.) 


42 


THE   CONNECTIVE   TISSUES 


[CH.  IV. 


up  the  spaces  between,  the  bundles  of  fibres.     The  cells  are  generaUy 
marked  by  one  or  more  lines  or  stripes  when  viewed  longitudinally. 


Fio.  61. — Caudal  tendon  of  young  rat,  showing  the 
arrangement,  form,  and  structure  of  the  tendon 
cells.  The  bundles  of  white  fibres  between 
which  they  lie  have  been  rendered  transparent 
and  indistinct  by  the  application  of  acetic 
acid.     X  300.    (Klein.) 


Fig.  62. — Transverse  section  of 
tendon  from  a  cross  section  of 
the  tail  of  a  rabbit,  showing 
sheath,  fibrous  septa,  and 
branched  tendon  cells.  The 
spaces  left  white  in  the  draw- 
ing represent  the  tendinous 
bundles  in  transverse  section. 
X  250.    (Klein.) 


This  appearance  is  really  produced  by  the  wing-like  processes  of  the 
cell,  which  project  away  from  the  chief  part  of  the  cell  in  different 
directions.  These  processes  not  being  in  the  same  plane  as  the  body 
of  the  cell  are  out  of  focus,  and  give  rise  to  these  bright  stripes  when 
the  cells  are  looked  at  from  above  and  are  in  focus. 

The  branched  character  of  the  cells  is  seen  in  transverse  section 
in  fig.  62. 

The  cell  spaces  in  which  the  cells  lie  are  in  arrangement  like  the 


Fig.  63. — Cell  spaces  of  tendon,  brought  into  view  by  treatment  with  silver  nitrate. 
(After  Schafer.) 

cells  ;  they  can  be  brought  into  relief  by  staining  with  silver  nitrate 
(see  fig.  63). 


CH.  lY.] 


ELASTIC   TISSUK 


43 


Elastic  Tissue. 

This  is  a  form  of  connective  tissue  in  which  the  yellow  or  elastic 
fibres  predominate.  The  yellow  fibres  are  larger  than  those  found  in 
areolar  tissue  (see  fig.  64),  and  are  bound 
into  bundles  by  areolar  tissue.  It  is  found 
in  the  ligamentum  nuclide  of  the  ox,  horse, 
and  many  other  animals ;  in  the  liga- 
menta  subflava  of  man ;  in  the  arteries 
and  veins,  constituting  the  fenestrated  coat 
of  Henle ;  in  the  lungs  and  trachea ;  in 
the  stylo-hyoid,  thyro-hyoid,  and  crico- 
thyroid ligaments;  and  in  the  true  vocal 
cords. 

Elastic  tissue  occurs  in  various  forms, 
from  a  structureless,  elastic  membrane  to 
a  tissue  whose  chief  constituents  are  bundles 
of  fibres  crossing  each  other  at  different 
angles ;  when  seen  in  bundles  elastic  fibres 
are  yellowish  in  colour,  but  individual 
fibres  are  not  so  distinctly  coloured.  The 
larger  elastic  fibres  are  often  transversely 
marked,  indicating  their  mode  of  origin 
(see  p.  41),  and  on  transverse  section  are  seen 
(fig.  65). 

Elastic  tissue,  being  extensible  and  elastic  (i.e.,  recoiling  after  it 
has  been  stretched),  has  a  most  important  use 
in  assisting   muscular  tissue   in    a   mechanical 

O 

way,  and  so  lessening  the  wear  and  tear  of  such 
an  important  tissue  as  muscle.  Thus,  in  the 
ligamenta  subflava  of  the  human  vertebral 
column  it  assists  in  the  maintenance  of  the 
erect  posture;  in  the  ligamentum  nuchas  in 
the  neck  of  quadrupeds  it  assists  in  the  raising 
of  the  head  and  in  keeping  it  in  that  position. 
In  the  arterial  walls,  and  in  the  air  tubes  and 
lungs,  it  has  a  similar  important  action,  as  we 
shall  see  when  discussing  the  subjects  of  the 
circulation  and  respiration. 

We  now  come  to  those  forms  of  con- 
nective tissue  in  which  the  cells  rather  than  the  fibres  are  most 
prominent. 

Adipose  Tissue. 

In  almost  all  regions  of  the  human  body  a  larger  or  smaller  quantity 
of  adipose  or  fatty  tissue  is  present ;  the  chief  exceptions  being  the 


Fig.  64.— Elastic  libres  from  the 
ligamenta  subflava.  x  200. 
(Sharpoy.) 


to    be    angular 


Q-^Q&^SfS, 


Qg^ 


VcP 


Fig.  65. — Transverse  section 
of  a  portion  of  lig.  nuchae, 
showing  the  outline  of 
the  fibres.   (After  St.ihr.) 


44 


THE   CONNECTIVE   TISSUES 


[cH.  rv. 


subcutaneous  tissue  of  the  eyelids,  penis  and  scrotum,  the  nymphae, 
and  the  cavity  of  the  cranium. 

Adipose  tissue  is  developed  in  connection  with  areolar  tissue,  and 
forms  in  its  meshes  little  masses  of  unequal  size  and  irregular  shape, 
to  which  the  term  lobules  is  applied. 

Under  the  microscope  adipose  tissue  is 
found  to  consist  essentially  of  little  vesicles 
or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light: 
they  are  about  ^^  or  -^^  of  an  inch  in 
diameter;  each  consists  of  a  structureless 
and  colourless  membrane  or  bag  formed  of 
the  remains  of  the  original  protoplasm  of 
the  cell,  filled  with  fatty  matter,  which  is 
liquid  during  life,  but  is  in  part  solidified 
(or  sometimes  crystallised)  after  death.  A 
nucleus  is  always  present  in  some  part  or 
other  of  the  cell  protoplasm,  but  in  the  ordinary  condition  of  the  cell 
it  is  not  easily  or  always  visible  (fig.  67). 

This  membrane  and  the  nucleus  can  generally  be  brought  into 
view  by  staining  the  tissue :  it  can  be  still  more  satisfactorily  demon- 
strated by  extracting  the  contents  of  the  fat-cells  with  ether,  when 
the  shrunken,  shrivelled  membranes  remain  behind.     By  mutual  pres- 


FiG.     66. — Fat-cells     from     the 
omentum  of  a  rat.    (Klein.) 


Fig.  67. — Group  of  fat-cells  (f  c)  with  capillary  vessels  (c).    (Xoble  Smith.) 

sure,  fat-cells  assume  a  polyhedral  figure  (fig.  68,  h).  When  stained 
with  osmic  acid  fat-cells  appear  black. 

The  oily  matter  contained  in  the  cells  is  composed  of  the  com- 
pounds of  fatty  acids  with  glycerin,  which  are  named  olein,  stearin, 
and  palmitin. 

Development  of  Adipose  Tissue. — Fat-cells  are  developed  from 


CH.  lY.] 


ADIPOSE  TISSUE 


45 


connective-tissue  corpuscles,  especially  the  "  mast  "-cells ;  these  cells 
may    be    found    exhibiting   every    intermediate    gradation    between 


Fig.  68. — Blood-vessels  of  adipose  tissue,  a,  Minute  fat-lobule, 
In  which  the  vessels  only  are  represented,  a,  artery ; 
V,  vein ;  b,  the  fat-vesicles  of  one  border  of  the  lobiile 
separately  represented,  x  100.  b,  Plan  of  the  arrange- 
ment of  the  capillaries  (c)  on  the  exterior  of  the  vesicles  ; 
more  highly  magnified.    (Todd  and  Bowman.) 


<•    L    d 

Fio.  69. — A  lobule  of  developing  adipose 
tissue  from  an  eight  months'  foetus. 
a,  Spherical  or,  from  pressure, 
polyhedral  cells  with  large  central 
nucleus,  surrounded  by  protoplasm 
staining  uniformly  with  haematoxy- 
lin.  b,  Similar  cells  with  spaces  from 
which  the  fat  has  been  removed  by 
oil  of  cloves,  c.  Similar  cells  show- 
ing how  the  nucleus  with  enclosing 
protoplasm  is  being  pressed  towards 
periphery,  d.  Nucleus  of  endo- 
thelium of  investing  capillaries. 
(M'Carthy.)    Drawn  by  Treves. 


an  ordinary  granular  corpuscle  and  a  mature  fat-cell.     The  process 
of  development  is  as  follows:  a  few  small  drops  of  oil  make  their 


Fio.  70. — Branched  connective-tissue  corpuscles,  developing  into  fiit-cells.    (Klein.) 

appearance  in  the  protoplasm,  and  by  their  confluence  a  larger  drop 
is  produced  (figs.  69  and  70) :  this  gradually  increases  in  size  at  the 
expense  of  the  original  protoplasm  of  the  cell,  which  becomes  cor- 


46  THE   CONNECTIVE   TISSUES  [CH.  lY 

respondingly  diminished  in  quantity  till  in  the  mature  cell  it  only  forms 
a  thin  film,  with  a  flattened  nucleus  imbedded  in  its  substance  (fig.  66). 

Vessels  and  Nerves. — A  large  number  of  blood-vessels  are  found 
in  adipose  tissue,  which  subdivide  until  each  lobule  of  fat  contains 
a  fine  meshwork  of  capillaries  ensheathing  each  individual  fat-cell 
(fig.  68).  Although  nerve  fibres  pass  through  the  tissue,  no  nerves 
have  been  demonstrated  to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose  tissue 
these  are  the  chief : — 

a.  It  serves  as  a  store  of  combustible  matter  which  may  be 
reabsorbed  into  the  blood  when  occasion  requires,  and,  being  used  up 
in  the  metabolism  of  the  tissues,  helps  to  preserve  the  heat  of  the  body. 

l.  The  fat  which  is  situated  beneath  the  skin  must,  by  its  want 
of  conducting  power,  assist  in  preventing  undue  waste  of  the  heat 
of  the  body  by  escape  from  the  surface. 

G.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up 
spaces,  to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to 
wrap  tender  and  delicate  structures,  or  form  a  bed  with  like  qualities 
on  which  such  structures  may  lie,  not  endangered  by  pressure.  As 
examples  of  situations  in  which  fat  serves  such  purposes  may  be 
mentioned  the  palms  of  the  hands,  the  soles  of  the  feet,  and  the  orbits. 

d.  In  the  long  bones  fatty  tissue,  in  the  form  known  as  yellow 
marrow,  fills  the  medullary  canal,  and  supports  the  small  blood- 
vessels which  are  distributed  from  it  to  the  inner  part  of  the  substance 
of  the  bone. 

Retiform  Tissue. 

Eetiform  or  reticular  tissue  is  a  kind  of  connective  tissue  in  which 
the  ground  substance  is  of  more  fluid  consistency  than  elsewhere. 


FiQ.  71. — Retiform  tissue  from  a  lymphatic  gland,  from  a  section  vvliicli  lias  been  treated  with  dilute 

potash.    (Schiifer.) 

There  are  few  or  no  elastic  fibres  in  it,  but  the  white  fibres  run  in 
very  fine  bundles  forming  a  close  network.     The  bundles  are  covered 


CH.  IV.] 


LYMPHOID    TISSUE 


47 


and  concealed  by  flattened  connective-tissue  corpuscles.     When  these 
are  dissolved  by  dilute  potash,  the  fibres  are  plainly  seen  (fig.  71). 

The  .statement  has  been  made  that  the  fibres  of  retiform  tissue  are  chemically 
different  from  those  of  areolar  tissue,  in  spite  of  the  fact  that  they  are  indis- 
tinguishable niicroscopieally,  and  in  many  places  continuous  with  each  other. 
Miss  Tebb  has  conttusively  proved  that  chemical  differences  do  not  exist  between 
the  two  groups  of  fibres  ;  botli  are  made  of  collagen,  and  the  substance  termed 
reticulin  by  vSiegfried  is  an  artifact ;  it  is  merely  coUagen  which  has  been  rendered 
resistant  and  insoluble  by  the  reagents  (alcohol,  ether)  used  in  its  preparation. 

Adenoid  or  Lymphoid  Tissue. 

This  is  retiform  tissue  in  which  the  meshes  of  the  network  are  largely 
occupied  by  lymph  corpuscles.     These  are  in  certain   foci   actively 


FiO.  72. — Part  of  a  section  of  a  lymphatic  gland,  from  which  the  corpuscles  have  been 
for  the  most  part  removed,  showing  the  supporting  retifonn  tissue.  (Klein  and 
Noble  Smith.) 

multiplying;  they  get  into  the  lymph  stream,  which  washes  them 
into  the  blood,  where  they  become  the  variety  of  colourless  corpuscles 
called  lymphocytes.  It  is  found  in  the  lymphatic  glands,  the  thymus, 
the  tonsils,  in  the  follicular  glands  of  the  tongue,  in  Peyer's  patches,  and 
in  the  solitary  glands  of  the  intestines,  in  the  Malpighian  corpuscles 
of  the  spleen,  and  under  the  epithelium  of  many  mucous  membranes. 


Basement  Membranes. 


These  are  homogeneous  in  appearance,  and  are  found  between  the 
epithelium  of  a  mucous  membrane  and  the  subjacent  connective  tissue. 
They  are  generally  formed  of  flattened  connective-tissue  corpuscles 


48 


THE   COITOECTIVE   TISSUES 


[CH.  IV. 


joined  together  by  their  edges,  but  sometimes  they  are  made  of  con- 
densed ground-substance,  not  of  cells,  and  in  other  cases  again  (as 
in  the  cornea)  they  are  of  elastic  nature. 


Jelly-like  Connective  Tissue. 

We  have  now  considered  connective  tissues  in  which  fibres  of  one 
or  the  other  kind  predominate,  and  some  in  which  the  cells  are  in 
preponderance.  We  come  lastly  to  a  form  of  connective  tissue  in 
which  the  ground  substance  is  in  excess  of  the  other  histological 
elements.  This  is  called  jelly-like  connective  tissue.  The  cells  and 
fibres  scattered  through  it  are  few  and  far  between.     It  is  found 


Fio.  73.— Tissue  of  tlie  jelly  of  Wharton  from  umbilical  cord,    a,  Connective-tissue 
corpuscles ;  6,  fasciculi  of  connective-tissue  fibres ;  c,  spherical  cells.    (Frey.) 

largely  in  the  embryo,  notably  in  the  Whartonian  jelly,  which  sur- 
rounds and  protects  the  blood-vessels  of  the  umbilical  cord.  In  the 
adult  it  is  found  in  the  vitreous  humour  of  the  eye. 

Various  points  in  the  structure  of  the  tissue  are  illustrated  in 
figs.  58  (p.  40)  and  73. 

The  occurrence  of  large  quantities  of  ground-substance  in  such 
tissues  has  enabled  physiologists  to  examine  its  chemical  nature. 
Its  chief  constituents  are  water,  and  one  or  more  varieties  of  mucin- 
like  substances  termed  mucoidf;  and  mineral  salts  (especially  sodium 
chloride). 


CHAPTER  V 

THE  CONNECTIVE  TISSUES  {continued) 
Cartilage,  Bone,  Teeth,  Blood 

Cartilage. 

Cartilage  is  popularly  termed  gristle.  It  may  be  divided  into  two 
chief  kinds :  Hyaline  cartilage ;  here  the  matrix  or  ground  substance 
is  clear  and  free  from  fibres :  Fihro-cartilage ;  here  the  matrix  is  per- 


l- ■  v^ 


lllll!lllil!ll!l!ilOilil;i!iili!;i!iill!i:!i;;;i>!j!li.;L::il::i!ii^^ 

Fio.  74. Section  of  articular  cartilage,    a,  Group  of  two  cells  ;  6,  group  of  four  cells  ;  d,  protoplasm  of 

cell  witli  e,  fatty  granules  ;  c,  nucleus.    (After  Schafer.) 

vaded  with  connective-tissue  fibres;  when  these  are  of  the  white 
variety,  the  tissue  is  tohite  fibro-cartilage ;  when  they  are  of  the  yellow 
or  elastic  variety,  the  tissue  is  yellow  or  elastic  fibro-cartilage. 

49  jj 


60 


THE   CONNECTIVE  TISSUES 


[CH.  V. 


Hyaline  Cartilage  is  found  in  the  following  places : — 

1.  Covering  the  articular  ends  of  bones ;  here  it  is  called  articular 
cartilage. 

2.  Forming  the  rib-cartilages ;  here  it  is  called  costal  cartilage. 

3.  The  cartilages  of  the  nose,  of  the  windpipe,  of  the  external 
auditory  meatus,  and  the  greater  number  of  the  laryngeal  cartilages. 

4.  Temporary  cartilage:   rods  of   cartilage   which   prefigure    the 
majority  of  the  bones  in  process  of  development. 

Articular  cartilage :  here  the  cells  are  rounded  and  scattered  in 
groups  of  two  and  four  through  the  matrix,  which  is  non-fibrillated 


Fig.  75. — Section  of  transitional  cartilage,     a,   Ordiuaiy  cartilage  cells  ;   h  h,  those   with  processes. 

(After  Schiifer.) 

(fio-.  74),  and  much  firmer  than  the  ground-substance  of  the  connective 
tissues  proper ;  but  it  is  affected  in  the  same  way  with  silver  nitrate. 

In  the  neighbourhood  of  synovial  membranes,  the  connective- 
tissue  fibres  of  which  extend  into  the  matrix,  the  cells  are  branched 
{transitional  cartilage),  (fig.  75). 

The  next  figure  (fig.  76)  shows  the  general  arrangement  of  the  cell- 
groups  in  a  vertical  section  of  articular  cartilage.  Cartilage  is  free 
from  blood-vessels,  and  also  from  nerves.  It  is  nourished  by  lymph, 
but  canals  connecting  the  cell-spaces  are  not  evident. 

Costal  cartilage :  here  the  matrix  is  not  quite  so  clear,  and  the  cells 


CH.  v.] 


CARTILAGE 


51 


are  larger,  more  angular,  and  collected  into  larger  groups  than  in 
articular  cartilage.  Under  the  perichondrium,  a  fibrous  membrane 
which  surrounds  the  rod  of  carti- 
lage, the  cells  are  flattened  and 
lie  parallel  to  the  surface ;  in  the 
deeper  parts  they  are  irregularly- 
arranged  ;  they  frequently  contain 
fat  (see  fig.  77). 

The  hyaline  cartilages  of  the 
nose,  larynx,  and  trachea  (fig.  78) 
resemble  costal  cartilage. 

Hyaline  cartilage  in  many 
situations  (costal,  laryngeal,  tra- 
cheal) shows  a  tendency  to  become  calcified  late  in  life. 

On  boiling,  the  ground-substance  of  cartilage  yields  a  material 
called  chondrin.  This  resembles  gelatin  very  closely,  and  the  differ- 
ences in  its  reactions  are  due  to  the  fact  that  chondrin  is  not  a 
chemical  individual,  but  a  mixture  of  gelatin  with  varying  amounts 
of  mucoid  substances. 


.  70.— Vertical  section  of  articular  cartilage  ; 
a,  cell-groups  arranged  parallel  to  surface; 
h,  cell-groups  irregularly  arranged  ;  e,  cell- 
groups  arranged  perpendicularly  to  surface. 


^ 


# 


6^$ 

0 


^ 


Fio.  77.— Costal  cartilage  from  an  adult 
dog,  showing  fat-globules  in  the 
cartilage-cells.    (Cadiat.) 


Fig.  78.—  Ordinary  hyaline  cartilage  from 
trachea  of  a  child.  The  cartilage- 
cells  are  enclosed  singly  or  in  pairs 
in  a  capsule  of  hyaline  substance. 
X  150  diams.  (Klein  and  Noble 
Smith.) 


White  Pibro-Cartilage  occurs — 

1.  As  inter -articular  fibro-cartilage — e.g.,  the  semilunar  cartilages 
of  the  knee-joint. 

2.  As  circumferential  or  marginal  cartilage,  as  on  the  edges  of  the 
acetabulum  and  glenoid  cavity. 

3.  As  connecting  cartilage — e.g.,  the  inter-vertebral  discs. 

4.  In  the  sheaths  of  tendons  and  sometimes  in  their  substance.     In 


52 


THE   CONNECTIVE   TISSUES 


[CH.  V. 


--..  ' 


the  latter  situation  the  nodule  of  fibro-cartilage  is  called  a  sesamoid 

fibro-cartilage,  of  which  a  specimen  may  be  found  in  the  tendon  of 
the  tibialis  posticus  in  the  sole  of  the  foot,  and  usually  in  the  neigh- 
bouring tendon  of  the  peroneus  longus. 

White  fibro-cartilage  (fig.  79)  is  composed  of  cells  and  a  matrix. 
The  latter  is  permeated  by  fibres  of  the  white  variety. 

In  this  kind  of  fibro-cartilage  it  is  not  unusual  to  find  portions  so 
densely  fibrous  that  no  cells  can  be  seen ;  but  in  other  parts  con- 
tinuous with  these,  cartilage-cells  are  freely  distributed. 

Yellow  or  Elastic  Fibro-Cartilage  is  found  in  the  pinna  of  the 


m: 


Cells  of  car- 
tilage. 


Fibrous 
matrix. 


'•;!   '     4  At   I       i,r'''"''i'lMV  ''"^^     •■'"  •~"*'\:-    :iJ?U■-■ 

Fio.  so. — Yellow  or  elastic  fibro-cartilage. 
Fig.  79.— White  fibro-cartilage.    (Cadiat.)  (Cadiat.) 

external  ear,  in  the  epiglottis  and  cornicula  laryngis,  and  in  the 
Eustachian  tube. 

The  cells  in  this  variety  of  cartilage  are  rounded  or  oval,  with 
well-marked  nuclei  and  nucleoli  (fig.  80).  The  matrix  in  which  they 
are  seated  is  pervaded  in  all  directions  by  fine  elastic  fibres,  which 
form  an  intricate  interlacement  about  the  cells :  a  small  and  variable 
quantity  of  non-fibrillated  hyaline  intercellular  substance  is  present 
around  the  cells. 

Development  of  Cartilage. — Like  other  connective  tissues,  car- 
tilage originates  from  mesoblast ;  the  cells  are  unbranched,  and  the 
disposition  of  the  cells  in  fully  formed  cartilage  in  groups  of  two, 
four,  etc.,  is  due  to  the  fact  that  each  group  has  originated  from  the 
division  of  a  single  cell,  first  into  two,  each  of  these  again  into  two, 
and  so  on.  This  process  of  cell  division  is  accompanied  with  the 
usual  karyokinetic  changes. 


cii.  v.] 


CARTILAGE 


53 


Each  coll  deposits  on  its  exterior  a  sheath  or  capsule;  on  division 
each  of  the  daughter-cells  deposits  a  new  capsule  within  this,  and 
the  process  may  he  repeated  (see  fig.  81). 

Thus  the  cells  get  more  and  more  separated.  The  fused  capsules 
form  a  very  large  part  of  the  matrix,  and  indications  of  their  previous 
existence  may  sometimes  be  seen  in  fully  formed  cartilage  by  the 
presence  of  faint  concentric  lines  around  the  cells  (see  fig.  77). 

Tn  a  variety  of  cartilage  found  in  the  ears  of  rats  and  mice  called 


Fig.  si.— Plan  of  multiplication  of  cells  in  cartilage.  a.  Cell  in  its  capsule;  h,  divirled  into  two, 
each  with  a  capsule  ;  c,  primary  capsule  disappeared,  secondary  capsules  coherent  with  matrix ; 
d,  tertiary  division  ;  f,  secondary  capsules  disappeared,  tertiary  coherent  with  matrix. 
(After  Sharpey.) 

cellular  cartilage,  the  cells  never  multiply  to  any  great  extent,  and 
they  are  only  separated  by  their  thickened  capsules. 

But  in  most  cartilages  the  cell-capsules  will  not  explain  the 
origin  of  the  whole  matrix,  but  intercellular  material  accumulates 
outside  the  capsules  and  still  further  separates  the  cells. 

By  certain  methods  of  double  staining,  this  twofold  manner 
of  formation  may  be  shown  very  markedly.  We  have  seen  that 
chondrin  obtained  by  boiling  cartilage  is  really  a  mixture  of  two 
substances ;  one  is  a  mucoid  material,  and  comes  from  the  capsules ; 
the  other  is  gelatin,  which  comes  from  the  rest  of  the  ground- 
substance  which  is  collagenous.  In  hyaline  cartilage,  however,  the 
collagen  does  not  become  precipitated  to  form  fibres,  but  in  white 


64  THE   CONNECTIVE   TISSUES  [CH.  V. 

fibro-cartilage  it  does.  In  yellow  fibro-cartilage  the  matrix  is  per- 
vaded by  a  deposit  of  elastin,  which  results  in  the  formation  of  a 
network  of  elastic  fibres. 

Bone. 

Bone  contains  nearly  50  per  cent,  of  water ;  the  solid  material  is 
composed  of  earthy  and  animal  matter  in  the  proportion  of  about  67 
per  cent,  of  the  former  to  33  per  cent,  of  the  latter.  The  earthy 
matter  is  composed  chiefly  of  calcium  phosphate,  but  besides  this, 
there  is  a  small  quantity  (about  11  of  the  67  per  cent.)  of  calcium 
carbonate,  calcium  fluoride,  and  magnesium  phosphate. 

The  animal  matter  is  chiefly  collagen,  which  is  converted  into 
gelatin  by  boiling. 

The  animal  and  earthy  constituents  of  bone  are  so  intimately 
blended  and  incorporated  the  one  with  the  other  that  it  is  only  by 
severe  measures,  as  for  instance  by  a  white  heat  in  one  case  and  by 
the  action  of  concentrated  acids  in  the  other,  that  they  can  be 
separated.  Their  close  union,  too,  is  further  shown  by  the  fact  that 
when  by  acids  the  earthy  matter  is  dissolved  out,  or  on  the  other 
hand  when  the  animal  part  is  burnt  out,  the  shape  of  the  bone  is 
alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies 
slightly  in  different  bones  in  the  same  individual  and  in  the  same 
bone  at  different  ages. 

To  the  naked  eye  there  appear  two  kinds  of  structure  in  different 
bones,  and  in  different  parts  of  the  same  bone,  namely,  the  dense  or 
compact,  and  the  spongy  or  cancellous  tissue.  Thus,  in  making  a 
longitudinal  section  of  a  long  bone,  as  the  humerus  or  femur,  the 
articular  extremities  are  found  capped  on  their  surface  by  a  thin 
shell  of  compact  bone,  while  their  interior  is  made  up  of  the  spongy 
or  cancellous  tissue.  The  shaft,  on  the  other  hand,  is  formed  almost 
entirely  of  a  thick  layer  of  the  compact  bone,  and  this  surrounds  a 
central  canal,  the  medullary  cavity — so  called  from  its  containing  the 
medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  the  can- 
cellous structure  (diploe)  lies  between  two  layers  of  the  compact 
tissue,  and  in  the  short  and  irregular  bones,  as  those  of  the  carpus 
and  tarsus,  the  cancellous  tissue  fills  the  interior,  while  a  thin  shell 
of  compact  bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red 
and  yellow. 

Red  marrow  is  the  connective  tissue  which  occupies  the  spaces  in 
the  cancellous  tissue ;  it  is  highly  vascular,  and  thus  maintains  the 
nutrition  of  the  spongy  bone,  the  interstices  of  which  it  fills.  It 
contains  a  few  fat-cells  and  a  large  number  of  marrow-cells.     The 


en.  v.] 


MARROW 


55 


marrow-cells  are  amoeboid,  and  resemble  large  leucocytes ;  the 
granules  of  sonic  of  these  cells  stain  readily  with  acid  and  neutral 
dyes,  but  a  considerable  number  have  coarse  granules  which  stain 
readily  with  basic  dyes  like  methylene  blue.  Among  the  cells  are 
some  nucleated  cells  of  the  same  tint  as  coloured  blood-corpuscles. 
These  are  termed  erythrdblasts.  From  them  the  coloured  corpuscles 
of  the  blood  are  developed.  There  are  also  a  few  large  cells  with 
many  nuclei,  termed  giant  cells  or  myeloplaxes  (fig.  82). 

Yellow  marrow  fills  the  medullary  cavity  of  long  bones,  and  con- 
sists chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its 
cells  also  are  the  colourless  marrow-cells  just  mentioned. 


Fitt.  82.— Cells  of  the  red  marrow  of  the  guinea-pig,  highly  mapifiert.  a,  A  large  cell,  the  nucleus  of 
which  appears  to  be  partly  divided  into  three  by  constrictions,;  h,  a  cell,  the  nucleus  of  which 
shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei ;  c,  a  so-called  giant  cell 
or  myeloplaxe,  with  many  nuclei ;  d,  a  smaller  myeloplaxe,  with  three  nuclei ;  c — i,  proper  cells  of 
the  marrow.     (E.  A.  Schiifer.) 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of 
bones,  except  the  part  covered  with  articular  cartilage,  are  clothed 
by  a  tough,  fibrous  membrane,  the  periosteum ;  and  it  is  from  the 
blood-vessels  which  are  distributed  in  this  membrane,  that  the  bones, 
especially  their  more  compact  tissue,  are  in  great  part  supplied  with 
nourishment ;  minute  branches  from  the  periosteal  vessels  enter  the 
little  foramina  on  the  surface  of  the  bone,  and  find  their  way  to  the 
Haversian  canals,  to  be  immediately  described.  The  long  bones  are 
supplied  also  by  a  proper  nutrient  artery  which,  entering  at  some 
part  of  the  shaft  so  as  to  reach  the  medullary  cavity,  breaks  up  into 
branches  for  the  supply  of  the  marrow,  from  which  again  small 
vessels  are  distributed  to  the  interior  of  the  bone.  Other  small 
blood-vessels  pierce  the  articular  extremities  for  the  supply  of  the 
cancellous  tissue. 

Microscopic  Structure  of  Bone. — Notwithstanding  the  differ- 
ences of  arrangement  just  mentioned,  the  structure  of  all  bone  is 
found  under  the  microscope  to  be  essentially  the  same, 


56 


THE  CONNECTIVE   TISSUES 


[CH.  V. 


Examined  with  a  rather  high  power  its  substance  is  found  to 
contain  a  multitude  of  small  irregular  spaces,  approximately  fusi- 
form in  shape,  called  lacunce,  with  very  minute  canals  or  canaliculi 
leading  from  them,  and  anastomosing  with  similar  little  prolonga- 
tions from  other  lacunae  (fig.  83).  In  very  thin  layers  of  bone,  no 
other  canals  but  these  may  be  visible  ;  but  on  making  a  transverse 
section  of  the  compact  tissue  as  of  a  long  bone,  e.g.,  the  humerus  or 
ulna,  the  arrangement  shown  in  fig.  83  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or 
about  the  centre  of   each  of   which  is  a  hole,  around  which  is  an 


Fin.  83. — Transverse  section  of  compact  bony  tissue  (of  humerus).  Three  of  the  Haversian  canals  are 
seen,  witli  tlieir  concentric  rings  ;  also  the  lacuniL',  with  the  canaliculi  extending  from  them  across 
the  direction  of  the  laniellie.  The  Haversian  apertures  were  tilled  with  air  and  debris  in  grinding 
down  the  section,  and  therefore  appear  black  in  the  figure,  which  represents  the  object  as  viewed 
with  transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this  section,  that  scarcely 
any  interstitial  lamellaj  are  visible,     x  150.    (Sharpey.) 

appearance  as  of  concentric  layers ;  the  lacunce  and  canaliculi  follow 
the  same  concentric  plan  of  distribution  around  the  small  hole  in  the 
centre,  with  which  indeed  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  found  to 
be  simply  the  cut  extremities  of  small  canals  wliich  run  lengthwise 
through  the  bone,  anastomosing  with  each  other  by  lateral  branches 
(fig.  84);  these  canals  are  called  Haversian  cajials,  after  the  name 
of  the  physician,  Clopton  Havers,  who  first  accurately  described 
them. 

The  Haversian  canals,  the  average  diameter  of  which  is  -5^  of 
an  inch,  contain  blood-vessels,  and  by  means  of  them  blood  is  conveyed 
to  all,  even  the  densest  parts  of  the  bone ;  the  minute  canaliculi  and 


en.  v.] 


BONE 


FiO.  S4, 


lacunoe  tako  up  tho  lymph  oxudod  from  tho  Haversian  blood-vessels, 

and  convey  it  to  tho  substance  of  tho  bone  which  they  traverse. 
The  blood-vessels  enter  the 

Haversian     canals    both     from 

without,  by  traversing  the  small 

holes  which  exist  on  the  surface 

of  all  bones  beneath  the  perios- 
teum, and  from  within  by  means 

of  small  channels  which  extend 

from  the   medullary  cavity,  or 

from  the  cancellous  tissue.    Tho 

arteries  and  veins  usually  occupy 

separate  canals,  and  the  veins, 

which  are  the  larger,  often  pre- 
sent, at  irregular  intervals,  small 

pouch-  like    dilatations.      Nerve 

filaments  are  also  found  in  the 

Haversian   canals,  and  a   little 

connective  tissue  with  cleft-like 

lymph  spaces.    The  larger  canals 

may  contain  a  few  marrow  cells. 
The  lacunae  are  occupied  by 

branched  cells,  which  are  called 

hone-cells,  or  lone-corpuscles  (fig. 

85) ;    these    closely    resemble    ordinary    branched    connective-tissue 

corpuscles.  Bone  is  thus  essentially  connective  tissue,  the  ground- 
substance  of  which  is  impregnated 
with  lime  salts.  The  bone-cor- 
puscles with  their  processes,  occu- 
pying the  lacunae  and  canaliculi, 
correspond  exactly  to  the  connec- 
tive-tissue corpuscles  lying  in 
branched  spaces.  The  connection 
of  the  lacvmse  by  the  canaliculi 
allows  the  nutrient  lymph  to  pass 
from  place  to  place. 

Lamellae  of  Compact  Bone. — 
In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamellae  can  be 
clearly  recognised. 

1.  Circumferential  lamellae ; 
these  are  concentrically  arranged 
just  beneath  the  periosteum,  and 

Fio.  86.— Bone-corpuscles  with  their  processes    around  the  medullary  cavity. 
JroSJ" '""" '''''°'' °^ ''"'"'"'' ''°"'-  2.  Haversian    lamella;     these 


Longitudinal  section  from  theliunian  ulna, 
showing  Haversian  canals,  lacuna;,  and  canali- 
culi.   (Rollett.) 


58 


THE   CONNECTIVE   TISSUES 


[CH. 


are  concentrically  arranged  around  the  Haversian  canals  to  the 
number  of  six  to  eighteen  around  each. 

3.  Interstitial  lamellae ;  these  connect  the  systems  of  Haversian 
lamellae,  filling  the  spaces  between  them,  and  consequently  attaining 
their  greatest  development  where  the  Haversian  systems  are  few,  and 
vice  versd. 

The  ultimate  structure  of  the  lamellae  is  fibrous.  If  a  thin  film 
be  peeled  off  the  surface  of  a  bone,  from  which  the  earthy  matter  has 
been  removed  by  acid,  and  examined  with  a  high  power  of  the  micro- 
rfcope,  it  will  be  found  composed  of  very  slender  fibres  decussating 


//0j''?'^mi% 


Fig.  so.— Tliin  layer  peeled 
off  from  a  softened  bone. 
This  figure,  whlcli  is  in- 
tended to  represent  the 
reticular  structure  of  a 
lamella,  gives  a  better 
idea  of  the  object  when 
held  rather  farther  off 
than  usual  from  the  eye. 
X  400.    (Sharpey.) 


Fig.  87. — Lanielke  torn  ofl'from  a  decalcified  human 
Darietal  bone  at  some  depth  from  the  surface. 

a,  a,   Lamellie,   showing  intercrossing  fibres  ; 

b,  darker  part,  where  several  lamella-  are  super- 
posed ;  c,  perforating  fibres.  Apertures,  through 
which  perforating  fibres  had  passed,  are  seen 
especially  in  the  lower  part,  a,  a,  of  the  figure. 
(Allen  Tliomson.) 


obliquely,  but  coalescing  at  the  points  of  intersection,  as  if  here  the 
fibres  were  fused  rather  than  woven  together  (fig.  86).  These  are 
called  the  intercrossing  Jibres  of  Sharpey ;  they  correspond  to  the  white 
fibres  of  connective  tissue,  and  form  the  source  of  the  gelatin  obtained 
by  boiling  bone. 

In  many  cases,  as  in  the  parietal  bone,  the  lamellae  are  perforated 
by  tapering  fibres  called  the  perforating  fibres  of  Sharpey,  resembling 
in  character  the  ordinary  white  or  more  rarely  the  elastic  fibres, 
which  bolt  the  neighbouring  lamellae  together,  and  may  be  drawn  out 
when  the  latter  are  torn  asunder  (fig.  87).  These  perforating  fibres 
originate  from  ingrowing  processes  of  the  periosteum,  and  in  the  adult 
still  retain  their  connection  with  it. 


CH.  v.]  OSSIFICATION  59 

Development  of  Bone. — From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes: — 

(«.)  Those  which  are  ossified  directly  or  from  the  first  in  a  fibrous 
membrane  afterwards  called  the  periosteum— 6.<7.,  the  bones  forming 
the  vault  of  the  skull,  parietal,  frontal,  and  a  certain  portion  of  the 
occipital  bones. 

(b.)  Those  whose  form,  previous  to  ossification,  is  laid  down  in 
hyaline  cartilage — e.g.,  humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied 
in  bones  which  are  not  preceded  by  cartilage;  and  without  a  know- 
ledge of  this  process  (ossification  in  membrane),  it  is  impossible  to 
understand  the  more  complex  series  of  changes  through  which  such 
a  structure  as  the  cartilaginous  femur  of  the  foetus  passes  in  its 
transformation  into  the  bony  femur  of  the  adult  (ossification  in 
cartilage). 

Ossification  in  Membrane. — The  membrane,  afterwards  forming 
the  periosteum,  from  which  such  a  bone  as  the  parietal  is  developed, 
consists  of  two  layers — an  external  ^5rows,  and  an  internal  cellular  or 
osteo-genetic. 

The  external  layer  is  made  up  of  ordinary  fibrous  tissue.  The 
internal  layer  consists  of  a  network  of  fine  fibrils  with  a  large  number 
of  nucleated  cells  (osteoblasts),  some  of  which  are  oval,  others  drawn 
out  into  long  branched  processes:  it  is  more  richly  supplied  with 
capillaries  than  the  outer  layer.  It  is  this  portion  of  the  periosteum 
which  is  immediately  concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  ossification  is  preceded  by  an  in- 
crease in  the  vascularity  of  this  membrane,  and  then  spicules,  starting 
from  a  centre  of  ossification  near  the  centre  of  the  future  bone,  shoot 
out  in  all  directions  towards  the  periphery.  These  primary  bone 
spicules  consist  of  fibres  which  are  termed  osteo-genetic  fibres ;  they 
are  composed  of  a  soft,  transparent  substance  called  osteogen,  around 
and  between  which  calcareous  granules  are  deposited.  The  fibres  in 
their  precalcified  state  are  likened  to  bundles  of  white  fibrous  tissue, 
to  which  they  are  similar  in  chemical  composition,  but  from  which 
they  differ  in  being  stiffer  and  less  wavy.  The  deposited  granules 
after  a  time  become  so  numerous  as  to  imprison  the  fibres,  and  bony 
spiculae  result.  By  the  junction  of  the  osteo-genetic  fibres  and  their 
resulting  bony  spicules  a  meshwork  of  bone  is  formed.  The  osteo- 
genetic  fibres,  which  become  indistinct  as  calcification  proceeds,  persist 
in  the  lamellae  of  adult  bone  as  the  intercrossing  fibres  of  Sharpey. 
The  osteoblasts,  being  in  part  retained  within  the  bony  layers  thus 
produced,  form  bone  corpuscles.  On  the  bony  trabeculse  first  formed, 
layers  of  osteoblastic  cells  from  the  osteo-genetic  layer  of  the  perios- 
teum repeat  the  process  just  described ;  and  as  this  occurs  in  several 
thicknesses,  and  also  at  the  edges  of  the  spicules  previously  formed. 


60 


THE   CONyECTIYE   TISSUES 


[CH.  V. 


the  bone  increases,  both  in  thickness,  length  and  breadth.  The  pro- 
cess is  not  completed  by  the  time  the  child  is  born ;  hence  the  fonta- 
nelles  or  still  soft  places  on  the  heads  of  infants.  Fig.  88  represents 
a  small  piece  of  the  growing  edge  of  a  parietal  bone. 

The  bulk  of  the  primitive  spongy  bone  is  in  time  converted  into 
compact  bony  tissue,  with  Haversian  systems.  Those  portions  in  the 
interior  not  converted  into  bone  become  filled  with  the  red  marrow 
of  the  cancellous  tissue. 

Ossification  in  Cartilage. — Under  this  heading,  taking  the  femur 


Fig.  88.— Part  of  the  growing  edge  of  the  developing  parietal  bone  of  a  f«tal  cat.  $p,  Bony  spicules  with 
some  of  the  osteoblasts  imbedded  in  them,  producing  the  lacunie;  of,  osteogenic  fibres  prolonging 
the  spicules  with  osteoblasts  (osi)  between  them  and  applied  to  them.    (Schiifer.) 


or  any  other  long  bone  as  an  example,  we  have  to  consider  the  process 
by  which  the  solid  cartilaginous  rod  which  represents  the  bone  in  the 
foetus  is  converted  into  the  hollow  cylinder  of  compact  bone  with 
expanded  ends  formed  of  cancellous  tissue  of  which  the  adult  bone  is 
made  up.  We  must  bear  in  mind  the  fact  that  this  foetal  cartila- 
ginous femur  is  many  times  smaller  than  even  the  medullary  cavity 
of  the  shaft  of  the  mature  bone,  and,  therefore,  that  not  a  trace  of  the 
original  cartilage  can  be  present  in  the  femur  of  the  adult.  Its  pur- 
pose is  indeed  purely  temporary;  and,  after  its  calcification,  it  is 
gradually  and  entirely  absorbed. 

The  cartilaginous  rod  which  forms  the  precursor  of  a  foetal  long 


en.  v.] 


OSSIFICATION 


61 


bone  is  sheathed  in  a  membrane 
exactly  resembles  the  periosteum 
layers,  in  the  deeper  one  of  which 
spheroidal  and  branched  cells 
predominate  and  blood-vessels 
abound,  while  the  outer  layer 
consists  mainly  of  fibres. 

Between  the  cartilaginous  pre- 
figurement  of  which  the  foetal 
long  bone  consists  and  the  adult 
bone  there  are  several  inter- 
mediate stages. 

The  process  may,  however,  be 
most  conveniently  described  as 
occurring  in  three  principal 
stages. 

The  first  stage  consists  of  two 
sets  of  changes,  one  in  the  carti- 
lage, the  other  under  the  peri- 
chondrium. These  take  place 
side  by  side.  In  the  cartilage 
the  cells  in  the  middle  *  become 
enlarged  and  separated  from  one 
another.  The  cartilage-cells  on 
each  side  get  arranged  in  rows  in 
the  direction  of  the  extremities 
of  the  cartilaginous  rod.  If  at 
this  stage  one  cuts  the  little  em- 
bryonic bone  with  a  knife,  the 
knife  encounters  resistance,  and 
there  is  a  sensation  of  grittiness. 
This  is  due  to  the  fact  that  cal- 
careous particles  are  deposited  in 
the  matrix;  and  in  consequence 
of  this  the  matrix  stains  differ- 
ently with  histological  reagents 
from  the  unaltered  matrix. 
Simultaneously  with  this,  the 
periosteal  tissue  is  forming  layer 
after  layer  of  true  bone ;  this  is 
formed  exactly  in  the  same  way 

*  This  is  the  case  in  nearly  all  the 
long  bones,  but  in  the  terminal  pha- 
langes the  change  occurs  first,  not  in 
the  middle  but  at  their  distal  extremities. 


termed  the  perichondrium,  which 
described  above ;  it  consists  of  two 


Fig.  89. — Section  of  two  fn-tal  phalanges  ;  the'carti- 
lage-cells  in  the  centre  of  B  are  enlarged  and 
separated  from  one  another  by  calcified  matrix. 
ini.  Layer  of  bone  deposited  under  the  perios- 
teum ;  0,  layer  of  osteoblasts  by  which  this 
layer  was  formed.  The  rows  of  cartilage-cells 
are  seen  on  each  side  of  the  centre  of  calcifica- 
tion. In  A,  the  terminal  phalanx,  the  changes 
begin  at  the  tip.    (After  Dixey.) 


62 


THE   CONNECTIVE   TISSUES 


[CH.  V. 


as  in  such  a  bone  as  the  parietal ;  bj  the  agency  of  the  osteoblasts, 
osteogenetic  fibres,  and  then  spicules  of  bone,  are  formed  by  deposit 
of  calcareous  matter.  As  the  layers  are  formed,  some  of  the  osteo- 
blasts get  walled  in  between  the  layers,  and  become  bone  cells. 

In  the  later  part  of  this  stage  the  calcareous  deposit  between  the 
cartilage-cells  cuts  them  off  from  nutrition,  and  they  in  consequence 
waste,  leaving  spaces  that  are  called  the  primary  areolce.  The 
calcareous  deposit   creeps   up   between    the  rows   of   cartilage-cells, 


Fig.  00. — Ossification  in  cartilage  showing  stage  of  irruption.  The  shrunken  cartilage-cells  are  seen 
in  tlie  primary  areolse.  At  ir  an  irruption  of  the  subperiosteal  tissue  has  penetrated  the  sub- 
periosteal bony  crust.    (After  Lawrence.) 

euclosing  them  in  calcified  boxes  containing  one,  two,  or  more  cells 
each.  The  wasting  of  the  cells  leads  here  also  to  the  formation  of 
primary  areolse. 

We  may  roughly  compare  the  two  sets  of  cells  engaged  in  the 
process  to  two  races  of  settlers  in  a  new  country.  The  cartilage-cells 
constitute  one  race,  and  so  successfully  build  for  themselves  calcareous 
homes  as  to  be  completely  boxed  up ;  so  they  waste  and  disappear, 
leaving  only  the  walls  of  their  homes  enclosing  the  spaces  called 
primary  areolae.  The  osteoblasts,  the  other  race  of  cells  under  the 
perichondrium,  are  forming  layers  of  true  bone  in  that  situation. 


CH.  v.] 


OSSIFICATION 


63 


Some,  it  is  true,  get  walled  in  in  the  process,  and  become  bone- 
corpuscles,  but  the  system  of  intercommunicating  lacunse  and 
canaliculi  maintains  their  nutrition. 

These  two  races  are  working  side  by  side,  and  at  first  do  not 
interfere  with  each  other.  But  soon  comes  a  declaration  of  war,  and 
we  enter  upon  the  second  stage  of  ossification,  which  is  very  appro- 
priately called  the  stage  of  irruption  (fig.  90).  Breaches  occur  in  the 
bony   wall   which    the   osteoblasts   have 

built  like  a  girdle  round   the  calcifying       ^  1   s"  ^  S  ^  M  s 
cartilacre,  and   through   these    the   peri-       P5'.?S<s  ^  ^  ^ 
chondrial  tissue  pours  an  invadmg  army       eS    ^s^s*    '^'^  % 
into   the   calcified    cartilage.     This   con-       ■?  ^  2^     ^  S  ^  ^ 
sists    of    osteoblasts,   the    bone    formers ;      ^  "^  S     ^  S  S  M" 
osteoclasts,  or   the   bone   destroyers;    the      ^  -^"^      g>   ^  S  ^ 
latter  are  large  ceUs,  similar  to  the  mye- 
loplaxes  found  in  marrow  (fig.  82).    There 
are   also    a    few   fibres,    and    a    store  of 
nutrient  supply  in  the   shape  of  blood- 
vessels. 

Having  got  inside,  the  osteoclasts  set 
to  work  to  demolish  the  homes  of  the 
cartilage-cells,  the  walls  of  the  primary 
areolae,  and  thus  large  spaces  are  formed, 
which  are  called  the  secondary  areolce,  or 
the  medullary  spaces.  On  the  ruins  of 
the  calcified  cartilage,  the  osteoblasts  pro- 
ceed to  deposit  true  bone  in  layers,  just 
as  they  were  wont  to  do  in  their  own 
country,  under  the  periosteum. 

The  third  stage  of  ossification  is  a 
repetition  of  these  two  stages  towards  the 
extremities  of  the  cartilage.  The  carti- 
lage-cells get  flattened  and  arranged  in 
rows ;  calcareous  deposit  occurs  around 
these,  and  primary  areolas  result;  then 
follows  the  advance  of  the  subperiosteal 
tissue,  the  demolition  of  the  primary  areolae,  the  formation  of 
secondary  areolae,  and  the  deposit  of  true  bone.  At  the  same  time, 
layer  upon  layer  is  still  being  deposited  beneath  the  periosteum, 
and  these,  from  being  at  first  a  mere  girdle  round  the  waist  of  the 
bone,  now  extend  towards  its  extremities. 

The  next  figure  (fig.  91)  is  a  magnified  view  of  the  Line  of  advance. 

The  bone  which  is  first  formed  is  less  regularly  lamellar  than  that 
of  the  adult.  The  lamellae  are  not  deposited  till  after  birth,  and 
their  formation  is  preceded  by  a  considerable  amount  of  absorption. 


Fig.  91. — Longitudinal  section  of  ossi- 
fying cartilage.  Calcified  trabeculae 
are  seen  extending  between  the 
columns  of  cartilage-ceUs.  c,  Car- 
tilage-cells ;  a,  b,  secondary  areolee. 
X  140.    (Sharpey.) 


G4  THE   CONNECTIVE   TISSUES  [CH.    V. 

To  carry  our  simile  further,  the  osteoblasts  are  not  satisfied  with  the 
rough  constructions  that  they  were  first  able  to  make,  but  having 
exterminated  the  cartilage,  they  destroy  (again  through  the  agency 
of  the  regiment  of  giant  osteoclasts)  their  first  work,  and  build  regular 
lamellae,  leaving  lacunae  for  the  accommodation  of  those  who  desire  to 
retire  from  active  warfare. 

About  this  time,  too,  the  marrow  cavity  is  formed  by  the  absorp- 
tion of  the  bony  tissue  that  originally  occupied  the  centre  of  the 
shaft.  Here  the  osteoclasts  have  again  to  do  the  work,  and,  with  tins 
final  act  of  destruction,  all  remains  of  any  calcified  cartilage  of  tho 
foetal  bone  entirely  disappear. 

The  formation  of  a  so-called  cartilage  bone  is  thus,  after  all,  a 
formation  of  bone  by  subperiosteal  tissue,  just  as  it  is  in  the  so-called 
membrane  bone. 

After  a  time  the  cartilage  at  the  ends  of  the  shaft  begins  to  ossify 
independently,  and  the  epiphyses  are  formed.  They  are  not  joined 
on  to  the  shaft  till  late  in  life,  so  that  growth  of  the  bone  in  length 
can  continue  till  union  takes  place. 

Bone  grows  in  width  by  the  deposition  of  layers  under  the  perios- 
teum, like  successive  rings  formed  under  the  bark  of  a  growing  tree. 
This  was  shown  long  before  the  liistological  details  which  we  have 
described  were  made  out  by  Sharpey.  Silver  rings  were  placed  by 
Duliamel  around  the  bones  of  young  pigeons.  "When  killed  later,  the 
rings  were  completely  covered  in  by  bone ;  and  in  the  animals  killed 
last,  were  even  found  in  the  central  ca%'ity.  Another  series  of  experi- 
ments was  performed  upon  pigs.  The  young  animals  were  fed 
alternately  on  ordinary  food  and  food  dyed  by  the  red  pigment 
madder.  The  new  bony  tissue  acts  like  what  dyers  called  a 
"  mordant " :  it  fixes  the  dye,  and  the  rings  of  bone  deposited  during 
the  madder  periods  were  distinctly  red  in  colour. 

The  importance  of  the  periosteum  in  bone  formation  is  now 
recognised  by  surgeons.  When  removing  a  piece  of  bone  they  are 
careful,  if  possible,  to  leave  the  periosteum  behind :  this  leads  to 
regeneration  of  the  lost  bone.  If  it  is  absolutely  necessary  to  remove 
the  periosteum,  successfid  cases  have  occurred  in  which  the  living 
periosteum  from  an  animal  has  effectively  been  transplanted. 


The  Teeth. 

During  the  course  of  his  life,  man,  in  common  with  most  other 
mammals,  is  provided  with  two  sets  of  teeth ;  the  first  set,  called  the 
temporary  or  milk-teeth,  makes  its  appearance  in  infancy,  and  is  in 
the  course  of  a  few  years  shed  and  replaced  by  the  second  or  per- 
manent set. 


(11.  V.J 


THE   TKKTll 


65 


The  temporary  or  milk-teeth  havo  only  a  ^■Gry  limited  tenu  of 
existence. 

They  are  ten  in  number  in  each  jaw,  namely,  on  either  side  from 
the  middle  line  two  incisors,  one  canine,  and  two  deciduous  molars, 
and  are  replaced  by  ten  permanent  teeth.     The  numher  of  permanent 


Fio.  92.— Normal  well-formed  jaws,  from  which  the  alveolar  plate  has  been  in  great  part  removed   so 
as  to  expose  the  developing  permanent  teeth  in  their  crj'pts  in  the  jaws.    (Tomes.)  ' 

teeth  in  each  jaw  is,  however,  increased  to  sixteen  by  the  develop- 
ment of  three  molars  on  each  side  of  the  jaw,  which  are  called  the 
permanent  or  true  molars. 

The  following  formula  shows,  at  a  glance,  the  comparative  arrano-e- 
ment  and  number  of  the  temporary  and  permanent  teeth : — 


MOLARS. 

2 


Temporary  Teeth. 
Middle  Line  of  Jaw. 


CANINE. 
1 


INCISOR.S. 
2 


INCISORS. 

2 


CANINE. 
1 


MOLARS. 

2  =  10 


2  =  10 


=  20 


TRUE 
MOLARS. 


BICUSPIDS 
OK  PRE- 
MOLARS. 


Permanent  Teeth. 

Middle  Line  of  Jaw. 


CANINE. 
1 


BICUSPIDS 
OR  PRE- 
MOLARS. 

2 


TRUE 
MOLARS, 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  or  pre- 
molar teeth  in  the  adult  are  the  successors  of   the  two  deciduous 

E 


66 


THE   CONNECTIVE   TISSUES 


[CH.  V. 


molars  in  the  child.  They  differ  from  them,  however,  in  some 
respects,  the  temporary  molars  having  a  stronger  likeness  to  the  per- 
manent than  to  their  immediate  descendants  the  so-called  bicuspids, 
besides  occupying  more  space  in  the  jaws. 

The  temporary  incisors  and  canines  differ  from  their  successors 
but  little  except  in  their  smaller  size  and  the  abrupt  manner  in  which 
their  enamel  terminates  at  the  necks  of  the  teeth,  forming  a  ridge  or 
thick  edge.  Their  colour  is  more  of  a  bluish- white  than  of  a  yellowish 
shade. 

The  following  tables  show  the  average  times  of  eruption  of  the 
Temporary  and  Permanent  teeth.  In  both  cases  the  eruption  of  any 
given  tooth  of  the  lower  precedes,  as  a  rule,  that  of  the  corresponding 
tooth  of  the  upper  jaw. 

Temporary  or  Milk  Teeth. 

The  figures  indicate  in  months  the  age  at  which  each  tooth  appears. 


INCISORS. 

DECIDUOUS 

FIRST 

MOLARS. 

CANINES.    . 

DECIDUOUS 
SECOND 
MOLARS. 

6 

12 

18 

24 

Permanent  Teeth. 
The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 


FIRST 
MOLARS. 

INCIE 
CENTRALS. 

ORS. 
LATERALS. 

BICUSPIDS  OR  PRE- 
MOLARS. 

FIRST.          SECOND. 

CANINES. 

SECOND 
MOLARS. 

THIRD 
MOLARS  OR 
WISDOMS. 

6 

7 

8 

9             10 

11 

12 

17  to  25 

The  times  of  eruption  given  in  the  above  tables  are  only  approxi- 
mate: the  limits  of  normal  variation  are  tolerably  wide.  Certain 
diseases  affecting  the  bony  skeleton,  e.g.  Rickets,  retard  the  eruptive 
period  considerably. 

It  is  important  to  notice  that  it  is  a  molar  which  is  the  first  tooth 
to  be  cut  in  the  permanent  dentition,  not  an  incisor  as  in  the  case  of 
the  temporary  set,  and  also  that  it  appears  behind  the  last  deciduous 
molar  on  each  side. 

The  third  molars,  often  called  Wisdoms,  are  sometimes  unerupted 
through  life  from  want  of  sufficient  jaw  space  and  the  presence  of 


CU.  v.]  THE  TEETH  67 

the  other  teeth ;  cases  of  whole  families  in  which  their  absence  is  a 
characteristic  feature  are  occasionally  met  with. 

When  the  teeth  are  fully  erupted  it  will  be  observed  that  the  upper 
incisors  and  canines  project  obliquely  over  the  lower  front  teeth,  and 
the  external  cusps  of  the  upper  bicuspids  and  molars  lie  outside  those 
of  the  corresponding  teeth  in  the  lower  jaw.  This  arrangement 
allows  to  some  extent  of  a  scissor-like  action  in  dividing  and  biting 
food  in  the  case  of  incisors ;  and  a  grinding  motion  in  that  of  the 
bicuspids  and  molars  when  the  side  to  side  movements  of  the  lower 
jaw  bring  the  external  cusps  of  the  lower  teeth  into  direct  articula- 
tion with  those  of  the  upper,  and  then  cause  them  to  glide  down  the 
inclined  surfaces  of  the  external  and  up  the  internal  cusps  of  these 
same  upper  teeth  during  the  act  of  mastication. 

The  work  of  the  canine  teeth  in  man  is  similar  to  that  of  his 
incisors.  Besides  being  a  firmly  implanted  tooth  and  one  of  stronger 
substance  than  the  others,  the  canine  tooth  is  important  in  preserving 
the  shape  of  the  angle  of  the  mouth,  and  by  its  shape,  whether 
pointed  or  blunt,  long  or  short,  it  becomes  a  character  tooth  of  the 
dentition  as  a  whole  in  both  males  and  females. 

Another  feature  in  the  fully  developed  and  properly  articulated 
set  of  teeth  is  that  no  two  teeth  oppose  each  other  only,  but  each 
tooth  is  in  opposition  with  two,  except  the  upper  Wisdom,  usually  a 
small  tooth.  This  is  the  result  of  the  greater  width  of  the  upper 
incisors,  which  so  arranges  the  "  bite "  of  the  other  teeth  that  the 
lower  canine  closes  in  front  of  the  upper  one. 

Should  a  tooth  be  lost,  therefore,  it  does  not  follow  that  its  former 
opponent  remaining  in  the  mouth  is  rendered  useless  and  thereby 
liable  to  be  removed  from  the  jaw  by  a  gradual  process  of  extrusion 
commonly  seen  in  teeth  that  have  no  work  to  perform  by  reason  of 
absence  of  antagonists. 

Structure  of  a  Tooth. 

A  tooth  is  generally  described  as  possessing  a  crown,  neck,  and  root. 

The  crovjn  is  the  portion  which  projects  beyond  the  level  of  the 
gum.  The  nech  is  that  constricted  portion  just  below  the  crown 
which  is  embraced  by  the  free  edges  of  the  gum ;  and  the  root  includes 
all  below  this. 

On  making  longitudinal  and  transverse  sections  through  its  centre 
(figs.  93,  94),  a  tooth'  is  found  to  be  composed  of  a  hard  material, 
■  dentine  or  ivory,  which  is  moulded  around  a  central  cavity  which 
resembles  in  general  shape  the  outline  of  the  tooth  ;  the  cavity  is 
called  the  pidp  cavity  from  its  containing  the  very  vascular  and 
sensitive  pulp. 

The  tooth-pulp  is  composed  of  loose  connective  tissue,  blood-vessels, 


68 


THE   CONNECTIVE   TISSUES 


[CH.  V. 


nerves,  and  large  numbers  of  cells  of  varying  shapes ;  on  the  sur- 
face in  close  connection  with  the  dentine  is  a  specialised  layer  of 


Fig.  93. — A,  Longitudinal  section  of  a  human  molar  tooth  ;  c,  cement ;  (?,  dentine ;  e,  enamel ;  v,  pulp- 

cavitj.    (Owen.) 
B,  Transverse  section.    The  letters  indicate  the  same  as  in  A. 

cells  called  odontoblasts,  which  are  elongated  columnar  cells  with  a 
large  nucleus  at  the  tapering  ends  farthest  from  the  dentine. 


Enamel  -- 


Dentine. 


Periosteum  of 
alveolus. 


Cement  - 


--  Cement. 


Lower  jaw-bone. 


t'iG.  94. — Premolar  tooth  of  cat  in  situ. 


CH.V.]  DENTINE  69 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  open- 
ing at  the  apical  extremity  of  each  root.  The  exact  terminations  of  the 
nerves  are  not  definitely  known.  They  have  never  heen  observed  to 
enter  the  dentinal  tubes.     No  lymphatics  have  been  seen  in  the  pulp. 

A  layer  of  very  hard  calcareous  matter,  the  enamel,  caps  that  part 
of  the  dentine  which  projects  beyond  the  level  of  the  gum ;  while 
sheathing  the  portion  of  dentine  which  is  beneath  the  level  of  the 
gum,  is  a  layer  of  true  bone,  called  the  cement  or  crusta  petrosa. 

At  the  neck  of  the  tooth,  where  the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an  exceedingly  thin  layer ;  here  the  cement 
overlaps  the  enamel,  and  is  prolonged  over  it.  On  the  surface  of  the 
crown  of  the  tooth,  when  it  first  comes  through  the  jaw,  is  a  thin 
membrane  called  Nasmyth's  membrane,  or  the  cuticle  of  the  tooth. 
The  covering  of  enamel  becomes  thicker  towards  the  crown,  and  the 
cement  towards  the  lower  end  or  apex  of  the  root. 

Dentine  or  Ivory. 

Dentine  closely  resembles  bone  in  chemical  composition.  It  con- 
tains, however,  only  10  per  cent,  of  water.  The  proportion  in  a 
hundred  parts  of  the  solids  is  about  twenty-eight  animal  to  seventy- 
two  of  earthy  matter.  The  former,  like  the  animal  matter  of  bone, 
may  be  converted  into  gelatin  by  boiling.  It  also  contains  a  trace  of 
fat.  The  earthy  matter  is  made  up  chiefly  of  calcium  phosphate,  with 
a  small  portion  of  the  carbonate,  and  traces  of  calcium  fluoride  and 
magnesium  phosphate. 

Under  the  microscope  dentine  is  seen  to  be  finely  channelled 
by  a  multitude  of  delicate  tubes,  which  by  their  inner  ends  com- 
municate with  the  pulp-cavity,  and  by  their  outer  extremities  come 
into  contact  with  the  under  part  of  the  enamel  and  cement,  and 
sometimes  even  penetrate  them  for  a  greater  or  less  distance  (figs.  95, 
97).  The  matrix  in  which  these  tubes  lie  is  composed  of  "  a  reticulum 
of  fine  fibres  of  connective  tissue  modified  by  calcification,  and  where 
that  process  is  complete,  entirely  hidden  by  the  densely  deposited  lime 
salts  "  (Mummery). 

In  their  course  from  the  pulp-cavity  to  the  surface,  the  minute 
tubes  form  gentle  and  nearly  parallel  curves,  and  divide  and  subdivide 
dichotomously,  but  without  much  lessening  of  their  calibre  until  they 
approach  their  peripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary 
canals,  which  extend  into  the  dentine  between  the  tubules  and 
anastomose  with  each  other.  The  tubules  of  the  dentine,  the  average 
diameter  of  which  at  their  inner  and  larger  extremity  is  xsVo  of  an 
inch,  contain  fine  prolongations  from  the  tooth-pulp,  which  give  the 
dentine  a  certain  faint  sensitiveness  under  ordinary  circumstances,  and. 


70 


THE   CONXECTIYE  TISSUES 


[CH.  V. 


without  doubt,  have  to  do  also  with  its  nutrition.  These  prolonga- 
tions from  the  tooth-pulp  are  processes  of  the  dentine-cells  or  odonto- 
hlasts,  the  columnar  cells  lining  the  pulp-ca%"ity ;  the  relation  of 
these  processes  to  the  tubules  in  which  they  lie  is  precisely  similar  to 
that  of  the  processes  of  the  bone-corpuscles  to  the  canaliculi  of  bone. 
The  outer  portion  of  the  dentine,  underlying  the  cement,  and  the 
enamel  to  a  much  lesser  degree,  forms  a  more  or  less  distinct  layer 
termed  the  granular  or  interglobular  layer  (fig.  95).     It  is  characterised 


Fig.  95  -Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  mcisor  tooth. 
a.  Dentinal  tubulwramifsing  and  terminating,  some  of  them  in  the  mterglobnlar  spaces  b  and  c ;  d, 
inner  layer  of  the  cement  with  numerous  closely  set  canaliculi ;  e,  out«r  layer  of  cement ;  /,  lacun* , 
g,  canalicali.     x  350.    (Kolliker.) 

by  the  presence  of  a  number  of  ii-regular  minute  ca\ities.  The 
explanation  of  these  will  be  seen  when  we  study  the  development  of 
a  tooth. 

Enamel. 

Enamel  is  by  far  the  hardest  tissue  in  the  body ;  it  is  composed  of 
the  same  inorganic  compounds  that  enter  into  the  composition  of 


Fig.  9o.— Enimei  prisms.  A,  fragments  and  single  prisms  of  the  transversely-striated  enamel,  isolated 
by  the  action  of  hydrochloric  acid.  B,  surface  of  a  smaU  firagment  of  enamel,  showing  the  haxa- 
gonal  ends  of  the  fibres  with  darker  centres,     x  3aO.    (KoUikar.) 


CH.  v.] 


ENAMEL 


71 


dentine  and  hone.  According  to  Tomes,  it  contains  no  animal  matter 
at  all,  and  only  2  or  3  per  cent,  of  water.  Gelatin  is  a  characteristic 
product  of  connective  tissue,  and  enamel  is  not  a  connective  tissue, 
but  is  epithelial  in  origin. 

Examined  under  the  microscope,  enamel  is  found  composed  of  six- 
sided  prisms  (figs.  96,  97)  ^iny  of  an  inch  in  diameter,  which  are  set 
on  end  on  the  surface  of  the  dentine,  and  fit 
into  corresponding  depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the 
dentine  that  at  the  top  of  the  tooth  they  are 
more  or  less  vertical,  while  towards  the  sides 
they  tend  to  the  horizontal  direction.  Like 
the  dentine  tubules,  they  are  not  straight,  but 
disposed  in  wavy  and  parallel  curves.  The 
prisms  are  marked  by  transverse  lines  and  are 
solid. 

The  enamel  prisms  are  connected  together 
by  a  very  minute  quantity  of  hyaline  cement 
substance.  In  the  deeper  part  of  the  enamel, 
between  the  prisms,  are  often  small  lammce, 
which  have  the  processes  or  fibrils  Ij'ing  in 
the  dentinal  tubes  in  connection  with  them 
(fig.  97,  c). 

Crusta  Petrosa. 

The  crusta  petrosa  or  cement  (fig.  95,  e,  d)  is 
composed  of  true  bone,  and  in  it  are  lacunse  (/) 
and  canaliculi  {g),  which  sometimes  communi- 
cate with  the  outer  finely  branched  ends  of 
the  dentinal  tubules,  and  generally  with  the 
interglobular  spaces.  Its  laminae  are  bolted  to- 
gether by  perforating  fibres  like  those  of  ordi- 
nary bone  (Sharpey's  fibres).  Cement  differs 
from  ordinary  bone  in  possessing  no  Haversian 
canals,  or,  if  at  all,  only  in  the  thickest  part. 
Such  canals  are  more  often  met  with  in  teeth 
with  the  cement  hypertrophied  than  in  the 
normal  tooth. 


Fig.  97.— Thill  section  of  the 
enamel,  and  a  part  of  the 
dentine.  or,  Cuticular 
pellicle  of  the  enamel 
(Xasmyth's  membrane) ; 
6,  enamel  colunms  with 
fissures  between  them 
and  cross  strise  ;  c,  larger 
ca\-ities  in  the  enamel, 
communicating  with  the 
extremities  of  some  of 
the  dentinal  tubules  (d). 
X  350.    (Kolliker.) 


Development  of  the  Teeth. 

The  first  step  in  the  development  of  the  teeth  consists  in  a  down- 
ward growth  (fig.  98,  A,  1)  from  the  deeper  layer  of  stratified  epi- 
thelium of  the  mucous  membrane  of  the  mouth,  which  becomes 
thickened  in  the  neighbourhood  of  the  maxillae  or  jaws  now  in  the 
course  of  formation.     Tliis  process  passes  downward  into  a  recess  of 


72 


THE   CONNECTIVE  TISSUES 


[CH.  V. 


B 


/ 


tho  imperfectly  developed  tissue  of  the  embryonic  jaw.  The  down- 
ward epithelial  growth  forms  the  common  enamel  or  dental  germ,  and 
its  position  is  indicated  by  a  slight  groove  in  the  mucous  membrane 

of  the  jaw.  After  this  there 
is  an  increased  development 
at  certain  points  correspond- 
ing to  the  situations  of  the 
future  milk-teeth.  The  com- 
mon enamel  germ  thus  be- 
comes extended  by  further 
growth  into  a  number  of 
special  enamel  germs  (fig. 
98,  B,)  corresponding  to  each 
of  the  milk-teeth,  and  con- 
nected to  the  common  germ 
by  a  narrow  neck  (/).  Each 
tooth  is  thus  placed  in  its 
own  special  recess  in  the 
embryonic  jaw. 

As  these  changes  proceed, 
there  grows  up  from  the 
underlying  connective  tissue 
into  each  enamel  germ  (fig. 
98,  c,  p),  a  distinct  vascular 
papilla  {dental  papilla),  and 
upon  it  the  enamel  germ  be- 
comes moulded,  and  presents 
the  appearance  of  a  cap  of 
two  layers  of  epithehum 
separated  by  an  interval  (fig. 
98,  c,/).  Whilst  part  of  the 
subepithelial  tissue  is  ele- 
vated to  form  the  dental 
papilla,  the  part  which  bounds 
the  embryonic  teeth  forms 
the  dental  sac  (fig.  98,  c,  s) ; 
and  the  rudiment  of  the 
jaw  sends  up  processes  form- 
ing partitions  between  the 
teeth.  In  tliis  way  small 
chambers  are  produced  in  which  the  dental  sacs  are  contained, 
and  thus  the  sockets  of  the  teeth  are  formed.  The  papilla  is  com- 
posed of  nucleated  cells  arranged  in  a  mesh-work  of  connective 
tissue,  the  outer  or  peripheral  part  lieing  covered  with  a  layer  of 
columnar  nucleated  cells  called  odontoblasts. 


^>'xs>ii 


•W. 


:.  '.IS.— Section  of  the  upper  Jaw  of  a  total  sheep. 
A. — 1,  common  enamel  gorm  dipping  down  into  the 
mucous  membrane ;  2,  palatine  process  of  jaw ; 
3,  Rete  Malpighi.  B.— Section  similar  to  A,  but 
passing  through  one  of  the  special  enamel  germs 
here  becoming  flask-shaped ;  c,  c',  epithelium  of 
mouth;/,  neck;/,  body  of  special  enamel  germ. 
C— A  later  stage ;  c,  outline  of  epithelium  of  gum  ; 
/,  neck  of  enamel  germ  ;  /,  enamel  organ  ;  p,  papilla  ; 
s,  dental  sac  forming  ;  /  p,  the  enamel  germ  of  per- 
manent tooth  ;  7)1,  bone  of  jaw ;  f ,  vessels  cut  across. 
(Waldeyer  and  Kijlliker.) 


CH.  v.] 


DEVELOPMENT   OF   THE   TEETH 


73 


Tiiesft  cells  either  by  secretion,  or  as  some  think  by  direct  trans- 
formation of  the  outer  part  of  each,  form  a  layer  of  dentinal  matrix 
on  the  apex  of  the  papilla,  or  if  the  tooth  lias  more  than  one  cusp, 
then  at  the  apex  of  each  cusp.  This  layer  is  first  uncalcified 
(odo/itogen),  but  globules  of  calcareous  matter  soon  appear  in  it. 
These,  becoming  more  numerous,  blend  into  the  first  cap  of  dentine. 
In  the  meanwhile  the  odontoblasts  have  formed  a  second  layer  of 
odontogen  within  this  (fig,  99),  and  this  in  turn  becomes  calcified ; 
thus  layer  after  layer  is  formed,  each  extending  laterally  further  than 
its  predecessor ;  the  layers  blend  except  in  some  places ;  here  portions 
of  odontogen  remain,  which  in  a 
tooth  macerated  for  liistological 
purposes  get  destroyed,  and  appear 
as  the  interglobular  spaces  (fig.  95), 
so  called  because  bounded  by  the 
deposit  of  calcareous  salts,  which 
occurs,  as  we  have  already  seen,  in 
the  form  of  globules. 

As  the  odontoblasts  retire 
towards  the  centre,  depositing 
layer  after  layer  of  dentine,  they 
leave  beliind  them  long  filaments 
of  their  protoplasm  around  which 
the  calcareous  deposit  is  moulded  ; 
thus  the  dentinal  tubules  occupied 
by  the  processes  of  the  odonto- 
blasts are  formed. 

The  other  cells  of  the  dental 
papilla  form  the  cells  of  the  pulp. 

Formation  of  the  enamel. — The  portion  of  the  enamel  or  dental 
germ  that  covers  the  dental  papilla  is  at  this  stage  called  the  enamel 
organ.     This  consists  of  four  parts  (see  figs.  100  and  101). 

1.  A  layer  of  columnar   epithelium   cells   in    contact   with    the 

dentine.     These   are   called    the   enamel  cells,  or  aclamanto- 
hlasts. 

2.  Two  or  three  layers  of  smaller  polyhedral  nucleated  cells,  the 

stratum  intermedium  of  Hannover. 

3.  A  matrix  of  non-vascular  jelly-like  tissue  containing  stellate 

cells. 

4.  An  outer  membrane  of  several  layers  of  flattened  epithelium 

cells. 
The  first  three  layers  on  an  enlarged  scale  are  seen  in  fig.  101. 
The  enamel  prisms  are  formed  by  the  agency  of  the  ends  of  the 
adamantoblasts  which  abut  on  the  dental  papilla.     Each  forms  a  fine 


Fig.  9',i. — Part  of  section  of  developing  tooth  of  a 
young  rat,  showing  the  mode  of  deposition  of 
the  dentine.  Highly  magnified,  a,  Outer 
layer  of  fully  formed  dentine;  b,  uncalcified 
matrix  with  one  or  two  nodules  of  calcareous 
matter  near  the  calcified  parts ;  c,  odonto- 
blasts sending  processes  into  the  dentine ; 
d,  pulp ;  e,  fusiform  or  wedge-shape  cells 
found  between  odontoblasts ;  /,  stellate  cells 
of  pulp  in  fibrous  connective  tissue.  The 
section  is  stained  with  carmine,  which  colours 
the  uncalcified  matrix  but  not  the  calcified 
part.    (B.  A.  Schafer.) 


74 


THE    CONNECTIVE   TISSUES 


[CH.  V. 


i^J- 


y_ 


deposit  of  globules  staining  with  osmic  acid  and  resembling  keratin 
in  its  resistance  to  mineral  acid.  At  one  time  it  was  believed  that 
each  adamantoblast  was  itself  calcified  and  converted  into  an  enamel 
prism,  but  this  view  has  been  disproved  by  recent  research.  The 
layer  of  keratin-like  material  is  outside  the  bodies  of  the  cells,  although 
a  process  of  each  adamantoblast  extends  into  it  as  a  tapering  fibre 
(process  of  Tomes),  and  it  is  usually  produced  simultaneously  with 
^^^^-^-^r"-^  the  first  layer  of  uncalcified  den- 

'"  "^        ^  tine;  when  it  undergoes  calcifica- 

tion, the  first  layer  of  enamel  is 
complete.  The  adamantoblasts 
then  repeat  the  process,  first 
causing  a  deposition  of  keratin- 
like material,  and  this  in  turn  is 
calcified,  and  so  on.  During  the 
formation  of  layer  after  layer  of 
enamel,  the  adamantoblasts  retire. 
By  the  time  the  enamel  is  ap- 
proaching completion  the  other 
layers  of  the  enamel  organ  have 
almost  disappeared,  and  they  en- 
tirely disappear  when  the  tooth 
emerges  through  the  gum.  But 
for  some  little  time  there  is  a 
somewhat  more  persistent  mem- 
brane covering  the  crown ;  this  is 
Nasmyth's  membrane,  or  the 
enamel  cuticle ;  this  is  the  last 
formed  keratinous  layer  of  enamel 
which  has  remained  uncalcified. 

As  with  the  dentine,  the  for- 
mation of  enamel  appears  first  on 
the  apex  of  each  cusp. 

The  cement  or  crusta  petrosa  is 
formed  from  the  internal  tissue  of  the  tooth  sac,  the  structure  and 
function  of  which  are  identical  with  those  of  the  osteogenetic  layer 
of  the  periosteum;  or,  in  other  words,  ossification  in  membrane 
occurs  in  it. 

The  outer  layer  or  portion  of  the  membrane  of  the  tooth  sac  forms 
the  dental  periosteum. 

This  periosteum,  when  the  tooth  is  fully  formed,  is  not  only  a 
means  of  attachment  of  the  tooth  to  its  socket,  but  also  in  conjunction 
with  the  pulp  a  source  of  nourishment  to  it.  Additional  laminse  of 
cement  are  added  to  the  root  from  time  to  time  during  the  life  of 
the  tooth  (as  is  especially  well  seen  in  the  abnormal  condition  called 


Fio.  100.— Vertical  transverse  section  of  the 
dental  sac,  pulp,  etc.,  of  a  kitten,  a,  Dental 
papilla  or  pulp  ;  h,  the  cap  of  <lentine  formed 
upon  the  summit ;  c,  its  covering  of  enamel ; 
d,  inner  layer  of  epithelium  of  the  enamel 
organ  ;  e,  gelatinous  tissue  ;  /,  outer  epithe- 
lial layer  of  the  enamel  organ ;  g,  inner  layer, 
and  h,  outer  layer  of  dental  sac.  x  14. 
(Thiersch.) 


CH.  v.] 


DEVELOPMENT   OF   THE   TEETH 


75 


an  exostosis),  by  the  process  of  ossificaiion  taking  place  in  the  perios- 
teum. On  the  other  hand,  absorption  of  the  root  (such  as  occurs 
when  the  milk-teeth  are  shed)  is  due  to  the  action  of  the  osteoclasts 
of  the  same  membrane. 

In  this  manner  the  first  set  of  teeth,  or  the  milk-teeth,  are  formed ; 
and  each  tooth,  as  it  grows,  presses  at  length  on  the  wall  of  the 
sac  enclosing  it,  and,  causing  its  absorption,  is  cut,  to  use  a  familiar 
phrase. 

The  temporary  or  milk-teeth  are  later  replaced  by  the  growth  of 
the  permanent  teeth,  which  push  their  way  up  from  Joeneath  them. 


Fig.  101. — Highly  magnified  view  of  a  piece  of  the  enamel  organ  in  a  kitten's  canine,  rf,  Superlicial 
layer  of  dentine,  e.  Newly  formed  enamel  stained  black  by  osmic  acid.  T,  Tomes'  processes  from 
the  adamantoblasts,  ad. ;  str.  int.,  stratum  intermedium  of  the  enamel  organ,  p.  Branched  cells  of 
the  enamel  pulp.    (After  Rose.) 


Each  temporary  tooth  is  replaced  by  a  tooth  of  the  permanent  set 
which  is  developed  from  a  small  sac  which  was  originally  an  offshoot 
from  the  sac  of  the  temporary  tooth  which  precedes  it,  and  called  the 
cavity  of  reserve  (fig.  98,  c,  fp).  Thus  the  temporary  incisors  and 
canines  are  succeeded  by  the  corresponding  permanent  ones,  the 
temporary  first  molar  by  the  first  bicuspid ;  the  temporary  second 
molar  develops  two  offshoots,  one  for  the  second  bicuspid,  the  other 
for  the  permanent  first  molar.  The  permanent  second  molar  is  budded 
off  from  the  first  permanent  molar,  and  the  wisdom  from  the  perma- 
nent second  molar. 

The  development  of  the  temporary  teeth  commences  about  the 
sixth  week  of  intra-uterine  life,  after  the  laying  down  of  the  bony 
structure  of  the  jaws.  Their  jjermanent  successors  Ijegin  to  form 
about  the  sixteenth  week  of  intra-uterine  life.     The  second  permanent 


76  THE   CONNECTIVE   TISSUES  [CH.  V, 

molars  originate  about  the  third  month  after  birth,  and  the  wisdom 
teeth  about  the  third  year. 

The  Blood. 

A  full  consideration  of  the  blood  will  come  later,  when  we  know 
more  about  the  chemical  aspects  of  physiology,  but  it  will  be  impos- 
sible to  discuss  all  the  other  phenomena  we  shall  have  to  study  in 
the  meanwhile  without  some  elementary  knowledge  of  the  principal 
properties  of  this  fluid.  For  that  reason,  and  also  to  complete  our 
list  of  the  connective  tissues,  we  may  here  rapidly  and  briefly 
enumerate  its  principal  characters. 

The  blood  is  a  fluid  which  holds  in  suspension  large  numbers  of 
solid  particles  which  are  called  the  corpuscles.  The  fluid  itself  is 
called  th.Q  plasma  or  liquor  sanguinis.  It  is  a  richly  albuminous  fluid ; 
and  one  of  the  proteins  in  it  is  called  fibrinogen. 

After  blood  is  shed  it  rapidly  becomes  viscous,  and  then  sets  into 
a  jelly.  The  jelly  contracts  and  squeezes  out  of  the  clot  a  straw- 
coloured  fluid  called  serum,  in  which  the  shrunken  clot  then  floats. 

The  formation  of  threads  of  a  solid  protein  called  yi5rm  from  the 
soluble  proteid  we  have  called  fibrinogen  is  the  essential  act  of 
coagulation ;  this,  with  the  corpuscles  it  entangles,  is  called  the  clot. 
Serum  is  plasma  minus  the  fibrin  which  it  yields.  The  following 
scheme  shows  the  relationships  of  the  constituents  of  the  blood  at  a 
glance : — 

f  Serimi 

-r,,     I  f  Plasma  Fibrin  )  ^,  , 

Blood  -  ^  ,  "^  \  Clot. 

(  Corpuscles  j 

The  corpuscles  are  of  two  chief  kinds,  the  red  and  the  white. 
The  white  corpuscles  are  typical  animal  cells,  and  we  have  already 
made  their  acquaintance  when  speaking  about  amoeboid  movements. 

The  red  corpuscles  are  much  more  numerous  than  the  white, 
averaging  in  man  5,000,000  per  cubic  millimetre,  or  400  to  500  red 
to  each  white  corpuscle.  It  is  these  red  corpuscles  that  give  the  red 
colour  to  the  blood.  They  vary  in  size  and  structure  in  different 
groups  of  the  vertebrates.  In  mammals  they  are  biconcave  (except 
in  the  camel  tribe,  where  they  are  biconvex)  non-nucleated  discs,  in 
man  -yo-Vo-  i^ch  in  diameter ;  during  foetal  life  nucleated  red  corpuscles 
are,  however,  found.  In  birds,  reptiles,  amphibians  and  fishes  they 
are  biconvex  oval  discs  with  a  nucleus :  they  are  largest  in  the 
amphibia.  The  most  important  and  abundant  of  the  constituents 
of  the  red  corpuscles  is  the  pigment  which  is  called  hcem.oglobin. 
This  is  a  protein-like  substance,  but  is  remarkable  as  it  contains  a 
small  amount  of  iron  (about  0"4  per  cent.). 

The  blood  during  life  is  in  constant  movement.     It  leaves  the 


CH.  v.]  THE   BLOOD  77 

heart  by  the  vessels  called  arteries,  and  returns  to  the  heart  l)y  the 
vessels  called  veins;  the  terminations  of  the  arteries  and  the  com- 
mencements of  the  veins  arc,  in  the  tissues,  connected  by  the  thin- 
walled  microscopic  vessels  called  capillaries.  In  the  capillaries, 
leakage  of  the  blood-plasma  occurs ;  this  exuded  fluid  (lymph)  carries 
nutriment  from  the  blood  to  the  tissue-elements,  and  removes  from 
them  the  waste  products  of  their  activity.  Tlie  lymph  is  collected  by 
lymphatic  vessels,  which  converge  to  the  main  lymphatic,  called  the 
thoracic  diict.  This  opens  into  the  large  veins  near  to  their  entrance 
into  the  heart ;  and  thus  the  lymph  is  returned  to  the  blood. 

But  blood  is  also  a  carrier  of  oxygen,  and  it  is  the  pigment 
htemoglobin  which  is  the  oxygen  carrier ;  in  the  lungs  the  haemoglobin 
combines  with  the  oxygen  of  the  air,  and  forms  a  loose  compound  of 
a  bright  scarlet  colour  called  oxyhcemoglobin.  This  arterial  or  oxy- 
genated blood  is  taken  to  the  heart  and  thence  propelled  by  the 
arteries  all  over  the  body,  where  the  tissues  take  the  respiratory 
oxygen  from  the  haemoglobin,  and  this  removal  of  oxygen  changes 
the  colour  of  blood  to  the  bluish-red  tint  it  has  in  the  veins.  The 
veins  take  the  blood  minus  a  large  quantity  of  oxygen  and  plus  a 
large  quantity  of  carbonic  acid  received  in  exchange  from  the  tissues 
to  the  heart,  which  sends  it  to  the  lungs  to  get  rid  of  its  surplus 
carbonic  acid,  and  replenish  its  store  of  oxygen ;  then  the  same  round 
begins  over  again. 


CHAPTEE  VI 

MUSCULAE   TISSUE 

Muscle  is  popularly  known  as  flesh.  It  possesses  the  power  of  con- 
traction, and  is,  in  the  higher  animals,  the  tissue  by  which  their 
movements  are  executed.  The  muscles  may  be  divided  from  a 
physiological  standpoint  into  two  great  classes,  the  voluntary  muscles, 
those  which  are  under  the  control  of  the  will,  and  the  involuntary 
muscles,  those  which  are  not.  The  contraction  of  the  involuntary 
muscles  is,  however,  controlled  by  the  nervous  system,  only  by  a 
different  part  of  the  nervous  system  from  that  which  controls  the 
activity  of  the  voluntary  muscles. 

When  muscular  tissue  is  examined  with  the  microscope,  it  is 
seen  to  be  made  up  of  small,  elongated,  thread-Hke  structures,  which 
are  called  muscular  fibres ;  these  are  bound  into  bundles  by  connective 
tissue,  and  in  the  involuntary  muscles  there  is  in  addition  a  certain 
amount  of  cement  substance,  stainable  by  nitrate  of  silver,  between 
the  fibres. 

The  muscular  fibres  are  not  all  alike;  those  of  the  voluntary 
muscles  are  seen  by  the  microscope  to  be  marked  by  alternate  dark 
and  light  stripings  or  striations ;  these  are  caUed  transversely  striated 
muscular  fibres.  The  involuntary  fibres  have  not  got  these  markings 
as  a  rule.  There  is  one  important  exception  to  this  rule,  namely,  in 
the  case  of  the  heart,  the  muscular  fibres  of  which  are  involimtary, 
but  transversely  striated.  There  are,  however,  histological  differ- 
ences between  cardiac  muscle  and  the  ordinary  voluntary  striated 
muscles.  The  unstriated  involuntary  muscular  fibres  found  in  the 
walls  of  the  stomach,  intestine,  bladder,  blood-vessels,  uterus,  and 
other  contractile  organs  are  generally  spoken  of  as  plain  muscular 
fibres. 

From  the  liistological  standpoint  there  are,  therefore,  three 
varieties  of  muscular  fibres  found  in  the  body  of  the  higher 
animals :  two  of  them  are  transversely  striated,  and  one  is  not. 
The  relationship  of  this  histological  classification  to  the  physiological 


CII.  VI.]  VOLUNTARY   MUSCLE  79 

classification  into  voluntary  and  involuntary  is  shown  in  the  follow- 
ing table : — 

1.  Transversely  striated  muscular  fibres  : 

a.  In  skeletal  muscle     .         .         .  Voluntaiiv. 

/).  In  cardiac  muscle      .         .         .         \ 

2.  Plain  muscular  fibres  :  I  Invoiuntaky 

In  blood-vessels,  intestine,  uterus,     j 
bladder,  etc.  ...  J 

All  kinds  of  muscular  tissue  are  therefore  composed  of  fibres,  but 
the  fibres  are  essentially  different  from  those  we  have  hitherto  studied 
in  the  connective  tissues.  There,  it  will  be  remembered,  the  fibres 
are  developed  between  the  cells;  here,  in  muscle,  the  fibres  are 
developed  from  the  cells;  that  is,  the  cells  themselves  become 
elongated  to  form  the  muscular  fibres. 

Voluntary  Muscle. 

The  voluntary  muscles  are  those  which  are  sometimes  called 
skeletal,  constituting  the  whole  of  the  muscular  apparatus  attached  to 
the  bones.* 

Each  muscle  is  enclosed  in  a  sheath  of  areolar  tissue,  called  the 
Epimysium ;  this  sends  in  partitions,  or  septa,  dividing  off  the  fibres 


Fio.  102.— A  branched  muscular  fibre  from  the  frog's  tongue.    (Kulliker.) 

into  fasciculi,  or  bundles ;  the  sheath  of  each  btmdle  may  be  called 
the  Perimysium.  Between  the  individual  fibres  is  a  small  amount  of 
loose  areolar  tissue,  called  the  Endomysium.  The  blood-vessels  and 
nerves  for  the  muscle  are  distributed  in  this  areolar  tissue. 

The  fibres  vary  in  thickness  and  length  a  good  deal,  but  they 
average  -g-^  inch  in  diameter,  and  about  1  inch  in  length.  Each 
fibre  is  cylindrical  in  shape,  with  rounded  ends ;  many  become  pro- 
longed into  tendon  bundles  (fig.  Ill),  by  which  the  muscle  is  attached 
to  bone.  As  a  rule  they  are  unbranched,  but  the  muscle  fibres  of  the 
face  and  tongue  divide  into  numerous  branches  before  being  inserted 

*  The  muscular  fibres  of  the  pharynx,  part  of  the  oesophagus,  and  of  the 
muscles  of  the  internal  ear,  though  not  under  the  control  of  the  will,  have  the 
same  structure  as  the  voluntary  muscular  fibres. 


80 


MUSCULAR   TISSUE 


[CH.  VI. 


to  the  under  surface  of  the  skin,  or  mucous  membrane  (fig.  102). 
The  fibres  in  these  situations  are  also  finer  than  in  the  majority  of 
the  volimtary  muscles. 

Each  fibre  consists  of  a  sheath,  called  the  sarcolemma,  enclosing 
a  soft  material  called  the  contractile  sulstance.  The  sarcolemma  is 
homogeneous,  elastic  in  nature,  and  especially  tough  in  fish  and 
amphibia.  It  may  readily  be  demonstrated  in  a  microscopic  prepara- 
tion of  fresh  muscular  fibres  by  applpng  gentle  pressure  to  the  cover 
slip;  the  contractile  substance  is  thereby  ruptured,  leaving  the 
sarcolemma  bridging  the  space  (fig.  103).  To  the  sarcolemma  are 
seen  adhering  some  nucleL 

The  contractile  substance  within  the  sheath  is  made  up  of 
alternate  discs  of  dark  and  light  substance. 

Muscular  fibres  contain  oval  nuclei.  In  mammalian  muscle  these 
are  situated  just  beneath  the  sarcolemma;  but  in  frog's  muscle  thev 


Fig.  103. — Muscular  fibre  torn  across,  the  I    ' 

sarcolemma  still  connecting  the  two 
parts  of  the  fibre.  (Todd  and  Bow- 
man.) 

Fig.  104. — Muscular  fibre  of 
a  mammal  highly  mag- 
nified. The  surface  of 
the  fibre  is  accurately 
focussed.    (Schafer.) 

occur  also  in  the  thickness  of  the  muscular  fibre.  The  chromoplasm 
of  the  nucleus  has  generally  a  spiral  ai-rangement,  and  often  there  is 
a  little  granular  protoplasm  (well  seen  in  the  muscular  fibres  of  the 
diaphragm)  around  the  poles  of  each  nucleus. 

The  foregoing  facts  can  be  made  out  with  a  low  power  of  the 
microscope;  on  examining  muscular  fibres  with  a  high  power  other 
details  can  be  seen.  Treatment  with  different  reagents  brings  out 
still  further  points  of  structure.  These  are  differently  described  and 
differently  interpreted  by  different  histologists ;  and  perhaps  no 
subject  in  the  whole  of  microscopic  anatomy  has  been  more  keenly 
debated  than  the  structure  of  a  muscular  fibre,  and  the  meaning  of 
the  changes  that  occur  when  it  contracts.  A  good  deal  of  the 
difficulty  has  doubtless  arisen  from  the  fact  that  a  muscular  fibre  is 
cylindrical,  and  if  one  focusses  the  surface  one  gets  different  optical 
effects  from  those  obtained  by  focussing  deep  in  the  substance  of 
the   fibre.     I    shall,  in   the   following  accoxmt   of   the   structure   of 


CH.  VI.] 


VOLUNTARY    MUSCLE 


81 


striated  muscle,  adhere  very  closely  to  the  views  of  Professor 
Sch;ifer. 

If  the  surface  is  carefully  focussed  rows  of  apparent  granules  are 
seen  l)"ing  at  the  boundaries  of  the  light  streaks,  and  fine  longitudinal 
lines  passing  through  the  dark  streaks  may  be  detected  uniting  the 
apparent  granules  (fig.  104). 

In  specimens  treated  with  dilute  acids  or  gold  chloride,  the 
granules  are  seen  to  be  connected  side  by  side,  or  transversely  also. 
This  reticulum  (fig.  105),  with  its  longitudinal  and  transverse  meshes, 
was  at  one  time  considered  to  be  the  essential  contractile  portion  of 
the  muscular  fibre ;  it  was  thought  that  on  contraction  the  transverse 
networks,  with  their  enlargements,  the  granules,  became  increased  by 


Fig.  105. — Portion  of  muscle-fibre  of 
water-beetle,  showing  network 
very  plainly.  One  of  the  trans- 
verse networks  is  split  off,  and 
some  of  the  longitudinal  bars  are 
shown  broken  off.  (After  Mel- 
land,  j 


Fig.  10(3. — Transverse  section  through 
muscular  fibres  of  human  tongue. 
The  nuclei  are  deeply  stained, 
situated  at  the  inside  of  the  sar- 
colemma.  Each  muscle  fibre 
shows  "Cohnheim's  areas." 
X   450.  (Klein  and  Noble  Smith.) 


the  longitudinal  strands  diminishing  in  length  and  running  into  them. 
Most  histologists  have  rejected  this  idea,  and  regard  the  network  as 
mere  interstitial  substance  lying  between  the  essentially  contractile 
portions  of  the  muscle.  A  muscular  fibre  is  thus  made  up  of  what 
are  variously  called  fihrils,  miiscle-columns  or  sarcostyles ;  and  the 
longitudinal  interstitial  substance  with  cross  networks  comprising 
the  reticulum  just  referred  to  is  called  sarcoplasm.  By  the  use  of 
certain  reagents,  such  as  osmic  acid  or  alcohol,  the  muscle-columns  or 
sarcostyles  may  be  completely  separated  from  one  another. 

A  transverse  section  of  a  muscular  fibre  (fig.  106)  shows  the 
sections  of  these  sarcostyles ;  the  interstitial  sarcoplasm  is  represented 
as  white  in  the  drawing.  The  angular  fields  separated  by  sarcoplasm 
may  still  be  called  by  their  old  name,  areas  of  Cohnheijn. 

If,  instead  of  focussing  the  surface  of  a  fibre,  it  is  observed  in  its 


82 


MUSCULAR   TISSUE 


[CH.  VI. 


depth,  a  fine  clotted  line  is  seen  bisecting  each  light  stripe ;  this  has 
been  variously  termed  Dohie's  line,  or  Krause's  membrane  (fig.  107). 
At  one  time  this  was  believed  to  be  an  actual  membrane  continuous 
with  the  sarcolemma.  It  is  probably  very  largely  an  optical  effect, 
caused  by  light  being  transmitted  between  discs  of  different  refrangi- 
bility. 

If  cross  membranes  do  exist  they  are  not  very  resistant ;  this  was 
well  shown  by  an  accidental  observation  first  made  by  Kiihne,  and 
subsequently  seen  by  others.  A  minute  thread-worm,  called  the 
Myoredes,  was  observed  crawling  up  the  interior  of  the  contractile 


mi      ^mi\ 

ni  9*m  \ 
Sii  JVjS  i 
S   -^^  mm  x** 


Fio.  107. — A.  Portion  of  a  human  muscular  tibre,  x  800.  B.  Separated  bundles  of  fibrils  equally 
magnified;  a,  a,  larger,  and  b,  h,  smaller  collections;  c,  still  smaller;  d,  d,  the  smallest  which 
could  be  detached,  possibly  representing  a  single  series  of  sarcous  elements.    (Sharpey.) 

substance  of  a  muscular  fibre;  it  crawled  without  any  opposition 
from  membranes,  and  the  track  it  left,  closed  up  slowly  behind  it 
without  interfering  with  the  normal  cross-striations  of  the  contractile 
substance.  This  observation  strikingly  illustrates  the  fact  that  the 
contractile  substance  in  a  muscular  fibre  is  fluid,  but  only  semi-fluid, 
for  the  closing  of  the  thread-worm's  track  occurred  slowly  as  a  hole 
always  closes  in  a  viscous  material. 

Another  appearance  which  is  sometimes  seen  is  a  fine  clear  hne 
running  across  the  fibre  in  the  middle  of  eacli  dark  band.  It  is 
called  Hensen's  line  or  d'lsc. 

A  muscular  filjre  may  not  only  be  broken  up  into  fibrils  or  muscle- 


CH.  VI.]  8ARC0US    ELEMENTS  83 

columns,  but  under  the  influence  of  some  reagents  like  dilute  hydro- 
chloric acid,  it  can  be  broken  up  into  discs,  the  cleavage  occurring  in 
the  centre  of  each  light  stripe.  Bowman,  the  earliest  to  study 
muscular  fibres  with  profitable  results,  concluded  that  the  subdivision 
of  a  fibre  into  fibrils  was  a  phenomenon  of  the  same  kind  as  the  cross 
cleavage  into  discs.  He  considered  that  both  were  artificially  pro- 
duced by  a  separation  in  one  or  the  other  direction  of  particles  of  the 
fibre  he  called  "sarcous  elements."  The  cleavage  into  discs  is  how- 
ever much  rarer  than  the  separation  into  fibrils;  indeed,  indications 
of  the  fibrils  are  seen  in  perfectly  fresh  muscle  before  any  reagent 
has  been  added,  and  this  is  markedly  evident  in  the  wing  muscles  of 
many  insects.  It  is  now  believed  that  a  muscular  fibre  is  built  up 
of  contiguous  fibrils  or  sarcostyles,  while  cleavage  into  discs  is  a 
purely  artificial  phenomenon. 

Haycraft,  who  has  also  investigated  the  question  of  muscular 
structure,  concludes  that  the  cross  striation  is  entirely  due  to  optical 
phenomena.  The  sarcostyles  are  varicose,  and  where  they  are  en- 
larged different  refractive  effects  will  be  produced  from  those  caused 
by  the  intermediate  narrow  portions.  This  view  he  has  very  in- 
geniously supported  by  taking  negative  casts  of  muscular  fibres  by 
pressing  them  on  to  the  surface  of  collodion  films.  The  collodion 
cast  shows  alternate  dark  and  light  bands  like  the  muscular  fibres. 

Schiifer  is  unable  to  accept  this  view;  he  regards  the  substance  of 
the  sarcostyle  in  its  dark  stripes  as  being  of  different  composition, 
and  not  merely  of  different  diameter,  from  the  sarcostyle  in  the  region 
of  the  light  stripes ;  it  certainly  stains  very  differently  with  many 
reagents,  especially  chloride  of  gold.  His  views  regarding  the  inti- 
mate structure  of  a  sarcostyle  have  been  worked  out  chiefly  in  the 
wing  muscles  of  insects,  where  the  sarcostyles  are  separated  by  a 
considerable  quantity  of  interstitial  sarcoplasm,  and  a  brief  summary 
of  his  conclusions  is  as  follows : — 

Each  sarcostyle  is  subdivided  in  the  middle  of  each  light  stripe  by 
transverse  hues  (membranes  of  Krause)  into  successive  portions, 
which  may  be  termed  sarcomeres.  Each  sarcomere  is  occupied  by  a 
portion  of  the  dark  stripe  of  the  whole  fibre ;  this  portion  of  the 
dark  stripe  may  be  called  a  sarcous  element*  The  sarcous  element 
is  really  double,  and  in  the  stretched  fibre  (fig.  108,  b)  separates  into 
two  at  the  line  of  Hensen.  At  either  end  of  the  sarcous  element  is 
a  clear  interval  separating  it  from  Krause's  membrane;  this  clear 
interval  is  more  evident  in  the  extended  sarcomere  (fig.  108,  b),  but 
diminishes  on  contraction  (fig.  108,  a).  The  cause  of  this  is  to  be  found 
in  the  structure  of  the  sarcous  element.  It  is  pervaded  with  longi- 
tudinal canals  or  pores  open  towards  Krause's  membrane,  but  closed 

*  Notice  that  this  expression  has  a  different  meaning  from  what  it  originally 
had  when  used  by  Bowman. 


84 


MUSCULAR   TISSUE 


[CH.  VI. 


at  Hensen's  line.  In  the  contracted  muscle  the  clear  part  of  the 
muscle  substance  passes  into  these  pores,  disappears  from  view  to  a 
great  extent,  swells  up  the  sarcous  element,  widens  it  and  shortens 
the  sarcomere.  In  the  extended  muscle,  on  the  other  hand,  the  clear 
substance  passes  out  from  the  pores  of  the  sarcous  element,  and  lies 
between  it  and  the  membrane  of  Krause ;  this  lengthens  and  narrows 
the  sarcomere.*  This  is  shown  in  the  diagrams.  It  may  be  added 
that  the  sarcous  element  does  not  lie  free  in  the  middle  of  the  sarco- 
mere, but  is  attached  at  the  sides  to  a  fine  enclosing  envelope,  and  at 
either  end  to  Krause's  membrane  by  fine  lines  running  through  the 
clear  substance  (fig.  109,  a). 

This  view  is  interesting,  because  it  brings  into  harmony  amcBboid, 
ciliary,  and  muscular  movement.      In  all  three  instances  we  have 


-  S.R. 


lllllllllll) 


Pig.  108. — Sarcostyles  from  tlie  wing-muscles 
of  a  wasp. 

A,  a'.    Sarcostyles  showing  degrees  of  con- 

tractiou. 

B.  A  sarcostyle  extended  with  the  sarcous 

elements  separated  into  two  parts, 
c.    Sarcostyles  moderately  extended  (semidia- 
grammatic).     (E.  A.  Schafer.) 


S.E. 


FiQ.109. — Diagram  of  a  sarcomere 
in  a  moderately  extended  con- 
dition, A,  and  in  a  contracted 
condition,  b. 
K,   K,  Krause's  membranes ;  h, 
plane  of  Hensen ;  s.e., 
poriferous   sarcous    ele- 
ment.   (E.  A.  Schafer.) 


protoplasm  composed  of  two  materials,  spongioplasm  and  hyaloplasm. 
In  amoeboid  movement  the  irregular  arrangement  of  the  spongioplasm 
allows  the  hyaloplasm  to  flow  in  and  out  of  it  in  any  direction.  In 
ciliary  movement  the  flow  is  limited  by  the  arrangement  of  the 
spongioplasm  to  one  direction ;  hence  the  limitation  of  the  movement 
in  one  direction  (see  p.  30).  In  muscle,  also,  the  definite  arrangement 
of  the  spongioplasm  (represented  by  the  sarcous  element)  in  a  longi- 
tudinal direction  limits  the  movement  of  the  hyaloplasm  (represented 
by  the  clear  substance  of  the  light  stripe),  so  that  it  must  flow  either 
in  or  out  in  that  particular  direction.  The  muscular  fibre  is  made  up 
of  sarcostyles  and  the  sarcostyle  of  sarcomeres.     The  contraction  of 

*  The  existence  of  open  pores  is  not  admitted  by  all  observers.  These  regard 
the  passage  of  fluid  in  and  out  of  the  sarcous  element  as  due  to  diffusion  through 
its  membrane. 


CH.  VI.] 


SARCOPLASM 


85 


the  whole  muscle  is  only  the  sum  total  of  the  contraction  of  all  the 
constituent  sarcomeres. 

In  au  ordinary  muscular  fibre  it  is  stated  that  when  it  contracts, 
not  only  does  it  l)ecome  thicker  and  shorter,  but  the  light  stripes 
become  dark  and  the  dark  stripes  light.  This  again  is  only  an  optical 
illusion,  and  is  produced  by  the  alterations  in  the  shape  of  the  sarco- 
styles,  affecting  the  sarcoplasm 
that  lies  between  them.  When 
the  sarcous  elements  swell  during 
contraction,  the  sarcoplasm  accu- 
mulates opposite  the  membranes 
of  Krause,  and  diminishes  in 
amount  opposite  the  sarcous 
elements ;  the  accumulation  of 
sarcoplasm  in  the  previously 
light  stripes  makes  them  appear 
darker  by  contrast  than  the  dark 
stripes  proper.  This  is  very 
well  shown  in  fig.  110.  There 
is  no  true  reversal  of  the  strip- 
ings  in  the  sarcostyles  them- 
selves. 


.f,i)>i!,$a»i»MM««tM«M««M»««n«tM*««i«M««eeiiS'v 


,.^iti<j»»*"??SS!!^ 


That  this  is  thd  case  can  be  seen 
very  well  when  a  muscular  fibre  is 
examined  with  polarised  light.  A 
polarising  microscope  contains  a  Nicol's 
prism  beneath  the  stage  of  the  micro- 
scope which  polarises  the  light  passing 
through  the  object  placed  on  the  stage. 
The  eye-piece  contains  another  Nicol's 
prism,  which  detects  this  fact.  If  the 
two  Nicols  are  parallel,  the  light  pass- 
ing through  the  first  passes  also  through 
the  second  ;  but  if  the  second  is  at  right 
angles  to  the  first,  the  light  cannot 
traverse  it  and  the  field  appears  dark. 
If  an  object  on  the  microscope  stage  is 
doubly  refracting  it  will  appear  bright 
in  this  dark  field ;  if  it  remains  dark 
it  is  singly  refracting.  The  sarcoplasm 
is  singly  refracting  or  isotropous ;  it 
remains  dark  in  the  dark  field  of  the 
polarising  microscope.  The  muscle  columns  or  sarcostyles  are  in  great  measure 
doubly  refracting  or  anisotropous,  and  appear  bright  in  the  dark  field  of  the 
polarising  microscope.  The  sarcostyle,  however,  is  not  wholly  doubly  refracting ; 
the  sarcous  elements  are  doubly  refracting,  and  the  clear  intervals  are  singly 
refracting.  On  contraction  there  is  no  reversal  of  these  appearances,  though  of 
course  the  relative  thickness  of  the  singly  refracting  intervals  varies  inversely 
with  that  of  the  doubly  refracting  sarcous  elements. 

Ending  of  Muscle  in  Tendon. — A  tendon-bundle  passes  to  each 
muscular  fibre,  and  becomes  firmly  imited  to  the  sarcolemma.     The 


,  110. — Wave  of  coutractiou  passing  over  a  mus- 
cular fibre  of  water-beetle,  k,  r,  portions  of 
the  fibre  at  rest ;  c,  contracted  part ;  i,  i,  inter- 
mediate condition.    (Schiifer.) 


86 


MUSCULAR   TISSUE 


[CH.  VI, 


Up  into  capillaries, 

transverse  branches 

ever  penetrate  the 

like    other   tissues, 


areolar  tissue  between  the  tendon-bundles  becomes  also  continuous 
with  that  between  the  muscular  fibres  (fig.  111). 
Blood-vessels  of  Muscle. — The  arteries  break 
which  run  longitudinally  in  the  endomysium, 
connecting  them  (fig.  112).  No  blood-vessels 
sarcolenima.  The  muscular  fibres  are  thus, 
nourished  by  the  exudation  from  the  blood  called  lymph.  The  lymph 
is  removed  by  lymphatic  vessels  found  in  the 
perimysium. 

The  nerves  of  voluntary  muscle  pierce  the 
sarcolemma,    and    terminate     in    expansions 
called  end-plates,  to  be  described  on  p,  9o. 
JSfeuro-musGular  Spindles. — Bundles  of  fine 


Fio.  112. — Three  muscular  fibres 
running  longitudinally,  and 
two  bundles  of  fibres  in  trans- 
verse section,  M,  from  the 
tongue.  The  capillaries,  C, 
are  injected,  x  150.  (Klein 
and  Noble  Smith.) 


Fig.  111.— Termination  of  a 
muscular  fibre  in  a  tendon- 
bundle.  TO,  sarcolemma ;  s, 
the  same  passing  over  the 
end  of  bundle ;  p,  extremity 
of  muscular  substance  c, 
retracted  from  the  end  of 
sarcolemma  tube ;  I,  tendon 
bundle  fixed  to  sarcolemma. 
(Ranvior.) 


muscular  fibres  enclosed  within  a  thick  lamel- 
lated  sheath  of  connective  tissue  are  found 
scattered  through  voluntary  muscles ;  they 
are  especially  numerous  near  the  tendons  and 
in  the  proximity  of  intra-muscular  septa.  It 
is  remarkable  that  they  have  not  been  found 
in  the  ocular  or  tongue  muscles.  These  structures  are  called  neuro- 
muscular spindles;  they  vary  in  length  from  J^  to  J  inch,  and  are 
about  yfg-  inch  in  diameter.  Each  receives  a  nerve  fibre  which 
divides  into  secondary  and  tertiary  branches.  The  myelin  sheath 
is  lost,  and  the  tertiary  branches  encircle  the  muscular  fibres, 
breaking  up  usually  into  a  network.  It  is  believed  that  these 
are  sensory  end  organs  in  the  muscle.  (See  further,  chapter  LII.  on 
Touch.) 


CII.  VI. J 


INVOLUNTARY    MUSCLE 


87 


Red  Muscles. 

Ill  many  animals,  such  as  the  rabbit,  anil  some  fishes,  most  of  the 
muscles  are  pale,  but  some  few  (like  the  diaphragm,  crureus,  soleus, 
semi-membranosus  in  the  rabbit)  are  red.  These  muscles  contract 
more  slowly  than  the  pale  muscles,  and  their  red  tint  is  due  to  luemo- 
globin  contained  within  their  contractile  substance. 

In  addition  to  these  physiological  distinctions,  there  are  histo- 
logical differences  between  them  and  ordinary  striped  muscle.  These 
histological  differences  are  the  following : — 

1.  Their  muscular  fibres  are  thinner. 

2.  They  have  more  sarcoplasm. 

3.  Longitudinal  striation  is  therefore  more  distinct. 

4.  Transverse  striation  is  more  irregular  than  usual. 

5.  Their  nuclei  are  situated  not  only  under  the  sarcolemma,  but 
also  in  the  thickness  of  the  fibre. 

6.  The  transverse  loops  of  the  capillary  network  are  dilated  into 
little  reservoirs,  far  beyond  the  size  of  ordinary  capillaries. 


Cardiac  Muscle. 

The  muscular  fibres  of  the  heart,  unlike  those  of  most  of  the 
involuntary  muscles,  are  striated ;  but  although,  in  this  respect,  they 
resemble  the  skeletal  muscles,  they  have 
distinguishing  characteristics  of  their  own. 
The  fibres  which  he  side  by  side  are 
united  at  frequent  intervals  by  short 
branches  (fig.  113).  The  fibres  are  smaller 
than  those  of  the  ordinary  striated  muscles, 
and  their  transverse  striation  is  less 
distinct.  No  sarcolemma  can  be  dis- 
cerned. Each  fibre  has  only  one  nucleus 
which  is  situated  in  the  middle  of  its 
substance.  At  the  junctions  of  the  fibres 
there  is  a  certain  amount  of  cementing 
material,  stainable  by  silver  nitrate.  This 
is  bridged  across  by  fine  fibrils  from  cell 
to  cell. 


Plain  Muscle. 


Fig.  113.— Muscular  fibre-cells  from 
the  heart.    (R.  A.  Schafer.) 


Plain  muscle  forms  the  proper  muscular  coats  (1.)  of  the  digestive 
canal  from  the  middle  of  the  oesophagus  to  the  internal  sphincter 
ani ;  (2.)  of  the  ureters  and  urinary  bladder ;  (3.)  of  the  trachea  and 
bronchi ;  (4.)  of  the  ducts  of  glands ;  (5.)  of  the  gall-bladder ;  (6.)  of 


MUSCULAR  TISSUE 


[CII.  VI. 


the  vesicul^e  seminales  ;  (7.)  of  the  uterus  and  Fallopian  tubes  ;  (8.)  of 
blood-vessels  and  lymphatics ;  (9.)  of  the  iris,  and  ciliary  muscle  of  the 
eye.  This  form  of  tissue  also  enters  largely  into  the  composition  (10.) 
of  the  tunica  dartos,  the  contraction  of  which  is  the  principal  cause  of 
the  wrinkling  and  contraction  of  the  scrotum  on  exposure  to  cold.  It 
occurs  also  in  the  skin  generally,  being  found  surrounding  the  secret- 
ing part  of  the  sweat  glands  and  in  small  bundles  attached  to  the  hair 
follicles ;  it  also  occurs  in  the  areola  of  the  nipple.  It  is  composed  of 
long,  fusiform  cells  (fig.  114),  which  vary  in  length,  but  are  not  as  a 
rule  more  than  ^i^-  inch  long.  Each  ceU  has  an  oval  or  rod-shaped 
nucleus.     The  cell  substance  is  longitudinally  but  not  transversely 


Pia.  114. — Muscular  fibre-cells  from  the  muscular  coat  of  intestine — highly  magnified.     Note  the  longi- 
tudinal striation,  and  in  the  broken  fibre  the  sheath  is  visible. 

striated.  Each  cell  or  fibre,  as  it  may  also  be  termed,  has  a  delicate 
sheath.  The  fibres  are  united  by  cementing  material,  which  can  be 
stained  by  silver  nitrate.  This  intercellular  substance  is  bridged 
across  by  fine  filaments  passing  from  cell  to  cell. 

The  nerves  in  involuntary  muscle  (both  cardiac  and  plain)  do  not 
terminate  in  end-plates,  but  by  plexuses  or  networks,  which  ramify 
between  and  around  the  muscular  fibres. 


Development  of  Muscular  Fibres. 

All  muscular  fibres  (except  those  of  the  sweat  glands  which  are 
epiblastic)  originate  from  the  mesoblast.  The  plain  fibres  are  simply 
elongated  cells  in  which  the  nucleus  becomes  rod-shaped.     In  cardiac 


CII.  VI.] 


DEVELOPMENT    OF    MUSCLE 


89 


\~/> 


fe 


muscle,  the  likeness  to  the  original  cells  from  which  the  filjrcs  arc 
formed  is  not  altogether  lost,  and  in  certain  situations  (immediately 
beneath  the  lining  membrane  of  the  ventricles)  there  are  found  peculiar 
fibres  called  after  their  discoverer  Purkinje' s  fibres  ;  tliese  are  large  clear 
quadrangular  cells  with  granular  protoplasm  contain- 
ing several  nuclei  in  the  centre,  and  striated  at  the 
margin.  It  appears  that  the  differentiation  of  these 
cells  is  arrested  at  an  early  stage,  though  they  con- 
tinue to  grow  in  size. 

Voluntary  muscular  fibres  are  developed  from  cells 
which  become  elongated,  and  the  nuclei  of  which  mul- 
tiply. In  most  striated  muscle  fibres  the  nuclei  ulti- 
mately take  up  a  position  beneath  the  cell-wall  or 
sarcolemma  wliich  is  formed  on  the  surface.  Stria- 
tions  appear  first  along  one  side,  and  extend  round  the 
fibre  (fig.  115),  then  they  extend  into  the  centre. 

During  Life  new  fibres  appear  to  be  formed  in  part 
by  a  longitudinal  splitting  of  pre-existing  fibres ;  this 
is  preceded  by  a  multipUcation  of  nuclei ;  and  in  part 
by  the  lengthening  and  differentiation  of  embryonic 
cells  (sarcoplasts)  found  between  the  fully  formed 
fibres. 

In  plain  muscle,  growth  occurs  in  a  similar  way : 
this  is  well  illustrated  in  the  enlargement  of  the  uterus  during 
pregnancy;  tliis  is  due  in  part  to  the  growth  of  the  pre-existing 
fibres,  and  in  part  to  the  formation  of  new  fibres  from  small 
granular  cells  lying  between  them.  After  parturition  the  fibres 
shrink  to  their  original  size,  but  many  undergo  fatty  degeneration 
and  are  removed  by  absorption. 


Fig 


115.  — Develop- 
ing muscular  fibre 
from  ftt-tus  of  two 
months.  (Ran- 
vier). 


CHAPTEE  VII 


NERVE 


Nervous  tissue  is  the  material  of  which  the  nervous  system  is  com- 
posed. The  nervous  system  is  composed  of  two  parts,  the  central 
nervous  system,  and  Vhq peripheral  nervous  system.  The  central  nervous 
system  consists  of  the  brain  and  spinal  cord ;  the  peripheral  nervous 
system  consists  of  the  nerves,  which  conduct  the  impulses  to  and  from 


.  110. — Two  nerve-fibres  of  sciatic 
nerve,  a.  Node  of  Eanvier. 
B.  Axis-cylinder,  c.  Sheath  of 
Schwann,  with  nuclei.  Medul- 
lary sheath  is  not  stained,  x  300. 
(Klein  and  Noble  Smith.) 


Fig.  117. —  A.\is  cylinder, 
highly  magnified, 
showing  its  com- 
ponent fibrils.  (M. 
Schultze.) 


the  central  nervous  system,  and  thus  bring  the  nerve  centres  inLo 
relationship  with  other  parts  of  the  body. 

Some  of  the  nerves  conduct  impulses  from  the  nerve-centres  and 
are  called  efferent ;  those  which  conduct  impulses  in  the  opposite 
direction  are  called  afferent.  When  one  wishes  to  move  the  hand,  the 
nervous  impulse  starts  in  the  brain  and  passes  down  the  efferent  or 
motor  nerve-tracts  to  the  muscles  of  the  hand,  which  contract ;  when 


CH.  VII.] 


NERVE-FIBRES 


91 


one  feela  pain  in  the  hand,  afferent  or  sensory  nerve-tracts  convey  an 
impulse  to  the  brain  which  is  thoro  interpreted  as  a  sensation.  If  all 
the  nerves  going  to  the  hand  are  cut  through,  all  com- 
niunication  with  the  nerve-centres  is  destroyed,  and 
the  liand  loses  the  power  of  moving  under  tlie  influence 
of  the  will,  and  the  brain  receives  no  impulses  from 
the  hand,  or,  as  we  say,  the  hand  has  lost  sensibility. 

This  distinction  between  efferent  and  afferent 
nerves  is  a  physiological  one,  which  we  shall  work 
out  more  thoroughly  later  on.  No  histological  dis- 
tinction can  be  made  out  between 
motor  and  sensory  nerves,  and  it 
is  histological  structure  which 
we  wish  to  dwell  upon  in  this 
chapter. 

Under  the  microscope  nervous 
tissue  is  found  to  consist  essen- 
tially of  nerve-cells  and  their 
branches.  The  nerve-cells  are 
contained  in  the  brain  and  spinal 
cord,  and  in  smaller  collections 
of  cells  on  the  course  of  the 
nerves  called  ganglia.  The  part 
of  the  nerve-centres  containing 
cells  is  called  grey  matter. 

Long  branches  of  the  nerve- 
cells  are  known  as  nerve-fibres. 
These  become  sheathed  in  a 
manner  to  be  immediately  de- 
scribed, and  are  contained  in  the 
nerves,  and  in  the  white  matter  of 
brain  and  spinal  cord.  The  bodies 
of  nerve-cells  differ  in  size,  shape, 
B  and  arrangement,  and  we  shall 
discuss  these  fully  when  we  get 
to  the  nerve-centres.  For  the 
present  it  will  be  convenient  to  confine  ourselves  to 
the  nerve-fibres  as  they  are  found  in  a  nerve. 

Nerve-fibres  are  of  two  histological  kinds,  medul- 
lated   and   non-medullated.      Medullated   nerve-fibres 
are  found  in  the  white  matter  of  the   nerve-centres 
pj,,     lis.  -  Nerve-  ^^^  ^^  ^^^   ncrvcs  Originating  from    the   brain   and 
tibre  stained  with  spinal   cord.     Non-mcdullated   nerve-fibres    occur   in 

osmic     acid.      A,      f^  ,  i      ,  • 

node ;  B,  nucleus,  the  Sympathetic  nerves. 

iS  ''"'^    ^''^  The  medullated  or  white  fibres  are  characterised 


14.'£ 


Pig.  119.— a  node  of  Ranvier 
in  a  medullated  nen'e-fibre, 
viewed  from  above.  The 
medullary  sheath  is  in- 
terrupted, and  the  primi- 
tive sheath  thickened. 
Copied  from  Axel  Key  and 
Retzius.  X  750.  (Klein 
and  Noble  Smith.) 


92 


NERVE 


[CH.  VII. 


by  a  sheath  of  white  colour,  fatty  in  nature,  and  stained  black  by 
osmic  acid ;  it  is  called  the  medullary  sheath  or  white  substance  of 
Schwann;  this  sheathes  the  essential  part  of  tlio  filjre  which  is  a 
process  from  a  nerve-cell,  and  is  called  the  axis  cylinder.  Outside 
the  medullary  sheath  is  a  thin  homogeneous  membrane  of  elastic 
nature  called  the  primitive  sheath  or  neurilemma. 

The  axis  cylinder  is  a  soft  transparent  thread  in  the  middle  of  the 
fibre;  it  is  made  up  of  exceedingly  fine  fibrils  (fig.  117)  which  stain 
readily  with  gold  chloride.  The  medullary  sheath  gives  a  character- 
istic double  contour  and  tubular  appearance  to  the  fibre.  It  is  inter- 
rupted at  regular  intervals  known  as  the  nodes  of  Ranvier.  The 
stretch  of  a  nerve  fibre  between  two  nodes  is  called  an  inter-node,  and 
in  the  middle  of  each  inter-node  is  a  nucleus  which  belongs  to  the 


Fig.  120. — Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  division  of  the 
fibres,    a,  into  two  ;  6,  into  three,     x  350.    (KoUiker.) 


primitive  sheath.  Besides  these  interruptions,  a  variable  number  of 
oblique  clefts  are  also  seen  dividing  the  sheath  into  medullary  seg- 
ments (fig.  118);  but  most  if  not  all  of  these  are  produced  artificially 
in  the  preparation  of  the  specimen. 

The  medullary  sheath  also  contains  a  horny  substance  called 
neurokeratin :  the  arrangement  of  this  substance  is  in  the  form  of  a 
network  or  reticulum  holding  the  fatty  matter  of  the  sheath  in  its 
meshes.  The  occurrence  of  horny  matter  in  the  epidermis,  in  the 
development  of  the  enamel  of  teeth  and  in  nerve  is  an  interesting 
chemical  reminder  that  all  these  tissues  originate  from  the  same 
embryonic  layer,  the  epiblast.  The  fatty  matter  consists  largely  of 
lecithin,  a  phosphorised  fat,  and  cholesterin,  a  monatomic  alcohol. 

Near  their  terminations  the  nerve-fibres  branch :  the  branching 
occurs  at  a  node  (fig.  120). 


CH.  VTI.] 


NERVE-FIBRES 


93 


Stainin<;'  with  silver  nitrate  producos  a  peculiar  appearance  at  the 
nodes,  forming  what  is  known  as  the  crosses  of  Banvier. 

One  limb  of  the  cross  is  produced  by  the  dark  staining  of  cement 


Fig.  121.— Several  libres  of  a  bundle  of  medullated  nerve-fibres  acted  upon  by  silver  nitrate  to  sliow 
behaviour  of  nodes  of  Ranvier,  M,  towards  this  reagent.  The  silver  has  penetrated  at  the  nodes, 
and  has  stained  the  axis-cylinder,  M,  for  a  short  distance.  8,  the  white  substance.  (Klein  and 
Noble  Smith.) 

substance  which  occurs  between  the  segments  of  the  neurilemma ;  the 
other  limb  of  the  cross  is  due  to  the  staining  of  a  number  of  minute 


Fig.  l:i'2.— Transverse  section  of  the  sciatic  nerve  of  a  cat  about  x  100.— It  consists  of  bundles 
(/iini'cuZi)  of  nerve-fibres  ensheathed  in  a  fibrous  supporting  capsule,  epincuriuin,  A;  each  bundle 
has  a  special  sheath  (not  sufficiently  marked  out  from  the  cpiiuuHum,  in  the  figure)  or  pcrineunnm 
B;  the  nerve-fibres  N/  are  separated  from  one  another  by  endo7ieurium ;  L,  lymph  spaces;  Ar, 
artery  ;  V,  vein  ;  F,  fat.    Somewhat  diagrammatic.    (V.  D.  Harris.) 

transverse  bands  in  the  axis  cylinder  (Fromann's  lines),  which  is  here 
not  closely  invested  by  the  medullary  sheath  (fig.  121). 


94 


NERVE 


[CH.  VII. 


The  arrangement  of  the  nerve-fibres  in  a  nerve  is  best  seen  in  a 
transverse  section. 

The  nerve  is  composed  of  a  number  of  bundles  or  funiculi  of  nerve- 
fibres  bound  together  by  connective  tissue.  The  sheath  of  the  whole 
nerve  is  called  the  epineurium  ;  that  of  the  funiculi  the  perineurium ; 
that  which  passes  between  the  fibres  in  a  funiculus,  the  endoneurium 
(fig.  122).  Single  nerve-fibres  passing  to  their  destination  are  sur- 
rounded by  a  prolongation  of  the  perineurium,  known  as  the  Sheath 


Fig    123  —Section   across   the  .second   thoracic  anterior  root  of  'the  dog,  stained   with  osmic  acid. 

(Gaskell.) 


of  Henle.     The  nerve  trunks  themselves  receive  nerve-fibres  which 
ramify  and  terminate  as  end-bulbs  in  the  epineurium. 

The  size  of  the  nerve-fibres  varies ;  the  largest  fibres  are  found  in 
the  spinal  nerves,  where  they  are  14-4  to  19/x  in  diameter.*  Others 
mixed  with  these  measure  I'S  to  3-6^.  These  small  nerve-fibres  are 
the  visceral  nerves ;  they  pass  to  collections  of  nerve-cells  called  the 
sympathetic  gangha,  whence  they  emerge  as  non-medullated  fibres, 
and  are  distributed  to  involuntary  muscle.     They  are  well  seen  in 


IX  —  micro-millimetre  = 


millimetre. 


CH.  VII.] 


KND-PLATES 


95 


sections   stained  by  osmic  acid,  the  black  rings  being  the  stained 
medullary  sheaths  (fig.  123). 

The  non-medullated  fibres  or  fibres  of  Remah  have  no  medullary 
sheath,  and  are  therefore  devoid  of  the  double  contour  of  the  medul- 
lated  fibres,  and  are  unaffected  in  appearance  by  osmic  acid.     They 


Fig.  124.— Grey,  or  non-medullated  nerve-fibres.  A.  From  a  branch  of  the  olfactory  nerve  of  the 
sheep ;  two  dark-bordered  or  white  fibres  from  the  fifth  pair  are  associated  with  the  pale  olfactory 
fibres.     B.  From  the  sympathetic  nerve,     x  450.     (Max  Schultze.) 

consist  of  an  axis  cylinder  covered  by  a  nucleated  fibrillated  sheath. 
They  branch  frequently. 

Though  principally  found  in  the  sympathetic  nerves,  a  few  are 
found  in  the  spinal  nerves  mixed  with  the  medullated  fibres. 


Termination  of  Nerves  in  Muscle. 

In  the  voluntary  muscles  the  motor  nerve-fibres  have  special  end 
organs  called  end-plates.  The  fibre  branches  two  or  three  times  (figs. 
120,  125),  and  each  branch  goes  to  a  muscular  fibre.  Here  the 
neurilemma  becomes  continuous  with  the  sarcolemma,  the  medullary 
sheath  stops  short,  and  the  axis  cylinder  branches  repeatedly.  This 
ramification  is  embedded  in  a  layer  of  granular  protoplasm  containing 
numerous  nuclei.  Considerable  variation  in  shape  of  the  end-plates 
occurs  in  different  parts  of  the  animal  kingdom.  Somewhat  similar 
nerve-endings  are  seen  in  tendon;  these,  however,  are  doubtless 
sensory  (figs.  126,  127). 

In  the  involuntary  muscles,  the  fibres,  which  are  for  the  most  part 
non-medullated,  form  complicated  plexuses  near  their  termination. 
The  plexus  of  Auerbach  (fig.  128)  between  the  muscular  coats  of  the 
intestine  is  a  typical  case.  Groups  of  nerve-cells  will  be  noticed  at 
the  junctions  of  the  fine  nervous  cords.  From  these  plexuses  fine 
branches  pass  off  and  bifurcate  at  frequent  intervals,  until  at  last 
ultimate  fibrillfe  are  reached.  These  subdivisions  of  the  axis  cylinders 
do  not  anastomose  with  one  another,  but  they  come  into  close  relation- 


96 


NERVE 


[CH.  VII. 


ship  with  the  involuntary  muscular  fibres ;  though  some  histologists 
have  stated  that  they  end  in  the  nuclei  of  the  muscular  fibres,  it  is 
now  beHeved  that  they  do  not  pass  into  their  interior. 


Pig.  125. — Prom  a  preparation  of  the  iierve-termlnation  in  the  muscular  fibres  of  a  snalte.    a.  End- 
plate  seen  in  surface  view,     h,  End-plate  seen  in  jiroiile.    (Lingard  and  Klein.) 

The  terminations  of  sensory  nerves  are  in  some  cases  plexuses, 
in  others  special  end  organs.  We  shall  deal  with  these  in  our  study 
of  sensation. 


"Wf^-/^ 


J 


I 


Pifi.  120. — Termination  of  meduUated 
nerve-fibres  in  tendon  near  the  mus- 
cular insertion,    (Golgi.) 


..  127. — One  of  the  reticulated  end-plates 
of  fig.  126,  more  highly  magnified,  re, 
medullated  nerve-fibres ;  h,  reticulated 
end-plates.    (Golgi.) 


Development  of  Nerve-fibres. 

A  nerve-fibre  is  primarily  an  out-growth  from  a  nerve-cell,  as  is 
shown  in  the  accompanying  diagram  (fig.  129).  A  nerve-cell,  though 
it  may  have  many  branches,  only  gives  off  one  process  which  becomes 
the  axis  cylinder  of  a  nerve-fibre.  This  acquires  a  medullary  sheath 
when  it  passes  into  the  white  matter  of  the  brain  or  spinal  cord,  and 


CH.  VII.] 


DKVELOrMENT    OF    NEUVE-FIHUES 


97 


a  primitive  sheath  when  it  leaves  the  nerve-centre  and  gets  into  tho 
nerve.     But  at  first  the  axis  cyhnder  is  not  sheathed  at  all. 


Fig.  128. — Plexus  of  Auerbach,  between  the  two  layers  of  the  muscular  coat  of  the  intestine.    (Cadiat.) 

The  formation  of  the  sheaths  is  still  a  matter  of  doubt,  but  the 
generally  accepted  opinion  is  that  the  primitive  sheath  is  formed  by 


FiQ.  129. — Multipolar  nerve-cell  from  anterior  horn  of  spinal  cord ;  a,  axis  cylinder  process.    (Max 

Schultze.) 

mesoblastic  cells  which  become  flattened  out  and  wrapped  round  the 
fibre  end  to  end.  These  are  separated  at  the  nodes  by  intercellular  or 
cement  substance  stainable  by  silver  nitrate  (fig.  121).    These  cells  are 

G 


98  NERVE  [CH.  VII. 

probably  mesoblastic.  The  medullary  sheath  is  formed,  according  to 
some,  by  a  fatty  change  occurring  in  the  parts  of  these  same  cells 
which  are  nearest  to  the  axis  cylinder,  but  it  is  much  more  probable 
that  it  is  formed  from  the  peripheral  layer  of  the  axis  cylinder ;  the 
presence  of  neurokeratin  in  it  distinctly  points  to  an  epiblastic  origin. 
The  fact  also  that,  in  the  nerve  centres,  the  medullated  nerve-fibres 
have  no  primitive  sheath,  and  the  phenomena  of  Wallerian  degenera- 
tion, to  be  described  later,  all  tend  to  confirm  the  same  view. 


CHAPTEE  VIII 

IRKITABILITY  AND   CONTRACTILITY 

Irritability  or  Excitability  is  the  power  that  certain  tissues  possess 
of  responding  by  some  change  (transformation  of  energy)  to  the  action 
of  an  external  agent.     This  external  agent  is  called  a  stimulus. 

Undifferentiated  cells  such  as  white  blood-corpuscles  are  irritable ; 
when  stimuli  are  applied  to  them  they  execute  the  movements  we 
have  learnt  to  call  amoeboid. 

Ciliated  epithelium  cells  and  muscular  fibres  are  irritable ;  they 
also  execute  movements  under  the  influence  of  stimuli. 

Nerves  are  irritable ;  when  they  are  stimulated,  a  change  is  pro- 
duced in  them;  this  change  is  propagated  along  the  nerve,  and  is 
called  a  nervous  impulse ;  there  is  no  change  of  form  in  the  nerve 
visible  to  the  highest  powers  of  the  microscope ;  much  more  delicate 
and  sensitive  instrimients  than  a  microscope  must  be  employed  to 
obtain  evidence  of  a  change  in  the  nerve ;  it  is  of  a  molecular  nature. 
But  the  irritabihty  of  nerve  is  readily  manifested  by  the  results  the 
nervous  impulse  produces  in  the  organ  to  which  it  goes;  thus  the 
stimulation  of  a  motor  nerve  produces  a  nervous  impulse  in  that  nerve 
which,  when  it  reaches  a  muscle,  causes  the  muscle  to  contract: 
stimulation  of  a  sensory  nerve  produces  a  nervous  impulse  in  that 
nerve  which,  when  it  reaches  the  brain,  causes  a  sensation. 

Secreting  glands  are  irritable ;  when  irritated  or  stimulated  they 
secrete. 

The  electrical  organs  found  in  many  fishes  hke  the  electric  eel, 
and  torpedo  ray,  are  irritable ;  when  they  are  stimulated  they  give 
rise  to  an  electrical  discharge. 

Contractility  is  the  power  that  certain  tissues  possess  of  respond- 
ing to  a  stimulus  by  change  of  form.  Contractility  and  irritability 
do  not  necessarily  go  together ;  thus  both  muscle  and  nerve  are 
irritable,  but  of  the  two,  only  muscle  is  contractile. 

Some  movements  visible  to  the  microscope  are  not  due  to  con- 
tractihty ;  thus  granules  in  protoplasm  or  in  a  vacuole  may  often  be 


100 


IRRITABILITY    A2^D    CONTRACTILITY 


[CH.  vm. 


seen  to  exhibit  irregular,  shaking  movements  due  simply  to  vibrations 
transmitted  to  them  from  the  outside.  Such  movement  is  known 
as  Brownian  movement. 

Instances  of  contractility  are  seen  in  the  following  cases : — 

1.  The  movements  of  protoplasm  seen  in  simple  animal  and 
vegetable  cells ;  in  the  former  we  have  already  considered  streaming, 
gliding,  and  amoeboid  movement  (see  p.  12) ;  in  the  latter  case  we 
have  noted  the  rotatory  movements  of  the  protoplasm  within  the  cell 
wall  in  certain  plants  (see  p.  13). 

2.  The  movements  of  pigment  cells.  These  are  well  seen  under 
the  skin  of  such  an  animal  as  the  frog ;  under  the  influence  of  elec- 
tricity and  of  other  stimuli,  especially  of  light,  the  pigment  granules 
are  massed  together  in  the  body  of  the  ceU,  leaving  the  processes 
quite  transparent  (fig.  130).  If  the  stimulus  is  removed  the  granules 
gradually  extend  into  the  processes  again.  Thus  the  skin  of  the 
frog   is    sometimes   uniformly   dusky,   and    sometimes    quite    light 


-n^ 


Fio.  130.— Frog's  pigment  cells. 


.  131. — Pigment  cells  from  the  retina,  a,  cells 
still  cohering,  seen  on  their  surface ;  a,  nu- 
cleus indistinctly  seen.  In  the  other  cells  the 
nucleus  is  concealed  by  the  jjigment  granules. 
B,  two  cells  seen  in  profile ;  a,  the  outer  or 
posterior  part  containing  scarcely  any  pig- 
ment.    X  370.    (Henle.) 


coloured.  The  chamseleon  is  an  animal  which  has  become  almost 
proverbial,  since  it  possesses  the  same  power  to  a  marked  degree. 
This  function  is  a  protective  one  ;  the  animal  approximates  in  colour 
that  of  its  surroundings,  and  so  escapes  detection. 

In  the  retina  we  shaU  find  a  layer  of  pigment  cells  (fig.  131),  the 
oranules  in  which  are  capable  of  moving  in  the  protoplasm  in  a  some- 
what similar  way ;  the  normal  stimulus  here  also  is  light. 

3.  CiHary  movement ;  here  we  have  a  much  more  orderly  move- 
ment which  has  already  been  described  (see  p.  29). 

4  In  Vorticellse,  a  spiral  thread  of  protoplasm  in  their  stalk 
enables  them  by  contracting  it  to  lower  the  bell  at  the  end  of  the 
stalk. 

5.  In  certain  of  the  higher  plants,  such  as  the  sensitive  and  carni- 
vorous plants,  movements  of  the  stalks  and  sensitive  hairs  of  the 
leaves  occur  under  the  influence  of  stimuli. 

6.  Muscular  movement.     This  for  the  student  of  human  physio- 


CII.  VIII.]  RHYTHMICALITY  101 

logy  is  the  most  important  of  the  series;  it  is  by  their  muscles  that 
the  higher  animals  (man  included)  execute  most  of  their  movements. 

If  we  contrast  together  am ojhoid,  ciliary,  and  muscular  movement, 
we  hnd  that  they  differ  from  each  other  very  consideral)ly.  Amoeboid 
movement  can  occur  in  any  part  of  an  amoeboid  cell,  and  in  any 
direction.  Ciliary  and  muscular  movement  are  limited  to  one  direc- 
tion ;  but  they  are  all  essentially  similar,  consisting  of  the  movement 
of  hyaloplasm  in  and  out  of  spongioplasm ;  it  is  the  arrangement  of 
the  spongioplasm  that  limits  and  controls  the  movement  of  the  hyalo- 
plasm (see  also  p.  84). 

Rhythmicality. — In  some  forms  of  movement  there  is  not  only 
order  in  direction,  but  order  in  time  also.  This  is  seen  in  ciliary 
movement,  and  in  many  involuntary  forms  of  muscular  tissue,  sucli 
as  that  of  the  heart.  Here  periods  of  contraction  alternate  with 
periods  of  rest,  and  this  occurs  at  regular  intervals.  Under  the  influ- 
ence of  certain  saline  solutions,*  voluntary  muscles  may  be  made 
artificially  to  exhibit  rhythmic  contractions. 

A  familiar  instance  of  rhythmic  movement  in  the  inorganic  world 
is  seen  in  a  water-tap  nearly  turned  off  but  dripping ;  water  accumu- 
lates at  the  mouth  of  the  tap  till  the  drop  is  big  enough  to  fall ;  it 
falls,  and  the  process  is  repeated.  If,  instead  of  water,  gum  or 
treacle,  or  some  other  viscous  substance  is  watched  under  similar 
circumstances,  the  drops  fall  much  more  slowly ;  each  drop  has  to  get 
bigger  before  it  possesses  enough  energy  to  fall.  Thus  we  may  get 
different  degrees  or  rates  of  rhythmic  movement.  So  in  the  body, 
during  the  period  of  rest,  the  cilium  or  the  heart  is  accumulating 
potential  energy,  till,  as  it  were,  it  becomes  so  charged  that  it  dis- 
charges ;  potential  energy  is  converted  into  kinetic  energy  or  move- 
ment. 

When  contraction  travels  as  a  wave  along  muscular  fibres,  or  from 
one  muscular  fibre  to  another,  the  term  peristalsis  is  employed. 
These  waves  are  well  seen  in  such  a  muscular  tube  as  the  intestine, 
and  are  instrumental  in  moving  its  contents  along.  The  heart's  con- 
traction is  a  similar  but  more  complicated  peristalsis  occurring  in  a 
rhythmic  manner. 

Muscle  and  nerve  are  admirable  tissues  for  studying  irritability 
and  contractility. 

The  question  may  be  first  asked,  what  evidence  there  is  of  irrita- 
bility in  muscle  ?  May  not  the  irritability  be  a  property  of  the 
nerve-fibres  which  are  distributed  throughout  the  muscle  and  ter- 
minate  in  its  fibres  ?     The  doctrine  of  independent  muscular  irrita- 

*  Biedermann's  fluid  has  the  following  composition : — Sodium  chloride  5 
grammes,  alkaline  sodium  phosphate  2  gr.,  sodium  carbonate  0*5  gr. ,  water  1  litre. 
If  one  end  of  the  sartorius  of  a  curarised  frog  is  dipped  into  this  fluid,  it  contracts 
rhythmically  in  a  manner  analogous  to  the  heart.  A  solution  of  pure  sodium 
chloride  (0*65  per  cent.)  has  a  similar  action. 


102  IRRITABILITY   AND    CONTRACTILITY  [CII.  VIII. 

liility  was  enunciated  by  Haller  more  than  a  century  ago,  and  was 
afterwards  keenly  debated.  It  was  finally  settled  by  an  experiment  of 
Claude  Bernard  which  can  l)e  easily  repeated  by  every  student. 

If  a  frog  is  taken  and  its  brain  destroyed  by  pithing,  it  loses  con- 
sciousness, but  the  circulation  goes  on,  and  the  tissues  of  its  body 
retain  their  vitality  for  a  considerable  time.  If  now  a  few  drops  of  a 
solution  of  curare,  the  Indian  arrow  poison,  are  injected  with  a  small 
syringe  under  the  skin  of  its  back,  it  loses  in  a  few  minutes  all  power  of 
movement.  If  next  the  sciatic  or  any  other  nerve  going  to  muscle  is 
dissected  out  and  stimulated,  no  movement  occurs  in  the  muscles  to 
which  it  is  distributed.  Curare  paralyses  the  motor  end-plates,  so 
that  for  all  practical  purposes  the  muscles  are  nerveless ;  or  rather 
nervous  impulses  cannot  get  past  the  end-plates  and  cause  any  effect 
on  the  muscles.  But  if  the  muscles  are  stimulated  themselves,  they 
contract. 

Another  proof  that  muscle  possesses  inherent  irritability  was 
adduced  by  Kiihne.  In  part  of  some  of  the  frog's  muscles  {e.g.  part 
of  the  sartorius)  there  are  no  nerves  at  all ;  yet  these  parts  are 
irritable  and  contract  when  stimulated. 

The  evidence  of  the  statement  just  made  that  the  poisonous  effect 
of  curare  is  on  the  end-plates  is  the  following: — The  experiment 
described  proves  it  is  not  the  muscles  that  are  paralysed.  It  must 
therefore  be  either  the  nerves,  or  the  links  between  the  nerve-fibres 
and  the  muscular  fibres.  By  a  process  of  exclusion  we  arrive  at  the 
conclusion  that  it  is  these  links,  for  the  following  experiment  shows  it 
is  not  the  nerves.  The  frog  is  pithed  as  before,  and  then  one  of  its 
legs  is  tightly  ligatured  so  as  to  include  everything  except  the  sciatic 
nerve  of  that  leg.  Curare  is  injected  and  soon  spreads  by  the  circu- 
lating blood  all  over  the  body  except  to  the  leg  protected  by  the  liga- 
ture. It  can  get  to  the  sciatic  nerve  of  that  leg  because  that  was  not 
tied  in  with  the  rest.  The  sciatic  nerve  of  the  other  leg  is  now 
dissected  out;  when  the  muscles  supplied  by  it  cease  to  contract 
when  the  nerve  is  stimulated,  the  frog  may  be  considered  to  be  fully 
under  the  influence  of  the  drug.  But  on  stimulating  the  sciatic 
nerve  of  the  protected  limb,  the  muscles  respond  normally;  this 
shows  that  the  nerve  which  has  been  exposed  to  the  action  of  the 
poison  has  not  been  affected  by  it. 

Varieties  of  Stimuli. 

The  normal  stimulus  that  leads  to  muscular  contraction  is  a 
nervous  impulse ;  this  is  converted  into  a  muscular  impulse  (visible 
as  a  contraction)  at  the  end-plates.  This  nervous  impulse  starts  at 
the  nerve-centre,  brain  or  spinal  cord,  and  travels  down  the  nerve  to 
the  muscle.     In  a  reflex  action  the  nervous  impulse  in  the  nerve- 


CH.  VIII.] 


VARIETIES   OF   STIMULI 


103 


centre  is  started  by  a  sensory  impulse  from  the  poripliery  ;  thus 
when  one  puts  one's  hand  on  something-  unpleasantly  hot,  the  hand  is 
removed ;  the  hot  object  causes  a  nervous  impulse  to  travel  to  the 
brain,  and  the  brain  reflects  down  to  the  muscles  of  the  hand  another 
impulse  by  the  motor  nerves  which  causes  the  muscles  to  contract  in 
such  a  manner  as  to  move  the  hand  out  of  the  way. 

But  the  details  of  muscular  contraction  can  be  more  readily 
studied  in  muscles  removed  from  the  body  of  such  an  animal  as  the 
frog,  and  made  to  contract  by  artificial  stimuli.  When  we  have  con- 
sidered these,  we  can  return  to  the  lessons  they  teach  us  about  the 
normal  contractions  in  our  own  bodies. 

The  first  thing  to  do  is  to  make  from  a  pithed  frog  a  muscle-nerve 
preparation ;  the  muscle  usually  selected  is  the  gastrocnemius,  the 
large  muscle  of  the  calf  of  the  leg,  with  the  sciatic  nerve  attached. 
For  some  experiments  the  sartorius  or  gracilis  may  be  used;  but 
nearly  all  can  be  demonstrated  on  the  gastrocnemius. 

The  tendon  of  the  gastrocnemius  may  ])e  tied  to  a  lever  with  a 
flag  at  the  end  of  it,  and  thus  its 
contractions  rendered  more  evi- 
dent; the  bone  at  the  other  end 
is  fixed  in  a  clamp.  Stimuli  may 
be  applied  either  to  the  nerve  or 
to  the  muscle.  If  the  stimidus  is 
applied  to  the  nerve,  it  is  called 
indirect  stimulation  ;  the  stimulus 
starts  a  nervous  impulse  which 
travels  to  the  muscle ;  the  muscle 
is  thus  stimulated  as  it  is  in  voluntary  contraction  by  a  nervous 
impulse.  Stimulation  of  the  muscle  itself  is  called  direct  stimulation. 
These  stimuli  may  be  : 

1.  Mechanical ;  for  instance  a  pinch  or  blow. 

2.  Chemical ;  for  instance  salt  or  acid  sprinkled  on  the  nerve  or 
muscle. 

3.  Thermal ;  for  instance  touching  the  nerve  or  muscle  with  a  hot 
wire. 

4.  Electrical ;  the  constant  or  the  induced  current  may  be  used. 

In  all  oases  the  result  of  the  stimulation  is  a  muscular  contrac- 
tion. Of  all  methods  of  artificial  stimulation,  the  electrical  is  the 
one  most  generally  employed,  because  it  is  more  under  control  and 
the  strength  and  duration  of  the  stimuli  (shocks)  can  be  regulated 
easily.     We  shall  therefore  have  to  study  some  electrical  apparatus. 

Chemical  stimuli  are  peculiar,  for  some  which  affect  muscle  do 
not  affect  nerve,  and  vice  versd ;  thus  glycerine  stimulates  nerve,  but 
not  muscle ;  ammonia  stimulates  muscle,  but  not  motor  nerves. 

We  may  regard  stimuli  as  liberators  of  energy ;  muscle  and  nerve 


Fig.  132.- Muscle-nerve  preparation,     f,  femur; 
N,  nerve  ;  t,  teudo  Achillis.     (M'Kendrick.) 


104  IRRITABILITY    AND    CONTRACTILITY  [CH.  VIII. 

and  other  irritable  structures  undergo  disturbances  in  consequence  of 
a  stimulus.  The  disturbance  is  some  form  of  movement,  visiljle 
movement  in  the  case  of  muscle,  molecular  movement  in  the  case  of 
nerve.  A  stimulus  may  be  regarded  as  added  motion.  Sir  William 
Gowers  compares  it  to  the  blow  that  causes  dynamite  to  explode,  or 
the  match  applied  to  a  train  of  gunpowder.  A  very  slight  blow  will 
explode  a  large  quantity  of  dynamite;  a  very  small  spark  will  fire  a 
long  train  of  gunpowder.  So  in  muscle  or  nerve  the  effect  is  often 
out  of  all  proportion  to  the  strength  of  the  stimulus ;  a  light  touch 
on  the  surface  of  the  body  may  elicit  very  forcible  nervous  and 
muscular  disturbances ;  and  moreover,  the  effect  of  the  stimulus  is 
propagated  along  the  nerve  or  muscle  without  loss. 


CHAPTEK   IX 

CONTRACTION   OF   MUSCLE 

Muscle  undergoes  many  changes  when  it  contracts ;  they  may  he 
enumerated  under  the  following  five  heads : — 

1.  Changes  in  form. 

2.  Changes  in  extensibility  and  elasticity. 

3.  Changes  in  temperature. 

4.  Changes  in  electrical  condition. 

5.  Chemical  changes. 

In  brief,  each  of  these  changes  is  as  follows : — 

1.  Changes  inform. — The  muscle  becomes  shorter,  and  at  the  same 
time  thicker.  The  amount  of  shortening  varies  so  that  the  length  of 
the  muscle  when  contracted  is  from  65  to  85  per  cent,  of  what  it  was 
originally.  Up  to  a  certain  point,  increase  of  the  strength  of  the 
stimulus  increases  the  amount  of  contraction.  Fatigue  diminishes, 
and  up  to  about  33'  C.  the  application  of  heat  increases  the  amount 
of  contraction.  Beyond  this  temperature  the  muscular  substance 
begins  to  be  permanently  contracted,  and  a  condition  called  heat  rigor, 
due  to  coagulation  of  the  muscle  proteins,  sets  in  a  little  over  40°  C. 

What  the  muscle  loses  in  length  it  gains  in  width ;  there  is  no 
appreciable  change  of  volume. 

Among  the  changes  in  form  must  also  be  mentioned  those  changes 
in  the  individual  muscular  fibres  which  require  a  microscope  for  their 
investigation ;  these  have  been  already  considered  (see  p.  84). 

2.  Changes  in  elasticity  and  extensibility. — The  contracted  muscle 
is  more  stretched  by  a  weight  in  proportion  to  its  length  than  an 
uncontracted  muscle  with  the  same  weight  applied  to  it;  the 
extensibihty  of  contracted  muscle  is  increased ;  its  elasticity  is 
diminished. 

3.  Changes  in  temperature. — When  muscle  is  at  work  or  contract- 
ing, more  energetic  chemical  changes  are  occurring  than  when  it  is 
at  rest ;  more  heat  is  produced  and  its  temperature  rises. 

4.  Changes  in  electrical  condition. — A  muscle  when  it  contracts 
undergoes  a  dipliasic  variation  in  its  electrical  condition. 


106  CONTRACTION   OF  MUSCLE  [CH.  IX. 

5.  Chemical  changes. — These  consist  in  an  increased  consumption 
of  oxygen,  and  an  increased  output  of  waste  materials  such  as  car- 
bonic acid,  and  sarco-lactic  acid.  After  prolonged  contraction  the 
muscle  consequently  acquires  an  acid  reaction. 

These  five  sets  of  changes  will  form  the  subjects  of  the  following 
five  chapters. 


CHAPTER   X 

CHANGE    IN    FORM    IN    A    MUSCLE   WHEN    IT   CONTRACTS 

Though  it  has  been  known  since  the  time  of  Erasistratus  (b.c.  :J04) 
that  a  muscle  becomes  thicker  and  shorter  when  it  contracts,  it  was 
not  until  the  invention  of  the  graphic  method  by  Ludwig  and  Helm- 
holtz,  about  sixty  years  ago,  that  we  possessed  any  accurate  knowledge 
of  this  change.  The  main  fact  just  stated  may  be  seen  by  simply 
looking  at  a  contracting  muscle,  such  as  the  biceps  of  one's  own  arm ; 
but  more  elaborate  apparatus  is  necessary  for  studying  the  various 
phases  in  contraction  and  the  different  kinds  of  contraction  that  may 
occur. 

These  may  be  readily  demonstrated  on  the  ordinary  muscle-nerve 
preparation  (gastrocnemius  and  sciatic  nerve)  from  a  frog.  By  the 
graphic  method,  one  means  that  the  movement  is  recorded  by  a  writ- 
ing. We  shall  find  that  the  same  method  is  applied  to  the  heart's 
movements,  respiratory  movements,  blood  pressure,  and  many  other 
important  problems  in  physiology.  The  special  branch  of  the  graphic 
method  we  have  now  to  study  is  called  myography ;  the  instrument 
for  writing  is  called  a  myograph;  the  writing  itself  is  called  a  myogram. 
Put  briefly,  a  myograph  consists  of  a  writing  point  at  the  end  of  a 
lever  attached  to  the  muscle,  and  a  writing  surface  wliich  travels  at  a 
uniform  rate,  on  which  the  writing  point  inscribes  its  movement. 

The  first  thing,  however,  that  is  wanted  is  something  to  stimulate 
the  muscle  and  make  it  contract ;  the  stimulus  is  usually  applied  to 
the  nerve,  and  the  form  of  stimulus  most  frequently  employed  is 
electrical. 

The  galvanic  battery  in  most  common  use  is  the  Daniell  cell.  It 
consists  of  a  well-amalgamated  zinc  rod  immersed  in  a  cyhnder  of 
porous  earthenware  containing  10  per  cent,  sulphuric  acid;  this  is 
contained  within  a  copper  vessel  (represented  as  transparent  for 
diagrammatic  purposes  in  fig.  133)  filled  with  saturated  solution  of 
copper  sulphate.  Each  metal  has  a  binding  screw  attached  to  it,  to 
which  wires  can  be  fastened.  The  zinc  rod  is  called  the  positive 
element,  the  copper  the  negative  element.     The  distal  ends  of  the  wires 


108         CHANGE   IN   FORM    IN   A    MUSCLE   WHEN   IT   CONTRACTS        [CH.  X. 


cusa 


attached  to  these  are  called  2Joles  or  electrodes,  and  the  pair  of  electrodes 
may  be  conveniently  held  in  a  special  form  of  holder.  The  electrode 
attached  to  the  positive  element  (zinc)  is  called  the  negative  pole  or 

kathode ;  that  attached  to  the  negative  ele- 
ment (copper)  is  called  the  positive  pole  or 
anode.  If  now  the  two  electrodes  are  con- 
nected together,  an  electrical,  galvanic  or 
constant  current  flows  from  the  copper  to 
the  zinc  outside  the  battery,  and  from  the 
zinc  to  the  copper  through  the  fluids  of  the 
battery ;  if  the  electrodes  are  not  connected 
the  circle  is  broken,  and  no  current  can 
flow  at  all.  If  now  a  nerve  or  muscle  is 
laid  across  the  two  electrodes  the  circuit  is 
completed,  and  it  will  be  noticed  at  the 
moment  of  completion  of  the  circuit  the 
muscle  enters  into  contraction ;  if  the 
muscle  is  lifted  off  the  electrodes,  another  contraction  occurs  at  the 
moment  the  circuit  is  broken.  The  same  thing  is  done  more  con- 
veniently by  means  of  a  key:  fig.  134  represents  two  common 
forms  of  key.     A  key  is  a  piece  of  apparatus  by  which  the  current 


CiiSO: 


-Diagram  oi  a  Daniell's 
Battery. 


.Fig.  134.— a.  Du  Bois  Reymoiul's  Key. 


B.  Mercury  Key. 

can  be  allowed  to  pass  or  not 
through  the  nerve  or  muscle  laid 
on  the  electrodes.  When  the  key 
is  open  the  current  is  broken,  as  in 
the  next  figure  (fig.  135);  when  it  is  closed  the  current  is  allowed 
to  pass.  The  opening  of  the  key  is  called  hreak ;  the  closing  of  the 
key  is  called  make.  A  contraction  occurs  only  at  make  and  break, 
not  while  the  current  is  quietly  traversing  the  nerve  or  muscle. 


CH.  X.]  BATTEKIES    /VNU    KKYS  109 

But  it  will  be  seen  iu  the  Du  Bois  Reymond  key  (fig.  134)  that 
there  are  four  binding  screws.  This  key  is  used  as  a  bridge  or  short 
circuiting  key,  and  for  many  reasons  this  is  the  best  way  to  use  it. 
The  next  diagram  (fig.  136)  represents  this  diagrammatically.  The 
two  wires  from  the  battery  go  one  to  each  side  of  the  key ;  the  elec- 
trodes come  off  one  from  each  side  of  the  key.  When  the  key  is  open 
no  current  can  get  across  it,  and  therefore  all  the  current  has  to  go  to 
the  electrodes  with  the  nerve  resting  on  them  ;  but  when  the  key  is 
closed,  the  current  is  cut  off  from  the  nerve,  as  then  practically  all  of 
it  goes  by  the  metal  bridge,  or  short  cut,  back  to  the  battery.  Theo- 
retically a  small  amount  of  current  goes  through  the  nerve ;  but  the 
resistance  of  animal  tissues  to  electrical  currents  is  enormous  as  com- 
pared to  that  of  metal,  and  the  amount  of  electricity  that  flows  through 
a  conductor  is  inversely  proportional  to  the  resistance ;  the  resistance 
in  the  metal  bridge  is  so  small  that  for  all  practical  purposes,  all  the 
current  passes  through  it. 

Another  form  of  electrical  stimulus  is  the  induced  current,  pro- 
duced in  an  induction  coil 

In  a  battery  of  which  the  metals  are  connected  by  a  wire,  we  have 


Fig.  135.  Fig.  136. 

seen  that  the  current  in  the  wire  travels  from  the  copper  to  the  zinc ; 
if  we  have  a  key  on  the  course  of  this  wire  the  current  can  be  made 
or  broken  at  will.  If  in  the  neighbourhood  of  this  wire  we  have  a 
second  wire  forming  a  complete  circle,  nothing  whatever  occurs  in  it 
while  the  current  is  flowing  through  the  first  wire,  but  at  the  instant 
of  making  or  breaking  the  current  in  the  first  or  primary  wire,  a 
momentary  electrical  current  occurs  in  the  secondary  wire,  which  is 
called  an  induced  current ;  and  if  the  secondary  wire  is  not  a  complete 
circle,  but  its  two  ends  are  connected  by  a  nerve,  this  induction  shock 
traverses  the  nerve  and  stimulates  it;  this  causes  a  nervous  impidse 
to  travel  to  the  muscle,  which  in  consequence  contracts. 

If  the  first  and  second  wires  are  coiled  many  times,  the  effect  is 
increased,  because  each  tui'n  of  the  primary  coil  acts  inductively  on 
each  turn  of  the  secondary  coil. 

The  direction  of  the  current  induced  in  the  secondary  coil  is 
the  same  as  that  of  the  current  in  the  primary  coil  at  the  break ;  in 
the  opposite  direction  at  the  make.  The  nearer  the  secondary  coil 
is  to  the  primary,  the  stronger  are  the  currents  induced  in  the 
former. 


110  CHANGE   IN    FORM    IN    A    MUSCLE    WHEN    IT   CONTRACTS      [CH.  X. 

Fig.  137  represents  the  Du  Bois  Eeymond  coil,  the  one  generally 
employed  in  physiological  experiments,  c  is  the  primary  coil,  and  d 
and  d'  its  two  ends,  which  are  attached  to  the  battery,  a  key  being 
interposed  for  making  and  breaking ;  g  is  the  secondary  coil,  the  two 
terminals  of  which  are  at  its  far  end ;  to  these  the  electrodes  to  the 
nerve  are  attached ;  the  distance  between  the  two  coils,  and  so  the 
strength  of  the  induction  currents,  can  be  varied  at  will.  It  is  only 
when  the  primary  current  is  made  or  broken,  or  its  intensity  increased 
or  diminished,  that  induction  shocks  occur  in  the  secondary  circuit 
which  stimulate  the  nerve.  When  one  wishes  to  produce  a  rapid 
succession  of  make  and  break  shocks  the  automatic  interrupter  or 


Fio.  137. — Du  Bois  Reymond's  Induction  Coil. 

Wagner's  hammer  seen  at  the  right-hand  end  of  the  diagram  is 
included  in  the  circuit. 

The  next  thing  to  be  noticed  is  that  the  break  effects  are  stronger 
than  the  make  effects ;  this  is  easily  felt  by  placing  the  electrodes 
on  the  tongue.  This  is  due  to  what  is  called  Faraday's  extra 
current.  This  is  a  current  produced  in  the  primary  coil  by  the 
inductive  influence  of  contiguous  turns  of  that  wire  on  each  other ; 
its  direction  is  against  that  of  the  battery  current  at  make,  and  so 
the  make  shock  is  lessened.  At  the  break  the  extra  current  is  of 
such  short  duration  (because  when  the  circuit  is  broken  there  can  be 
no  current  at  all)  that  for  all  practical  purposes  it  may  be  considered 
as  non-existent. 

The  same  difference  of  strength  occurs  alternately  in  the  repeated 
shocks  produced  by  Wagner's  hammer,  Helmholtz,  to  obviate  this, 
introduced  a  modification  now  known  after  him.  It  consists  in 
bridging   the   current   by  a   side  wire,   so  that   the   current  never 


CH.  X.] 


THE   INDUCTION    COIL 


111 


Fio.  138. 


entirely  ceases  in  the  primary  coil,  but  is  alternately  strengthened 
and  weakened  by  the  rise  and  fall  of  the  hammer ;  the  strengthening 
corresponds  to  the  ordinary  make,  and  is  weakened  by  the  make 
extra  current,  which  occurs  in  the  opposite  direction  to  the  battery 
current ;  the  break  is  also  incomplete,  and  so  it  is  weakened  by  the 
break  extra  current,  which 
being  in  the  same  direction 
as  the  battery  current  im- 
pedes its  disappearance. 

The  two  next  diagrams 
show  the  way  the  interrupter 
acts.  "We  are  supposed  to  be 
looking  at  the  end  of  the 
primary  coil ;  the  battery 
wires  are  attached  to  the 
binding  screws  A  and  E  (fig. 
138).  The  current  now  passes 
to  the  primary  coil  by  the 
pillar  on  the  left  and  the  spring  or  handle  of  the  hammer  as  far  as 
the  screw  (C) ;  after  going  round  the  primary  coil,  one  turn  only  of 
which  is  seen,  it  twists  round  a  pillar  of  soft  iron  on  the  right-hand 
side,  and  then  to  the  screw  E  and  back  to  the  battery ;  the  result 
of  a  current  going  around  a  bar  of  soft  iron  is  to  make  it  a  magnet, 
so  it  attracts  the  hammer,  and  draws  the  spring  away  from  the  top 
screw  C,  and  thus  breaks  the  current;  the  current  ceases,  the  soft 

iron  is  no  longer  a  magnet,  so 
it  releases  the  hammer,  and 
contact  is  restored  by  the 
spring;  then  the  same  thing 
starts  over  again,  and  so  a 
succession  of  break  and 
make  shocks  occurs  alter- 
nately and  automatically. 

In   Helmholtz's  modifica- 
tion   (fig.    139)    the    battery 
wires  are  connected  as  before. 
The  interrupter  is  bridged  by 
a   wire   from    B    to    C   (also 
shown  in  fig.  137,  e).     C   is 
raised  out  of  reach,  and  the  lower  screw  F  is  brought  within  reach 
of  the  spring.     Owing  to  the  wire  BC,  the  vibration  of  the  hammer 
never  entirely  l)reaks  the  current. 

Instead  of  Wagner's  hammer  a  long  vibrating  reed  constructed 
on  the  same  principle  is  often  used.  This  has  the  advantage  that 
the  rate  of  vibration  can  be  varied  at  will  by  means  of  a  sliding 


Fio.  139. 


112         CHANGE   IN    FORM    IN    A    MUSCLE    WHEN    IT    CONTRACTS       [CH.  X. 

clamp  which  fixes  the  reed,  so  that  different  lengths  of  it  can  be 
made  to  vibrate.  If  a  long  piece  of  reed  vibrates,  it  does  so  slowly, 
and  thus  successive  induction  shocks  at  long  intervals  can  be  sent 
into  the  nerve.  But  if  one  wishes  to  stimulate  a  nerve  more  rapidly, 
the  length  of  reed  allowed  to  vibrate  can  be  shortened. 

In  Ewald's  modification  of  the  coil  there  is  another  simple  method 
of  modifying  the  rate  of  the  interrupter.  But  an  hour  spent  in  the 
laboratory  with  an  induction   coil  and  cell  will  teach   the  student 


Fig.  140. — Myograph  of  von  Helmholtz,  shown  in  an  incomplete  form,  a,  forceps  for  holding  frog's 
femur;  h,  gastrocnemius;  c,  sciatic  nerve ;  cf,  scale  pan;  e,  marker  recording  on  cylinder;/, 
counterpoise.    (M'Kendrick.)  • 

much  more  easily  all  these  facts  than  any  amount  of  reading  and 
description. 

We  can  pass  now  to  the  myograph.  There  are  many  different 
forms  of  this  instrument.     Fig.  140  shows  Helmholtz's  instrument. 

The  bony  origin  of  the  gastrocnemius  is  held  firmly  by  forceps, 
and  the  tendo  Achillis  tied  to  a  weighted  lever ;  the  end  of  the  lever 
is  provided  with  a  writing-point  such  as  a  piece  of  pointed  parch- 
ment; when  the  muscle  contracts  it  pulls  the  lever  up,  and  this 
movement  is  magnified  at  the  end  of  the  lever.  The  writing-point 
scratches  on  a  piece  of  glazed  paper  covered  with  a  layer  of  soot ;  the 
paper  is  wrapped  round  a  cylinder.  When  the  lever  goes  up  the 
writing-point  will  mark  an  up-stroke ;  when  it  falls  it  will  mark  a 


cir.  X.] 


MYOGRAPHS 


IIJ 


down-stroke,  and  if  the  cylinder  is  travelling,  the  down-stroke  will 
be  written  on  a  different  part  of  the  paper  than  the  up-stroke;  thus 
a  muscle  curve  or  myogram  is  obtained.  The  paper  may  then  bo 
removed,  varnished,  and  preserved. 

Fig.  141  shows  a  somewhat  different  arrangement. 

The  muscle  is  fixed  horizontally  on  a  piece  of  cork  B,  one  end 
being  fixed  by  a  pin  thrust  through  the  knee-joint  into  the  cork ;  the 


FiQ.  141. — Arrangement  of  the  ajj^jaratus  necessary  for  recording  muscle  contractions  with  a  revolving 
cylinder  carrj'ing  smoked  paper.  A,  revolving  cylinder ;  B,  the  muscle  arranged  upon  a  cork- 
covered  board  which  is  capable  of  being  raised  or  lowered  on  the  upright,  which  also  can  be  moved 
along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording  apparatus — the  tendon  of 
the  gastrocnemius  is  attached  to  the  writing  lever,  properly  weighted,  by  a  ligature.  The 
electrodes  from  the  secondary  coil  pass  to  the  nerve — being,  for  the  sake  of  convenience,  first  of  all 
brought  to  a  short-circuiting  key,  D  (Du  Bois  Keymond's)  ;  C,  the  induction  coil ;  F,  the  battery 
(in  this  fig.  a  bichromate  one) ;  E,  the  key  (Morse's)  in  the  primaiy  circuit. 


tendo  Achillis  is  tied  to  a  lever  which  is  weighted  near  its  fulcrum : 
the  lever  is  so  arranged  that  it  rests  on  a  screw  till  the  muscle  begins 
to  contract;  the  muscle  therefore  does  not  feel  the  weight  till  it 
begins  to  contract,  and  gives  a  better  contraction  than  if  it  had  been 
previously  strained  by  the  weight.  This  arrangement  is  called  after- 
loading. 

The  writing  surface  is  again  a  travelling  cylinder  tightly  covered 
with  smoked  glazed  paper.     The  rest  of  the  apparatus  shows  how 

H 


114  CHANGE    IN    FORM    IN    A    MUSCLE   WHEN    IT    CONTRACTS      [CH.  X. 

cell,  coil,  keys,  and  electrodes  are  applied  with  the  object  of  stimulat- 
ing the  nerve. 

The  key  E  makes  and  breaks  the  primary  circuit,  but  the  effect  is 
only  felt  by  the  muscle-nerve  preparation  when  the  short-circuiting 
key  D  in  the  secondary  circuit  is  opened. 

Instead  of  the  key  E  it  is  better  to  have  what  is  called  a  "  kick- 
over  "  key  which  the  cylinder  by  means  of  a  bar  projecting  from  it 
knocks  over  and  so  breaks  the  primary  circuit  during  the  course  of  a 
revolution.  The  exact  position  of  the  writing-point  at  the  moment 
of  break,  that  is  the  moment  of  excitation,  can  then  be  marked  on 
the  blackened  paper. 

Besides  the  travelling  cylinder  there  are  other  forms  of  writing 


Fio.  142. — Du  Bois  Reymond's  Spring  Myograph.    (M'Kendrick.) 

surface.  Thus  fig.  142  represents  the  spring  myograph  of  Du  Bois 
Eeymond.  Here  a  blackened  glass  plate  is  shot  along  by  the  recoil 
of  a  spring ;  as  it  travels  it  kicks  over  a  key,  and  the  result  of  this, 
the  muscular  contraction,  is  written  on  the  plate. 

The  pendulum  myograph  (fig.  143)  is  another  form.  The  pen- 
dulum carries  a  smoked  glass  plate  upon  which  the  writing-point  of 
the  muscle  lever  is  made  to  mark.  The  break  shock  is  sent  into  the 
muscle-nerve  preparation  by  the  pendulum  in  its  swing  opening  a 
key  in  the  primary  circuit.  This  is  shown  in  an  enlarged  scale  in  BC 
(fig.  143), 

To  keep  the  preparation  fresh  during  an  experiment,  it  should  be 
covered  with  a  glass  shade,  the  air  of  which  is  kept  moist  by  means 


CII.  X.] 


MYOGRArHS 


115 


of  wet  blotting-paper.     A  somewhat  elaborate  form  of  moist  chamber 
is  shown  in  fitj.  144. 


^.^'^ 


Fig.  143.— Pendulum  myograph  and  accessory  parts  (Pick's  pattern).  A,  pivot  upon  which  pendulum 
swings  ;  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  saving ;  D,  a  spring-catch 
which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the  handle  of  which 
the  pendulum  swings  along  the  arc  to  Xi  on  the  left  of  figure,  and  is  caught  by  its  spring. 

The  last  piece  of  apparatus  necessary  is  a  time-marker,  so  that 
the  events  recorded  in  the  myogram  can  be  timed.     The  simplest 


Pig.  144.— Moist  Chamber. 


116  CHANGE    IN   FORM   IN    A    MUSCLE    WHEN    IT   CONTRACTS      [CH.  X. 

time-marker  is  a  tmiing-fork  vibrating  100  times  a  second.  This  is 
struck,  and  by  means  of  a  writing-point  fixed  on  to  one  of  the  prongs 
of  the  fork,  these  vibrations  may  be  written  beneath  the  myogram. 
More  elaborate  forms  of  electrical  time-markers  or  chronographs  are 
frequently  employed. 

The  Simple  Muscle  Curve. 

We  can  now  pass  on  to  results,  and  study  first  the  result  of  a 
single  instantaneous  stimulus  upon  a  muscle.  This  causes  a  single 
or  simple  muscular  contraction,  or  as  it  is  often  called  a  twitch.  The 
graphic  record  of  such  a  contraction  is  called  the  simple  muscle  curve. 
One  of  these  is  shown  in  the  accompanying  figure  (fig.  145). 

The  upper  line  (w)  is  traced  by  the  end  of  the  lever  in  connection 


Fig.  145. — Simple  muscle  curve.     (M.  Foster.) 

with  a  muscle  after  stimulation  of  the  muscle  by  a  single  induction- 
shock  :  the  middle-line  {I)  is  that  described  by  a  lever,  which  indicates 
by  a  sudden  drop  the  exact  instant  at  which  the  induction-shock  is 
given.  The  lower  wavy  line  {t)  is  traced  by  a  tuning-fork  vibrating 
200  times  a  second,  and  serves  to  measure  precisely  the  time  occupied 
in  each  part  of  the  contraction. 

It  will  be  observed  that  after  the  stimulus  has  been  applied  as 
indicated  by  the  vertical  line  s,  there  is  an  interval  before  the  con- 
traction commences,  as  indicated  by  the  line  c.  This  interval,  termed 
the  latent  period,  when  measured  by  the  number  of  vibrations  of  the 
tuning-fork  between  the  lines  s  and  c,  is  found  to  be  about  y^y-sec. 
During  the  latent  period  there  is  no  apparent  change  in  the 
muscle. 

The  second  part  is  the  stage  of  contraction  proper.  The  lever 
is  raised  by  the  shortening  of  the  muscle.  The  contraction  is  at  first 
very  rapid,  but  then  progresses  more  slowly  to  its  maximum,  indicated 


CII.  X.]  THE   SIMPLE   MUSCLE   CURVE  117 

by  the  lino  mx,  drawn  through  its  highest  point.  It  occupies  in  the 
figure  TT^^sec. 

The  next  stage  is  the  stage  of  elongation.  After  reaching  its 
highest  point,  the  lever  begins  to  descend,  in  consequence  of  the 
elongation  of  the  muscle.  At  first  the  fall  is  rapid,  but  then  be- 
comes more  gradual  until  the  lever  reaches  the  abscissa  or  base  line, 
and  the  muscle  attains  its  pre-contraction  length,  indicated  in  the 
figure  by  the  line  c'.  The  stage  occupies  ..VVsec.  Very  often  after 
the  main  contraction  the  lever  rises  once  or  twice  to  a  slight  extent, 
producing  small  curves  (as  in  fig.  147).  These  contractions  are  simply 
due  to  the  elasticity  of  the  muscle  and  recording  apparatus,  and  are 
most  marked  when  the  contraction  is  rapid  and  vigorous. 

The  whole  contraction  occupies  about  -jV  of  a  second.  With 
regard  to  the  latent  period,  it  should  be  pointed  out  that  if  the  muscle 
is  stimulated  indirectly,  i.e.,  through  its  nerve,  some  of  the  apparent 
lost  time  is  occupied  in  the  propagation  of  the  nervous  impulse  along 
the  nerve.  To  obtain  the  true  latent  period,  this  must  be  deducted. 
Then  there  is  latency  in  the  apparatus  (friction  of  the  lever,  etc.)  to 
be  taken  into  account.  This  can  be  got  rid  of  by  photographing  the 
contracting  muscle,  on  a  sensitive  photographic  plate  travelling  at 
an  accurately-timed  rate.  By  such  means  it  is  found  that  the  true 
latent  period  is  much  shorter  than  was  formerly  supposed.  It  is 
only  ^i^  of  a  second.     In  red  muscles  it  is  longer. 

We  now  come  to  the  action  of  various  factors  in  modifying  the  character  of  the 
simple  muscle  curve. 

1.  Influence  of  strength  of  stimulus.— A.  minimal  stimulus  is  that  which  is  just 
strong  enough  to  produce  a  contraction.  If  the  strength  of  stinmlus  is  increased  the 
amount  of  contraction  as  measured  by  the  height  of  the  curve  is  increased,  until  a 
certain  point  is  reached  (maximal  stimulus),  beyond  which  increase  in  the  stimulus 
produces  no  increase  in  the  amount  of  contraction.  The  latent  period  is  shorter 
with  a  strong  than  with  a  weak  stimulus. 

2.  Infliience  of  /ond— Up  to  a  certain  point  increase  of  load  increases  the 
amount  of  contraction,  beyond  which  it  diminishes,  until  at  last  a  weight  is  reached 
which  the  muscle  is  unable  to  lift.  The  latent  period  is  somewhat  longer  with  a 
heavy  load  than  with  a  light  one. 

3.  Influence  offatiffue.—Thif.  can  be  very  well  illustrated  by  letting  the  muscle 
write  a  curve  with  every  revolution  of  the  cylinder,  until  it  ceases  to  contract 
at  all.     The  next  diagram  shows  the  early  stages   of  fatigue.     At  first  the  con- 


Fio.  140. — Fatigue. 

tractions  improve,  each  being  a  little  higher  than  the  preceding ;  this  is  known  as 
the  heneflcial  effect  of  contraction,  and  the  graphic  record  is  called  a  staircase.  Then 
the  contractions  get  less  and  less.     But  what  is  most  noticeable  is  that  the  contrac- 


118  CHANGE   IN    FORM    IN    A    MUSCLE   WHEN    IT    CONTRACTS      [CH.  X. 

tion  is  much  more  prolonged ;  the  latent  period  gets  longer ;  the  period  of 
contraction  gets  longer  ;  and  the  period  of  relaxation  gets  very  nuich  longer  ;  there 
is  a  condition  known  as  contracture,  so  that  the  original  base  line  is  not  reached  by 
the  time  the  next  stimulus  arrives.  In  tiie  last  stages  of  fatigue,  contracture 
passes  off. 

4.    Effect  of  tfimperature.. — Cold  at  first  increases  the  height  of  contraction,  then 


Fig.  147. — Kllect  of  temperature  on  a  single  muscular  contraction  ;  N,  normal ;  H,  warm  ;  61,  cooling  ; 
G'2,  very  cold ;  P,  point  of  stimulation.  The  above  tracing  is  a  considerably  reduced  facsimile  of  a 
tracing  taken  with  the  pendulum  myograph. 

diminishes  it ;  otherwise  the  effect  is  very  like  that  of  fatigue  increasing  the 
duration  of  all  stages  of  the  curve. 

Moderate  warmth  increases  the  height  and  diminishes  the  duration  of  all  stages 
of  the  curve,  latent  period  included.  This  may  be  readily  shown  by  dropjjing  some 
warm  salt  solution*  on  to  the  nmscle  before  taking  its  curve.  Too  great  heat 
(above  42"  C.)  induces  heat  riqor  due  to  the  coagulation  of  the  muscle  proteids. 

5.  Effect  of  veralrine. — If  this  is  injected  into  the  frog  before  the  muscle-nerve 
preparation   is   made,   the    very   remarkable   result   seen   in  the   next  diagram  is 


Fig.  148.— Veratrine  curve,  taken   on  a   very   slowly-travelling   cylinder ;  the  time   tracing  indicates 

seconds. 

produced  on  stimulation  ;  there  is  an  enormous  prolongation  of  the  period  of  relaxa- 
tion ;  marked  by  a  secondary  rise,  and  sometimes  by  tremors.  After  repeated 
stimulation  this  effect  passes  off,  but  returns  after  a  period  of  rest. 

The  Muscle-Wave. 

The  first  pari  of  a  nmscle  which  contracts  is  the  part  where  the 
nerve-fibres  enter ;  but  nerve  impulses  are  so  rapidly  carried  to  all 
the  fibres  that  for  practical  purposes  thoy  all  contract  together. 
But  in  a  nerveless  muscle,  that  is  one  rendered  physiologically  nerve- 

*  Physiological  saline  solution  used  for  bathing  living  tissue  is  a  07  to  09  per 
cent,  solution  of  sodium  chloride  in  ordinary-  tap  water. 


CH.  X.] 


THE    MUSCLE-WAVE 


119 


less  by  curare,  if  one  end  of  the  muscle  is  stimulated,  the  contraction 
travels  as  a  wave  of  thickening  to  the  other  end  of  the  muscle,  and 
the  rate  of  propagation  of  this  wave  can  be  recorded  graphically. 
The  next  figure  (fig.  149)  represents  one  of  the  numerous  methods 
that  have  been  devised  for  this  purpose.  A  muscle  with  long  parallel 
fibres,  like  the  sartorius,  is  taken ;  it  is  represented  diagrammatically 
in  the  figure.  It  is  stimulated  at  the  end,  where  the  two  wires, 
+  and  — ,  are  placed ;  it  is  grasped  in  two  places  by  pincers,  which 
are  opened  by  the  wave  of  thickening ;  the  opening  of  the  first  pair 
of  pincers  (1)  presses  on  a  drum  or  tambour  connected  to  a  second 
tambour  with  a  recording  lever  (1'),  and  this  lever  goes  up  first;  the 


Fig.  149.— Arrangement  for  tracing  the  muscle-wave.     (McKendrick.) 

lever  (2')  of  the  tambour  connected  with  the  second  pair  of  pincers 
(2)  goes  up  later.  If  the  length  of  muscle  between  the  pairs  of 
pincers  is  measured,  and  by  a  time-tracing  the  delay  in  the  raising 
of  the  second  lever  is  ascertained,  we  have  the  arithmetical  data  for 
calculating  the  rate  of  propagation  of  the  muscle-wave.  It  is  about 
3  metres  per  second  in  frog's  muscle,  but  is  hastened  by  warmth  and 
delayed  by  cold  and  fatigue. 

The  Effect  of  T-wo  successive  Stimuli. 

If  a  second  stimulus  follows  the  first  stimulus,  so  that  the  muscle 
receives  the  second  stimulus  before  it  has  finished  contracting  under 
the  influence  of  the  first,  a  second  curve!  will  be  added  to  the  first, 
as  shown  in  the  accompanying  diagram  (fig.  150).     The  third  little 


120  CHANGE   IN    FORM    IN    A    MUSCLE   WHEN    IT    CONTRACTS      [CH.  X. 

curve  is  only  due  to   elastic  after-vibration.     This  is  called  super- 
position, or  summation  of  effects. 

If  the  two  stimuli  are  in  such  close  succession  that  the  second 
occurs  during  the  latent  period  of  the  first,  the  result  will  differ 
according  as  the  stimuli  are  maximal  or  submaximal.  If  they  are 
maximal,  the  second  stimulus  is  without  effect ;  but  if  submaximal, 


Fig.  150.— Tracing  of  a  double  muscle-curve.  To  be  reail  from  left  to  right.  Wliile  the  muscle  was 
engaged  in  the  first  contraction  (whose  complete  course,  liad  nothing  intervened,  is  indicated  by 
the  dotted  line),  a  second  induction-shock  was  thrown  in,  at  such  a  time  that  the  second  con- 
traction began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to  start  from 
the  first,  as  does  the  lirst  from  the  base  line.     (M.  Foster.) 

the  two  stimuli  are  added  together,  and  though  producing  a  simple 
muscle-curve,  produce  one  which  is  bigger  than  either  would  have 
produced  separately.     This  is  called  summation  of  stimuli. 

Effect  of  More  than  Two  Stimuli. 

Just  as  a  second  stimulus  adds  its  curve  to  that  written  as  the 
result  of  the  first,  so  a  third  stimulus  superposes  its  effect  on  the 


Fic.  151.— Curve  of  incomplete  tetanus,  obtained  from  the  gastrocnemius  of  a  frog,  where  the  shocks 
were  sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption  of  the 
primary  current  by  means  of  a  vibrating  spring,  which  dipped  into  a  cup  of  mercury,  and  broke 
the  primary  current  at  each  vibration.    (Tracing  to  be  read  right  to  left.) 

second  ;  a  fourth  on  the  third,  and  so  on.     Each  successive  increment 
is,    however,  smaller   than   the  preceding,  and  at  last  the  muscle 


CH.  X.]  TETANUS  121 

remains  at  a  maximum  contraction,  till  it  begins  to  relax  from 
fatigue. 

A  succession  of  stimuli  may  be  sent  into  the  nerve  of  a  nerve- 
muscle  preparation  by  means  of  the  "Wagner's  hammer  of  a  coil,  or 
the  vibrating  reed  previously  mentioned  (p.  111).  This  method  of 
stimulation  is  caMed  fa7'adisation.  Figs.  151  and  152  show  the  kind 
of  tracings  one  obtains.  The  number  of  contractions  corresponds  to 
the  number  of  stimulations ;  the  condition  of  prolonged  contraction 
so  produced,  the  muscle  never  relaxing  completely  between  the 
individual  contractions  of  which  it  is  made  up,  is  called  tetanus: 
incomplete  tetamis,  or  domes,  when  the  individual  contractions  are 
discernible  (fig.  151) ;  complete  tetanus,  as  in  fig.  152,  when  the  con- 
tractions are  so  rapid  as  to  be  completely  fused  to  form  a  continuous 
line  without  waves. 

The  rate  of  faradisation  necessary  to  cause  complete  tetanus  varies 
a  good  deal;  for  frog's  muscle  it  averages  15  to  20  per  second;  for 


Fig.  152.— Curve  of  complete  tetanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 
(Tracing  to  be  read  right  to  left.) 

the  pale  muscles  of  the  rabbit,  20  per  second ;  for  the  more  slowly 
contracting  red  muscles  of  the  same  animal,  10  per  second  ;  and  for 
the  extremely  slowly  contracting  muscles  of  the  tortoise  2  per  second 
is  enough.  With  fatigue,  the  rate  necessary  to  produce  complete 
tetanus  is  diminished. 

Voluntary  Tetanus. 

We  have  seen  that  voluntary  muscles  under  the  influence  of 
artificial  stimuli  may  be  made  to  contract  in  two  ways :  a  single 
excitation  causes  a  single  contraction;  a  rapid  series  of  excitations 
causes  a  series  of  contractions  which  fuse  to  form  tetanus. 

We  now  come  to  the  important  question,  in  which  of  these  two 
ways  does  voluntary  muscle  ordinarily  contract  in  the  body  ?  The 
answer  to  this  is,  that  voluntary  contraction  resembles,  though  it  is 
not  absolutely  identical  with,  tetanus  artificially  produced.  It  is 
certainly  never  a  twitch.  The  nerve-cells  from  which  the  motor 
fibres  originate  do  not  possess  the  power  of  sending  isolated  impulses 
to  the  muscles ;  they  send  a  series  of  impulses  which  result  in  a 


122  CHANGE   IN   FORM    IN    A    MUSCLE   WHEN    IT    CONTRACTS      [CII.  X. 

muscular  tetanus,*  or  voluntary  tetanus,  as  it  may  conveniently  be 
termed. 

If  a  stethoscope  is  placed  over  any  contracting  muscle  of  the 
human  body,  such  as  the  biceps,  a  low  sound  is  heard.  The  tone  of 
this  sound,  which  was  investigated  by  Wollaston,  and  later  by 
Helmholtz,  corresponds  to  thirty-six  vibrations  per  second ;  this  was 
regarded  as  the  first  overtone  of  a  note  of  eighteen  vibrations  per 
second,  and  for  a  long  time  18  per  second  was  believed  to  be  the 
rate  of  voluntary  tetanus. 

The  so-called  "  muscle  sound "  is,  however,  no  indication  of  the 
rate  of  muF.cular  vibration.  Any  irregular  sound  of  low  intensity 
will  produce  the  same  note ;  it  is,  in  fact,  the  natural  resonance-tone 
of  the  membrana  tympani  of  the  ear,  and,  therefore,  selected  by  the 
organ  of  hearing  when  we  listen  to  any  irregular  mixture  of  faint, 
low-pitched  tones  and  noises. 

A  much  more  certain  indication  of  the  rate  of  voluntary  tetanus 
is  obtained  by  the  graphic  method.  The  myographs  hitherto  de- 
scribed are  obviously  inapplicable  to  the  investigation  of  such  a 
problem  in  man.  The  instrument  employed  is  termed  a  transmis- 
sion myograph.  The  next  figure  shows  the  recording  part  of  the 
apparatus. 

It  is  called  a  Marey's  Tambour.     It  consists  of  a  drum,  on  the 

Screw  to  regulateielevation  of  lever. 


Wiitiug  lever. 


Tube  to  receiving 
tambour. 


Fig.  153.— Marey's  Tambour,  to  which  the  movement  of  the  column  of  air  in  the  first  tambour  is 
conducted  by  a  tube,  and  from  which  it  is  commuidcated  by  the  lever  to  a  revolving  cylinder,  so 
that  the  tracing  of  the  movement  is  obtained. 

membrane  of  which  is  a  metallic  disc  fastened  near  one  end  of  a 
lever,  the  far  extremity  of  which  carries  a  writing  point.  The  interior 
of  the  drum  is  connected  by  an  india-rubber  tube  (seen  at  the  right- 
hand  end  of  the  drawing)  to  a  second  tambour  called  the  receiving 
tambour,  in  which  the  writing  lever  is  absent.  Now  if  the  receiving 
tambour  is  held  in  the  hand,  and  the  thumb  presses  on  the  metallic 

*  The  u,se  of  the  word  tetanus  in  phy.siology  must  not  be  confounded  with 
the  disea.se  known  by  tlie  same  name,  in  which  the  most  marked  symptom  is  an 
intense  condition  of  muscular  tetanus  or  cramp. 


Cir.  X.]  VOLUNTARY    TETANUS  123 

disc  on  the  surface  of  its  membrane,  the  air  within  it  is  set  into 
vibrations  of  the  same  rate  as  those  occurring  in  the  thumb  muscles ; 
and  these  are  propagated  to  the  recording  tambour  and  are  written 
in  a  magnified  form  by  the  end  of  the  lever  on  a  recording  travelling 
surface. 

The  tracing  obtained  is  very  like  that  in  fig.  151 ;  it  is  an  incom- 
plete tetanus,  which  by  a  time  marker  can  be  seen  to  be  made  up  of 
10  to  12  vibrations  a  second. 

In  some  diseases  these  tremors  are  much  increased,  as  in  the 
clonic  convulsions  of  epilepsy,  or  those  produced  by  strychnine 
poisoning,  but  the  rate  is  the  same. 

Similar  tracings  can  be  obtained  in  animals  by  strapping  the 
receiving  tambour  on  the  surface  of  a  muscle,  and  causing  it  to 
contract  by  stimulating  the  brain  or  spinal  cord.  The  rate  of  stimu- 
lation makes  no  difference ;  however  slow  or  fast  the  stimuli  occur, 
the  nerve-cells  of  the  central  nervous  system  give  out  impulses  at 
their  own  normal  rate. 

The  same  is  seen  in  a  reflex  action.  If  a  tracing  is  taken  from  a 
frog's  gastrocnemius,  the  muscle  being  left  in  connection  with  the 
rest  of  the  body,  its  tendon  only  being  severed  and  tied  to  a  lever, 
and  if  the  sciatic  nerve  of  the  other  leg  is  cut  through,  and  the  end 
attached  to  the  spinal  cord  is  stimulated,  an  impulse  passes  up  to  the 
cells  of  the  cord,  and  is  then  reflected  down  to  the  gastrocnemius, 
under  observation.  The  impulse  has  thus  to  traverse  nerve-cells  ;  the 
rate  of  stimulation  then  makes  no  difference;  the  reflex  contraction 
occurs  at  the  same  rate,  10  or  12  per  second. 

But  now  a  difficulty  arises ;  if  a  twitch  only  occupies  yV  of  a 
second,  there  would  be  time  for  ten  complete  twitches  in  a  second  ; 
they  would  not  fuse  to  form  even  an  incomplete  tetanus.  There  must 
be  some  means  by  which  each  individual  contraction  can  be  lengthened 
till  it  fuses  with  the  next  contraction ;  or,  in  other  words,  our  results 
of  electrical  stimulation  of  excised  muscles  must  not  be  applied 
without  reserve  to  the  contraction  of  the  intact  muscles  in  the  living 
body  in  response  to  the  will.  Eecent  experiments  made  by  Sir  J. 
Burden  Sanderson  on  the  electrical  variation  that  accompanies 
voluntary  movements,  have  shown  that  this  is  the  case :  each  com- 
ponent of  the  so-called  voluntary  tetanus  is  a  somewhat  prolonged 
single  contraction ;  a  condition  which  closely  resembles  the  tonic 
contraction  of  involuntary  muscle. 

Lever  Systems. — The  arrangement  of  the  muscles,  tendons,  and 
bones  presents  examples  of  the  three  systems  of  levers  which  will  bo 
known  to  anyone  who  has  studied  mechanics  ;  the  student  of  anatomy 
will  have  no  difficulty  in  finding  examples  of  all  three  systems  in 
the  body.  "What  is  most  striking  is  that  the  majority  of  cases  are 
levers  of  the  third  kind,  in  which  there  is  a  loss  of  the  mechanical 


124  CHANGE   IN   FORM    IN   A    MUSCLE   WHEN    IT   CONTRACTS      [CH.  X. 

power  of  a  lever,  though  a  gain  in  the  rapidity  and  extent  of  the 
movement. 

Most  muscular  acts  involve  the  action  of  several  muscles,  often 
of  many  muscles.  The  acts  of  walking  and  running  are  examples  of 
very  complicated  muscular  actions  in  which  it  is  necessary  not  only 
that  many  muscles  should  take  part,  but  also  must  do  so  in  their 
proper  order  and  in  due  relation  to  the  action  of  auxiliary  and 
antagonistic  muscles.  This  harmony  in  a  complicated  muscular 
action  is  called  co-ordination. 

By  the  device  of  taking  instantaneous  photographs  at  rapidly 
repeated  intervals  during  a  muscular  act,  the  details  of  different 
modes  of  locomotion  in  man  and  other  animals  have  been  very 
thoroughly  worked  out.  With  this  branch  of  research  the  name 
of  Prof.  Marey  is  intimately  associated. 


CHAPTEK  XI 


EXTENSIBILITY,  ELASTICITY,  AND  WORK  OF  MUSCLE 

Muscle  is  both  extensible  and  elastic.  It  is  stretched  by  a  weight, 
that  is,  it  possesses  extensibility ;  when  the  weight  is  taken  off,  it 
returns  to  its  original  length,  that  is,  it  possesses  elasticity.  The  two 
properties  do  not  necessarily  go  together ;  thus  a  piece  of  putty  is 
very  extensible,  but  it  is  not  elastic ;   a  piece  of  steel  or  a  ball  of 


^ 

n 

- 

t\ 

71 

^^n 

'^q 

r-. 

^^.^ 

Elastic  Band 

^ 

T^ 

~i 

Muscle 

Fio.  154.— (After  Waller.) 

ivory  are  only  slightly  extensible,  but  after  the  stretching  force  has 
been  removed  they  return  to  their  original  size  and  shape  very 
perfectly. 

A  substance  is  said  to  be  strongly  clastic,  when  it  offers  a  great 
resistance  to  external  forces ;  steel  and  ivory  are  strongly  elastic. 

A  substance  is  said  to  be  perfectly  elastic,  when  its  return  to  its 
original  shape  is  absolute ;  again  steel  and  ivory  may  be  quoted  as 
examples. 

Muscle  is  very  extensible,  i.e.,  it  is  easily  stretched ;  it  is  feebly 


126  EXTENSIBILITY,    ELASTICITY,    AND   WORK    OF   MUSCLE      [CH.  XI. 

elastic,  i.e.,  it  opposes  no  great  resistance  to  external  force;  it  is, 
however,  perfectly  elastic;  that  is,  it  returns  to  its  original  shape 
very  exactly  after  stretching.  This  is  true  in  the  case  of  living  muscle 
within  the  body,  but  after  very  great  stretching  even  in  the  body, 
and  still  more  so  after  removal  from  the  body,  when  it  begins  to 
undergo  degenerative  changes  culminating  in  death,  its  elasticity  is 
less  perfect. 

The  cohesion  of  muscular  tissue  is  less  than  that  of  tendon. 
E.  Weber  stated  that  a  frog's  muscle  one  centimetre  square  in 
transverse  section  will  support  a  weight  of  a  kilogramme  (over 
2  lbs.)  without  rupture,  but  this  diminishes  as  the  muscle  gradually 
dies. 

The  extensibility  of  any  material  may  be  studied  and  recorded  by 
measuring  the  increase  of  length  which  occurs  when  that  material  is 
loaded  with  different  weights.  In  Helmholtz's  myograph  (fig.  140), 
different  weights  may  be  placed .  in  the  scale-pan  beneath  the  muscle, 
and  the  increase  of  length  recorded  on  a  stationary  blackened  cylinder 
by  the  downward  movement  of  the  writing  point ;  the  cyHnder  may 
then  be  moved  on  a  short  distance,  more  weight  added,  and  the 
additional  increase  of  length  similarly  recorded,  and  so  on  for  a 
succession  of  weights. 

If  this  experiment  is  done  with  some  non-living  substance,  like 
a  steel  spring  or  a  piece  of  india-rubber,  instead  of  a  living  muscle, 
it  is  found  that  the  amount  of  stretching  is  proportional  to  the  weight ; 
a  weight  =  2  produces  an  extension  twice  as  great  as  that  produced 
by  a  weight  =  1 ;  in  this  way  one  obtains  a  tracing  like  that  seen  on 
the  left  hand  of  figure  154,  and  the  dotted  line  drawn  through  the 
lowest  points  of  the  extensions  is  a  straight  one. 

With  muscle,  however,  this  is  different ;  each  successive  addition 
of  the  same  weight  produces  smaller  and  smaller  increments  of  ex- 
tension, and  the  dotted  line  obtained  is  a  curve. 

A  continuous  curve  of  extensibility  may  be  obtained  by  placing 
a  gradually  and  steadily  increasing  force  beneath  the  muscle  instead 
of  a  succession  of  weights  added  at  intervals.  The  most  convenient 
way  of  doing  this  is  to  use  a  steel  spring,  which  is  gradually  and 
steadily  extended;  and  the  writing  point  connected  to  the  muscle 
inscribes  its  excursion  on  a  slowly  moving  cylinder.  If,  then,  after 
the  muscle  has  been  stretched,  the  steel  spring  is  gradually  and 
steadily  relaxed,  the  muscle  retracts  and  again  writes  a  curve  now  in 
the  reverse  direction,  until  it  regains  its  original  length.*  But  in 
muscles  removed  from  the  body,  unless  they  are  very  slightly  loaded, 
the  return  to  the  original  length  is  never  complete ;  the  muscle  is 

*  A  mathematical  examination  of  these  curves  shows  that  they  are  not  rect- 
angular hyperbolas  as  they  were  once  considered.  They  are  very  variable  in  form, 
and  cannot  be  identified  with  any  known  mathematical  curve. 


CII.  XI.] 


CURVES   OF   EXTENSIBILITY 


127 


permanently  longer  to  a  slight  extent,  which  varies  with  the  amount 
of  the  previous  loading. 

If  the  muscle  is  slowly  loaded  and  slowly  unloaded,  the  curvature 
of  its  tracing  is  much  more  marked  than  if  the  experiment  is  done 
rapidly. 

The  following  three  tracings  are  reproduced  from  some  obtained 
by  Dr  Brodie.  In  the  method  used,  the  records  are  not  complicated 
by  the  curve  of  a  lever,  but  the  movement  was  simply  magnified  by 
a  beam  of  light  falling  on  a  mirror  attached  to  the  end  of  the  muscle, 
and  reflected  on  to  a  travelling  photographic  plate.  Each  tracing  is 
to  be  read  from  right  to  left ;  the  first  one  (A)  shows  the  result  of 
stretching  a  steel  spring  by  a  steadily  increasing  force ;  the  end  of 
the  spring  gets  lower  and  lower, 
and  describes  a  straight  line;  at 
the  apex  of  the  tracing  unloading 
began  and  went  on  steadily  till 
the  spring  once  more  regained  its 
initial  length.  The  upstroke,  like 
the  downstroke,  is  a  straight  line. 
In  B  and  C  muscles  were  used ; 
it  will  be  noticed  that  the  muscle 
does  not  regain  its  original  length 
after  unloading  is  completed,  and 
the  upward  tendency  of  the  tracing 
beyond  this  point  represents  after- 
retraction.  In  B,  the  extension 
was  applied  rapidly,  the  tracing 
is  almost  a  straight  line;  in  C, 
the  extension  was  brought  about 
more  slowly,  and  the  tracing  is  a 
curve;  in  both  cases  the  tracing 
of  the  period  of  unloading  shows 
more  curvature. 

This  introduces  us  to  what  is 
called  after-extension  and  after- 
retraction.  That  is  to  say,  after  a  muscle  is  weighted  there  is  an 
immediate  elongation,  followed  by  a  gradual  elongation  which 
continues  for  some  time ;  or  if  a  muscle  has  been  weighted  and  is 
then  unloaded  there  is  an  immediate  slackening,  followed  by  a 
gradual  after-retraction. 

This  may  be  shown  by  looking  at  the  graphic  records  shown  in 
the  next  diagram.  It  will  be  noticed  that  the  extension  is  greatest 
when  the  muscle  is  in  a  contracted  condition,  and  smallest  when  it  is 
dead  (in  rigor).  In  fatigue  the  after-extension  is  very  marked,  and 
the  return  after  unloading  very  imperfect. 


Fig.  155. — Curves  of  extensibility.    (Brodie.) 


128  EXTENSIBILITY,   ELASTICITY,   AND   WORK   OF   MUSCLE        [ciI.  XL 

We  may  now  give  .the  results  of  an  actual  experiment ;  a  muscle 
was  loaded  with  successive  weights  of  50,  100,  150,  etc.,  grammes, 
and  its  length  carefully  measured  in  centimetres. 


Load     .... 

50 

100 

150 

200 

250 

300 

Total  extension     . 

3-2 

6 

8 

9-5 

10 

10-3 

Increment  of  extension 

— 

2-8 

2 

1-5 

0-5 

0-3 

Figure  156  shows  that  the  contracted  muscle  is  more  extensible 
than  the  uncontracted  muscle.     This  may  be  still  further  illustrated 

by  an  example  given  on  the  opposite 
page  in  the  form  of  a  diagram. 

The  thick  lines  represent  the  con- 
tracted muscle,  the  thin  ones  the  un- 
contracted. It  is  represented  as  being 
stretched  by  different  weights  indicated 
along  the  top  line ;  and  the  lengths 
under  the  influence  of  these  weights 
are  separated  by  equal  distances. 
Thus  A  C  represents  the  length  of  the 
uncontracted  muscle,  A  B  of  the  con- 
tracted muscle  when  unloaded.  A'  C 
and  A'  B'  the  same  under  the  influence 
of  a  weight  of  50  grammes,  and  so  on. 

The  curve  connecting  the  ends  of 
the  lengths  of  the  contracted  muscle 
falls  faster  than  that  obtained  from 
the  uncontracted  one,  until  at  the 
point  P  under  the  influence  of  a  weight 
of  250  grammes,  the  two  curves  meet ; 
that  is  to  say,  250  grammes  is  the 
weight  which  the  muscle  was  just  un- 
able to  lift.  Suppose  a  muscle  has  to 
lift  the  weight  of  200  grammes,  it 
begins  with  a  length  A"  C",  but  when 
it  contracts  it  has  a  length  A"  B",  that 
is,  it  has  contracted  a  distance  of  B"  C", 
which  is  very  small;  when  it  has  to 
lift  a  less  weight  it  shortens  more, 
when  a  greater  weight  it  shortens  less ;  till  when  it  shortens  least  it 
lifts  the  greatest  weight. 

This  experiment  illustrates  the  general  truth  that  when  a  muscle 
is  contracted  it  is  more  extensible.  At  the  point  P  the  energy 
tending  to  shorten  the  muscle -(its  contractile  power)  is  exactly  equal 
to  the  energy  tending  to  lengthen  it  against  its  elastic  force.  Thus 
we  have   the  apparent  paradox   at  this  point  that   a  muscle  when 


!n  rigor 

f 

Normal 
Fatigued 

-J 

- 

^ 

Fio.  15i;.— Extensibility  of  muscle  in 
different  states  ;  tested  by  GO  grammes 
applied  for  short  periods.  Tracings 
to  be  read  from  left  to  right.  (After 
Waller.) 


CH.  XI.] 


WEBER'S    PARADOX 


129 


contracted  has  exactly  the  same  length  as  when  uncontracted ;  but 
this  is  a  matter  of  everyday  experience ;  if  one  tries  to  lift  a  weight 
beyond  one's  strength,  one  fails  to  raise  it,  but  nevertheless  one's 
muscles  have  been  contracting  in  the  effort;  they  have  not  contracted 
in  the  restricted  sense  of  becoming  shorter,  but  that  is  not  the  only 
change  a  muscle  undergoes  when  it  contracts;  the  other  changes, 
electrical,  thermal,  chemical,  etc.,  have  taken  place,  as  evidenced  in 
one's  own  person  by  the  fact  that  the  individual  has  got  warm  in  his 
efforts,  or  may  even  feel  fatigue  afterwards. 

But  the  paradox  does  not  end  here,  for  if  diagram  157  is  again 
looked  at,  it  will  be  seen  that  beyond  the  point  P  the  two  curves 
cross ;  in  other  words,  the  muscle  may  even  elongate  due  to  increase 
of  extensibility  when  it  contracts.  This  is  known  after  its  discoverer 
as   Weber's  paradox.     The  increase  of  extensibility  of  muscle  during 


Contracted' 
Uncontracted- 


Fio.  157. 


contraction  is  protective  and  tends  to  prevent  rupture  in  efforts  to 
raise  heavy  weights. 

Infiuence  of  Temperature  on  Extensibility. — If  a  piece  of  iced 
india-rubber  is  taken  and  stretched  by  a  weight,  its  retractility  when 
the  weight  is  removed  is  very  small.  If,  now,  when  the  weight  is  on 
it,  it  is  warmed  at  one  point  as  by  placing  the  hand  on  it,  its 
retractility  is  increased  and  it  contracts,  raising  the  weight.  Some 
physiologists  have  considered  that  muscular  contraction  can  be 
explained  in  this  way ;  they  have  supposed  that  the  heat  formed  in 
muscular  contraction  acts  like  warmth  as  applied  to  india-rubber. 
This  view  is,  however,  incorrect.  It  is  much  more  probable  that 
there  is  no  causal  relationship  between  the  temperature-change  and 
the  extensibiUty-change  which  occur  when  muscle  contracts;  both 
are  simultaneously  produced  by  the  stimulus. 

Moreover,  the  influence  of  heat  on  muscle  is  by  no  means  the 
same  as  that  on  india-rubber.     This  influence  is  not  invariable,  and 


130  EXTENSIBILITY,    ELASTICITY,    AND    WORK    OF    MUSCLE        [CH.  XI. 

at  certain  temperatures  near  the  freezing-point,  and  under  the 
influence  of  certain  weights,  actual  elongation  may  occur  when  the 
temperature  is  raised. 

Muscular  Tonus. 

In  the  living  animal,  muscles  are  more  or  less  stretched,  but 
never  taut  between  their  two  attachments.  They  are  in  a  state  of 
tonicity  or  tonus,  and  when  divided  they  contract  and  the  two  parts 
separate.  Thus  a  muscle,  even  at  rest,  is  in  a  favourable  condition 
to  contract  without  losing  time  or  energy  in  taking  in  slack. 

Muscular  tonus  is  under  the  control  of  the  nervous  system  (on 
the  reflex  character  of  this  control,  see  later,  under  Tendon  Eeflexes) ; 
the  muscles  lengthen  when  their  nerves  are  divided,  or  when  they 
are  rendered  physiologically  nerveless  by  curare.  Besides  the  nervous 
system,  the  state  of  muscular  nutrition  dependent  on  a  due  supply 
of  healthy  blood  must  also  be  reckoned  as  important  in  maintaining 
muscular  tonus. 

Work  of  Muscle. 

The  question  of  muscular  work  is  intimately  associated  with  that 
of  elasticity.  In  a  technical  sense,  work  (W)  is  the  product  of  the 
load  {I)  and  the  height  {h)  to  which  it  is  raised.     W  =  lxh. 

Thus  in  fig.  157,  when  the  muscle  is  unloaded  the  work  done  is 
nil:  W^BCxO^O.  When  the  load  is  250,  again  the  work  done 
is  nil,  because  then  h  =  0.     With  the  load  50,  W  =  B'  C  x  50. 

If  the  height  is  measured  in  feet  and  the  load  in  pounds,  work  is 
expressed  in    terms  of   foot-pounds.     If   the  height  is  measured   in 


Fig.  158. — Diagram  to  sliow  the  mode  of  measuring  muscle  work.    (M'Kendrick.) 

millimetres  or  metres,  and  the  load  in  grammes,  the  work  is  expressed 
in  gramme-millimetres  or  gramme-metres  respectively. 

This  may  be  shown  diagrammatically  by  marking  on  a  horizontal 
base  line  or  abscissa,  distances  proportionate  to  different  weights, 
and  vertical  Hnes  (ordinates)  drawn  through  these  represent  the 
height  to  which  they  are  lifted  (see  fig.  158). 

In  the  diagram  (fig.  158)  the  figures  along  the  base  line  represent 
grammes,  and  the  figures  along  the  vertical  line  represent  milli- 
metres.    The  work  done  as  indicated  by  the  first  line  is  10  x  5  =  50 


CII.  XI.] 


MUSCULAR   WORK 


131 


gramme-millimetres,  the  next  20x6  =  120  gramme-millimetres,  and 
so  on,  while  the  last  on  the  right,  100x3  =  300  gramme-millimetres. 
It  is  thus  seen  that  the  height  of  a  muscle-curve  is  no  measure  of  the 
work  done  by  the  muscle  unless  the  weight  lifted  is  taken  into 
account  as  well. 

The  following  figures  are  taken  from  an  actual  experiment  done 
with  the  frog's  gastrocnemius  (Weber) : — 


Weight  lifted. 

Height. 

Work  (lone. 

5  grammes        27*6  millimetres 

15         .,               25-1 
25          „               11-45 
30         „                 7-3 

138  gramme-millimetres 

376 

286 

219 

Fig.  159. — Dynamometer. 


The  work  increases  with  the  weight  up  to  a  certain  maximum, 
after  which  a  diminution  occurs,  more  or  less  rapidly,  according  as 
the  muscle  is  fatigued. 

Similar  experiments  have  been  made  in  himian  beings,  weights 
being  lifted  by  the  calf  muscles,  or  elbow  muscles,  leverage  being 
allowed  for.  In  the  higher 
animals  the  energy  so  ob- 
tained compared  with  the  frog 
is  about  twice  as  great  for 
the  same  volume  of  muscular 
tissue. 

Fig.  159  represents  a  com- 
mon form  of  dynamometer  for 
clinical  use,  employed  in  test- 
ing the  muscles  of  the  arms 
and  hands.  It  is  squeezed  by  the  hand,  and  an  index  represents 
kilogrammes  of  pressure. 

The  muscle,  regarded  as  a  machine,  is  sometimes  compared  to 
artificial  machines  like  a  steam-engine.  A  steam-engine  is  supplied 
with  fuel,  the  latent  energy  of  which  is  transformed  into  work  and 
heat.  The  carbon  of  the  coal  unites  with  oxygen  to  form  carbonic 
acid,  and  it  is  in  this  process  of  combustion  or  oxidation  that  heat 
and  work  are  liberated.  Similar,  though  more  complicated,  combus- 
tions occur  in  muscle.  In  a  steam-engine  a  good  deal  of  fuel  is  con- 
sumed, but  there  is  great  economy  in  the  consumption  of  the  living 
muscular  material.  Take  the  work  done  by  a  gramme  (about  15 
grains)  of  muscle  in  raising  a  weight  of  4  grammes  to  the  height  of 
4  metres  (about  13  feet) ;  in  doing  this  work  probably  less  than  a 
thousandth  part  of  the  muscle  has  been  consumed. 

Next  let  us  consider  the  relationship  between  the  work  and  the 


132  EXTENSIBILITY,    ELASTICITY,    AND    WORK    OF    MUSCLE         [CH.  XI. 

heat  produced.  An  ordinary  locomotive  wastes  about  96  per  cent,  of 
its  available  energy  as  heat,  only  4  per  cent,  being  represented  as 
work.  In  the  best  triple-expansion  steam-engine  the  work  done  rises 
to  12-5  per  cent,  of  the  total  energy. 

In  muscle,  various  experimenters  give  different  numbers.  Thus, 
Tick  calculated  that  33  per  cent,  of  the  mechanical  energy  is  avail- 
able as  work ;  later  he  found  this  estimate  too  high,  and  stated  the 
number  as  25  ;  Chauveau  gives  12  to  15 ;  M'Kendrick  17.  Thus 
muscle  is  a  little  more  economical  that  the  best  steam-engines ;  but 
the  muscle  has  this  great  advantage  over  any  engine,  for  the  heat  it 
produces  is  not  wasted,  but  is  used  for  keeping  up  the  body  tempera- 
ture, the  fall  of  which  below  a  certain  point  would  lead  to  death  not 
only  of  the  muscles  but  of  the  body  generally. 

So  far  we  have  been  speaking  as  though  the  only  active  phase  of  muscular  con- 
traction is  the  period  of  shortening.  It  is,  however,  extremely  probable  that 
lengthening  is  also  an  active  process.  This  was  originally  mooted  by  Fick,  who 
pointed  out  that  the  fall  of  a  muscle  lever  during  the  relaxation  period  is  of  variable 
speed,  and  is  obviously  not  due  to  the  passive  elongation  of  the  muscle  by  gra\ity ; 
the  way  in  which  this  part  of  the  curve  is  varied  by  such  agencies  as  temperature, 
and  drugs  like  veratrine,  also  indicates  that  relaxation  is  an  independent  process. 

Isotonic  and  Isometric  Curves.  — U,  in  recording  the  contraction  of  a  muscle,  the 
load  is  applied  vertically  under  the  muscle,  its  pull  upon  the  muscle  varies  during 
the  successive  stages  of  a  single  contraction,  owing  to  the  inertia  of  the  load.  In 
order  to  avoid  this  variation  in  tension,  it  is  usual  to  apply  the  weight  at  a  point 
close  to  the  fulcrum  of  the  recording  lever,  so  that  when  the  lever  is  raised,  the 
weight  remains  practically  stationary,  and  thus  the  error  due  to  its  inertia  is  avoided. 
In  order  to  apply  the  necessary  tension  to  the  muscle,  the  weight  hanging  on  the 
lever  must  be  increased  in  the  ratio  of  the  distances  of  the  muscle  and  weight  from 
the  fulcrum.  A  twitch  recorded  under  such  circumstances  is  called  isotonic,  i.e.,  one 
in  w'hich  the  tension  remains  constant  throughout.  If,  on  the  other  hand,  the 
muscle  is  fixed  at  both  ends,  and  then  excited,  the  resulting  activity  expresses  itself 
in  a  phase  of  increasing  tension  followed  by  one  of  decreasing  tension.  If  the 
alterations  of  tension  are  recorded,  we  obtain  what  is  called  an  isometric  curve. 
This  curve  is  obtained  by  making  the  muscle  pull  against  a  spring  which  is  so  strong 
that  the  muscle  can  only  move  it  to  a  very  slight  extent.  This  slight  movement  is 
then  highly  magnified.  The  curve  thus  obtained  resembles  in  its  main  features  an 
isotonic  contraction,  but  its  maximum  is  reached  earlier,  and  it  returns  to  the  zero 
position  sooner.  The  flat  top  of  the  isometric  curve  described  by  the  earlier 
observers  was  due  to  the  imperfection  of  the  instruments  employed.  The  tracings 
of  muscle  curves  given  in  previous  illustrations  (see  figs.  14.")  to  147)  were  obtained 
by  the  isotonic  method,  but  it  is  probable  that  the  isometric  curve  is  a  more  faithful 
record  of  the  variations  in  the  intensity  of  the  contraction  process  than  that  yielded 
by  the  isotonic  method.  The  momentum  or  swing  of  a  light  lever  such  as  is  used 
for  obtaining  isotonic  curves  will  no  doubt  account  for  the  extra  upward  movement 
it  executes.  The  whole  matter  has  been  keenly  discussed,  and  the  foregoing  view 
is  that  expressed  bv  Kaiser.  Schenk,  on  the  other  hand,  maintains  what  appears  to 
be  an  improbable  idea  that  there  are  really  two  kinds  of  change  in  muscle,  which 
account  for  the  difference  obtained  by  the  two  methods. 


CHAPTER  XII 

THE    ELECTRICAL   PHENOMENA    OF   MUSCLE 

We  have  seen  that  the  chemical  processes  occurring  in  muscular  con- 
traction lead  to  a  transformation  of  energy  into  work  and  heat. 
These  changes  are  accompanied  by  electrical  disturbances  also. 

The  history  of  animal  electricity  forms  one  of  the  most  fascinat- 
ing of  chapters  in  physiological  discovery.  It  dates  from  1786, 
when  Galvani  made  his  first  observations.  Galvani  was  Professor  of 
Anatomy  and  Physiology  at  the  University  of  Bologna,  and  his  wife 
was  one  day  preparing  some  frog's  legs  for  dinner,  when  she  noticed 
that  the  apparently  dead  legs  became  convulsed  when  sparks  were 
emitted  from  a  frictional  electrical  machine  which  stood  by.  Galvani 
then  wished  to  try  the  effect  of  lightning  and  atmospheric  electricity 
on  animal  tissues.  So  he  hung  up  some  frogs'  legs  to  the  iron  trellis- 
work  round  the  roof  of  his  house  by  means  of  copper  hooks,  and  saw 
that  they  contracted  whenever  the  wind  blew  them  against  the  iron. 
He  imagined  this  to  be  due  to  electricity  secreted  by  the  animal 
tissues,  and  this  new  principle  was  called  Galvanism.  But  all  his 
contemporaries  did  not  agree  with  this  idea,  and  most  prominent 
among  his  opponents  was  Yolta,  Professor  of  Physics  at  another 
Italian  university,  Pavia.  He  showed  that  the  muscular  contractions 
were  not  due  to  animal  electricity,  but  to  artificial  electricity  pro- 
duced by  contact  with  different  metals. 

The  controversy  was  a  keen  and  lengthy  one,  and  was  terminated 
by  the  death  of  Galvani  in  1798.  Before  he  died,  however,  he  gave 
to  the  world  the  experiment  known  as  "  contraction  without  metals," 
which  we  shall  study  presently,  and  which  conclusively  proved  the 
existence  of  animal  electricity.  Volta,  however,  never  believed  in  it. 
In  his  hand  electricity  took  a  physical  turn,  and  the  year  after 
Galvani's  death  he  invented  the  Voltaic  pile,  the  progenitor  of  pur 
modern  batteries.  Volta  was  right  in  maintaining  that  galvanism 
can  be  produced  independently  of  animals,  but  wrong  in  denying  that 
electrical  currents  could  be  obtained  from  animal  tissues.  Galvani 
was  right  in  maintaining  the  existence  of   animal  electricity,  but 

138 


134 


mt,  ELECTRICAL  PHENOMENA   OP  MUSCLE 


[cH.  xn. 


wrong  in  supposing  that  the  contact  of  dissimilar  metals  with  tissues 
proved  his  point. 

This  conclusion  has  been  arrived  at  by  certain  new  methods  of 
investigation.  In  1820  Oersted  discovered  electro-magnetism :  that 
is,  when  a  galvanic  current  passes  along  a  wire  near  a  magnetic 
needle,  the  needle  is  deflected  one  way  or  the  other,  according  to 
the  direction  of  the  current.  This  led  to  the  invention  of  the 
astatic  needle  and  the  galvanometer,  an  instrument  by  which  very 
weak  electrical  currents  can  be  detected.  For  a  long  time  the  subject 
of  animal  electricity,  however,  fell  largely  into  disrepute,  because  of 
the  quackery  that  grew  up  around  it.  It  is  not  entirely  free  from 
this  evil  nowadays ;  but  the  scientific  investigation  of  the  subject  has 
led  to  a  considerable  increase  of  knowledge,  and  among  the  names 
of  modern  physiologists  associated  with  it  must  be  particularly 
mentioned  those  of  Du  Bois  Reymond  and  Hermann. 


i 


i 


Fig.  100. 


Before  we  can  study  these  it  is,  however,  necessary  that  we  should 
understand  the  instruments  employed. 

The  Galvanometer. — The  essential  part  of  a  galvanometer  is  a 
magnetic  needle  suspended  by  a  delicate  thread ;  a  wire  coils  round 
it ;  and  if  a  current  flows  through  the  wire,  the  needle  is  deflected. 
Suppose  a  man  to  be  swimming  with  the  current  with  his  face  to  the 
needle,  the  north-seeking  pole  is  turned  to  the  left  hand.  But  such  a 
simple  instrument  as  that  shown  in  fig.  160  would  not  detect  the  feeble 
currents  obtained  from  animal  tissues.  It  is  necessary  to  increase 
the  delicacy  of  the  apparatus,  and  this  is  done  in  several  ways.  In 
the  first  place,  the  needle  must  be  rendered  astatic,  that  is,  independent 
of  the  earth's  magnetism.  The  simplest  way  of  doing  this  is  to  fix 
two  needles  together  (as  shown  in  fig.  161),  the  north  pole  of  one 
pointing  the  same  way  as  the  south  pole  of  the  other.  The  current 
is  led  over  one  needle  and  then  over  the  other ;  the  effect  is  to  pro- 
duce a  deflection  in  each  in  the  same  direction,  and  so  the  sensitive- 
ness of  the  instrument  is  doubled.  If  now  the  wire  is  coiled  not  only 
once,  but  twice  or  more  in  the  same  position,  each  coil  has  its  effect 


CII.  XII.] 


THE    r.ALVANOMETER 


135 


on  the  ncccUos;  the  multiplication  of  the  effect  of  a  weak  current  in 
this  way  is  accomplished  in  actual  galvanometers  by  many  hundreds 
of  turns  of  fine  wire. 

Fig.  162  illustrates  the  best  galvanometer:  that  of  Sir  William 
Thomson  (now  Lord  Kelvin).  It  is  called 
a  reflecting  galvanometer,  because  the  ob- 
server does  not  actually  watch  the  moving 
needle,  but  a  spot  of  light  reflected  on  to  a 
scale  from  a  little  mirror,  which  is  attached 
to  and  moves  with  the  needle.  A  very 
small  movement  of  the  needle  is  rendered 
evident,  because  the  movement  of  the  spot 
of  light  being,  as  it  were,  at  the  end  of  a 
long  lever — namely,  the  beam  of  light, 
magnifies  it. 


Fig.  162.— Reflecting  galvanometer.  (Thomson.)  A.  The  galva- 
nometer consists  of  two  systems  of  small  astatic  needles 
suspended  by  a  fine  hair  from  a  support,  so  that  each  set 
of  needles  is  within  a  coil  of  fine  insulated  copper  wire,  that 
forming  the  lower  coil  being  wound  in  an  opposite  direction 
to  the  upper.  Attached  to  the  upper  set  of  needles  is  a 
small  mirror  about  \  inch  in  diameter ;  the  light  from  the 
lamp  at  B  is  thrown  upon  this  little  mirror,  and  is  reflected 
upon  the  scale  on  the  other  side  of  B,  not  shown  in  figure. 
The  coils  u  I  are  arranged  upon  brass  uprights,  and  their 
ends  are  carried  to  the  binding  screws.  The  whole  appar- 
atus is  placed  upon  a  vulcanite  plate  capable  of  being 
levelled  by  the  screw  supports,  and  is  covered  by  a  brass- 
bound  glass  shade,  the  cover  of  which  is  also  of  brass,  and 
supports  a  brass  rod  h,  on  which  moves  a  weak  curv'ed 
magnet  m.  0  is  the  shunt  by  means  of  which  the  amount  of 
the  current  sent  into  the  galvanometer  may  be  regulated. 
When  in  use  the  scale  is  placed  about  three  feet  from  the 
galvanometer,  which  is  arranged  east  and  west,  the  lamp  is 
lighted,  the  mirror  is  made  to  swing,  and  the  light  from  the 
lamp  is  adjusted  to  fall  upon  it,  and  it  is  then  regulated 
until  the  reflected  spot  of  light  from  it  falls  upon  the  zero 
of  the  scale.  The  wires  from  the  non-polarisable  electrodes 
touching  the  muscle  are  attached  to  the  outer  binding 
screws  of  the  galvanometer,  a  key  inter\^ening  for  short  circuiting,  or  if  a  portion  only  of  the 
current  is  to  pass  into  the  galvanometer,  the  shunt  should  intervene  as  well  with  tlie  appropriate 
plug  in.  When  a  current  passes  into  the  galvanometer  the  needles  and,  with  them,  the  mirror, 
are  turned  to  the  right  or  left  according  to  the  direction  of  the  current.  The  amount  of  the  deflec- 
tion of  the  needle  is  marked  on  the  scale  by  the  spot  of  light  travelling  along  it. 

Non-polarisable   Electrodes. — If  a  galvanometer  is  connected 


136 


THE   ELECTRICAL   PHENOMENA    OF   MUSCLE 


[CH.  xn. 


with  a  muscle  by  wires  which  touch  the  muscle,  electrical  currents 
are  obtained  in  the  circuit  which  are  set  up  by  the  contact  of  metal 
with  muscle.  The  currents  so  obtained  form  no  evidence  of  electro- 
_  motive   force   in   the   muscle   itself.     It  is 

therefore  necessary  that  the  wires  from  the 
galvanometer  should  have  interposed  be- 
tween them  and  the  muscle  some  form  of 
electrodes  which  are  non-polarisable.  Fig, 
163  shows  one  of  the  earliest  non-polaris- 
able electrodes  of  Du  Bois  Eeymond.  It 
consists  of  a  zinc  trough  on  a  vulcanite  base. 
The  inner  surface  of  the  trough  is  amalga- 
mated and  nearly  filled  with  a  saturated  so- 
lution of  zinc  sulphate.  In  the  trough  is 
placed  a  cushion  of  blotting-paper,  which 
projects  over  the  edge  of  the  trough;  on  it  there  is  a  pad  of  china 
clay  or  kaolin,  moistened  with  physiological  salt  solution  (0'8  per 
cent.  NaCl);  on  this  pad  one  end  of  the  muscle  rests.  The  binding 
screw  (k)  connects  the  instrument  to  the  galvanometer;  the  other 
end,  or  some  other  part  of  the  same  muscle,  is  connected  by  another 
non-polarisable  electrode  in  the  same  way  to  the  other  side  of  the 
galvanometer.     If  there  is  any  electrical  difference  of  potential  (that 


!.  163.— Xon-polarisable  elec- 
trode of  Du  BMs  Reymond. 
(M'Kendrick.) 


Fig.  104. — Diagram  of  Du  Buis  Reyjnond'.s  non-polarisable  electrode.s.  a,  glass  lube  liUed  with  a  satu- 
rated solution  of  zinc  sulphate,  in  the  end,  c,  of  which  is  china  clay  drawn  out  to  a  point ;  the  clay 
is  moistened  with  O'S  NaCl  solution  ;  in  the  .solution  a  well  amalgamated  zinc  rod  is  immersod  and 
connected,  by  means  of  the  wire  a,  with  the  galvanometer.  The  remainder  of  the  apparatus  is 
simply  for  convenience  of  application.  The  muscle  and  the  end  of  the  second  electrode  are  to  the 
right  of  the  tigure. 

is,  difference  in  amount  of  positive  or  negative  electricity)  between 
the  two  parts  of  the  muscle  thus  led  off,  there  will  be  a  swing  of  the 
galvanometer  needle;  the  galvanometer  detects  the  existence  and 
direction  of  any  current  that  occurs. 


CH.  XII.] 


THE   ELECTROMETER 


137 


Fig.  164  shows  a  more  convenient  form  of  non-polarisable  elec- 
trodes. 

In  order  to  measure  the  strength  (elec- 
tromotive force)  of  such  currents,  the  mere 
amount  of  swing  of  the  needle  is  only  a  very 
rough  indication,  and  in  accurate  work  the 
arrangement  shown  in  fig.  Itio  nnist  be  used. 
The  electromotive  force  is  usually  measured 
in  terms  of  a  standard  Daniell  cell.  The 
two  surfaces  of  the  nmscle  (M)  are  led  off 
to  a  galvanometer  (B) ;  the  needle  swings, 
and  then  a  fraction  of  a  Daniell  cell  is  intro- 
duced in  the  reverse  direction  so  as  to  neu- 
tralise the  muscle  current,  and  bring  back 
the  needle  to  rest.  From  the  Daniell  cell  K, 
wires  pass  to  the  ends  a,  h  of  a  long  platinum 
wire  of  high  resistance,  called  the  compen- 
sator ;  r  is  a  slider  on  this  wire  ;  o  and  c  are 
connected  to  the  galvanometer,  the  com- 
mutator C  enabling  the  observer  to  ensure 
that  the  current  from  the  Daniell  passes  in 
the  opposite  direction  to  that  produced  by 

the  muscle.     If  the  slider  c  is  placed  at  the  end  /'  of  the  compensator,  the  whole 
strength  of  the  Daniell  will  be  sent  through  the  galvanometer  and  will  more  than 


Fig.  165. — Arrangement  for  measuring  the  elec- 
tromotive force  of  muscle     (M'Kendrick.) 


I    I    I    I    I    I I I I I I 

123456789   10/ 


Fig.  166.— Lippmauu's  Capillary  Electrometer.    (After  Waller.) 

1.  Pressure  apparatus  and  microscope  on  stand  of  which  tlie  capillary  tube  is  fixed. 

2.  Capillarj-  tube,  fixed  in  outer  tube  containing  10  per  cent,  sulphuric  acid  ;  the  platinum 
wires  are  also  shown. 

3.  Capillary  and  column  of  mercury  as  seen  in  the  field  of  the  microscope. 


138 


■THE   ELECTRICAL   PHENOMENA    OF   MUSCLE  [CH.  XlL 


neutralise  the  muscle  current ;  if  (•  is  half  way  between  a  and  l>,  half  the  Daniell's 
strength  Mill  be  sent  in  ;  but  this  is  also  too  much  ;  ac  will  be  found  to  be  only 
quite  a  small  fraction  of  al>  ;  and  this  fraction  will  c-orrespond  to  a  proportional 
fraction  of  the  electromotive  force  of  the  Daniell  cell. 

Lippmann's  Capillary  Electrometer. — This  instrument  is  often  used  instead 
of  the  galvanometer.  It  consists  of  a  glass  tube  drawn  out  at  one  end  to  a  fine 
capillary  and  filled  with  mercury.     It  is  connected  to  an  apparatus  by  which  the 


Fig.  167. — Frog's  heart.  Diphasic  variation.  Simultaneous  photograph  of  a  single  beat  (upper  black 
line),  and  the  accompanying  electrical  change  indicated  by  the  level  of  the  black  area,  which  shows 
the  varying  level  of  mercury  in  a  capillary  electrometer.    (Waller.) 

pressure  on  this  mercury  can  be  lowered  or  increased.  The  open  capillary  tube  is 
enclosed  within  another  tube  filled  with  10  per  cent,  sulphuric  acid.  Two  platinum 
wires  fused  through  the  glass,  pass  respectively  into  the  mercury  and  the  acid,  and 
the  other  ends  of  these  wires  are  connected  by  electrodes  to  two  portions  of  the 
surface  of  a  muscle.  The  capillary  tube  is  observed  by  a  microscope  (see  fig.  166). 
The  surface  of  the  mercury  is  in  a  state  of  tension  which  is  easily  increased  or 
diminished  by  variations  of  electrical  potential,  and  the  mercury  moves  in  the 
direction  of  the  negative  pole. 

If  the  shadow  of  the  mercurial  column  is  thrown  upon  a  travelling  sensitive 
photographic  plate,  photographs  are  obtained  which  show  the  electrical  variations 


Fig.  l(iS.— Human  heart.  Bipliasie  variation,  ee,  and  simultaneous  cardiogram,  cg.  Time  it  is 
marked  in  iVitli  second.  The  lead-otl's  to  the  capillary  electrometer  were  from  the  mouth  to  the 
sulphuric  acid,  and  from  the  left  foot  to  the  mercury.    (Waller.) 

in  a  living  tissue  in  a  graphic  manner.  The  instrument  is  exceedingly  sensitive, 
and  its  indications  are  practically  instantaneous.  Figs.  167  and  168  indicate  the 
kind  of  result  one  obtains  with  the  heart,  which  will  be  more  fully  discussed  when 
we  are  considering  that  organ. 

The  Rheotome. — This  is  an  instrument  by  means  of  which  the  time  of  the 
occurrence  of  electrical  disturbances  in  relation  to  the  contraction  of  a  nmscle  can 
be  determined.  This  is  in  principle  effected  by  a  revolving  bar  carrying  two  contacts, 
one  in  the  primary  or  exciting  circuit  (1,  1,  1,  1),  one  in  the  galvanometer  circuit 


CH.  XII.] 


tHE  RIIlilOTOME 


130 


(2,  2,  2,  2).     The  bar  revolves,  and  by  making  or  breaking  the  primary  circuit  sends 
an  induction  shock  into  the  nerve  at  the  same  instant. 

The  muscle  is  connected  by  non-polarisable  electrodes  to  the  galvanometer  ; 
this  circuit  includes  the  brass  blocks  2,  2,  on  the  disc  over  which  the  bar  revolves, 
and  a  compensator  not  shown  in  the  figure  to  neutralise  any  current  set  up  by  the 
muscle  in  a  state  of  rest.  If  an  electrical  change  occurs  in  the  muscle,  it  is  only 
noticed  by  the  galvanometer  if  at  the  same  time  the  bar  on  its  revolution  connects 
the  two  brass  blocks  on  the  disc,  and  so  completes  the  circuit.  The  apparatus  can 
be  set  so  that  the  bar  makes  the  primary  contact  (1,  1)  simultaneously  with  the 
galvanometer  contacts,  or  that  the  galvanometer  contact  is  made,  1,  2,  3,  etc., 
hundredths  of  a  second  later  than  the  primary  contact.     If  the  two  are  closed 


Fig.  100.— Scheme  of  a  liheotome.    (Waller.) 

simultaneously  the  electrical  condition  of  the  muscle  is  tapped  off  at  the  moment  of 
excitation  ;  if  the  galvanometer  contact  is  closed  ^Iji,  j^u,  ffir,  etc.  second  after 
excitation,  the  electrical  condition  of  the  muscle  at  that  particular  instant  is  ascer- 
tained. By  a  number  of  experiments  with  different  intervals  between  the  making 
of  the  two  contacts,  one  ascertains  how  long  after  the  excitation  the  change  in  the 
electrical  condition  of  the  muscle  takes  place. 


We  can  now  pass  on  to  a  consideration  of  results. 

In  muscles  that  are  removed  from  the  body,  it  is  found  that  on 
leading  off  two  parts  of  their  surface  to  a  galvanometer,  the  galvano- 
meter needle  generally  swings.  The  most  marked  result  is  obtained 
with  a  piece  of  muscle  in  which  the  fibres  run  parallel  to  one  another, 
and  the  longitudinal  surface  is  connected  with  one  of  the  cut  ends 
by  a  wire  (2  in  fig.  170). 

On  the  course  of  the  wire  a  galvanometer  indicates  that  a  current 
flows  from  the  centre  to  the  cut  end  outside  the  muscle,  and  from 
the  cut  end  to  the  centre  inside  the  muscle.     If,  now,  the  muscle  is 


140 


THE   ELECTRICAL   PHENOMENA   OF   MUSCLE 


[CH,  XIL 


thrown   into  tetanic  contraction,  the  needle   returns  more  or  less 
completely  to  the  position  of  rest. 

Du  Bois  Reymond,  who  first  described  these  facts,  called  the  first 
current  the  current  of  rest,  and  the  second  current,  the  current  of 
action;  the  change  in  direction  is  indicated  by  the  expression 
negative  variation ;  this  means  that  the  current  of  action  is  in  the 
opposite  direction  to  the  current  of  rest,  and  therefore  lessens  or 
neutrahses  it.  The  word  negative  is  therefore  used  in  its  arithmetical, 
not  its  electrical  sense.  Du  Bois  Reymond  explained  this  by  sup- 
posing that  a  muscular  fibre  is  built  up  of  molecules,  each  of  which 
is  galvanometrically  positive   in   the  centre    and  galvanometrically 


Fig.  170. — Diagram  of  the  currents  in  a  muscle  prism.    (Du  Bois  Iteymond.) 

negative  at  both  ends.  So  when  a  muscle  is  cut  across,  a  number 
of  the  galvanometrically  negative  ends  of  these  molecules  is  exposed. 
On  contraction  the  difference  between  the  centre  and  ends  of  each 
molecule  is  lessened,  and  the  resultant  effect  on  the  whole  muscle 
(made  up  of  such  molecules)  is  similar. 

In  the  foregoing  sentence  I  have  employed  the  rather  cumbrous  adjectives, 
gaJranometriraJlif  posit'we  and  i/alvcmomefriralli/  nei/afire.  instead  of  the  terms 
positive  and  negative  which  are  usually  employed  by  physiologists. 

If  we  take  a  Daniellcell  and  connect  it  to  a  galvanometer,  the  zinc,  as  we  have 
seen,  is  the  electro-positive  element,  and  the  copper  the  electro-negative  element, 
but  the  ends  of  the  wires  which  connect  these  metals  to  the  galvanometer  have  the 
reverse  names  ;  the  kathode  or  negative  pole  is  connected  to  the  zinc  or  positive 
metal  ;  the  anode  or  positive  pole  is  connected  to  the  copper  or  negative  metal. 
The  current  enters  the  galvanometer  by  the  anode,  and  leaves  it  on  its  way 
back  to  the  zinc  by  the  kathode.  Therefore,  although  the  copper  is  electro- 
negative, it  may  be  spoken  of  as  galvanometrically  positive,  and  the  zinc  though 
electro-positive,  as  galvanometrically  negative. 

If  we  apply  this  to  a  muscle,  we  have  seen  that  the  current  flows  (in  the  wire 
that  connects  the  uninjured  longitudinal  surface  to  the  cut  end)  from  the  longi- 
tudinal surface  to  the  cut  end ;  the  longitudinal  surface  thus  corresponds  to  the 
copper  of  the  Daniellcell,  and  is  therefore  electro-negative,  though  galvanometrically 
positive  ;  similarly  the  cut  end  corresponds  to  the  zinc,  and  is  electro-positive  though 
galvanometrically  negative. 

The  omission  of  the  qualifying  prefix  to  positive  and  negative  has  led  to  a  good 
deal  of  confusion  in  physiological  writings.     A  physicist  uses  the  terms  positive  and 


CH.  XII.] 


THE    DIPHASIC    VARIATION 


141 


negative  as  meaning  electro-positive  and  electro-negative  respectively,  and  as  Dr 
Waller  has  pointed  out,  it  is  time  that  physiologists  adopted  the  same  nomenelature. 
In  what  now  follows,  I  propose  to  adopt  Dr  Waller's  suggestion. 

There  is  no  doubt  about  the  facts  as  described  by  Du  Bois 
Eeymond.  We  now  adopt,  however,  an  entirely  different  view  of 
their  meaning :  in  causing  this  revolution  of  ideas  the  principal  part 
has  been  played  by  Hermann.  Hermann  showed  that  the  so-called 
current  of  rest  does  not  exist;  it  is  really  a  current  produced  by 
injury,  and  is  now  generally  called  a  demarcation  current :  the  more 
the  ends  of  the  muscle  are  injured  the  more  positive  they  become ; 
and  when  they  are  connected  to  the  uninjured  centre,  a  current 
naturally  is  set  up  as  described  by  Du  Bois  Eeymond.  If  a  muscle 
is  at  rest  and  absolutely 
uninjured  it  is  iso-electric ; 
that  is,  it  gives  no  current  at 
all  when  two  parts  of  it  are 
connected  together  by  a  wire. 

Since  Du  Bois  Eey- 
mond's  researches,  the  elec- 
trical changes  which  occur 
during  a  single  twitch  have 
been  studied  also,  and  before 
we  can  understand  the  "  neg- 
ative variation"  of  tetanus, 
it  is  obviously  necessary  to 
consider  the  electrical  varia- 
tion which  takes  place  during  a  twitch,  for  tetanus  is  made  up  of  a 
fused  series  of  twitches. 

The  electrical  change  during  a  twitch  is  called  a  diphasic 
variation.  The  contracting  part  of  a  muscle  becomes  first  more 
positive  than  it  was  before  ;  it  then  rapidly  returns  to  its  previously 
negative  condition.  The  increase  of  positivity  indicates  a  disturb- 
ance of  the  stability  of  the  tissue  ;  the  disappearance  of  this  increased 
positivity  is  the  result  of  a  return  of  the  muscular  tissue  to  a  state  of 
rest.  If  the  muscle  is  stimulated  at  one  end,  a  wave  of  contraction 
travels  along  it  to  the  other  end.  This  muscle-wave  (see  p.  118)  may 
be  most  readily  studied  in  a  curarised  muscle,  that  is,  in  a  muscle 
which  is  physiologically  nerveless.  The  electrical  variation  travels 
at  the  same  rate  as  the  visible  contraction,  but  precedes  it. 

Suppose  two  points  {p)  and  {d)  of  the  muscle  are  connected  by 
non-polarisable  electrodes  to  a  galvanometer,  and  that  the  muscle- 
wave  is  started  by  a  single  stimulus  applied  at  A ;  as  soon  as  the 
wave  reaches  {p)  this  point  becomes  positive  to  {d),  and  therefore  a 
current  flows  from  {d)  to  {p)  through  the  galvanometer  (G).  A 
moment  later  the  two  points  are  equi-potential  and  no  current  flows ; 


Fio.  171. 


142 


THE   ELECTRICAL   PHENOMENA   OF   MUSCLE 


[CH.  XII, 


a  minute  fraction  of  a  second*  later  this  balance  is  upset,  and  now 
when  the  wave  reaches  the  point  {d),  that  point  is  positive  to  (;:>), 
and  the  galvanometer  needle  moves  in  the  opposite  direction. 

The  electrical  variations  may  also  be  investigated  by  the  capillary 
electrometer;  the  mercury  moves  first  in  one  direction,  and  then 
in  the  other.     The  deep  black  curve  in  the  next  figure  (fig.  172) 


Pio.  172. — Diphasic  curve  (black)  of  tlie  normal  sartorius.  The  grey  curve  is  tlie  monophasic  curve  of 
the  same  muscle  when  one  electrometer  contact  was  placed  on  the  injured  end.  The  two  photo- 
graphic curves  are  placed  one  over  the  other  so  that  the  beginnings  coincide.    (Burdon  Sanderson.) 

shows  the  record  obtaining  by  photographing  the  movement  of  the 
column  of  mercury  on  a  rapidly  travelling  photographic  plate. 

The  capillary  electrometer  has  the  advantage  of  giving  us  the  means  of  measur- 
ing the  time  of  onset  and  duration  of  the  electrical  disturbance,  and  experiments 
made  with  this  instrument  confirm  the  earlier  experiments  made  with  the  rheotome. 
They  show  that  the  change  only  lasts  a  few  thousandths  of  a  second,  and  is  over 
long  before  the  other  changes  in  form,  etc.,  are  completed.  Sir  J.  Burdon  Sander- 
son gives  the  following  numbers  from  experiments  with  the  frog's  gastrocnemius. 
When  the  muscle  was  excited  through  its  nerve  the  electrical  response  began  tu*ott  and 
the  change  of  form  -i-^T,w  second  after  the  stimulation  ;  the  second  phase  of  the 
electrical  response  began  ,ii^  second  after  excitation.  When  the  muscle  was 
directly  excited,  the  latent  period  was  much  shorter,  the  change  in  form  beginning 
y^u  and  the  electrical  change  in  less  than  jr,Vir  second  after  excitation. 


Fig.  173. 


If,  however,  instead  of  examining  the  electrical  change  in    the 
muscle  in  the  manner  depicted  in  fig.  171,  one  electrode  is  placed  on 

'  The  time  will  vary  with  the  distance  between  (/y)  and  ((7). 


en.  XII.] 


THE    ELECTROMETER   RECORD 


143 


the  uninjured  surface  and  the  other  on  the  cut  end  (see  fig.  173),  the 
electrical  response  is  a  different  one. 

Under  these  circumstances,  the  electrical  change  is  a  monophasic 
variation,  for  when  the  muscle-wave  reaches  {d),  this  part  of  the 
muscle,  owing  to  its  injured  state,  does  not  respond  to  the  excitatory 
condition,  and  the  electrical  response  is  also  extinguished. 

The  grey  curve  in  fig.  172  is  the  graphic  record  of  the  change  as 
revealed  by  the  capillary  electrometer.  It 
will  be  seen  that  the  ascending  limb  of  the 
curve  is  identical  in  the  two  cases,  but  that 
the  second  phase  is  absent.  From  the  point 
at  which  the  diphasic  curve  approaches  its 
culmination  the  injury  curve  diverges  from 
it,  continuing  to  ascend ;  the  line  soon  after 
becomes  horizontal,  and  then  begins  slowly 
to  decline.  This  long  tail  denotes  only  the 
gradual  disappearance  of  polarisation  of  the 
mercury  meniscus. 

The  meaning  of  such  photographic  records  becomes 
clear  by  testing  the  electrometer  with  known  differ- 
ences of  potential,  and  from  such  data  it  is  possible  to 
construct  what  may  be  called  an  interpretation  dia- 
gram (fig.  174).  The  horizontal  line  is  that  of  equi- 
potentiality  of  the  two  surfaces  of  contact  {p)  and  {d). 
The  curve  P'  expresses  the  relative  positivity  of  the 
surface  {p);  the  curve  D',  the  corresponding  relative 
positivity  of  the  surface  {(1).  S'  is  a  curve  of  which 
the  ordinates  are  the  algebraic  sums  of  the  correspond- 
ing ordinates  of  P'  and  D'.  S  is  the  photographic 
curve  which  expresses  S' ;  P  is  the  photographic  curve 
which  expresses  P'  (monophasic  variation).  The 
numbers  under  the  horizontal  line  indicate  hundredths 
of  a  second  ;  the  distance  t  t'  expresses  the  time  taken 
by  the  wave  in  its  progress  from  {p)  to  (fZ). 

From  these  considerations  we  can  now 
pass  to  study  what  occurs  when  the  muscle 
enters  into  tetanus.  The  simplest  case  is 
that  which  was  first  observed  by  Du  Bois 
Eeymond.  He  placed  his  non-polarisable 
electrodes  in  the  positions  indicated  in  fig.  173,  one  {p)  on  the  com- 
paratively uninjured  surface,  the  other  {d)  on  the  devitalised  cut 
end.  He  sent  in  the  tetanising  series  of  shocks  at  A.  The  elec- 
trical response  is  under  these  circumstances  a  summation  of  the 
individual  electrical  responses  evoked  by  instantaneous  stimuli ;  and 
the  monophasic  character  of  the  single  response  explains  easily  what 
occurs  during  tetanus ;  the  centre  of  the  muscle  becomes  more 
positive  than  it  was  before,  and  so  the  electrical  difference  of  potential 
between  the  centre  and  the  injured  end  is  lessened.     But  with  regard 


Fio.  174. — Interpretation  dia- 
gram.   (Burdon  Sanderson.) 


144  THE   ELECTRICAL   PHENOMENA   OF   MUSCLE  [CH.  XII. 

to  uninjured  muscle  the  problem  is  not  so  easy.  It  is  at  first  sight 
difficult  to  see  why  the  summed  effects  of  a  series  of  diphasic  varia- 
tions should  take  the  direction  of  the  first  phase,  as  was  found  to  be 
the  case  by  Du  Bois  Eeymond  in  experiments  with  the  frog's  gastroc- 
nemius. One  would  have  anticipated  that  "negative"  variation  in 
the  arithmetical  sense  would  be  absent  altogether,  and  this  is  the  case 
in  absolutely  normal  muscles;  Hermann  has  shown  that  it  is  so 
during  tetanus  of  the  human  forearm.  But  a  muscle  removed  from 
an  animal's  body  cannot  be  considered  absolutely  normal,  and  if  the 
two  contacts  be  placed  on  the  comparatively  uninjured  longitudinal 
surface,  as  in  fig.  171,  a  negative  variation  is  observed,  each  excitatory 
phase  becoming  weaker  as  it  progresses,  and  the  second  phase  of 
each  diphasic  effect  is  weaker  than  the  first.  The  following  figure 
illustrates  the  record  obtained  by  the  capillary  electrometer  from  an 


Fig.  175. — Electrometer  record  of  injured  sartorius  during  tetanus.    (Burden  Sanderson.) 

injured  sartorius  excited  14  times  a  second;  each  oscillation  repre- 
sents a  single  monophasic  variation.  The  individual  oscillations  can, 
however,  be  seen  when  the  excitations  follow  one  another  more 
rapidly,  even  up  to  80  or  100  per  second. 

Muscle  is  not  the  only  tissue  which  exhibits  electrical  phenomena. 
A  nerve  which  is  uninjured  is  iso-electric ;  injury  causes  a  demar- 
cation current ;  activity  is  accompanied  with  a  similar  diphasic  wave 
travelling  along  the  nerve  simultaneously  with  the  nervous  impulse. 
The  activity  of  secreting  glands,  vegetable  tissues,  retina,  etc.,  is 
accompanied  with  somewhat  similar  electrical  changes,  which  we 
shall  study  in  detail  later. 

But  the  most  prominent  exhibition  of  animal  electricity  is  seen 
in  the  electric  organs  of  electric  fishes.  In  some  of  these  fishes  the 
electric  organ  is  modified  muscle,  in  which  a  series,  as  it  were,  of 
hypertrophied  end-plates  correspond  to  the  plates  in  a  voltaic  pile. 
In  other  fishes  the  electric  organ  is  composed  of  modified  skin  glands. 


CH.  XII.] 


THE    RHEOSCOPIC    FROO 


145 


But  in  each  case  the  electric  discharge  is  the  principal  phenomenon 
that  accompanies  activity.  • 


The  Rheoscopic  Prog. 

The  electrical  changes  in  muscle  can  be  detected  not  only  by 
the  galvanometer  and  electrometer,  but  also  by  what  is  known  as 
the  physiological  rheoscope ;  this  consists  of  an  ordinary  muscle-nerve 
preparation  from  a  fresh  and  vigorous  frog.     The  nerve  is  stimulated 


Fig.  176. — Galvani's  experiment  without  metals. 

by  the  electrical  changes  occurring  in  muscles,  and  the  nervous 
impulse  so  generated  causes  a  contraction  of  the  muscles  of  the  rheo- 
scopic preparation.  The  following  are  the  principal  experiments  that 
can  be  shown  in  this  way : — 

1.  Contraction  without  metals.  If  the  nerve  of  a  nerve-muscle 
preparation  A  is  dropped  upon  another  muscle  B  (fig.  176)  or  upon 
its  own  muscle,  it  will  be  stimulated  by  the  injury  current  of  the 
muscle  on  which  it  is  dropped,  and  this  leads  to  a  contraction  of  the 
muscle  (A)  which  it  supplies.     The  experiment  succeeds  best  if  the 


Fio.  177. — Secondary  contraction.     (After  Waller.) 


nerve  is  dropped  across  a  longitudinal  surface  and  a  freshly  made 
transverse  section. 

2.  Secondary  contraction.  This  is  caused  by  the  current  of 
action.  If,  while  the  nerve  of  A  is  resting  on  the  muscle  B  (fig. 
177),  the  latter  is  made  to  contract  by  the  stimulation  of  its 
nerve,  the  nerve  of  A  is  stimulated  by  the  electrical  variation 
which  accompanies  the  contraction  of  the  muscle  B,  and  so  a  con- 
traction of  muscle  A  is  produced.  This  is  called  secondary  con- 
traction.    It  may  be  either  a  secondary  twitch  or  secondary  tetanus, 

K 


146  THE   ELECTRICAL   PHENOMENA   OF   MUSCLE  [CH.  XII. 

according  as  to  whether  the  muscle  B  is  made  to  contract  singly  or 

tetanically. 

3.  Secondary  contraction  from  the  heart.  If  an  excised  but  still 
beating  frog's  heart  is  used  instead  of  muscle  B,  and  the  nerve  of 
A  laid  across  it,  each  heart's  beat,  accompanied  as  it  is  by  an  electrical 
variation,  will  stimulate  the  nerve  and  cause  a  twitch  in  the  rheo- 
scopic  muscle  A. 


CHAPTEE  XIII 

THERMAL   AND   CHEMICAL   CHANGES    IN    MUSCLE 

In  muscular  contraction  there  is  a  transformation  of  the  potential 
energy  of  chemical  affinity  into  other  forms  of  energy,  especially 
molar  motion  and  heat.  Heat  is  a  form  of  motion  in  which  there  is 
movement  of  molecules ;  in  molar  motion  there  is  movement  of 
masses.  The  fact  that  when  a  blacksmith  hammers  a  piece  of  iron 
it  becomes  hot  is  a  familiar  illustration  of  the  transformation  of  one 
mode  of  movement  into  the  other.  Heat  is  measured  in  heat-units  or 
calories.  One  calorie  is  the  energy  required  to  raise  the  temperature 
of  1  gramme  of  water  from  0"  to  V  C. ;  and  this  in  terms  of  work  is 
equal  to  425"5  gramme-metres,  that  is,  the  energy  required  to  raise 
the  weight  of  425 "5  grammes  to  the  height  of  1  metre. 

A  muscle  when  uncontracted  is  nevertheless  not  at  absolute  rest. 
We  have  already  seen  that  it  possesses  tonus  or  tone ;  it  also  possesses 
what  we  may  call  chemical  tone ;  that  is,  chemical  changes  are 
occurring  in  it,  and  consequently  heat  is  being  produced.  But  when 
it  contracts,  the  liberation  of  energy  is  increased ;  work  is  done,  and 
more  heat  is  produced;  the  heat  produced  represents  more  of  the 
energy  than  the  work  done.  The  more  resistance  that  is  offered  to  a 
muscular  contraction,  the  more  is  the  work  done  relatively  increased 
and  the  heat  diminished.  The  amount  of  heat  produced  is  increased 
by  increasing  the  tension  of  the  muscle.  It  diminishes  as  fatigue 
comes  on.  On  increasing  the  strength  of  the  stimulus  the  amount 
of  heat  increases  faster,  proportionately,  than  the  work  performed. 

If  work  is  done  by  a  few  large  contractions,  more  heat  is  produced 
than  if  the  same  work  is  done  by  a  larger  number  of  smaller  contrac- 
tions ;  that  is,  more  chemical  decomposition  occurs,  and  fatigue 
ensues  more  rapidly  in  the  first  case.  This  fact  is  within  the  personal 
experience  of  everyone.  If  one  ascends  a  tower,  the  work  done  is 
the  raising  of  the  weight  of  one's  body  to  the  top  of  the  tower.  If 
the  staircase  in  the  tower  has  a  gentle  slope,  each  step  being  low, 
far  less  fatigue  is  experienced  than  if  one  ascended  to  the  same  height 
by  a  smaller  number  of  steeper  steps. 


148  THERMAL   AND    CHEMICAL   CHANGES    IN    MUSCLE        [CH.  XIIL 

On  a  cold  day  one  keeps  oneself  warm  by  muscular  exercise ;  this 
common  fact  is  confirmed  by  more  accurate  experiments  on  isolated 
muscles,  the  heat  produced  being  sufficient  to  raise  temporarily  the 
temperature  of  the  muscle.  This  can  be  shown  in  large  animals  by  in- 
serting a  thermometer  between  the  thigh  muscles  and  stimulating  the 
spinal  cord.    The  rise  of  temperature  may  amount  to  several  degrees. 

In  the  case  of  frog's  muscles,  Helmholtz  found  that,  after  tetanis- 
ing  them  for  two  or  three  minutes,  the  temperature  rises  014'  to 
018°  C. ;  and  for  each  single  twitch  Heidenhain  gives  a  rise  of 
temperature  of  from  0-001°  to  0005°  C. 

For  the  detection  of  such  small  rises  in  temperature,  a  themiopile, 
and  not  a  thermometer,  is  employed. 

A  thermopile  consists  of  a  junction  of  two  different  metals;  the 
metals  are  connected  by  wires  to  a  galvanometer.  If  the  junction 
is  heated  an  electrical  current  passes  round  the  circuit,  and  is 
detected  by  the  galvanometer.     The   metals  usually  employed  are 


B->A  A^B  B-^A        A<-^^B  Q-^-^-^A 

1  Couple.  2  Couples.  3  Couples. 

Flu.  ITS.— Scheme  of  thermo-electric  couples.    (After  Waller.) 

iron  and  German  silver,  or  antimony  and  bismuth.  If  the  number 
of  couples  in  the  circuit  is  increased,  each  is  affected  in  the  same 
way,  and  thus  the  electrical  current  is  increased  through  the  galvano- 
meter. The  arrangement  is  shown  in  the  fig.  178,  which  also  indicates 
the  direction  of  the  currents  produced,  the  metals  employed  being 
antimony  and  bismuth.  By  using  16  couples  of  this  kind  Helmholtz 
was  able  to  detect  a  change  of  xoVo  of  ^  degree  Centigrade. 

Within  certain  limits,  the  strength  of  the  current  is  directly 
proportional  to  the  rise  of  temperatm-e  at  the  junction. 

If  two  couples  are  in  circuit,  as  shown  in  the  second  diagram,  and 
they  are  heated  equally,  no  current  will  pass  through  the  galvano- 
meter, the  current  through  one  couple  being  opposed  by  the  current 
through  the  other.  But  if  the  two  couples  are  heated  unequally,  the 
direction  of  swing  of  the  galvanometer  needle  indicates  which  is 
the  warmer.  To  apply  this  to  the  frog's  gastrocnemius,  plunge  several 
needle-shaped  couples  (diagram  3)  into  a  frog's  gastrocnemius  of  one 
side  and  the  same  number  of  couples  into  the  gastrocnemius  of  the 
other  side,  and  then  excite  first  one  then  the  other  sciatic  nerve ; 
a  deflection  of  the  galvanometer  will  be  observed  first  in  one,  then  in 
the  other  direction,  indicating  the  production  of  heat  first  on  one 
side,  then  on  the  other. 


CIL  XIII.]  THE   GASES    OF   MUSCLE  149 

Chemical  Changes  in  Muscles. 

The  chemical  cliaiiges  which  are  normally  occurring  hi  a  resting 
muscle  are  much  increased  when  it  contracts.  Waste  products  of 
oxidation  are  discharged,  and  the  most  abundant  of  these  is  carbonic 
acid.  Sarco-lactic  acid  is  also  produced,  and  the  alkaline  reaction  of 
a  normal  muscle  is  replaced  by  an  acid  one.  The  muscles  of  animals 
hunted  to  death  are  acid  ;  the  acid  reaction  to  litmus  paper  of  a  frog's 
gastrocnemius  can  be  readily  shown  after  it  has  been  tetanised  for  10 
to  15  minutes. 

When  a  muscle  contracts,  the  quantity  of  oxygen  consumed  is 
increased,  and  at  the  same  time  there  is  a  corresponding  increase  in 
the  discharge  of  carbonic  acid.  This  will  be  illustrated  by  numerical 
data  when  later  we  are  studying  tissue  respiration,  and  the  way  in 
which  the  blood  gases  may  be  obtained  and  analysed  (Chapter  XXIV.) 

For  a  certain  time  after  its  removal  from  the  body,  an  excised 
muscle  can  be  made  to  contract  and  give  off  oxidation  products  like 
carbonic  acid  in  an  atmosphere  containing  no  oxygen  at  all.  The 
oxygen  used  is  thus  stored  up  in  the  muscle  previously.  The  oxygen 
is  not,  however,  present  in  the  free  state,  for  no  oxygen  can  be 
detected  in  the  gases  obtained  from  muscles  by  means  of  an  air- 
pump.  Excised  muscles,  however,  must  be  regarded  as  partially 
asphyxiated,  for  their  individual  fibres  are  largely  cut  off  from  that 
ready  supply  of  oxygen  which  normally  reaches  them  by  the  blood. 
During  life  (and  the  living  condition  can  be  imitated  by  placing  an 
excised  muscle  in  an  atmosphere  of  pure  oxygen)  the  muscular 
substance  breaks  down  into  a  number  of  somewhat  simpler  bodies ; 
one  of  these  is  carbonic  acid.  The  others,  however,  or  some  of  them, 
are  at  once  built  up  again  with  the  inclusion  of  oxygen  and  some 
carbon-containing  substance,  perhaps  sugar,  into  living  material. 
The  muscle,  therefore,  does  not  contain  any  of  the  bye-products  of 
its  own  metabolism.  In  excised  muscle,  when  the  oxygen  supply  is 
deficient  the  bye-products  accumulate,  as  a  result  of  which  very 
striking  alterations  take  place.  (1)  The  reaction  of  the  muscle 
changes  and  the  phenomena  of  fatigue  and  functional  death  set  in. 
(2)  The  proteins  become  coagulated,  and  this  is  the  physical  basis  of 
rif/oi'  mortis. 

There  are  other  chemical  changes  in  the  muscle  when  it  contracts, 
for  instance,  a  change  of  glycogen  into  sugar.  The  question  whether 
nitrogenous  waste  is  increased  during  muscular  activity  is  a  much 
debated  one,  and  we  shall  return  to  it  when  we  are  studying  the 
urine.  What  is  certain  is  that  the  increased  consumption  of  carbon 
(possibly  in  large  measure  derived  from  the  carbohydrate  stored  in 
the  muscle)  is  a  much  more  marked  and  immediate  feature  than  an 
increase  in  the  consumption  of  nitrogen. 


150  THERMAL   AND   CHEMICAL   CHANGES    IN   MUSCLE        [CH.  XIH. 

Fatigue. 

If  the  nerve  of  a  nerve-muscle  preparation  is  continually  stimu- 
lated, the  muscular  contractions  become  more  prolonged  (see  p.  117), 
smaller  in  extent,  and  finally  cease  altogether. 

The  muscle  is  said  to  be  fatigued :  this  is  due  to  the  consump- 
tion of  the  substances  available  for  the  supply  of  energy  in  the 
muscle,  but  more  particularly  to  the  accumulation  of  waste  products 
of  contraction ;  of  these,  sarco-lactic  acid  is  probably  an  important 
one.  Fatigue  may  be  artificially  induced  in  a  muscle  by  feeding  it  on 
a  weak  solution  of  lactic  acid,  and  then  removed  by  washing  out  the 
muscle  with  salt  solution  containing  a  minute  trace  of  an  alkali.  If 
the  muscle  is  left  to  itself  in  the  body,  the  blood-stream  washes  away 
the  accumulation  of  acid  products,  and  fatigue  passes  off. 

The  question  next  presents  itself,  where  is  the  seat  of  fatigue  ? 
Is  it  in  the  nerve,  the  muscle,  or  the  end-plates  ?  If,  after  fatigue  has 
ensued  and  excitation  of  the  nerve  of  the  preparation  produces  no 
more  contractions,  the  muscle  is  itself  stimulated,  it  contracts ;  this 
shows  it  is  still  irritable,  and,  therefore,  not  to  any  great  extent  the 
seat  of  fatigue. 

If  an  animal  is  poisoned  with  curare,  and  it  is  kept  alive  by  arti- 
ficial respiration,  excitation  of  a  motor  nerve  produces  no  contraction 
of  the  muscles  it  supplies.  If  one  goes  on  stimulating  the  nerve  for 
many  hours,  until  the  effect  of  the  curare  has  disappeared,  the  block 
at  the  end-plates*  is  removed  and  the  muscles  contract:  the  seat  of 
exhaustion  is  therefore  not  in  the  nerves. 

By  a  process  of  exclusion  it  has  thus  been  localised  in  the  nerve- 
endings. 

When  the  muscle  is  fatigued  in  the  intact  body,  there  is,  however, 
another  factor  to  be  considered  beyond  the  mere  local  poisoning  of 
the  end-plates.  This  is  the  effect  of  the  products  of  contraction 
passing  into  the  circulation  and  poisoning  the  central  nervous  system. 
It  is  a  matter  of  common  experience  that  one's  mental  state  influ- 
ences markedly  the  onset  of  fatigue  and  the  amount  of  muscular 
work  one  can  do.  This  aspect  of  the  question  has  been  specially 
studied  by  Waller  and  by  Mosso.  Mosso  devised  an  instrument 
called  the  ergograph,  which  is  a  modification  of  Waller's  dynamograph 
invented  many  years  previously.  The  arm,  hand,  and  all  the  fingers 
but  one  are  fixed  in  a  suitable  holder ;  the  free  finger  repeatedly  lifts 
a  weight  over  a  pulley,  and  the  height  to  which  it  is  raised  is  regis- 
tered by  a  marker  on  a  blackened  surface. 

By  the  use  of  this  and  similar  instruments  it  has  been  shown 
that  the  state  of  the  brain  and  central  nervous  system  generally  is  a 

*  Another  convenient  block  which  is  sometimes  used  is  to  throw  a  constant 
current  into  the  nerve  between  the  point  of  excitation  and  the  muscles.  This  pre- 
vents the  nerve  impulses  from  reaching  the  muscles. 


CH.  XIII.]  FATIGUE  151 

most  iiupurlant  factor  in  fatigue,  and  that  the  fatigue  products  pro- 
duced in  the  muscles  during  work  cause  most  of  their  injurious 
effects  by  acting  on  the  central  nervous  system  and  diminishing  its 
power  of  sending  out  impulses. 

One  of  the  most  striking  of  Mosso's  experiments  illustrates  in  a 
very  forcible  manner  the  fact  that  the  central  nervous  system  is  more 
easily  fatigued  than  the  nerve-endings  in  muscle.  A  person  goes  on 
lifting  the  weight  until,  under  the  influence  of  the  will,  he  is  unable 
to  raise  it  any  more.  If  then  without  waiting  for  fatigue  to  pass  off, 
the  nerves  going  to  the  finger  muscles  are  stimidated  artificially  by 
induction  shocks,  they  once  more  enter  into  vigorous  contraction. 

Mosso  has  also  shown  that  the  introduction  of  the  blood  of  a 
fatigued  animal  into  the  circulation  of  a  normal  one  will  give  rise  in 
the  latter  to  all  the  symptoms  of  fatigue.  The  blood  of  the  fatigued 
animal  contains  the  products  of  activity  of  its  muscles,  but  still 
remains  alkaline ;  the  poisonous  substance  cannot  therefore  be  free 
lactic  acid ;  and  lactates  do  not  produce  the  effect.  Lactic  acid  is 
doubtless  one  only  of  the  products  of  muscular  activity ;  we  have  at 
present  no  accurate  knowledge  of  the  chemical  nature  of  the  others. 

The  statement  that  nerves  are  not  fatiguable,  does  not  mean  that  the  nerve 
fibres  undergo  no  metabolic  changes  when  transmitting  a  nerve  impulse,  but  that 
the  change  is  so  slight,  and  the  possibilities  of  repair  so  great,  that  fatigue  in  the 
usual  acceptation  of  the  term  cannot  be  demonstrated.  Waller  made  the  interesting 
but  tentative  suggestion  that  the  medullary  sheath  is  a  great  factor  in  repair,  or,  in 
his  own  words,  "  the  active  grey  axis  both  lays  down  and  uses  up  its  own  fatty 
sheath,  and  it  is  inexhaustible  not  because  there  is  little  or  no  expenditure,  but 
because  there  is  an  ample  re-supply." 

A  year  or  two  after  these  words  were  written.  Miss  Sowton,  at  Dr  Waller's 
suggestion,  undertook  a  piece  of  work  in  order  to  test  the  truth  of  this  hypothesis. 
If  the  absence  of  fatigue  is  due  to  the  presence  of  the  fatty  sheath,  fatigue  ought 
to  be  demonstrable  in  nerve-fibres  in  which  the  fatty  sheath  is  absent.  She 
selected  the  olfactory  nerve  of  the  pike  as  the  non-medullated  nerve  with  which  to 
try  the  experiment,  and  her  results  confirmed  Dr  Waller's  expectation ;  the 
galvanometric  replies  of  the  nerve  became  somewhat  feebler  after  repeated  stimu- 
lation. 

It  appeared  to  me  advisable  to  test  the  question  in  another  way.  The  splenic 
nerves  seemed  to  be  the  most  convenient  large  bundles  of  non-medullated  fibres 
for  the  purpose.  Dr  T.  G.  Brodie  was  associated  with  me  in  carrying  out  the  in- 
vestigation. A  dog  is  anaesthetised,  the  abdomen  opened,  the  spleen  exposed,  and 
the  splenic  nerves  which  lie  by  the  side  of  the  main  splenic  artery  are  laid  bare. 
It  is  quite  easy  to  dissect  out  a  length  of  nerve  sufficient  for  the  experiment  (H  to  2 
inches).  The"  nerve  is  then  cut  as  far  from  the  spleen  as  possible,  and  the  spleen 
is  enclosed  in  an  air  oncometer  connected  to  the  bellows  volume  recorder  invented 
by  Dr  Brodie.  On  stimulating  the  nerve  with  a  weak  faradic  current  the  organ 
contracts,  and  the  recording  lever  falls.  The  diminution  of  the  size  of  the  spleen 
is  quite  visible  to  the  naked  eye,  however,  without  the  use  of  any  apparatus.  The 
next  thing  to  do  is  to  put  a  block  on  the  course  of  the  nerve,  which  will  prevent 
the  nerve  impulses  from  reaching  the  spleen.  Here  we  met  with  some  difficulty. 
Curare  and  atropine  are  both  ineffective :  the  constant  current  has  a  great  dis- 
advantage ;  non-medullated  nerves  are  so  much  affected  that  very  feeble  constant 
currents  will  completely  block  the  transmission  of  impulses,  and  not  only  that,  but 
the  nerve  remains  blocked  after  the  current  is  removed.  After  the  current  has 
been  allowed  to  flow  for  two  minutes  the  nerve  remains  impassable  to  nerve 


152 


THERMAL   AND   CHEMICAL   CHANGES    IN    MUSCLE       [CH.  XIII 


impulses  for  an  hour  or  more,  and  then  slowly  recovers.  If,  therefore,  faradic 
excitation  of  the  nerve  is  kept  up  all  this  time  and  fails  to  excite  the  contraction  of 
the  spleen  after  the  removal  of  the  constant  current,  it  is  impossible  to  say  whether 


c 


z> 


Fio.  179.— Apparatus  for  obtaining  splenic  curves,  s,  spleen  in  oncometer  o,  which  is  made  of  gutta. 
percha,  and  covered  with  a  glass  plate  (g.p.)  luted  on  with  vaseline,  ii  is  the  splenic  mesentery 
containing  vessels  and  nerves  ;  this  passes  through  a  slit  in  the  base  of  the  oncometer  which  is  made 
air-tight  with  vaseline.  The  oncometer  is  connected  to  the  flexible  bellows  (b)  by  the  india-rubber 
tube  (r),  the  side  tube  (t)  being  closed  during  an  experiment  by  a  piece  of  glass  rod.  The  recording 
lever  (l)  writes  on  a  revolving  drum. 

this  is  due  to  fatigue  of  the  nerve-fibres  on  the  proximal  side  of  the  block,  or  whether 

it  may  not  be  due  to  the  fact  that  the  block  created  by  the  constant  current  is  still 

effective. 

Our  best  results  were  obtained  by  using  cold  instead  of  a  constant  current  as 

our  blocking  agent. 

Fig.  179  is  an  outline  drawing  of  the  apparatus  used,  and  fig.  180  shows  the 
arrangement  adopted  in  connection  with  the  nerve. 
The  nerve  (n)  rests  on  a  metal  tube  (t)  through  which 
water  can  be  kept  flowing,  e  is  the  situation  of  the 
electrodes.  If  the  nerve  is  excited,  the  spleen  con- 
tracts, and  the  recording  lever  (in  fig.  179)  falls.  If 
now  brine  at  0  to  2°  C.  is  kept  flowing  through  t,  the 
nerve  impulses  are  blocked  by  the  cold,  and  cannot 
reach  the  spleen.  Immediately  the  cold  brine  is  re- 
placed by  warm  water  at  30°  C,  the  nerve  again  becomes 
passable  by  nerve  impulses,  and  the  spleen  contracts 
once  more. 

If  while  the  fluid  in  t  is  kept  at  the  low  tempera- 
ture mentioned,  the  nerve  is  being  excited  with  strong 
induction  shocks  all  the  time,  the  spleen  remains  irre- 
sponsive ;  the  nerve  impulses  are  able  to  reach  t  but 
not  to  pass  it.  If  then  warm  water  is  passed  through  r, 
and  the  block  produced  by  the  cold  is  thus  removed, 
and  the  spleen  continues  to  be  irresponsive,  we  have  a 
proof  that  the  piece  of  nerve  between  e  and  r  has  been 
fatigued.  But  our  experiments  have  shown  us  that 
non-raedullated  nerve  is  just  as  difficult  to  fatigue  as 
meduUated   nerve.     Even   after   six   hours'  continuous 

excitation  the  nerve  is  just  as  excitable  as  it  was  at  the  start,  and  a  full  splenic 

contraction  is  obtained  when  the  cold  block  is  removed. 

We  have  made  similar  experiments  with  vaso-motor  nerves,  such  as  the  cervical 

sympathetic  nerve  in  the  rabbit,  the  splanchnic  nerve  of  the  dog,  and  the  sciatic 

nerve  in  a  curarised  dog,  and  have  obtained  corresponding  results.     This  confirms 


Fig.  180. — Arrangement  of  ap- 
paratus in  connection  with 
the  splenic  nerve,  s  is  the 
spleen,  and  n  the  main 
bundle  of  nerves.  The 
nerve  rests  on  the  metal 
tube  (T)through  which  fluid 
at  the  required  temperature 
is  Icept  flowing,  and  on  the 
electrodes  (e)  which  come 
from  the  secondary  coil  of 
an  inductorium. 


CH.  XIIl]  RIGOR   MORTIS  153 

tlu'  work  previously  piiblislu-d  by  Eve.  Eve  excitt'd  the  cervical  synipatlietic  for 
twelve  hours,  and  found  no  loss  of  excitability  at  the  end  of  that  time.  Eve 
stimulated  the  nerve  l)elow  the  upper  cervical  gaufjlion,  and  the  main  object  of  his 
work  was  to  ascertain  whether  any  iiistoloj^ical  eviilence  of  fatigue  could  be  found 
in  the  cells  of  the  ganglion.  The  only  change  he  could  find  there  was  a  somewhat 
diffuse  staining  of  the  cells  by  methylene  blue,  which  he  attributes  to  the  formation 
of  acid  substances  in  the  cells.  A  blue  stain  of  similar  appearance  may  be  induced 
in  the  motor  cells  of  the  spinal  cord,  after  exhaustion  is  produced  in  them  by  giving 
strychnine.  In  such  experiments  the  spinal  cord  becomes  as  a  rule  distinctly  acid 
to  litmus  paper.  Max  Verworn  has  more  recently  employed  strychnine  as  a  means 
of  producing  fatigue.  He  considers  that  the  only  specific  effect  of  this  alkaloid  is 
increase  of  reflex  activity,  and  he  attributes  the  subsequent  paralysis  to  vascular 
conditions  and  the  accumulation  of  fatigue  products,  among  which  he  places  carbon 
dioxide  in  the  first  rank.  Eve,  on  the  contrary,  did  not  find  that  carbonic  acid 
alone  produces  the  effects. 

We  must  conclude  from  such  experiments  that  Dr  Waller's  theory  is  unproved, 
and  that  while  fatigue  is  demonstrable  in  nerve-cells,  it  has  never  yet  been  shown 
to  occur  in  nerve-fibres  of  either  the  meduUated  or  non-meduUated  variety. 

In  carrying  out  these  experiments  we  noticed  that  though  no  functional  fatigue 
can  be  demonstrated,  there  is  noticeable,  especially  in  vaso-motor  nerves,  a 
phenomenon  which  Howell  terms  stimulatiun  fathfue  ;  this  means  that  the  actual 
spot  of  nerve  stimulated  becomes  after  a  time  less  excitable,  and  finally,  inexcitable, 
though  it  will  still  transmit  impulses,  if  the  excitation  is  applied  above  the  spot 
originally  stimulated.  We  think  that  the  use  of  the  terra  "fatigue"  in  this  con- 
nection is  a  mistake ;  the  prolonged  electrical  excitation  causes  injurious  polarisa- 
tion (due  to  electrolytic  changes)  of  the  nerve,  which  renders  it  less  excitable.  This 
view  has  been  confirmed  by  Prof.  Gotch  by  means  of  experiments  with  the  capillary 
electrometer.  This  so-called  "stimulation  fatigue"  was  not  excluded  in  Miss 
Sowton's  experiments,  and  will  possibly  explain  her  results.  The  splenic  nerves, 
curiously  enough,  do  not  exhibit  this  phenomenon  in  any  marked  degree,  and  so 
were  peculiarly  well  adapted  to  test  the  question  of  functional  fatigue.  On  a  priori 
grounds  we  should  hardly  expect  non-medullated  nerves  to  be  peculiarly  susceptible 
of  real  fatigue,  when  one  considers  how  many  of  them,  like  the  vasoconstrictors, 
are  in  constant  action  throughout  life. 

Rigor  Mortis. 

After  death,  the  muscles  gradually  lose  their  irritability  and  pass 
into  a  contracted  condition.  This  affects  all  the  muscles  of  the  body, 
and  usually  fixes  it  in  the  natural  posture  of  equilibrium  or  rest. 
The  general  stiffening  thus  produced  constitutes  rigor  mortis  or  post- 
mortem rigidity. 

The  cause  of  rigor  is  the  coagulation  of  the  muscle-plasma,  which 
is  more  fully  described  in  the  next  section.  This  coagulation  results 
in  the  formation  of  myosin,  and  is  gradual  in  onset.  Simultaneously 
the  muscles  (a)  become  shortened  and  opaque,  (b)  heat  is  evolved,  (c) 
they  give  off  carbonic  acid,  and  (d)  become  acid  in  reaction ;  this  is  due 
in  part  to  the  formation  of  sarco-lactic  acid,  and  in  part  to  the  forma- 
tion of  acid  phosphates. 

After  a  varying  interval,  the  rigor  passes  off,  and  the  muscles  are 
once  more  relaxed.  This  sometimes  occurs  too  quickly  to  be  caused 
by  putrefaction,  and  the  suggestion  that  in  such  cases  at  any  rate 
such  relaxation  is  due  to  a  ferment-action  is  very  plausible.  It  is 
known  that  a  pepsin -like  or  proteolytic  ferment  is  present  in  muscle, 


154  THERMAL   AND    CHEMICAL   CHANGES    IN   MUSCLE       [CH.  XIII. 

as  in  many  other  animal  tissues,  kidney,  spleen,  etc.  (Hedin),  and 
that  such  ferments  act  best  in  an  acid  medium.  The  conditions  for 
the  solution  of  the  coagulated  myosin  are  therefore  present,  as  the 
reaction  of  rigored  muscle  is  acid. 

Order  of  Occurrence. — The  muscles  are  not  affected  simultaneously 
by  rigor  mortis.  It  affects  the  neck  and  lower  jaw  first ;  next,  the 
upper  extremities,  extending  from  above  downwards;  and  lastly, 
reaches  the  lower  limbs ;  in  some  rare  instances  it  affects  the  lower 
extremities  before,  or  simultaneously  with,  the  upper  extremities. 
It  usually  ceases  in  the  order  in  which  it  begins :  first  at  the  head, 
then  in  the  upper  extremities,  and  lastly  in  the  lower  extremities. 
It  seldom  commences  earlier  than  ten  minutes,  or  later  than  seven 
hours  after  death ;  and  its  duration  is  greater  in  proportion  to  the 
lateness  of  its  accession. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous 
existence  of  paralysis  in  a  part,  provided  the  paralysis  has  not  been 
attended  with  very  imperfect  nutrition  of  the  muscular  tissue. 

In  some  cases  of  sudden  death  from  lightning,  violent  injuries,  or  paroxysms  of 
passion,  rigor  mortis  has  been  said  not  to  occur  at  all ;  but  this  is  not  always  the 
case.  It  may,  indeed,  be  doubted  whether  there  is  really  a  complete  absence  of 
the  post-mortem  rigidity  in  any  such  cases  ;  for  the  experiments  of  Brown-Sequard 
make  it  probable  that  the  rigidity  may  supervene  immediately  after  death,  and 
then  pass  away  with  such  rapidity  as  to  be  scarcely  observable. 

Chemical  Composition  of  Muscle. 

The  phenomena  of  rigor  mortis  will  be  more  intelligible  if  we 
consider  the  chemical  composition  of  muscle. 

The  connective  tissue  of  muscle  resembles  connective  tissue  else- 
where; the  gelatin  and  fat  obtained  in  analyses  of  muscle  are 
derived  from  this  tissue.  The  sarcolemma  is  composed  of  a  substance 
which  resembles  elastin  in  its  solubilities. 

The  contractile  substance  within  the  muscular  fibres  is,  during 
life,  of  semi-liquid  consistency,  and  contains  a  large  percentage  of 
proteins  and  smaller  quantities  of  extractives  and  inorganic  salts. 
By  the  use  of  a  press  this  substance  can  be  squeezed  out  of  perfectly 
fresh  muscles,  and  it  is  then  called  the  muscle-plasma. 

After  death,  muscle-plasma,  like  blood-plasma,  coagulates  (thus 
causing  the  stiffening  known  as  rigor  mortis).  The  solid  clot  corre- 
sponding to  the  fibrin  from  blood-plasma  is  called  myosin,  and  the 
liquid  residue  is  called  the  muscle-serum. 

Pursuing  the  analogy  further,  it  is  found  that  the  coagulation  of 
both  muscle-plasma  and  blood-plasma  can  be  prevented  by  cold,  by 
strong  solutions  of  neutral  salts,  and  by  potassium  oxalate,  which 
precipitates,  as  the  insoluble  oxalate  of  calcium,  the  lime  salts 
essential  for  the  coagulation  process.     In  both  cases  the  clotting  is 


CH.  XIII.] 


CHEMICAL   COMPOSITION   OF   MUSCLE 


155 


produced  by  the  action  of  a  ferment  developed  after  death.  Tn  both 
cases  the  precursor  of  the  solid  clot  is  a  protein  of  the  globulin  class 
which  previously  existed  in  solution. 

Fibrin  in  the  blood-clot  is  formed  from  the  previously  soluble 
fibrinogen  of  the  blood-plasma.  Myosin  in  the  muscle-clot  is  formed 
from  the  previously  soluble  myosinogcn  *  of  the  muscle-plasma.  When 
the  blood-clot  contracts  it  squeezes  out  blood-serum ;  when  the 
muscle-clot  contracts  it  squeezes  out  muscle-serum.  The  muscle- 
serum  contains  small  quantities  of  albuminous  material,  together  with 
the  extractives  and  salts  of  the  muscle.  The  origin  of  the  sarco- 
lactic  acid  is  a  controversial  question  :  some  believe  it  originates  from 
the  carbohydrate  (glycogen  and  sugar) ;  others  think  it  comes  from 
the  protein  molecules  in  the  muscle. 

The  general  composition  of  muscular  tissue  is  the  following : — 

per  cent. 


Water      . 

.        75 

Solids 

25 

Proteins  . 

18 

Gelatin     . 

Fat           .             .             . 

• )  2  to  5 

Extractives 

0-5 

Inorganic  salts    . 

.    1  to  2 

The  proteins,  as  already  stated,  chiefly  pass  into  the  clot :  very 
little  is  found  in  the  muscle-serum. 

The  extractives  comprise  a  large  number  of  organic  substances, 
all  present  in  small  quantities,  some  of  which  are  nitrogenous,  like 
creatine,  creatinine,  xanthine,  and  hypoxanthine :  the  rest  are  non- 
nitrogenous — namely,  fats,  glycogen,  sugar,  inosite,  and  the  variety 
of  lactic  acid  known  as  sarco-lactic  acid.  The  inorganic  salts  are 
chiefly  salts  of  potassium,  especially  potassium  phosphate. 

The  condition  of  dead  muscle  reminds  one  somewhat  of  contracted 
muscle.  Indeed,  the  similarity  is  so  striking  that  Hermann  has 
propounded  the  idea  that  contracted  muscle  is  muscle  on  the  road  to 
death,  the  differences  between  the  two  being  of  degree  only.  He 
considers  that,  on  contraction,  a  hypothetical  material  termed  inogen 
is  broken  up  into  carbonic  acid,  sarco-lactic  acid,  and  myosin;  on 
death  the  same  change  occurs,  only  to  a  much  more  marked  extent. 

This  idea  is  a  far-fetched  one,  but  it  is  a  useful  reminder  of  the 
similarities  of  the  two  cases.  In  chemical  condition,  contracted  and 
dead  muscle  are  alike,  so  far  as  the  formation  of  acid  products  is 
concerned ;  there  is,  however,  no  evidence  of  any  formation  of  a 
muscle-clot  (myosin)  during  the  contraction  of  living  muscle,  as 
there  is  in  dead  muscle.  Then  heat  is  produced  in  both  cases, 
and  in  both  cases  also  the  muscle  is  electro-positive  to  uncontracted 
muscle. 

*  For  further  details  see  small  text  at  the  end  of  this  chapter. 


156 


THERMAL   AND    CHEMICAL   CHANGES    IN   MUSCLE         [CH.  XIIL 


Here,  however,  the  analogy  must  end :  for  living  contracted 
muscle  is  irritable,  dead  muscle  is  not.  Living  contracted  muscle  is 
more  extensible  than  uncontracted  muscle ;  muscle  in  rigor  mortis  is 
not  so  (see  fig.  156,  p.  128).  The  contraction  of  living  muscle  is 
favoured  by  feeding  it  with  a  solution  of  dextrose,  while  the  process 
of  rigor  is  hindered  by  the  same  solution.     (F.  S.  Lee.) 

Our  correct  knowledge  of  the  proteins  of  muscle  and  of  the  phenomena  of  rh/or 
mortis  date  from  the  year  1864,  when  Kiihne  obtained  muscle-plasma  by  subjecting 
frozen  frog's  muscle  to  strong  pressure.  A  good  many  years  later  I  was  successful 
in  repeating  these  experiments  with  mammalian  muscle.  By  fractional  heat  coagula- 
tion, and  by  their  varying  solubilities  in  neutral  salts,  I  was  able  to  separate  four 
different  proteins  in  the  muscle-plasma. 

1.  A  globulin  precipitable  by  heat  at  47°  C.  This  is  analogous  to  the  cell- 
globulin  found  in  most  protoplasmic  structures.     I  gave  it  the  name  paramyosinogen. 

2.  A  proteid  with  many  of  the  characters  of  a  globulin,  coagulable  by  heat  at 
.56°  C.  ;    and  this  I  termed  myosmogen. 

3.  A  globulin  (miio-iflohnliu),  precipitable  by  heat  at  63°  C. 

4.  An  albumin  similar  in  its  properties  to  serum  albumin  is  also  present ;  but 
this  and  the  myo-globulin  only  occur  in  quite  small  amounts. 

In  addition  to  these,  there  is  a  small  quantity  of  nuclei-protein  from  the  nuclei, 
and  in  the  red  muscles  haemoglobin  is  present ;  the  normal  pigment  of  the  so-called 
.pale  muscles  is  termed  niyo-hcBmatin  by  MacMunn,  and  this  is  doubtless  a  derivative 
of  haemoglobin. 

The  two  most  abundant  and  important  proteins  are  the  first  two  in  the  list, 
namely,  paramyosinogen  and  myosinogen.  They  occur  in  the  proportion  of  about 
1  to  4,  and  both  enter  into  the  formation  of  the  muscle-clot  (myosin).  The  myo- 
globulin  is  probably  derived  from  the  adherent  connective  tissue  and  the  albumin 
from  adherent  blood  and  lymph. 

In  1895  V.  Fiirth  took  up  the  subject.  On  the  main  question  we  are  in  substantial 
agreement,  namely,  that  in  the  muscle-plasma  there  are  the  two  proteins  just  alluded 
to,  and  that  these  both  contribute  to  the  formation  of  the  muscle-clot.  The  main 
points  of  difference  between  us  are  in  the  names  of  the  proteins.  He  uses  physio- 
logical saline  solution  to  extract  the  muscle-plasma,  and  this  extract  coagulates 
spontaneously  on  standing ;  he  is  doubtful  whether  a  specific  myosin-ferment  brings 
about  the  change.  Paramyosinogen  he  terms  myosin,  and  this  passes  directly  into 
the  clotted  condition  ;  but  myosinogen,  called  myogen  by  v.  Fiirth,  first  passes  into 
a  soluble  condition  (coagulable  by  heat  at  the  remarkably  low  temperature  of 
40°  C. )  before  it  clots  :  the  soluble  stage  he  calls  solul>le  myogen-Jihrin  ;  a  better  name 
is  soluble,  myosin. 

We  may  put  this  in  a  diagrammatic  way  as  follows :  — 


Proteins  of  the  living  muscle. 


Paramyosinogen 


Myosinogen. 

I 
Soluble  myosin. 


Myosin 
(the  protein  of  the  Muscle-clot). 


CH.  XIII.]  HEAT   RIGOR  157 

V.  Fiirth  also  calls  attention  to  some  characters  of  mj^osinogen  which  separate 
it  from  the  typical  globulins  ;  f^.r/.,  it  is  not  precipitable  by  dialysing  the  salts  away 
from  its  solutions.     It  may  be  therefore  called  an  a/i/piral  globulin. 

In  mammalian  muscle,  soluble  myosin  is  only  found  as  a  stage  in  the  process 
of  ri(/or  morfin,  but  in  the  nuiscles  of  the  frog  and  other  amphibia  it  is  present 
as  such  in  the  living  muscle. 

The  muscle-plasma  from  fishes'  muscle  contains  another  protein  termed  mi/o- 
prolein  by  v.  Fiirth.     It  is  precipitable  by  dialysis,  but  not  coagulable  by  heat. 

Brodie,  and  later,  Vernon,  did  some  interesting  experiments  on  heat  rif/or. 
When  a  muscle  is  heated  above  a  certain  temperature  it  becomes  contracted  and 
stiff,  losing  its  irritability  completely.  This  is  due  to  the  coagulation  of  the  muscle 
proteins.  If  a  tracing  is  taken  of  the  contraction,  it  is  found  to  occur  in  a  series  of 
steps  :  the  first  step  in  the  shortening  occurs  at  the  coagulation  temperature  of  the 
paramyosinogen  (47°-50°  C),  and  if  the  heating  is  continued,  a  second  shortening 
occurs  at  56°  C,  the  coagulation  temperature  of  myosinogen.  If,  however,  a  frog's 
muscle  is  used,  there  are  three  steps,  namely,  at  40^  (coagulation  temperature  of 
soluble  myosin),  47%  and  .56°.  This  work  of  Brodie's  is  especially  valuable  because 
it  teaches  us  that  the  proteins  in  muscle-plasma,  or  in  saline  extracts  of  muscle, 
are  present  also  in  the  actual  muscle-substance.  He  also  made  clear  another 
important  point,  namely,  that  the  irritability  of  the  muscle  is  lost  after  the  first 
step  in  the  shortening  has  occurred.  In  other  words,  in  order  to  destroy  the 
vitality  of  muscular  tissue,  it  is  not  necessary  to  raise  the  temperature  sufficiently 
high  to  coagulate  all  its  proteins,  but  that  when  one  of  the  muscular  proteins  has 
been  coagulated,  the  living  substance  as  such  is  destroyed ;  the  proteins  of  muscle 
cannot  therefore  be  regarded  as  independent  units ;  the  unit  is  protoplasm,  and  if 
one  of  its  essential  constituents  is  destroyed,  protoplasm  as  such  ceases  to  live. 

Hans  Przibram  has  attempted  to  classify  the  animal  kingdom  on  the  basis  of 
the  muscle-proteins  ;  his  conclusions  are  based  on  the  examination  of  only  thirty 
species  of  animals,  and  may  require  revision  in  the  future,  but  such  as  they  are,  they 
are  as  follows  : — 

Invertebrates  :  para-myosinogen  present  ;  myosinogen  absent. 

Vertebrates  :  para-myosinogen  and  myosinogen  both  present. 

Fishes :  in  addition  to  these  two  principal  proteids,  soluble  myosin  and  myo- 
protein  (in  large  quantities)  occur. 

Amphibians  :  like  fishes,  except  that  myoprotein  is  only  present  in  traces. 

Reptiles,  birds,  mammals  :  myoprotein  is  absent,  and  soluble  myosin  is  only 
present  when  rigor  mortis  commences. 

Steyrer  has  recently  stated  that  on  prolonged  tetanisation  (in  rabbits'  muscle) 
the  amount  of  paramyosinogen  diminishes,  but  when  degeneration  occurs  after  the 
motor  nerves  are  cut,  the  amount  of  this  protein  increases.  Such  results  must, 
however,  be  accepted  with  caution  until  more  satisfactory  methods  than  those  at 
present  in  use  are  adopted  for  the  estimation  of  the  muscle-proteins. 


CHAPTER  XIV 

COMPARISON   OF   VOLUNTARY   AND   INVOLUNTARY   MUSCLE 

The  main  difference  between  voluntary  and  involuntary  muscle  is  the 
difference  expressed  in  their  names.  Voluntary  muscle  is  under  the 
control  of  that  portion  of  the  central  nervous  system  the  activity  of 
which  is  accompanied  by  volition.  Involuntary  muscle,  on  the  other 
hand,  is,  as  a  rule,  also  under  the  control  of  the  central  nervous 
system,  but  of  a  portion  of  the  central  nervous  system  the  activity 
of  which  is  independent  of  volition.  There  appear,  however,  to  be 
exceptions  to  this  rule,  and  the  involuntary  muscle  executes  its  con- 
tractions independently  of  nervous  control ;  that  is  to  say,  it  is 
sometimes  in  the  truest  sense  of  the  term  really  involuntary.  This 
is  very  markedly  seen  in  the  developing  heart  of  the  embryo,  which 
begins  to  beat  before  any  nerve-fibres  have  grown  into  it  from  the 
central  nervous  system. 

Another  characteristic  of  involuntary  muscle  is  a  tendency  to 
regular  alternate  periods  of  rest  and  activity,  or  rhythmicality.  This 
is  best  exemplified  in  the  heart,  but  it  is  also  seen  in  the  lymphatic 
vessels,  especially  the  lymph  hearts  of  the  frog,  and  the  mesenteric 
lymphatic  vessels  (lacteals)  of  many  animals.  It  is  seen  in  the 
veins  of  the  bat's  wing,  and  in  the  muscular  tissue  of  the  spleen, 
stomach,  intestine,  bladder,  and  other  parts. 

A  third  characteristic  of  involuntary  muscle  is  peristalsis.  If 
any  point  of  a  tube  of  smooth  muscle  such  as  the  small  intestine  is 
stimulated,  a  ring-like  constriction  is  produced  at  this  point.  After 
lasting  some  time  at  this  spot  it  slowly  passes  along  the  tube  at  the 
rate  of  20  to  30  millimetres  per  second.  This  advancing  peristaltic 
wave  normally  takes  place  in  only  one  direction,  and  so  serves  to 
drive  on  the  contents  of  the  tube. 

Involuntary  muscle  nearly  always  contains  numerous  plexuses  of 
non-medullated  nerve-fibres  with  ganglion  cells ;  so  that  much  dis- 
cussion has  taken  place  on  the  question  whether  the  phenomena  of 
rhythmicality  and  peristalsis  are  properties  of  the  muscular  tissue 
itself  or  of  the  nerves  mixed  with  it.     The  evidence  available  (namely, 


CH.  XIV.]  CONTRACTION   OF   INVOLUNTARY   MUSCLE  159 

that  portions  of  muscular  tissue  entirely  free  from  nerves  act  in  the 
same  way  as  those  that  possess  nerves)  indicates  that  it  is  the 
muscular  rather  than  the  nervous  tissues  that  possess  these  properties ; 
though  it  can  hardly  be  doubted  that  under  normal  conditions  the 
contraction  of  involuntary  muscle  is  influenced  and  controlled  by 
nervous  agency. 

As  instances  of  nerveless  involuntary  muscles  which  possess  the 
property  of  rhythmical  action,  we  may  take  the  ventricle  apex  of  the 
frog's  or  tortoise's  heart.  If  this  is  cut  off  and  fed  with  a  suitable 
nutritive  fluid  at  considerable  pressure  it  will  beat  rhythmically 
(G-askell).  The  apparatus  by  which  this  may  be  demonstrated  is 
described  at  the  end  of  Chapter  XX.  The  middle  third  of  the  ureter 
is  another  instance  of  muscular  tissue  free  from  nerves,  but  which 
nevertheless  executes  peristaltic  movements.  Perhaps,  however,  the 
most  striking  example  is  that  of  the  foetal  heart  which  begins  to 
beat  directly  it  is  formed,  long  before  any  nerves  have  grown  into  it. 
The  artificial  stimuli  employed  for  involuntary  are  the  same  as 
those  used  for  voluntary  muscle  ;  single  induction  shocks  are,  however, 
often  ineffectual  to  produce  contraction,  but  the  make,  and  to  a  less 
extent  the  break,  of  a  constant  current  will  act  as  a  stimulus. 

The  faradic  current  is  a  good  stimulus,  but  it  never  throws 
involuntary  muscle  into  tetanus;  in  the  heart,  strong  stimulation 
will  sometimes  effect  a  partial  fusion  of  the  beats,  but  never  complete 
tetanus.  The  rate  of  stimulation  makes  no  difference ;  in  fact,  very 
often  a  rapid  rate  of  stimulation  calls  forth  less  rapidly  occurring 
contractions  than  a  slow  rate. 

A  stimulus  strong  enough  to  produce  a  contraction  in  the  heart 
elicits  a  maximum  contraction  ("  all  or  nothing  "  Waller)  ;  the  pheno- 
menon known  as  the  staircase  (see  p.  117)  is  generally  better  marked 
in  the  case  of  the  heart  than  in  that  of  voluntary  muscle. 

The  contraction  of  smooth  muscle  is  so  sluggish  that  the  various 
stages  of  latent  period,  shortening  and  relaxation,  can  be  followed 
with  the  eye;  the  latent  period  often  exceeds  half  a  second  in 
duration.     It  does  not  obey  the  "  all  or  nothing  "  law. 

The  normal  contraction  of  voluntary  muscle  is  a  kind  of  tetanus 
(see  p.  121) ;  the  normal  contraction  of  cardiac  and  plain  muscle 
is  a  much  prolonged  single  contraction.  A  very  valuable  piece 
of  evidence  in  this  direction  is  seen  in  the  experiment  on  the  heart 
with  the  physiological  rheoscope  (see  p.  145).  Each  time  the 
heart  contracts  the  rheoscopic  preparation  executes  a  single  twitch, 
not  a  tetanus.  This  is  an  indication  that  the  electrical  change  is  a 
single  one,  and  not  a  succession  of  changes  such  as  occurs  in  tetanus. 
When  this  electrical  change  is  examined  with  the  electrometer, 
it  is  seen  that  it  is  a  diphasic  one  as  in  voluntary  muscle ;  but  in  a 
slowly  contracting  tissue  like  the  heart-muscle  the  two  phases  are 


160       COMPARISON  OF  VOLUNTARY  AND  INVOLUNTARY  MUSCLE     [CH.  XIV. 

separated  by  a  prolonged  period  of  equipotentiality,  and  thus  they 
are  rendered  more  distinct.  The  illustrations  already  given  (figs. 
167  and  168)  show  this  fact  graphically. 

When  the  heart  is  beating  sluggishly  in  the  rheoscopic  experiment  above 
referred  to,  the  separation  of  the  two  phases  of  the  electrical  change  will  sometimes 
cause  two  twitches  in  the  muscle-nerve  preparation.  Bayliss  and  Starling  describe 
the  ventricular  contraction  of  the  mammahan  heart  as  being  accompanied  by  a 
triphasic  electrical  variation  ;  this  is  due  to  the  contraction  at  the  base  outlasting 
that  at  the  apex  ;  if,  therefore,  base  and  apex  are  led  oiF  to  the  electrometer,  the 
first  phase  is  due  to  increased  positivity  at  the  base,  the  second  to  that  at  the  apex  ; 
this  quickly  subsides,  but  the  increased  positivity  at  the  base  which  still  continues 
accounts  for  the  third  excursion  of  the  mercury. 

But  though  involuntary  muscle  cannot  be  thrown  into  tetanus, 
it  has  the  property  of  entering  into  a  condition  of  sustained  contrac- 
tion called  tonus.  "We  shall  have  to  consider  this  question  again  in 
connection  with  the  plain  muscular  tissue  of  the  arterioles. 

Involuntary  muscle  when  it  contracts  undergoes  thermal  and 
chemical  changes  similar  to  those  we  have  dealt  with  in  the  case  of 
the  voluntary  muscles. 

Involuntary  muscle  is  usually  supplied  with  two  sets  of  nerves, 
one  of  which  (accelerator)  increases  and  the  other  of  which  (inhibitory) 
decreases  its  activity.  The  nerve-endings  in  involuntary  muscle 
require  a  much  larger  dose  of  curare  to  affect  them  than  the  end- 
plates  in  voluntary  muscle. 

The  phenomena  of  rigor  mortis  in  involuntary  muscle  have  not 
been  so  fully  studied  as  in  the  case  of  voluntary  muscle.  It  has, 
however,  been  shown  that  the  chemical  composition  of  involuntary 
muscle  differs  in  no  noteworthy  manner  from  that  of  voluntary  muscle, 
and  on  death  the  muscle  becomes  acid ;  such  products  as  carbonic 
acid  and  sarco-lactic  acid  are  formed.  In  the  heart,  stomach,  uterus, 
and  rectum,  post-mortem  rigidity  has  been  noted,  and  it  probably 
occurs  in  all  varieties  of  plain  muscle. 

Swale  Vincent  has  shown  that  the  characteristic  proteins  (paramyosinogen  and 
myosinogen)  occur  in  both  striped  and  unstriped  nmscle,  and  the  heat  rigor  curves 
of  involuntary  muscle  are  practically  identical  with  those  obtained  by  Brodie  (see 
p.  1.57).  He  is  inclined  to  think  that  the  two  proteins  are  formed  by  the  breaking 
down  of  a  compound  protein  which  in  living  muscle  mainly  coagulates  at  47' C. 
This  view  is  taken  by  Stewart  in  reference  to  striped  muscle  also,  but  has  been 
very  seriously  questioned  by  v.  Fiirth.  The  most  striking  chemical  difference 
between  unstriped  and  striped  muscle  is  seen  in  the  amount  of  nucleo-protein  which 
they  contain.  Plain  muscle  contains  six  to  eight  times  the  amount  found  in 
voluntary  muscle  ;  cardiac  muscle  contains  an  intermediate  quantity. 


CHAPTER  XV 

PHYSIOLOGY   OF   NEKVE 

Many  points  relating  to  the  physiology  of  nerve  have  been  already 
studied  in  connection  with  muscle.  But  there  still  remain  further 
questions  upon  which  we  have  hardly  touched  as  yet. 

Classification  of  Nerves. 

The  nerve-fibres  which  form  the  conducting  portions  of  the 
nervous  system  may  be  classified  into  three  main  groups,  according 
to  the  direction  in  which  they  normally  conduct  nerve  impulses. 
These  three  classes  are : — 

1.  Efferent  nerve-fibres. 

2.  Afferent  nerve-fibres. 

3.  Inter-central  nerve-fibres. 

1.  Efferent  or  centrifugal  nerves  are  those  which  conduct  im- 
pulses from  the  central  nervous  system  (brain  and  spinal  cord)  to 
other  parts  of  the  body.  When,  for  instance,  there  is  a  wish  to  move 
the  hand,  the  impulse  starts  in  the  brain,  and  travels  a  certain 
distance  down  the  spinal  cord ;  it  leaves  the  spinal  cord  by  one  or 
more  of  the  spinal  nerves,  and  so  reaches  the  muscles  of  the  hand 
which  are  thrown  into  contraction.  Such  nerves  are  called  motor, 
but  all  efferent  nerves  are  not  motor ;  some  cause  secretion  instead 
of  movement,  and  others  may  cause  a  stoppage  of  movement,  etc.  A 
list  of  the  classes  of  efferent  nerves  is  as  follows : — 

a.  Motor. 

h.  Accelerator. 

c.  Inhibitory. 

d.  Secretory. 

e.  Electrical. 
/.  Trophic. 

a.  Motor  nerves.  Some  of  these  go  to  voluntary  muscles ;  others 
to  involuntary  muscles,  such  as  the  vaso-motor  nerves  which 
supply  the  muscular  tissue  in  the  walls  of  arteries. 


162  PHYSIOLOGY   OF   NERVE  [CH.  XV. 

b.  Accelerator  nerves  are  those  which  produce  au  increase  in  the 

rate  of  rhythmical  action.  An  instance  of  these  is  seen  in 
the  sympathetic  nerves  that  supply  the  heart. 

c.  Inhibitory  nerves  are  those  which  cause  a  slowing  in  the  rate 

of  rhythmical  action,  or  it  may  he  its  complete  cessation. 
Inhibitory  nerves  are  found  supplying  many  kinds  of 
involuntary  muscle ;  a  very  typical  instance  is  found  in 
the  inhibitory  fibres  of  the  heart  which  are  contained  within 
the  trunk  of  the  vagus  nerve.* 

d.  Secretory  nerves  are  found  suppljdng  many  secreting  glands, 

such  as  the  salivary  glands,  gastric  glands,  and  sweat 
glands.  The  impulse  which  travels  down  a  secretory  nerve 
stimulates  secretion  in  the  gland  it  supplies. 

e.  Electrical  nerves  are  found  in  the   few  fishes   which   possess 

electrical  organs.     The  impulse  which  travels   down   these 

nerves   causes    the    electrical    organ    to   be    thrown    into 

activity. 
/.   TropMc  nerves  are  those  which  control  the  nutrition  of  the 

part  they  supply. 
2.  Afferent  or  centripetal  nerves  are  those  which  conduct 
impulses  in  the  reverse  direction,  namely,  from  all  parts  of  the 
body  to  the  central  nervous  system.  Wlien  one  feels  pain  in  the 
finger,  the  nerves  of  the  finger  are  stimulated,  an  impulse  travels 
up  the  nerves  to  the  spinal  cord,  and  then  to  the  brain.  The  mental 
process  set  up  in  the  brain  is  called  a  sensation ;  the  sensation,  how- 
ever, is  referred  to  the  end  of  the  nerve  where  the  impulse  started, 
and  the  sensation  of  pain  does  not  appear  to  occur  in  the  brain,  but 
in  the  finger.  This  is  an  instance  of  a  sensory  nerve ;  and  the  terms 
afferent  and  sensory  may  often  be  used  synonjonously.  The  nerves 
of  sensation  may  be  grouped  as  follows : — 

a.  The  nerves  of  special  sense ;  such  as,  of  sight,  hearing,  taste, 

smell,  and  touch. 

b.  The  nerves  of  general  sensibility ;  that  is,  of  a  vague  kind  of 

sensation  not  referable  to  any  of  the  special  senses;  as  an 
instance,  we  may  take  the  vague  feelings  of  comfort  or 
discomfort  in  the  interior  of  the  body. 

c.  Nerves  of  pain.     It  is  a  moot  point  whether  these  are  anatomi- 

cally distinct  from  the  others,  but  there  is  some  evidence 
that  this  is  the  case  (see  more  fully  Chapter  LII.). 

The  words  "sensory"  and  "afferent,"  however,  are  not  quite 
synonymous.      Just  as  we  may  have  efferent  impulses  leaving  the 

*  The  question  has  been  much  debated  whether  voluntary  muscle  is  provided 
with  inhibitory  nerves ;  they  do,  however,  appear  to  be  present  in  certain  nerves 
supplying  the  muscles  of  the  claws  of  lobsters  and  similar  crustaceans. 


CH.  XV.]  REFLEX   ACTION  163 

brain  for  the  heart  or  blood-vessels  of  which  we  have  no  con- 
scious knowledge,  so  also  afferent  impulses  may  travel  to  the 
central  nervous  system  which  excite  no  conscious  feelings.  The 
afferent  nerve-tracts  to  the  cerebellum  form  a  very  good  instance  of 
these. 

Then,  too,  the  excitation  of  many  afferent  nerves  will  excite  what 
are  called  reflex  actions.  We  are  very  often  conscious  of  the  sensa- 
tions that  form  the  cause  of  a  reflex  action,  but  we  do  not  necessarily 
have  such  sensations.  Many  reflex  actions,  for  instance,  occur  during 
sleep ;  many  may  be  executed  by  the  spinal  cord  even  after  it  has 
been  severed  from  the  brain,  and  so  the  brain  cannot  be  aware  of 
what  is  occurring. 

A  reflex  action  is  an  action  which  is  the  result  of  an  afferent 
impulse.  Thus  a  speck  of  dust  falls  into  the  eye,  and  causes  move- 
ments of  the  eyelids  to  get  rid  of  the  offending  object.  The  dust 
excites  the  sensory  nerve-endings  in  the  conjunctiva,  an  impulse 
travels  to  the  centre  of  this  nerve  in  the  brain,  and  from  the  brain 
a  reflected  impulse  travels  to  the  muscles  of  the  eyelid.  As  an 
instance  of  a  reflex  action  in  which  secretion  is  concerned,  take  the 
watering  of  the  mouth  which  occurs  when  food  is  seen  or  smelt.  The 
nerves  of  sight  or  smell  convey  an  afferent  impulse  to  the  brain, 
which  reflects,  down  the  secretory  nerves,  an  impulse  which  excites 
the  saHvary  glands  to  activity. 

These,  however,  are  instances  of  reflex  action  which  are  accom- 
panied with  conscious  sensation,  but  like  all  pure  reflex  actions  are 
not  under  the  control  of  the  will. 

An  instance  of  a  reflex  action  not  accompanied  with  consciousness 
is  seen  in  a  man  with  his  spinal  cord  cut  across  or  crushed,  so  that 
any  communication  between  his  brain  and  his  legs  is  impossible. 
He  cannot  move  his  legs  voluntarily,  and  is  unconscious  of  any 
feelings  in  them.  Yet  when  the  soles  of  his  feet  are  tickled  he  draws 
his  legs  up,  the  centre  of  reflex  action  being  in  the  grey  matter  of 
the  lower  region  of  the  spinal  cord. 

For  a  reflex  action,  three  things  are  necessary :  (1)  an  afferent 
nerve,  (2)  a  nerve-centre  consisting  of  nerve-cells  to  receive  the 
afferent  impulse  and  send  out  an  efferent  impulse,  and  (3)  an 
efferent  nerve  along  which  the  efferent  impulse  may  travel.  If  the 
reflex  action  is  a  movement,  the  afferent  nerve  is  called  excito-motor  ; 
if  it  is  a  secretion,  the  afferent  nerve  is  called  excito-secretory ;  and 
similarly,  afferent  nerves  may  also  be  excito-accelerator,  excito-inhihitory, 
etc. 

3.  Intercentral  nerve -fibres  are  those  which  connect  nerve- 
centres  together ;  they  connect  different  parts  of  brain,  and  of  the 
cord  to  one  another,  and  we  shall  find  in  our  study  of  the  nerve- 
centres  that  they  are  complex  in  their  arrangement. 


164  PHYSIOLOGY   OF   NERVE  [CH.  XV. 

Investigation  of  the  Functions  of  a  Nerve. 

There  are  always  two  main  experiments  by  which  the  function 
of  a  nerve  may  be  ascertained.  The  first  is  section,  the  second  is 
stimulation. 

Section  consists  in  cutting  the  nerve  and  observing  the  loss  of 
function  that  ensues.  Thus,  if  a  motor  nerve  is  cut,  motion  of  the 
muscles  it  supplies  can  no  longer  be  produced  by  activity  of  the 
nerve-centre ;  the  muscle  is  paralysed.  If  a  sensory  nerve  is  cut, 
the  result  is  loss  of  sensation  in  the  part  it  comes  from. 

Stimulation  of  the  cut  nerve  is  the  opposite  experiment.  When 
a  nerve  is  cut  across,  one  piece  of  it  is  still  connected  with  the  brain 
or  spinal  cord ;  this  is  called  the  central  end  ;  the  other  piece,  called 
the  peripheral  end,  is  still  connected  with  some  peripheral  part  of 
the  body.  Both  the  central  and  the  peripheral  end  should  be  stimu- 
lated ;  this  is  usually  done  by  means  of  induction  shocks.  In  the 
case  of  a  motor  nerve,  stimulation  of  the  central  end  produces  no 
result ;  stimulation  of  the  peripheral  end  produces  a  nervous  impulse 
which  excites  the  muscles  to  contract.  In  the  case  of  a  sensory 
nerve,  stimulation  of  the  peripheral  end  has  no  result,  but  stimula- 
tion of  the  central  end  causes  a  sensation,  usually  a  painful  one,  and 
reflex  actions,  which  are  the  result  of  the  sensation. 

When  a  nerve  is  cut  across,  there  are  other  results  than  the  loss 
of  function  just  mentioned;  for  even  though  the  nerve  is  still  left 
within  the  body  with  a  normal  supply  of  blood,  it  becomes  less  and 
less  irritable,  till  at  last  it  ceases  to  respond  to  stimuh  altogether. 
This  diminution  of  excitability  starts  from  the  point  of  section  and 
travels  to  the  periphery,  but  is  temporarily  preceded  by  a  wave  of 
increased  excitability  travelling  in  the  same  direction  (Eitter-Valli 
law). 

This  loss  of  excitability  of  nerve  is  accompanied  with  degenera- 
tive changes  which  are  of  so  great  importance  as  to  demand  a  separate 
section. 

Degeneration  of  Nerve. 

Suppose  a  nerve  is  cut  right  across,  the  piece  of  the  nerve  left  in 
connection  with  the  brain  or  spinal  cord  remains  healthy  both  in 
structure  and  functions ;  but  the  peripheral  piece  of  the  nerve  loses 
its  functions  and  undergoes  what  is  generally  called,  after  the  dis- 
coverer of  the  process,  Wallerian  degeneration.  A  nerve  is  made  up 
of  nerve-fibres,  and  each  nerve-fibre  is  essentially  a  branch  of  a  nerve- 
cell  ;  when  the  nerve  is  cut,  the  axis  cylinders  in  the  peripheral 
portion  are  separated  from  the  cells  of  which  they  are  branches  and 
from  which  they  have  grown.  These  separated  portions  of  the  axis 
cylinders  die,  and  the  medullary  sheath  of  each  imdergoes  a  gradual 


en.  XV.] 


DEGENERATION   OF   NERVE 


165 


process  of  disintegration  into  droplets  of  myelin,  which  are  ultimately 
absorbed  and  removed  by  the  lymphatics.  At  the  same  time  there  is 
a  multiplication  of  the  nuclei  of  the  primitive  sheath.  This  degenera- 
tive process  commences  two  or  three  days  after  the  section  has  been 
made.  In  the  case  of  the  non-medullated  fibres,  there  is  no  medullary 
sheath  to  exhibit  the  disintegrative  changes  just  alhided  to ;  and  the 


Fig.  181. — Degeneration  and  regeneration  of  nerve-tibres.  a,  nerve-libre,  lifty  hours  after  operation 
my,  medullary  sheath  breaking  up  into  myelin  drops,  p,  granular  protoplasm  replacing  myelin. 
11,  nucleus,  g,  primitive  sheath,  b,  nerve-flbre  after  four  days,  cy,  axis  cylinder  partly  broken 
up  and  enclosed  in  portions  of  myelin,  c,  a  more  advanced  stage  in  which  the  medullary  sheath 
has  almost  disappeared.  Numerous  nuclei,  n",  are  seen,  d,  commencing  regeneration;  several 
fibres  (i',  i")  have  sprouted  from  the  somewhat  bulbous  cut  end  (6)  of  the  nerve-fibre,  a,  an  axis 
cylinder  which  has  not  yet  acquired  its  medullary  sheath,  s,  s',  primitive  sheath  of  the  original 
fibre.    (Ranvier.) 

nuclei  of  the  sheath  do  not  multiply ;  there  is  simply  death  of  the 
axis  cylinder.  The  degeneration  occurs  simultaneously  throughout 
the  whole  extent  of  the  nerve ;  it  does  not  start  from  the  section  and 
travel  to  the  periphery.  Eanvier's  original  diagram  is  reproduced  in 
fig.  181.  Figs.  182  and  183  are  photo-micrographs  from  actual 
specimens. 

A  great  amount  of  attention  has  been  directed  to  this  process  of 
degeneration,  because  it  has  formed  a  valuable  method  of  research  in 


166 


PHYSIOLOGY   OF   NERVE 


[CH.  XV. 


tracing  nervous  tracts,  and  ascertaining  the  nerve-cells  from  which 
they  originate.  It  must  not,  however,  be  regarded  as  an  isolated 
phenomenon  in  physiology ;  it  is  only  an  illustration  of  the  universal 


Fig.  182. — Xerve-fibres  from  sciatic  nerve  of  cat,  four  days  after  the  nerve  had  been  cut.    This  shows  an 
early  stage  of  the  d^eneratlve  procejss.    600  diameters.    (Mott  and  Halliburton.) 

truth  that  any  portion  of  a  cell  (in  this  case  the  axis  cylinder  process) 
cut  off  from  the  nucleus  of  the  cell  degenerates  and  dies. 

If  a  nerve  is  simply  cut,  and  allowed  to  heal,  regeneration  of 
function  in  time  occurs.  This  is  hastened  by  the  surgeon  suturing 
the  cut  ends  of  the  nerve  together.  It  must  not,  however,  be  supposed 
that  this  is  due  to  a  restoration  of  the  structure  of  the  fibres  in  the 
peripheral  portion  of  the  cut  nerve.  It  is  due  to  very  fine  new 
nerve-fibres  sprouting  out  from  the  central  end  of  the  cut  nerve,  and 
growing  distalwards.      This  is  illustrated   in  J),   fig.   181.      "When 


Fig.  183. — These  are  fibres  from  ti.e  .^c;a;ic  nerve  of  another  cat,  ten  days  after  the  nerve  had  been  cut. 
This  shows  the  breaking-up  of  the  medullary  sheath  in  a  marked  way,  and  the  intense  black  colour 
the  myelin  droplets  take  with  osmic  acid.     600  diameters.     (3Iott  and  Halliburton.) 

regeneration  does  not  take  place,  the  central  ends  of  the  cut  fibres 
and  the  cells  from  which  they  originate  undergo  slow  atrophic 
changes  (disuse  atro]jhy). 

The  view  expressed  by  the  earlier  workers  on  nerve  regeneration 


CH.  XV.] 


REGENERATION    OF   NERVE 


167 


-4, 


that  the  new  fibres  grow  from  the  central  stump  of  the  cut  nerves 
has  been  recently  ques- 
tioned. Some  believe  that  §^^y  ^  '  .'•' 
regeneration  may  occur  in 
the  peripheral  structures. 
It  certainly  is  the  case  that 
the  neurilemmal  cells  ex- 
hibit a  great  deal  of  activity  ; 
they  multiply  (fig.  184) ;  at 
a  later  stage  they  exhibit  a 
phagocytic  action  in  the 
removal  of  the  degenerated 
fat  (fig.  185) ;  and  later 
still  they  become  elongated 
and  spindle-shaped ;  they 
then  join  together  as 
though  they  were  form- 
ing new  nerve-fibres  (fig. 
186).  But  the  elongat- 
ing and  contiguous  cells 
are  really  only  forming 
a  new  sheath  or  basis  into 
which    the     axis    cylinder 

ultimately  grows.     Howell  and  Huber,  who  have  recently  investi- 
gated this  question,  have  arrived  at  the  conclusion  that  the  peri- 


FiG.  1S4.— Single  fibre  from  a  degenerating  nerve,  eight 
days  after  the  nerve  was  cut,  stained  so  as  to  show 
the  division  of  a  neurilemmal  nucleus  into  two.  """ 
diameters.    (Mott  and  Halliburton.) 


870 


Flo.  1S5. — Degenerated  nerve,  twenty-seven  days 
after  the  nerve  had  been  cut.  The  numerous 
neurilemmal  cells,  perhaps  aided  by  phagocytes 
from  the  exterior  contain  within  them  fatty  par- 
ticles which  stain  black  with  osmic  acid.  They 
are  doubtless  active  in  removing  the  degenerated 
myelin.   450  diameters.   (Mott  and  Halliburton.) 


Fig.  18G.— Degenerated  ner\-e  forty-four  days 
after  section.  The  elongation  of  the 
neurilemmal  cells  to  form  what  look  like 
new  fibres  is  well  shown.  500  diameters. 
(Mott  and  Halliburton.) 


pheral  structures  are  active  in  preparing  the  scaffolding,  but  that 
the   axis   cylinder,  the   essential   portion  of   a  nerve-fibre,   has    an 


168 


PHYSIOLOGY    OF   XERTE 


[CH.  XV. 


exclusively  central  origin.  This  view  I  thoroughly  endorse.  Mott 
and  I  have  also  shown  that  when  the  regenerated  fibres  are  again 
cut,  degeneration  takes  place  in  the  peripheral  direction  only,  and 
this  is  a  strong  piece  of  evidence  that  growth  had  not  started  from 
the  periphery  centralwards,  for  the  direction  of  nutritive  control  is 
always  the  direction  of  growth. 

The  manifest  acti\'ity  of  the  neui'ilemmal  cells  is  probably  largely 
nutritive  rather  than  formative,  but  is  nevertheless  of  great  impor- 
tance, for,  in  situations  like  the  central  nervous  system,  where  the 
neurilemma  does  not  exist,  regeneration  does  not  occur. 


Functions  of  tlie  Roots  of  tlie  Spinal  Nerves. 

The  general  truths  enunciated  in  the  two  preceding  sections  are 
well  illustrated  by  the  experiments  made  to  determine  the  functions 

of  the  roots  of  the  spinal 
nerves.  Each  spinal  nerve 
originates  from  the  spinal 
cord  by  two  roots.  One  of 
these  is  called  the  anterior  or 
ixntral  root :  it  consists  of 
nerve-fibres  which  originate 
from  the  large  multipolar 
cells  in  that  portion  of  the 
grey  matter  in  the  interior 
of  the  spinal  cord  which  we 
shall  presently  learn  to  call 
the  anterior  horn.  These 
nerve-fibres  are  all  medul- 
lated ;  the  large  ones  join 
up  with  the  posterior  root 
to  form  the  spinal  nerve ; 
the  small  nerve-fibres  leave 
the  root  and  pass  to  the  sym- 
pathetic chain,  which  then 
distributes  non  -  medullated 
fibres  of   the  blood-vessels  and 


Fig.  187. — a,  Bipolar  cell  from  spinal  ganglion  of  a  4* 
weeks  embryo,  n,  nucleus ;  the  arrows  indicate  the 
direction  in  which  the  nerve  processes  grow,  one  to 
the  spinal  cord,  the  other  to  the  periphery,  b,  a 
cell  from  the  spinal  ganglion  of  the  adult ;  the  two 
processes  have  coalesced  to  form  a  T-shaped  junction. 
(Diagrammatic.) 

fibres  to  the  involuntarv  muscular 


viscera. 

The  other  root,  the  posterior  or  dorsal  root,  has  upon  it  a  collection 
of  nerve-cells  forming  the  spinal  ganglion.  Each  nerve-cell  is 
enclosed  within  a  nucleated  sheath  of  connective  tissue  origin,  and 
it  is  from  these  nerve-cells  that  the  fibres  of  the  posterior  roots 
grow.  In  the  embryo,  each  nerve-cell  has  two  processes  (fig.  187), 
one  of  which  grows  to  the  spinal  cord,  where  it  terminates  by 
branching  around  the  multipolar  cells  of  the  grey  matter ;  the  other 


CH.  XV.] 


RECURRENT  SENSIBILITY 


169 


process  <:jrows  outwards  to  the  periphery.  In  the  adult  mammal 
(not  in  fishes)  the  two  processes  coalesce  in  the  first  part  of  their 
course,  forming  a  T-shapcd  jundioji. 

The  first  experiments  on.  the  functions  of  the  spinal  nerve-roots 
were  performed  in  this  country  by  Sir  Charles  Bell  (1811),  and  in 
France  by  Magendie  (1822).  These  observers  found  that  on  section 
of  the  anterior  roots  there  resulted  paralysis  of  the  muscles  supplied 
by  the  nerves ;  on  section  of  the  posterior  roots  there  was  loss  of 
sensation.  These  experiments  clearly  pointed  to  the  conclusion  that 
the  anterior  roots  contain  the  efferent  (motor)  fibres;  and  the 
posterior  roots  the  afferent  (sensory)  fibres.  This  conclusion  was 
confirmed  by  the  experiment  of  stimulation.  Stimulation  of  the 
peripheral  end  of  the  cut  anterior  root  caused  muscular  movement ; 
of  the  central  end,  no  effect.  Stimulation  of  the  central  end  of  the 
cut  posterior  root  caused  pain  and 
reflex  movements;  of  the  peripheral 
end,  no  effect. 

Recurrent  sensibility. — One  of  the 
statements  just  made  requires  a  slight 
modification ;  namely,  excitation  of 
the  peripheral  end  of  a  divided  an- 
terior root  will  evoke  pain  and  reflex 
movements,  as  well  as  direct  move- 
ments; that  is  to  say,  the  anterior 
root,  though  composed  mainly  of 
motor  fibres,  contains  a  few  sensory 
fibres  coming  probably  from  the  mem- 
branes of  the  spinal  cord,  and  then 
running  into  the  posterior  root  with 
the  rest  of  the  sensory  fibres.  They  often,  however,  run  down  the 
mixed  nerve  a  considerable  distance  before  returning  to  the  posterior 
roots. 

The  diagram  on  this  page  (fig.  188)  illustrates  the  course  of  one  of 
these  recurrent  fibres  (r) ;  the  arrows  represent  the  direction  in  which 
it  conveys  impulses. 

Degeneration  of  roots. — The  facts  in  connection  with  this  subject 
were  made  out  by  Waller  (1850),  and  may  be  best  understood  by 
referring  to  the  next  diagram  (fig.  189). 

A  represents  a  section  of  the  mixed  nerve  beyond  the  union  of 
the  roots;  the  whole  nerve  beyond  the  section  degenerates,  and  is 
shaded  black. 

B  represents  the  result  of  section  of  the  anterior  root ;  only  the 
anterior  root-fibres  degenerate;  the  sensory  fibres  of  the  posterior 
root  remain  intact.  The  small  medullated  nerve-fibres  (not  shown  in 
the   diagram)  also  degenerate  as  far  as  the  ganglion  cells  of   the 


Spinal  /Venn 


Fig.  1S8. — Diagram  to  illustrate  recurrent 
sensibility. 


170 


PHYSIOLOGY   OF   NERVE 


[CII.  XV 


Fig.  189.^Diagram  to  illustrate  Wallerian  degem;- 
ration  of  nerve-roots. 


sympathetic  system  with  which  they  communicate.     The  recurrent 

sensory  fibres  in  this  root  do  not 
degenerate  with  the  others,  but 
are  found  degenerated  in  the 
part  of  the  anterior  root  at- 
tached to  the  spinal  cord. 

Section  of  the  posterior  root 
always  produces  the  same  phy- 
siological effect  (loss  of  sensa- 
tion) *  wherever  the  section  is 
made,  but  the  degeneration  effect 
is  different  according  as  the  sec- 
tion is  made  on  the  proximal  or 
distal  side  of  the  ganglion.  If 
the  section  is  made  beyond  the 
ganglion,  the  degeneration  occurs 
as  shown  in  C  beyond  the  sec- 
tion in  the  peripheral  portion  of 

the  posterior  root-fibres ;  the  anterior  root  remains  intact  except  for 

the  recurrent  sensory  fibres  which  it  con- 
tains.     If   the   section   is    made    as    in   D, 

between  the  ganglion  and  the  cord,  the  only 

piece  that  degenerates  is  the  piece  severed 

from    the   ganglion    and   running   into    the 

cord;  these  fibres  may  be  traced  up  in  the 

posterior   column  of   the  spinal  cord  until 

they  terminate  in  grey  matter,  which  they 

do  at   different  levels.     The  whole   of   the 

sensory  fibres  including  the  recurrent  ones 

which    are   still    attached    to   the   ganglion 

remain  histologically  healthy. 

The  accompanying  figure  (fig.  190)  is  one 

of    the    original   illustrations   made    by   Dr 

Waller,  and  I  am  indebted  to  the  present 

Dr  Waller  for  permission  to  reproduce  it. 
These   facts   of    degeneration   teach    us, 

what  we  also  learn  from  the  study  of  em- 
bryology, that  the  nerve-fibres  of  the  an- 
terior root  are  connected  to  the  nerve-cells 

within  the  spinal  cord,  while  the  posterior 

root-fibres  are  connected  to  the  cells  of  the 

spinal  ganglia ;  or,  to  put  it  another  way,  the  trophic  centres  which 


Fig.  190. — Groups  of  fibres  from 
the  anterior  and  posterior 
roots  several  days  after  sec- 
tion of  both  roots  close  to  the 
cord ;  the  anterior  fibres  are 
degenerated  ;  the  posterior, 
being  still  in  connection  with 
the  nerve-cells  from  which 
they  grew,  are  normal. 


*  In  order  to  obtain  any  appreciable  loss  of  motion  or  sensation,  it  is  necessary 
to  divide  several  roots  (anterior  or  posterior  as  the  case  may  be),  as  there  is  a  good 
deal  of  overlapping  in  the  peripheral  distribution  of  the  fibres. 


CH.  XV.]  ACTION   CURRENT   OF   NERVE  171 

control  the  nutrition  of  the  fibres  are  situated  within  the  cord  for  tlie 
anterior  roots,  and  within  the  spinal  ganglia  for  the  posterior  roots. 

Changes  in  a  Nerve  during  Activity. 

When  a  nerve  is  stimulated,  the  change  produced  in  it  is  called  a 
nervous  impulse ;  this  change  travels  along  the  nerve,  and  the  pro- 
pagation of  some  change  is  evident  from  the  effects  which  follow : 
sensation,  movement,  secretion,  etc. ;  but  in  the  nerve  itself  very  little 
change  can  be  detected.  There  is  no  change  in  form ;  the  most  deli- 
cate thermo-piles  have  failed  to  detect  any  production  of  heat,  and 
we  are  almost  com})letely  ignorant  of  any  chemical  changes.  The 
only  alteration  which  can  be  readily  detected  as  evidence  of  this 
molecular  change  in  a  nerve  is  the  electrical  one.  Healthy  nerve  is 
iso-electric,  but  during  the  passage  of  a  nervous  impulse  along  it 
there  is  a  very  rapid  diphasic  variation,  which  travels  at  the  same 
rate  as  the  nervous  impulse.  This  is  similar  to  the  diphasic  change 
in  muscle,  and  can  be  detected  and  measured  in  the  same  way. 

Waller  regards  the  current  of  action  of  any  excitable  tissue  as  an  index  of  the 
magnitude  of  action,  and  records  the  movement  of  the  galvanometer  by  photograph- 
ing the  excursion  of  the  spot  of  light  on  a  moving  photographic  plate.  He  has  in 
this  way  obtained  records  from  muscle,  nerve,  retina,  skin,  plant  tissues,  etc.  He 
points  out  that  the  only  available  index  of  action  within  the  nerve  itself  is  the 
electrical  sign  of  activity,  whereas  in  muscle  the  mechanical  action  can  be  compared 
with  its  accompanying  electrical  changes.  The  amount  of  contraction  hi  a  mnsrle 
caused  by  excitation  of  its  nerve  is  only  a  very  rough,  or  even  a  fallacious,  indica- 
tion of  the  excitability  of  the  nerve,  because  the  nerve  is  connected  to  the  muscle  by 
motor  end-plates,  and  these,  as  we  have  already  seen,  are  fatigued  long  before  the 
nerve  shows  any  sign  of  fatigue. 

Using  this  method.  Waller  has  obtained  a  number  of  interesting  results  on  the 
variation  in  nerve  action  produced  by  drugs  and  other  agents.  He  finds  that  the 
effect  of  carbonic  acid  is  to  cause  a  diminution,  and  finally  disappearance  of  the 
galvanometric  response  ;  when  this  gas  is  replaced  by  air  the  nerve  recovers,  and  the 
action-c-urrents  increase.  lather  acts  similarly  ;  but  with  chloroform  recovery  is 
difficult  to  obtain.  Small  doses  of  carbonic  acid  increase  the  action-currents,  and 
Waller  considers  that  the  staircase  effect  in  muscle  (p.  117),  and  the  similar  progres- 
sive increase  noted  in  the  action-currents  of  nerve  as  the  result  of  repeated  stimula- 
tion are  due  to  the  evolution  of  this  gas  during  activity. 

This  hypothesis  has  been  recently  confirmed  by  Ba^yer  and  Frohlich.  They 
have  shown  that  peripheral  nerves  participate  in  respiratory  exchanges,  using  up 
oxygen  and  producing  carbonic  acid  in  measurable  amounts.  In  the  absence  of 
oxygen,  stimulation  ceases  after  some  hours  to  evoke  the  activity  of  a  nerve,  but 
on  re-admission  of  the  gas  recovery  is  almost  instantaneous.  The  store  of  oxygen 
so  obtained  will  again  keep  up  nervous  activity  for  a  considerable  time  even 
although  no  fresh  oxygen  is  supplied.  This  illustrates  the  great  power  nerve  has 
in  repairing  itself  and  in  storing  oxygen. 

There  can  be  no  doubt  that  the  existence  of  the  electrical  variation  is  as  a  rule 
the  index  of  the  excitatory  alteration  in  a  nerve.  But  in  the  present  state  of  our 
knowledge  we  are  not  justified  in  assuming  that  it  gives  an  absolutely  faithful 
record.  The  electrical  variation  can  be  detected  in  a  nerve  for  many  days  after  its 
removal  from  the  body.  Although  the  electrical  change  is  a  concomitant  of  the 
real  excitatory  process,  the  former  may  be  therefore  perceptible  when  other  evidence 
of  the  existence  of  the  latter  fails.  Moreover,  Gotch  and  Burch  have  obtained 
further  e%idence  of  the  dissociation  of  the  electrical  response  from  the  excitatory 
process.     In  the  frog's  sciatic  nerve,  it  is  possible  with  two  stimuli  in  rapid  sue- 


172  PHYSIOLOGY   OF  NERVE  [CH.  XV. 

cession  to  obtain  only  one  electrical  response  near  the  seat  of  excitation  which  has 
been  cooled,  while  two  such  responses  occur  in  a  more  peripheral  warmer  region. 

E.vcitahiliti/  and  condurflvitii. — It  is  necessary  to  distinguish  between  these  two 
properties  of  nerve.  Changes  in  excitability,  and  in  the  power  of  conducting  nerve 
impulses,  do  not  necessarily  go  together,  as  shown  in  the  following  experiment  : — 
The  nerve  of  a  frog's  leg  is  led  through  a  glass  tube,  the  ends  of  which  are  sealed 
with  clay,  care  being  taken  that  the  nerve  is  not  compressed.  The  tube  is  provided 
with  an  inlet  and  outlet,  so  that  gases  may  be  passed  through  it.  Two  pairs  of 
electrodes  are  arranged,  so  that  the  nerve  can  be  stimulated  either  within  or  outside 
the  little  gas  chamber.  If  carbon  dioxide  or  ether  vapour  is  passed  through  the 
tube,  both  excitability  and  conductivity  are  in  time  abolished,  but  excitability 
disappears  first ;  at  this  stage,  if  the  nerve  is  stimulated  by  an  induction  shock 
inside  the  tube,  the  muscle  does  not  respond,  but  on  stimulating  the  nerve  at  the 
end  distant  from  the  muscle  and  outside  the  tube,  the  muscle  contracts.  The  nerve, 
therefore,  is  not  excitable,  though  it  will  conduct  impulses.  At  a  later  stage  shocks 
administered  by  either  pair  of  electrodes  provoke  no  contraction.  When  the 
poisonous  vapour  is  replaced  by  air,  the  nerve  recovers,  and  conductivity  returns 
before  excitability.  If  alcohol  vapour  is  used  conductivity  is  stated  to  vanish  before 
excitability. 

Gotch  has  shown  that  cold  applied  to  a  nerve  acts  very  much  like  carbonic 
acid.  Intense  cold  will  cause  disappearance  of  both  excitability  and  conductivity  ; 
but  cold  of  such  a  degree  which  abolishes  the  excitability  of  the  nerve  to  induction 
shocks,  increases  its  excitability  to  the  constant  current,  and  also  to  mechanical  and 
thermal  stimuli. 

Velocity  of  a  Nerve  Impulse. 

This  has  been  measured  in  motor  nerves  as  follows :  a  muscle- 
nerve  preparation  is  made  with  as  long  a  nerve  as  possible ;  the 
nerve  is  stimulated  first  as  near  to  the  muscle,  and  then  as  far 
from  the  muscle,  as  possible.  The  moment  of  stimulation  and  the 
moment  of  commencing  contraction  is  measured  by  taking  muscle 
tracings  on  a  rapidly  moving  surface  in  the  usual  way,  with  a  time- 
tracing  beneath.  The  contraction  ensues  later,  when  the  nerve  is 
stimulated  at  a  distance  from  the  muscle,  than  in  the  other  case, 
and  the  difference  in  the  two  cases  gives  the  time  occupied  in  the 
passage  of  the  impulse  along  the  piece  of  nerve,  the  length  of  which 
can  be  easily  measured. 

A  similar  experiment  can  be  performed  on  man  by  means  of  the 
transmission  myograph  (see  p.  122).  If  a  tracing  of  the  contraction 
of  the  thumb  muscles  is  taken,  the  two  stimuli  may  be  successively 
applied  through  the  moistened  skin,  first  at  the  brachial  plexus  below 
the  clavicle ;  and  secondly,  at  the  median  nerve  at  the  bend  of 
the  elbow. 

Another  method,  largely  employed  by  Bernstein,  is  to  take  the 
electrical  change  as  the  indication  of  the  impulse.  The  rheotome  is 
the  instrument  used.  If  fig.  169  (p.  139)  is  referred  to,  and  a  long 
nerve  substituted  for  the  muscle-nerve  preparation,  the  stimulus  is 
applied  at  one  end,  and  the  change  in  the  electrical  condition  of  the 
nerve  is  recorded  by  the  galvanometer,  which  is  connected  to  the 
other  end  of  the  nerve.  The  time  measurement  is  effected  by  the 
adjustment  of  the  rheotome,  which  must  be  such  as  to  tap  off  the 
electrical  chancre  at  the  moment  it  occurs. 


CH.  XV.]  NERVE    IMPULSES  173 

The  rate  of  the  transmission  of  nervous  impulses  discovered  by 
these  methods  is,  in  a  fro^^'s  motor  nerve,  28  to  30  metres  a  second ; 
in  human  motor  nerves,  33  metres  a  second ;  in  sensory  nerves,  30 
to  33  metres  a  second. 


Direction  of  a  Nerve  Impulse. 

Nerve  impulses  are  conducted  normally  in  only  one  direction :  in 
efferent  nerves  from,  in  afferent  nerves  to,  the  nerve-centres.  But 
there  are  some  experiments  which  point  to  the  conduction  occurring 
under  certain  circumstances  in  both  directions. 

Thus,  in  the  rheotome  experiment  just  described,  if  the  nerve  is 
stimulated  in  the  middle  instead  of  at  one  end, 
the   electrical  change  (the  evidence  of  an  im- 
pulse) is  found  to  be  conducted  tovs^ards  both 
ends  of  the  nerve. 

Kiihne's  gracilis  experiment  proves  the  same 
point.  The  gracilis  muscle  of  the  frog  (fig. 
191)  is  in  two  portions,  with  a  tendinous  in- 
tersection, and  supplied  by  nerve-fibres  that 
branch  into  two  bundles;  excitation  strictly 
limited  to  one  of  these  bundles,  after  division 
of  the  tendinous  intersection,  causes  both  por- 
tions of  the  muscle  to  contract. 

Another  striking  experiment  of  the  same 
kind  can  be  performed  with  the  nerve  that  ^"'"  ^Aft^r  waiiero  '^°°' 
supplies  the  electrical  organ  of  Malapterurus. 
This  nerve  consists  of  a  single  axis  cylinder  and  its  branches ;  stimu- 
lation of  its  posterior  free  end  causes  the  "  discharge  "  of  the  electrical 
organ,  although  the  nervous  impulse  normally  travels  in  the  opposite 
direction. 

Crossing  of  Nerves. 

Some  experiments  designed  to  prove  the  possibility  of  nervous 
conduction  in  both  directions  were  performed  many  years  ago  by 
Paul  Bert.  He  grafted  the  tip  of  a  rat's  tail  either  to  the  back  of 
the  same  rat,  or  to  the  nose  of  another.  When  union  had  been 
effected,  the  tail  was  amputated  near  its  base.  After  a  time,  irritation 
of  the  end  of  the  trunk -like  appendage  on  the  back  or  nose  of  the 
rat  gave  rise  to  sensation.  The  impulse  thus  passed  from  base  to 
tip,  instead  of  from  tip  to  base,  as  formerly.  This  experiment  does 
not,  however,  prove  the  point  at  all ;  for  all  the  original  nerve-fibres 
in  the  tail  must  have  degenerated,  and  the  restoration  of  sensation 
was  due  to  new  fibres,  which  had  grown  into  the  tail.  Exactly  the 
same  objection  holds  to  another  series  of  experiments,  in  which  the 


174  PHYSIOLOGY   OF   NERVE  [CH.  XV. 

motor  and  sensory  nerves  of  the  tongue  were  divided  and  united 
crosswise.  Restoration  of  both  movement  and  sensation  does  occur, 
but  is  owing  to  new  nerve-fibres  growing  out  from  the  central  stumps 
of  the  cut  nerves. 

Though  these  experiments  do  not  prove  what  they  were  intended 
to,  they  are  of  considerable  interest  in  themselves.  Dr  E.  Kennedy 
has  recently  carried  out  a  very  careful  piece  of  work  on  this  question 
of  nerve  crossing.  He  cut  in  a  dog's  thigh  the  nerves  supplying 
the  flexor  and  the  extensor  muscles,  and  sutured  them  together 
crosswise.  Regeneration  of  structure  and  restoration  of  function 
occurred  equally  quickly,  as  in  those  cases  in  which  the 
central  ends  had  been  united  to  the  peripheral  ends  of  their  own 
proper  nerves.  On  examining  the  cortex  of  the  brain  in  those 
animals  in  which  nerve-crossing  had  been  accomphshed,  it  was 
found  that  stimulation  of  the  region  which  in  a  normal  animal  gave 
flexion,  now  gave  extension  of  the  limb,  and  vice  versa. 

A  series  of  equally  important  experiments  have  more  recently 
been  carried  out  by  Langley,  in  which  he  shows  that  the  same  facts 
are  true  for  the  nerves  that  supply  involuntary  muscle.  These 
nerve-fibres  will  under  certain  experimental  conditions  terminate  by 
arborising  around  other  nerve-cells  than  those  which  they  normally 
form  connections  (synapses)  *  with.  It  will  be  sufficient  to  give  one 
typical  experiment.  If  the  vagus  nerve  is  cut  across  in  the  neck,  its 
peripheral  end  degenerates  downwards ;  if  the  cervical  sympathetic 
is  cut  across  below  the  superior  cervical  ganglion,  its  peripheral  end 
degenerates  upwards,  as  far  as  the  ganglion.  If  subsequently  the 
central  end  of  the  cut  vagus  is  united  to  the  peripheral  end  of  the 
cut  sympathetic,  in  the  course  of  some  weeks  the  vagus  fibres  grow 
into  the  sympathetic  and  form  synapses  around  the  cells  of  the 
superior  cervical  ganglion,  and  stimulation  of  the  united  nerve  now 
produces  such  effects  as  are  usually  obtained  when  the  cervical 
sympathetic  is  irritated ;  for  instance,  dilatation  of  the  pupil,  raising 
of  the  upper  eyelid,  and  constriction  of  blood-vessels  of  the  head  and 
neck.     (See  accompanying  diagram,  fig.  192.) 

Such  experiments  as  these  are  important  because  they  teach  us 
that  though  the  action  of  nerves  may  be  so  different  in  different 
cases  (some  being  motor,  some  inhibitory,  some  secretory,  some 
sensory,  etc.),  after  all  what  occurs  in  the  nerve  trunk  itself  is 
always  the  same ;  the  difference  of  action  is  due  to  difference  either 
in  the  origin  or  distribution  of  the  nerve-fibres.  If  we  remember 
the  familiar  illustration  in  which  nerve  trunks  are  compared  to 
telegraph  wires,  we  may  be  helped  in  reaUsing  this.  The  destina- 
tion of  a  certain  group  of  telegraph  wires  may  be  altered,  and  the 

*  The  meaning  of  the  term  "  synapse  "  is  fully  explained   in  Chapter  XVII. 

(p.  198). 


ClI.  XV.] 


CHEMISTRY   OF   NERVE 


175 


alteration  may  produce  different  consequences  at  different  places ; 
the  electric  change,  however,  in  the  wires  would  be  the  same  in  all 
cases.  So  the  nerve  impulse  going  along  a  nerve  is  always  the  same 
sort  of  molecular  disturbance;  if  it  is  made  as  in  the  experiment 
just  described,  to  go  by  a  wrong  channel,  it  produces  just  the  same 

A  B  C 


Superi 
Ceru 
Gang  I 


'.r'wrf     \ 
ical  I        ) 

7/0/)  \_y 


►~0o 

Fio.  192. — Diagram  to  illustrate  Langley's  experiment  on  vagus  and  cervical  sympathetic  nerves.  In 
A,  the  two  nerves  are  shown  intact ;  the  direction  of  the  impulses  they  normally  carry  is  shown  by 
arrows,  and  the  names  of  some  of  the  parts  they  supply  are  mentioned.  In  B,  both  nerves  are  cut 
througli.  The  degenerated  portions  are  represented  by  discontinuous  lines.  In  C,  the  union 
described  in  the  text  has  been  accomplished,  and  stimulation  at  the  point  a'  now  produces  the  same 
results  as  were  in  the  intact  nerves  (A)  produced  by  stimulation  at  a. 

results  as  though  the  impulse  had  reached  its  destination  by  the 
usual  channel. 

Chemistry  of  Nervous  Tissues. 

The  following  table  gives  some  typical  analyses  of  the  solids  of  nervous  tissues, 
but  these  tissues  also  contain  a  large  amount  of  water ;  this  is  present  in  larger 


Portion  of 
Nervous  System. 

1 

p-i 

1 

1  Choleste- 
Lecithin.      rin  and 
Fat. 

Neuro- 
keratin. 

Other 
Organic 
matters. 

i 

Grey  matter  of  Brain     . 
White  matter  of  Brain  . 

Spinal  Cord   .... 

Human  Sciatic  Nerve    . 

55 
25 

23 

36 

17              19          0-5 
10             52         9-5 

6-7 
3-3 

1-5 
0-6 

1-1 

75-1 

32       1       12          11            3        1        4 

176 


PHYSIOLOGY   OF   NERVE 


[CH.  XY. 


amount  (8"  per  cent.)  in  grey  matter  than  in  white  matter  (70  per  cent.) ;  in  early 
than  in  adult  lite  ;  in  the  brain  than  in  the  fij)inal  cord  ;  in  the  sj)inal  cord  than  in 
nerves. 

One  sliould  next  note  the  high  percentage  of  protein.  In  grey  matter,  where 
the  cells  are  prominent  structures,  this  is  most  marked,  and  of  the  solids,  protein 
material  here  comprises  more  than  half  of  the  total.  The  following  are  some  of  my 
analyses  which  give  the  mean  of  a  number  of  observations  on  the  nervous  tissues 
of  human  beings,  monkeys,  dogs,  and  cats  : 


Percentage  of 

Water. 

Solids. 

Proteins  in 
Solids. 

Cerebral  grey  matter  . 

83-5 

16-5 

51 

,,         white     ,, 

69-9 

30-1 

33 

Cerebellum  .... 

79-8 

20-2' 

42 

Spinal  cord  as  a  whole 

71-6 

28-4 

31 

Cervical  cord 

72-5 

27-5 

31 

Dorsal  cord 

69-8 

30-2 

28 

Lumbar  cord 

72-6 

27-4 

33 

Sciatic  nerves 

65-1 

34-9 

29 

The  most  abundant  protein  is  nndeo-protein  ;  there  is  also  a  certain  amount  of 
glolndm,  which,  like  the  paramyosinogen  of  muscle,  is  coagulated  by  heat  at  the  low 
temperature  of  47°  C.  A  certain  small  amount  of  neurokeratin  (especially  abundant 
in  white  matter)  is  included  in  the  above  table  with  the  proteins.  The  granules  in 
nerve  cells  (Nissl's  bodies),  which  stain  readily  M'ith  methylene  blue,  are  nucleo- 
protein  in  nature.  The  next  most  abundant  substances  are  of  a  fatty  nature  ;  the 
most  prominent  of  these  is  the  phosphorised  fat  called  lecithin.  Protac/on 
(which  crystallises  out  on  cooling  a  hot  alcoholic  extract  of  brain  or  other  nervous 
structures)  and  Kephalin  are  other  phosphorised  fats  of  uncertain  composition. 
Cerehrin  is  a  term  which  probably  includes  several  .substances,  which  are  nitro- 
genous glucosides  ;  they  yield  on  hydrolysis  the  sugar  called  galactose.  They  are 
sometimes  called  cerebrosides.  The  crystalline  monatomic  alcohol  cholesterin  is 
also  a  fairly  abundant  constituent  of  nervous  structures,  especially  of  the  white 
substance  of  Schwann.  Finally,  there  are  smaller  quantities  of  other  extractives 
and  a  small  proportion  of  mineral  salts  (about  1  per  cent,  of  the  solids). 

In  connection  with  the  substances  just  enumerated,  it  is  necessary  to  enter  a 
little  more  fully  into  the  composition  of  lecithin.  An  ordinary  fat  contains  the 
elements  carbon,  hj^drogen,  and  oxygen,  and  when  it  takes  up  water  it  is  split  or 
hydrolysed  into  its  constituent  parts,  glycerin  and  fatty  acid. 


Fat  +  water. 


Glycerin. 


I 
Fatty  acid. 


Lecithin  (Cj.jHg^NPOg)  contains  not  only  carbon,  hydrogen,  and  oxygen,  but 
nitrogen  and  phosphorus  as  well.  When  it  is  hydrolysed,  it  yields  not  only  glycerin 
and  a  fatty  acid,  but  ;ilso  phosphoric  acid,  and  a  nitrogenous  base  termed  choline. 

Lecithin  +  water. 


Glycerin. 


Fatty  acid. 


Phosphoric  acid. 


Choline, 


CII.  XV.]  CHEMISTRY   OF   NERVE   DEGENERATION  177 

Fresh  luTvous  tissues  are  alkaline,  but,  like  most  other  living  struetures,  they 
turn  aeiil  after  death.  The  change  is  particularly  rapid  in  grey  matter.  The 
aeidity  is  due  to  lactic  acid. 

Very  little  is  known  of  the  chemical  changes  nervous  tissues  undergo 
during  activity.  We  know  that  oxygen  is  very  essential,  especially  for  the  activity 
of  grey  matter ;  cerebral  anaemia  is  rapidly  foUowed  by  loss  of  consciousness  and 
death.  We  have  already  seen  that  similar  respiratory  exchanges,  though  less 
in  amount,  occur  in  peri]ihcral  nerves  (see  p.  171). 

Chemistry  of  nerve  degeneration. — Mott  and  I  have  shown  that  in  the 
disease  General  Paralysis  of  the  Insane,  the  marked  degeneration  that  occurs  in 
the  brain  is  accompanied  by  the  i)assing  of  the  products  of  degeneration  into  the 
cerebro-spinal  fluid.  Of  these,  micleo-protein  and  choline — a  decomj)osition  pro- 
duct of  the  lecithin — arc  those  which  can  be  most  readily  detected.  Choline  can 
also  be  found  in  the  blood.  But  this  is  not  peculiar  to  the  disease  just  mentioned, 
for  in  various  other  degenerative  nervous  diseases  (combined  sclerosis,  disseminated 
sclerosis,  meningitis,  ak-oholic  neuritis,  beri-beri,  etc.)  choline  can  also  be  detected 
in  these  situations.  The  tests  employed  to  detect  choline  are  mainly  three:  (1)  a 
chemical  test,  namely,  the  obtaining  of  the  characteristic  yellow  octahedral  crystals 
of  the  platinum  double  salt  from  the  alcoholic  extract  of  the  cerebro-spinal  fluid  or 
blood.  This  test  is  not  absolutely  trustworthy,  for  potassium  and  ammonium  salts 
may  give  crystals  very  similar  in  appearance,  although  different  in  composition ; 
(2)  this  test  is  free  from  any  such  objection,  and  consists  in  adding  a  strong  solution 
of  iodine  to  the  suspected  fluid  ;  if  choline  is  present  characteristic  brown  crystals 
of  the  periodide  of  choline  are  obtained ;  (3)  a  physiological  test,  namely,  the 
lowering  of  arterial  blood-pressure  (partly  cardiac  in  origin,  and  partly  due  to 
dilatation  of  peripheral  vessels)  which  a  saline  solution  of  the  residue  of  the  alcoholic 
extract  produces :  this  fall  is  abolished,  or  even  replaced  by  a  rise  of  arterial 
pressure,  if  the  animal  has  been  poisoned  with  atropine.  Such  tests  have  already 
been  shown  to  be  of  diagnostic  value  in  the  distinction  between  organic  and  so- 
c-alled  functional  diseases  of  the  nervous  system.  The  chemical  tests  can  frequently 
be  obtained  with  10  c.c.  of  fluid,  or  even  less. 

A  similar  condition  can  be  produced  artificially  in  animals  by  a  division  of 
large  nerve  trunks  ;  and  is  mpst  marked  in  those  animals  in  which  the  degenerative 
process  is  at  its  height  as  tested  histologically  by  the  Marchi  reaction.*  A  series 
of  cats  was  taken,  both  sciatic  nerves  divided,  and  the  animals  subsequently  killed 
at  intervals  varying  from  1  to  10(3  days.  The  nerves  remain  practic-ally  normal  as 
long  as  they  remain  irritable,  that  is  up  to  about  3  daJ^s  after  the  operation.  They 
then  show  a  progressive  increase  in  the  percentage  of  water,  and  a  progressive 
decrease  in  the  percentage  of  phosphorus  until  degeneration  is  complete.  When 
regeneration  occurs,  the  nerves  return  approximately  to  their  previous  chemical 
condition.  When  the  Marchi  reaction  disappears  in  the  later  stages  of  degenera- 
tion, the  non-phosphorised  fat  has  been  absorbed.  This  absorption  occurs  earlier 
in  the  peripheral  nerves  than  in  the  central  nervous  system. 

Further,  it  has  been  found  that  in  spinal  cords  in  which  a  unilateral  degenera- 
tion of  the  pyramidal  tract  has  been  produced  by  a  lesion  in  the  opposite  hemi- 
sphere, there  is  a  similar  increase  of  water  and  diminution  of  phosphorus  on  the 
degenerated  side. 

The  following  table  shows  these  main  results  in  the  experiments  on  cats  just 
described. 

The  figures  relate  to  the  peripheral  portions  of  the  nerves.  Noll  has  shown 
that  the  phosphorised  material  also  diminishes  somewhat  in  the  central  ends  of 
cut  nerves  due  to  "  disuse  atrophy," 

*  The  Marchi  reaction  is  the  black  staining  that  the  medullary  sheath  of  degenerated  nerve-fibres 
shows  when,  after  being  hardened  in  Muller's  fluid,  they  are  treated  with  Marchi's  reagent,  a  mixture 
of  Muller's  fluid  and  osmic  acid.  Healthy  nerve-flbres  are  not  affected  by  the  reagent,  but  normal 
adipose  tissue  is  blackened  like  degenerated  myelin.  The  osmic  acid  reaction  is  due  to  fats  like  olein 
which  belong  to  the  acrylic  series. 


M 


178 


PHYSIOLOGY   OF  NERVE 


[CH.  XV. 


Cat's  sciatic  nerves. 

Condition  of 
blood. 

Condition  of 
nerves. 

si 

"o 

Percentage 

of 

phosphorus 

in  solids. 

Normal  .... 
1  to  3  days  after  section 

4  to  6 

8 

10 

13 

25  to  27 
29 

44 
100  to  106 

65-1 
64-5 

69-3 

68-2 
70-7 
71-3 

72-1 
72-5 

72-6 
66-2 

34-9 
35-5 

30-7 

31-8 
29-3 

28-7 

27-9 
27-5 

27-4 
3-8 

ri 

0-9 

0-9 

0-5 
0-3 
0-2 

traces 
0 

0 
0-9 

( Minimal  traces 
-     of  choline 
[  present. 

(Choline    more 
\  abundant. 

(Choline  abun- 
\  dant. 

(Choline  much 
\  less. 

C  Choline  almost 
\  disappeared. 

("Choline  almost 
\  disappeared. 

[Nerves  irritable 

and  histologically 
[  healthy. 
[  Irritability  lost ; 

-  degeneration 
(  beginning. 
[Degeneration  well 

shown  by  Marchi 
(  reaction, 
f  Marchi       reaction 

still      seen,      but 

-  absorption  of  de- 
generated fat  has 
set  in. 

[Absorption  of  fat 

-  practically     com- 
(  plete. 

[  Return  of  function, 
nerves      regener- 
[  ated. 

Heat  contraction  of  nerve.— A  nerve,  when  heated,  shortens  ;  this  shortening 
occurs  in  a  series  of  steps  which,  as  in  the  case  of  muscle,  take  place  at  the  coagula- 
tion temperatures  of  the  proteins  present.  The  first  step  in  the  shortening  occurs 
in  the  frog  at  about  40%  in  the  mammal  at  about  47°,  and  in  the  bird  at  about  52"  C. 
The  nerve  is  killed  at  the  same  temperatures. 

Cerebro-spinal  fluid. — This  plays  the  part  of  the  lymph  of  the  central  nervous 
system,  but  differs  considerably  from  all  other  forms  of  lymph.  It  is  a  very  watery 
fluid,  containing,  besides  some  inorganic  salts  similar  to  those  of  the  blood,  a  trace 
of  protein  matter  (globulin)  and  a  small  amount  of  sugar.  It  contains  the  merest 
trace  of  choline  ;  but  this  is  not  devoid  of  significance,  for  this  fact  taken  in  con- 
junction with  anotiier — namely,  that  physiological  saline  solution  will  extract  from 
perfectly  fresh  nervous  matter  a  small  quantity  of  choline — shows  us  that  lecithin 
and  protagon  are  not  stable  substances,  but  are  constantly  breaking  down  and 
building  themselves  up  afresh  ;  in  fact,  undergoing  the  process  called  metabolism. 
This  is  most  marked  in  the  most  active  region  of  the  brain — viz.,  the  grey  matter. 

Potassium  salts  in  nervous  tissues.- — These,  as  in  muscle,  are  stated  to  be 
the  most  abundant  salts.  Macallum  uses  for  the  micro-chemical  detection  of 
potassium  an  acid  solution  of  cobalt  nitrite,  and  precipitates  in  situ  the  yellow 
hexanitrate  of  cobalt  and  potassium,  which  is  turned  black  on  the  addition  of 
ammonium  sulphide.  His  principal  results  are : — potassium  is  found  in  cell  proto- 
plasm, but  more  abundantly  in  intercellular  material ;  in  striped  muscle  it  is  limited 
to  the  dark  bands,  and  in  pancreatic  ceUs  to  the  granular  zone.  It  is  not  discoverable 
in  any  nuclei,  nor  in  nerve-cells,  but  in  nerve-fibres  is  found  in  patches  external  to 
the  axis  cylinder.  Macdonald  points  out  that  these  are  spots  which  have  been 
injured,  and  it  is  apparently  only  on  injury  that  the  potassium  is  liberated  in  a 
form  which  renders  it  detectable  by  Macallum's  reagent.  Macdonald  attributes 
many  of  the  phenomena  of  nervous  action  to  electrolytic  changes  in  the  potassium 
salts  of  the  nerve-fibres,  and  which  are  present  in  large  amounts. 


CHAPTER  XVI 


ELECTROTONUS 


When  a  constant  current  is  thrown  into  a  nerve,  there  is  an  excita- 
tion which  leads  to  a  nervous  impulse,  and  this  produces  a  contraction 
of  the  muscle  at  the  end  of  the  nerve.  Similarly,  there  is  another 
contraction  when  the  current  is  taken  out.  While  the  current  is 
flowing  through  the  nerve,  the  muscle  is  quiescent.  But  while  the 
current  is  flowing  there  are  changes  in  the  nerve,  both  as  regards  its 
electrical  condition  and  its  excitability.  These  changes  are  summed 
up  in  the  expression  eledrofonus. 

In  the  investigation  of  this  subject  the  instruments  employed  are 
the  same  as  those  already  described,  with  the  addition  of  two  others 
that  it  will  be  convenient  to  describe  before  passing  on  to  the  study 
of  electrotonus  itself.  These  are  the  reverser  or  commutator,  and 
the  rheochord. 

Pohl's  commutator  is  the  form  of  reverser  generally  employed.  It 
consists  of  a  block  of  ebonite  provided  with  six  pools  of  mercury, 


Fig.  193. — Pohl's  Commutator,  with  cross  wires.     (Alter  Waller.) 

each  of  which  is  provided  with  a  binding  screw.  The  corner  pools 
are  connected  by  diagonal  cross  wires,  and  by  a  cradle  consisting  of 
an  insulating  handle  fixed  to  two  arcs  of  copper  wire  which  can  be 
tilted  so  that  the  two  middle  pools  can  be  brought  into  communication 
with  either  of  the  two  lateral  pairs  of  pools.     Fig.  193  shows  how,  by 


180 


ELECTROTONUS 


[CH.  XVI. 


altering  the  position  of  the  cradle,  the  direction  of  the  current  from 
one  electrode  to  the  other  is  reversed.  The  numbers  1,  2,  3,  etc., 
indicate  the  path  of  the  current  in  the  two  cases. 

Sometimes  the  reverser  is  used  without  the  cross  wires  for  a  different  purpose. 
The  battery  wires  are  connected  as  before  with  the  middle  mercury  pools.  Each 
lateral  pair  of  pools  is  connected  by  wires  to  a  pair  of  electrodes.  The  two  pairs  of 
electrodes  may  be  applied  to  two  portions  of  a  nerve,  or  to  two  diiferent  nerves,  and 
by  tilting  the  cradle  to  right  or  left  the  current  can  be  sent  through  one  or  the  other 
pair  of  electrodes. 

The  rheochord  is  an  instrument  by  means  of  which  the  strength  of 
a  constant  current  passed  through  a  nerve  may  be  varied.  It  consists 
of  a  long  wire  (r,  r,  r)  of  high  resistance  stretched  on  a  board.     This 


Fig.  194. — Simple  Rheochord. 

is  placed  as  a  bridge  on  the  course  of  the  battery  current.  (See^fig. 
19-i.)  The  current  is  thus  divided  into  two  parts :  one  part  through 
the  bridge,  the  other  through  the  nerve,  which  is  laid  across  the  two 
non-polarisable  electrodes  at  the  ends  of  the  wires.  The  resistance 
through  the  bridge  is  varied  by  the  position  of  the  slider  (s  s).  The 
farther  the  slider  is  from  the  battery  end  of  the  instrument  the 
longer  is  the  bridge,  and  the  higher  its  resistance,  so  that  less  current 
goes  that  way  and  more  to  the  nerve. 

The  next  figure  shows  the  more  complicated  form  of  rheochord 
invented  by  Poggendorf.     The  number  of  turns  of  wire  is  greater,  so 


ge^-.^,^^i^---^=~^=:-.^- 


Fig.  195.— Poggeudorfs  Rheochord.    (M'Ken<lriek.) 

that  the  resistance  can  be  varied  to  a  much  greater  extent  than  in 
the  simpler  form  of  the  instrument. 


CH.  XTI.]  ELKCTROTONIC   CURRENTS  181 

The  term  "  electrotonus "  includes  two  sets  of  changes  in  the 
nerve;  first  an  electrical  cliange,  and  secondly  changes  in  excitability 
and  conductivity.     We  will  take  the  electrical  change  first. 

Blectrotonic  currents. — The  constant  current  is  passed  tlirough 
the  nerve  from  a  battery,  non-polarisable  electrodes  licing  used;  it  is 
called  the  polarising  current.  If  portions  of  the  nerve  Ijeyond  the 
electrodes  are  connected  ("led  off")  as  in  the  diagram  (fig.  196)  by 
non-polarisable  electrodes  to  galvanometers,  a  current  will  in  each 
case  be  indicated  by  the  swing  of  the  galvanometer  needles.  The 
electrotonic  current  in  the  neiglibourhood  of  the  negative  p)ole  or 
kathode  is  called  the  Icateledrotonic  current ;  and  that  in  the  neighbour- 
hood of  the  anode  is  called  the  anelectrotonic  current.  In  both  cases  the 
electrotonic  current  has  the  same  direction  as  the  polarising  current. 
These  currents  are  dependent  on  the  physical  integrity  of  medullated 


Anelectrotonic        y,  fy       Katelectrotonic 

Current  \\  >         |  |  Current 

Polarising 
Current 


Fig.  106. — Electrotonic  currents. 

nerve;  they  are  not  found  in  muscle,  tendon,  or  non-medullated 
nerve ;  they  are  absent  or  diminished  in  dead  or  degenerated  nerve. 
They  can,  however,  be  very  successfully  imitated  in  a  model  made  of 
zinc  wire  encased  in  cotton  soaked  with  salt  solution.  The  electro- 
tonic currents  must  be  carefully  distinguished  from  the  normal 
current  of  action,  which  is  a  momentary  change  rapidly  propagated 
with  a  nervous  impulse  which  may  be  produced  by  any  method  of 
stimulation.  The  electrotonic  currents  are  produced  only  by  an 
electrical  (polarising)  current;  they  vary  in  intensity  with  the 
polarising  current,  and  last  as  long  as  the  polarising  current  passes 
through  the  nerve. 

After  the  polarising  current  is  removed,  after-electrotonic  currents   occur   in 
different  directions  in  the  three  regions  tested. 

(«)  In  the  intrapolar  region,  the  after-current  is  opposite  in  direction  to  the 

original  polarising  current ;  unless  the  polarising  current  is  strong  and  of 

short  duration,  when  it  is  in  the  same  direction. 
{b)  In  the  katelectrotonic  region,  the  after-current  has  the  same  direction  as  the 

katelectrotonic  current. 
(c)  In  the  anelectrotonic  region,  the  after-current  has  at  first  the  same,  then 

the  opposite  direction  to  the  anelectrotonic  current. 


182 


ELKCTROTONUS 


[CH.  XVI. 


The  experiment  known  as  the  paradoxical  contraction  depends 
upon  electrotonie  currents.  The  sciatic  nerve  of  the  frog  divides 
in  the  lower  part  of  the  thigh  into  two  parts.  If  one  division  is 
cut  across,  and  its  central  end  stimulated  electrically  (the  spinal  cord 
having  been  previously  destroyed),  the  muscles  supplied  by  the  other 
branch  contract ;  the  nerve-fibres  in  this  branch  having  been  stimu- 
lated by  the  electrotonie  variation  in  the  divided  branch.* 

Electrotonie  alterations  of  excitability  and  conductivity. — 
When  a  constant  current  is  passed  through  a  nerve,  the  excitability 
and  conductivity  of  the  nerve  are  increased  in  the  region  of  the 
kathode,  and  diminished  in  the  region  of  the  anode.  "When  the 
current  is  taken  out  these  properties  are  temporarily  increased  in 
the  neighbourhood  of  the  anode,  and  diminished  in  that  of  the 
kathode. 

This  may  be  shown  in  the  case  of  a  motor  nerve  by  the  following 
experiment.     The  next  diagram  represents  the  apparatus  used. 


/<>_ 


^dellJ^'---..      \ 


Coil 
EXCITING     CIRCUIT 
F^G.  197. — Diagram  of  apparatus  used  in  testing  electrotonie  alterations  of  excitability. 

An  exciting  circuit  for  single  induction  shocks  is  arranged  in  the 
usual  way,  the  exciting  electrodes  being  placed  on  the  nerve  near  the 
muscle.  A  polarising  circuit  is  also  arranged,  and  includes  a  battery, 
key,  and  reverser ;  the  current  is  passed  into  the  nerve  by  means  of 
non-polarisable  electrodes.  When  the  polarising  current  is  thrown 
into  the  nerve,  or  taken  out,  a  contraction  of  the  muscle  occurs,  but 
these  contractions  may  be  disregarded  for  the  present. 

The  exciting  circuit  is  arranged  with  the  secondary  coil  so  far  from 
the  primary  that  the  muscle  responds  to  break  only,  and  the  tracing 

*  This  experiment  must  be  carefully  distinguished  from  Kiihne's  gracilis 
experiment  described  on  p.  173.  In  the  gracilis  experiment  the  nerve-fibres 
themselves  branch,  and  any  form  of  stimulation  applied  to  one  branch  will  cause 
contraction  of  both  halves  of  the  muscle.  In  the  paradoxical  contraction,  the 
bundles  of  nerve-fibres  are  merely  bound  side  hy  side  in  the  sciatic  trunk  ;  there  is 
therefore  no  possibility  of  conduction  of  a  nerve  impulse  in  both  directions ;  the 
stimulus,  moreover,  must  be  an  electrical  one. 


CH.  XVI.] 


CHANGES    IX    EXCITABILITY 


183 


may  be  recorded  ou  a  stationary  blackened  cylinder.  The  cylinder  is 
moved  on  a  short  distance,  and  this  is  repeated.  The  height  of  the 
lines  drawn  may  be  taken  as  a  measure  of  the  excitability  of  the  nerve. 
The  polarising  current  is  then  thrown  in,  in  a  descending  direction 
{i.e.,  towards  the  muscle);  the  kathode  is  thus  the  non-polarisable 
electrode  near  to  the  exciting  electrodes.  While  the  polarising  current 
is  flowing,  take  some  more  tracings  by  breaking  the  exciting  current. 
The  increase  in  the  excitability  of  the  nerve  is  shown  by  the  much 
larger  contractions  of  the  muscle;  probably  a  contraction  will  be 
obtained  now  at  both  make  and  break  of  the  exciting  current.  After 
removing  the  polarising  current,  the  contractions  obtained  by  excit- 
ing the  nerve  will  be  for  a  short  time  smaller  than  the  normal,  but 
soon  return  to  their  original  size. 

Exactly  the  reverse  occurs  when  the  polarising  current  is  ascend- 
ing, i.e.,  from  the  muscle  towards  the  spinal  cord.  The  non-polarisable 
electrode  near  the  exciting  electrodes  is  now  the  anode.  While  the 
polarising  current  is  passing,  the  excitability  of  the  nerve  is  diminished 
so  that  induction  shocks  which  previously  produced  contractions  of  a 
certain  size,  now  produce  smaller  contractions,  or  none  at  all.  On 
remo\T.ng  the  polarising  current,  the  after-effect  is  increase  of  excit- 
ability. 

The  following  figure  is  a  reproduction  of  a  tracing  from  an  actual 
experiment.  The  after-effects 
are  not  shown.  N  represents 
a  series  of  contractions  ob- 
tained when  the  nerve  is 
normal,  K  when  it  is  kat- 
electrotonic,  A  when  it  is 
anelectrotonic. 

Exactly  similar  results  are 
obtained  if  one  uses  mechani- 
cal stimuli,  such  as  hammer- 
ing the  nerve,  instead  of 
induction  shocks.  The  same 
is  true  for  chemical  stimuli. 
If  the  exciting  electrodes  are 
removed,  and  salt  sprinkled 
on  the  nerve  near  the  muscle, 
the  latter  soon  begins  to 
quiver ;  its  contractions  are 
increased  by  throwing  in  a  descending  and  diminished  by  an  ascend- 
ing polarising  current. 

The  increase  in  irritability  is  called  katelectrotoniis,  and  the 
decrease  is  called  anelectrotonus.  The  accompanying  diagram  (fig. 
199)  shows  how  the  effect  is  most  intense  at  the  points  (a  k)  where 


Fig.  198. — Electrotonos.    il,  make.    B,  break. 


184 


ELECTROTONUS 


[CH.  XVI. 


the  electrodes  are  applied,  and  extends  in  gradually  diminishing 
intensity  on  each  side  of  them.  Between  the  electrodes  the  increase 
shades  off  into  the  decrease,  and  it  is  evident  that  there  must  be  a 
neutral  point  where  there  is  neither  increase  nor  decrease  of  irritability. 
The  position  of  this  neutral  point  is  found  to  vary  with  the  intensity 


<  «<g 


if 


Fig.  199. — Diagram  illustrating  the  effects  of  various  intensities  of  the  polarising  current,  n,  n' ,  nerve ; 
a,  anode  ;  k,  kathode  ;  the  curves  above  indicate  increase,  and  those  below  decrease  of  irritability, 
and  when  the  current  is  small  the  increase  and  decrease  are  both  small,  with  the  neutral  point  near 
a,  and  as  the  current  is  increased  in  strength,  the  changes  in  irritability  are  greater,  and  the  neutral 
point  approaches  k. 

of  the  polarising  current — when  the  current  is  weak  the  point  is 
nearer  the  anode,  when  stronf^  nearer  the  kathode. 

Pfliiger's  law  of  contraction. — The  constant  current  sometimes 
causes  a  contraction  both  at  make  and  break,  sometimes  at  make  only, 
sometimes  at  break  only.  The  difference  depends  on  the  strength  and 
direction  of  the  current ;  and  follows  from  the  electrotonic  changes  of 
excitability  and  conductivity  we  have  been  studjing.  Increase  of  ex- 
citability acts  as  a  stimulus ;  so  that  at  the  make  the  kathode  is  the 
stimulating  electrode,  and  at  the  break  the  anode  is  the  stimulating 
electrode. 

The  facts  may  be  demonstrated  in  the  following  way  (fig.  200) : 


Key  ^jji^ 

Fig.  200.— Arrangement  of  apparatus  for  demonstrating  Pfliiger's  law. 

from  a  battery  lead  the  wires  to  the  middle  screws  of  a  reverser  (with 
cross  wires),  interposing  a  key ;  from  one  pair  of  end  screws  of  the 
reverser  lead  wires  to  the  binding  screws  of  the  rheochord  ;  from  these 
same  screws  of  the  rheochord  the  non-polarisable  electrodes  lead  to 
the  nerve  of  a  nerve-muscle  preparation.  The  strength  of  the  current 
is  varied  by  the  slider  S.     The  nearer  S  is  to  the  binding  screws  the 


CH.  XVL] 


pflDger's  law  of  contraction 


185 


less  is  the  resistance  in  the  rheochonl  circuit,  and  the  less  the  current 
through  the  nerve.  With  a  weak  current,  a  contraction  occurs  at 
make  only,  but  more  readily,  i.e.  with  a  weaker  current,  when  its 
direction  is  descending,  i.e.  towards  the  muscle.  With  a  stronger 
current  (ascending  or  descending)  contraction  occurs  both  at  make 
and  break.  With  a  very  strong  current  (six  Groves),  the  contraction 
occurs  only  at  make  with  a  descending  current ;  and  only  at  break 
with  an  ascending  current. 

The  contractions  produced  in  the  muscle  of  a  nerve-muscle 
preparation  by  a  constant  current  have  been  arranged  in  a  table 
which  is  known  as  Pfliiger's  Law  of  Contraction. 


Strength  op 
Current  osed. 

Descending  Citerent. 

Ascending  Current. 

Make. 

Break. 

Make. 

Break. 

Weak   . 
Moderate 
Strong  . 

Yes. 

Yes. 
Yes. 

No. 
Yes. 

No. 

Yes. 
Yes. 
No. 

No. 
Yes. 
Yes. 

The  increase  of  irritability  at  the  kathode  when  the  current  is 
made  is  greater,  and  so  more  potent  to  produce  a  contraction  than  the 
rise  of  irritability  at  the  anode  when  the  current  is  broken ;  and  so 
with  weak  currents  the  only  effect  is  a  contraction  at  the  make. 
But  when  the  strength  of  the  current  is  increased  the  rise  of 
excitability  is  in  all  cases  sufficient  to  provoke  a  contraction 
(moderate  effect  in  above  table).  The  alteration  in  conductivity 
is  not  sufficient  to  prevent  the  impulses  being  propagated  to  the 
muscle. 

With  strong  currents  the  case  is  a  little  more  complicated, 
because  here  the  diminution  of  conductivity  is  so  great  that  certain 
regions  of  the  nerve  become  impassable  by  nerve  impulses.  When 
the  current  has  an  ascending  direction,  the  impulse  at  the  break  is 
started  at  the  anode,  and  as  this  is  next  to  the  muscle  there  is  no 
hindrance  to  the  propagation  of  the  impulse,  but  at  the  make  the 
impulse  started  at  the  kathode  is  blocked  by  the  extreme  lowering 
of  conductivity  at  the  anode.  When  the  current  is  descending  the 
kathode  is  near  the  muscle,  and  so  the  impulse  at  make  reaches  the 
muscle  without  hindrance ;  but  at  the  break,  the  impulse  started  at 
the  anode  has  to  traverse  a  region  of  nerve,  the  conductivity  of  which 
is  so  lessened  that  the  excitation  is  not  propagated  to  the  muscle. 

G.  N.  Stewart  has  stated  in  opposition  to  the  foregoing  statements  that  at  the 
make  conductivity  is  most  lowered  at  the  kathode,  and  at  the  break  at  the  anode. 
In  other  words,  conductivity  and  excitability  vary  in  opposite  directions.  His 
results  have,  however,  not  been  accepted  by  other  physiologists,  and  are  due  to  a 
complex  set  of  excitatory  and  polarisation  changes  produced  by  the  galvanometric 


186  ELECTEOTONUS  [CH.  XVI. 

methods  he  adopted.  Gotchs  much  more  trustworthy  experiments  with  the 
electrometer  are  directly  ojiposed  to  those  of  Stewart.  The  following  simple 
experiment  devised  by  Gotch  appears  to  be  quite  conclusive  that  conductivity  like 
excitability  is  lessened  at  the  anode  when  the  current  is  made.  Three  non-polaris- 
able  electrodes  are  employed  (fig.  201J,  the  current  is  first  closed  from  Ao  to  K,  and 
the  time  which  intervenes  before  the  muscle  contracts  is  measured  ;  it  is  then 
closed  from  A,  to  K,  and  the  time  again  measured.  In  both  cases,  excitation 
occurs  at  K,  but  the  time  of  response  in  the  second  case  (A;  to  K)  is  longer,  because 
in  that  case  the  nerve  impulse  has  to  traverse  a  region  of  nerve  at  A,  in  which  the 
power  of  conduction  is  lessened. 


1 1- 1 — 

As  K  Aj 

Fig.  201. — Diagram  to  illustrate  Gotch's  experiment  with  triple  electrodes. 

Sometimes  (when  the  preparation  is  specially  irritable)  instead  of 
a  simple  contraction  a  tetanus  occurs  at  the  make  or  break  of  the 
constant  current.  This  is  due  to  chemical  (electrolytic)  changes  pro- 
duced by  the  current,  and  is  liable  to  occur  at  the  break  of  a  strong 
ascending  current  which  has  been  passing  for  some  time  into  the 
preparation,  or  at  the  make  of  a  strong  descending  current;  both 
being  conditions  which  increase  the  excitability  of  the  piece  of  nerve 
nearest  to  the  muscle ;  this  is  called  Ritter's  tetanus,  and  may  be 
stopped  in  the  first  case  by  throwing  in  the  current  in  the  same 
direction,  or  in  the  second  case  by  throwing  in  a  current  in  the 
opposite  direction,  i.e.,  by  conditions  which  lessen  the  irritability  of 
this  piece  of  nerve. 

The  same  general  laws  hold  for  muscle  as  well  as  for  nerve,  but 
are  more  difficult  to  demonstrate ;  the  main  fact,  however,  that  the 
kathode  is  the  stimulating  electrode  at  the  make,  and  the  anode  at 
the  break,  may  be  shown  by  the  following  experiment :  if  a  curarised, 
that  is,  a  physiologically  nerveless  muscle,  is  arranged,  as  in  the 
experiment,  for  demonstrating  the  muscle-wave  (see  fig.  149,  p.  119), 
and  a  non-polarisable  electrode  placed  at  each  end,  the  muscle-wave 
at  the  make  of  a  constant  current  starts  at  the  kathode  and  at  the 
break  at  the  anode. 

An  induced  current  in  the  secondary  circuit  of  an  inductorium 
may  be  regarded  as  a  current  of  such  short  duration  that  the  opening 
and  closing  are  fused  in  their  effects.  This  is  true  for  all  induction  cur- 
rents, whether  produced  by  the  make  or  break  of  the  primary  circuit. 
The  kathode  will  always  be  the  more  effective  in  causing  contraction. 

Eespo^ise  of  Human  Muscles  and  Xekves  to  Electrical 
Stimulation. 

Perhaps  the  most  important  outcome  of  this  study  of  the  response 
of  muscle  and  nerve  to  electrical  stimulation  is  its  application  to  the 


CH.  XTI.]  REACTION    OF   DEGENERATION  187 

muscles  and  nerves  of  the  human  body,  because  licre  it  forms  a  most 
valuable  method  of  diagnosis  in  cases  of  disease. 

In  the  normal  state,  nerves  can  be  stimulated  either  by  induction 
shocks,  or  by  the  make  and  break  of  a  constant  current.  In  the  case 
of  the  motor  nerves  this  is  shown  by  the  contraction  of  the  muscles 
they  supply ;  and  in  the  case  of  the  sensory  nerves  by  the  sensations 
that  are  produced.  In  the  case  of  the  sensory  nerves,  the  sensation 
produced  by  the  constant  current  is  most  intense  at  the  instant  of 
make  and  break,  or  when  the  strength  of  the  current  is  changed  in 
the  direction  either  of  diminution  or  increase ;  but  there  is  a  slight 
sensation  due  doubtless  to  the  electrotonic  alterations  in  excitability 
which  we  have  been  studying,  during  the  whole  time  that  the  current 
is  passing. 

When  the  nutrition  of  the  nerves  is  impaired,  much  stronger 
currents  of  both  the  induced  and  constant  kinds  are  necessary  to 
evoke  muscular  contractions  than  in  the  normal  state.  When  the 
nerves  are  completely  degenerated  (as,  for  instance,  when  they  are  cut 
ofif  from  the  spinal  cord,  or  when  the  cells  in  the  cord  from  which 
they  originate  are  themselves  degenerated,  as  in  infantile  paralysis) 
no  muscular  contraction  can  be  obtained  on  stimulating  the  nerves 
even  with  the  strongest  currents. 

The  changes  in  the  excitability  of  the  muscles  are  less  simple, 
because  in  them  there  are  two  excitable  structures,  the  terminations 
of  the  nerves,  and  the  muscular  fibres  themselves.  Of  these,  the 
nerve-fibres  are  the  more  sensitive  to  induction  currents,  and  the 
faradic  stimulation  of  a  muscle  under  normal  circumstances  is  by 
means  of  these  motor  nerve-endings.  Thus  we  find  that  its  excita- 
bility corresponds  in  degree  to  that  of  the  motor  nerve  supplying  it. 
The  muscular  fibres  are,  even  in  the  normal  state,  less  sensitive  to 
faradism  (that  is,  a  succession  of  induction  shocks)  than  the  nerve, 
because  they  are  incapable  of  ready  response  to  stimuli  so  very  short 
in  duration  as  are  the  shocks  of  which  a  faradic  current  consists. 
The  proof  of  this  consists  in  the  fact  that  under  the  influence  of 
curare,  which  renders  the  muscle  practically  nerveless,  the  muscle 
requires  a  much  stronger  faradic  current  to  stimulate  it  than  in  the 
normal  state.  When  the  nerve  is  degenerated,  the  make  or  break 
of  the  constant  current  stimulates  the  muscle  as  readily  as  in  the 
normal  state;  but  the  contraction  is  propagated  more  slowly  than 
that  which  occurs  when  the  nerve-fibres  are  intact,  and  is  due  to  the 
stimulation  of  the  muscular  fibres  themselves.  The  fact  that,  under 
normal  circumstances,  the  contraction  which  is  caused  by  the  constant 
current  is  as  quick  as  that  produced  by  an  induction  shock,  is  ground 
for  believing  that  in  health  the  constant,  like  the  induced  current, 
causes  the  muscle  to  contract  chiefly  by  exciting  the  motor  nerves 
within  it. 


188  ELECTEOTONUS  [CH.  XVI. 

When  the  motor  nerve  is  degenerated,  and  will  not  respond  to 
any  form  of  electrical  sbimulation,  the  muscle  also  loses  all  its  power 
of  response  to  induction  shocks.  The  nerve-degeneration  is  accom- 
panied by  changes  in  the  nutrition  of  the  muscular  fibres,  as  is 
evidenced  by  their  rapid  wasting,  and  any  power  of  response  to 
faradism  they  possessed  in  the  normal  state  is  lost.  But  the  response 
to  the  constant  current  remains,  and  is  indeed  more  ready  than  in 
health,  doubtless  in  consequence  of  nutritive  changes  which  develop 
what  the  older  pathologists  called,  truly  enough,  "  irritable  weakness." 
There  is,  moreover,  a  qualitative  as  well  as  a  quantitative  change. 
In  health  the  first  contraction  to  occur  on  gradually  increasing  the 
strength  of  the  current  is  at  the  negative  pole,  when  the  circuit  is 
closed  (see  Pfliiger's  law),  and  a  stronger  current  is  required  before 
closure-contraction  occurs  at  the  positive  pole.  But  in  the  morbid 
state  we  are  discussing,  closure-contraction  may  occur  at  the  positive 
pole  as  readily  as  at  the  negative  pole.  This  condition  is  called 
the  "  Reaction  of  Degeneration." 

Suppose  a  patient  comes  before  one  with  muscular  paralysis. 
This  may  be  due  to  disease  of  the  nerves,  of  the  cells  of  the  spinal 
cord,  or  of  the  brain.  If  the  paralysis  is  due  to  brain  disease,  the 
muscles  will  be  slightly  wasted  owing  to  disuse,  but  the  electrical 
irritability  of  the  muscles  and  nerves  will  be  normal,  as  they  are 
still  in  connection  with  the  nerve-cells  of  the  spinal  cord  that  control 
their  nutrition.  But  if  the  paralysis  is  due  to  disease  either  of  the 
spinal  cord  or  of  the  nerves,  this  nutritive  influence  can  no  longer 
be  exercised  over  the  nerves  or  muscles.  The  nerves  will  degenerate ; 
the  muscles  waste  rapidly;  the  irritabihty  of  the  nerves  to  both 
forms  of  electrical  stimulation  will  be  lost;  the  muscles  will  not 
respond  to  the  faradic  current,  but  in  relation  to  the  constant  current 
they  will  exhibit  what  we  have  called  the  "  reaction  of  degeneration." 

This  illustrates  the  value  of  the  electrical  method  as  a  means  of 
diagnosis,  that  is,  of  finding  out  what  is  the  matter  with  a  patient. 
It  is  also  a  valuable  means  of  treatment ;  by  making  the  muscles  con- 
tract artificially,  their  nutrition  is  kej^t  up  until  restoration  of  the 
nerves  or  nerve-centres  is  brought  about.  Another  illustration  will 
indicate  that  the  facts  regarding  electrotonic  variation  of  excitability 
are  true  for  sensory  as  well  as  for  motor  nerves ;  in  a  case  of 
neuralgia,  relief  will  often  be  obtained  by  passing  a  constant  current 
through  the  nerve ;  but  the  pole  applied  to  the  nerve  must  be  the 
anode  which  produces  diminution  of  excitability,  not  the  kathode 
which  produces  the  reverse. 

Waller  has  pointed  out  that  Pfliiger's  law  of  contraction,  as  formulated  for 
frogs'  muscles  and  nerves,  is  true  for  human  muscles  and  nerves  in  the  main,  but 
there  are  certain  discrepancies.  These  arise  from  the  method  necessarily  employed 
in  man  being  different  from  those  used  with  a  muscle-nerve  preparation.  In  a 
muscle-nerve  preparation  the  nerve  is  dissected  out,  the  two  electrodes  placed  on 


CH.  XVI.]  THE   LAW    OF    CONTRACTION    IN    MAN  189 

it,  and  the  current  has  of  necessity  to  traverse  the  piece  of  nerve  between  the  two 
electrodes.  In  man,  the  current  is  appUed  by  means  of  electrodes  or  rheophores 
which  consist  of  metal  discs  covered  with  wash  leather,  and  soaked  in  brine.  One 
of  these  is  placed  on  the  moistened  skin  over  the  nerve,  and  the  other  on  some 
indifferent  point,  such  as  the  back.  The  current  finds  its  way  from  one  electrode  to 
the  other,  not  necessarily  through  the  nerves  to  any  great  extent  (though  it  will  be 
concentrated  at  the  nerve  as  it  leaves  the  anode  or  reaches  the  kathode),  but  diffuses 
widely  through  the  body,  seeking  the  paths  of  least  resistance.  Thus  it  is  impos- 
sible to  get  pure  anodic  or  kathodic  effects.  If  the  anode  is  applied  over  the  nerve, 
the  current  enters  by  a  series  of  points  (polar  zone),  and  leaves  by  a  second  series 
of  points  (peripolar  zone).  The  second  series  of  points  is  very  close  to  the  first,  as 
the  current  leaves  the  nerve  as  soon  as  possible,  seeking  less  resistant  paths.     The 

Eolar  zone  will  be  in  the  condition  of  anelectrotonus,  the  peripolar  in  that  of 
atelectrotonus,  so  that  although  the  former  effect  will  predominate,  the  points  being 
more  concentrated,  the  latter  effect  may  prevent  a  pure  anelectrotonic  effect 
being  observed  (fig.  20.i). 

Pfliiger's  law  of  contraction  according  to  which  excitation  occurs  at  the  kathode 
on  the  make  of  a  constant  current,  and  at  the  anode  on  the  bi-eak,  holds  good  for 
all  excitable  tissues.  The  excitation  at  the  break  is  probably  really  due  to  the 
make  of  a  polarisation  current  having  its  kathode  at  the  former  anode,  and  is 
therefore  fundamentally  of  the  same  nature  as  the  make  contraction  ;  or,  in  general 


Fig.  202. — Electrodes  applied  to  the  skin  over  a  ner\'e-trunk.  In  a  the  polar  area  is  anelectrotonic, 
and  the  peripolar  katelectrotonic.  The  former  condition,  therefore,  preponderates,  since  the 
current  is  more  concentrated.  In  b  the  conditions  are  reversed,  the  polar  zone  corresponding  here 
to  the  kathode.    (After  Waller.) 

terms,  excitation  occurs  only  at  the  place  where  a  current  leaves  the  excitable 
tissue.  No  doubt  the  effect  is  determined  by  the  electrolytic  changes  occurring  at 
the  point  of  entry  and  exit  of  the  current ;  the  development  of  kat-ions  must  there- 
fore be  the  chemical  change  that  results  in  excitation.  It  is  difficult  to  imagine  that 
in  a  degenerated  muscle  there  should  be  a  reversal  of  such  a  fundamental  law,  and 
that  excitation  should  be  associated  with  the  development  of  an-ions.  Yet  this  is 
supposed  to  occur  in  the  qualitative  change  known  as  the  "  reaction  of  degenera- 
tion." Page  May  has  investigated  this  question  afresh,  and  finds  that  the  reversal 
of  the  law  is  only  apparent,  not  real,  and  is  due  to  the  imperfect  method  which 
clinical  observers  must  necessarily  employ  when  testing  the  electrical  reaction  of 
muscles  through  the  skin.  By  the  use  of  appropriate  electrodes  on  the  degenerated 
muscles  of  animals,  it  is  possible  to  detect  the  source  of  error.  Let  us  substitute  a 
muscle  for  a  nerve  in  the  diagrams  of  fig.  202  ;  the  current  enters  a  few  fibres  at 
the  anode,  then  spreads  in  all  directions,  and  leaves  the  muscle  by  a  number  of 
diffused  kathodic  points.  If  the  muscle  is  degenerated,  its  excitability  is  high, 
and  the  ready  response  at  the  anode  when  the  current  is  made  does  not  really  occur 
at  the  actual  anode,  but  in  the  neighbouring  and  more  widespread  peripolar 
kathodes.  In  other  words,  degenerated  muscle  obeys  the  general  law  of  excitable 
tissues,  and  excitation  occurs  only  at  the  situation  where  the  current  leaves  the 
muscle.  At  the  actual  anode  there  is  relaxation  or  absence  of  effect ;  this  is 
obviously  not  obsenable  through  the  human  skin  because  the  change  is  very 
limited  in  extent ;  it  can  be  actually  seen  in  the  exposed  muscles  of  an  animal. 


CHAPTEE  XYIl 

NEEVE-CENTRES 

The  nerve-centres  consist  of  the  brain  and  spinal  cord ;  they  are 
characterised  by  containing  nerve-cells,  from  which  the  nerve-fibres 
of  the  nerves  originate.  Small  collections  of  nerve-cells  are  found 
also  in  portions  of  the  peripheral  nervous  system,  where  they  are 
called  ganglia.  The  spinal  ganglia  on  the  posterior  roots  of  the 
spinal  nerves,  and  the  sympathetic  ganglia  are  instances  of  these. 

The  general  arrangement  of  the  cerebro-spinal  axis  is  given  in 
the  accompanying  diagram.  The  nerves  which  take  origin  from  the 
brain  are  called  cranial  nerves ;  there  are  twelve  pairs  of  these ; 
some  of  them,  like  the  olfactory,  optic,  and  auditory  nerves,  are  nerves 
of  special  sense ;  others  supply  the  region  of  the  head  with  motor 
and  sensory  fibres.  One  pair  (the  tenth),  called  the  pneumogastric 
or  vagus  nerves,  are  mainly  distributed  to  the  viscera  of  the  thorax 
and  abdomen,  and  a  part  of  another  pair  (the  eleventh),  called  the 
spinal  accessory  nerves,  unites  with  the  vagus  prior  to  such  distribu- 
tion. We  shall  in  our  subsequent  study  of  the  heart,  lungs,  stomach 
and  other  organs  have  frequently  to  allude  to  these  nerves.  The 
first  two  pairs  of  cranial  nerves  (the  olfactory  and  the  optic)  arise 
from  the  cerebrum.  The  remaining  ten  pairs  are  connected  with  the 
district  of  grey  matter  called  the  floor  of  the  fourth  ventricle  or  its 
immediate  neighbourhood ;  this  tract  of  grey  matter  is  situated  at 
the  lower  part  of  the  brain  where  it  joins  the  spinal  cord;  this 
portion  of  the  brain  is  called  the  Bulb  or  Medulla  oblongata. 

The  spinal  nerves  are  arranged  in  pairs,  31  in  number.  Their 
general  structure  and  functions  we  have  already  studied  (pp.  168-170). 

The  more  intimate  structure  of  the  brain  and  spinal  cord  we  shall 
consider  at  length  in  subsequent  chapters.  For  the  present  we  shall 
deal  with  some  of  the  general  aspects  of  the  nerve-centres,  both  as 
regards  structure  and  function. 

The  brain  and  spinal  cord  consist  of  two  kinds  of  tissue,  easily 
distinguishable  by  the  naked  eye.  They  are  called  respectively  white 
matter  and  grey  matter. 


CH.  XVII.] 


WHITE   AND    GREY   MATTER 


191 


White  matter  is  composed  of  niodullat 
in  structure  from  the  medul- 
lated    fibres    of    nerve    by 
having  no  primitive  sheath 
(neurilemma). 

Grey  matter  is  the  true 
central  material  so  far  as  re- 
gards function ;  that  is  to 
say,  it  is  the  part  which 
receives  and  sends  out 
nervous  impulses ;  it  is 
characterised  by  containing 
the  bodies  of  the  nerve- 
cells. 

In  the  brain  the  grey 
matter  is  chiefly  situated 
on  the  surface,  forming 
what  is  called  the  cortex; 
the  white  matter  and  cer- 
tain subsidiary  masses  of 
grey  matter  are  in  the 
interior. 

In  the  spinal  cord,  the 
grey  matter  is  in  the  in- 
terior, the  white  matter 
outside. 

In  both  grey  and  white 
matter  the  nerve-cells  and 
nerve-fibres  are  supported 
by  a  peculiar  tissue  which 
is  called  neuroglia.  It  is 
composed  of  cells  and  fibres, 
the  latter  being  prolonged 
from  the  cells.  Some  of  the 
fibres  are  radially  arranged. 
They  start  from  the  outer 
ends  of  the  ciliated  epithe- 
lium cells  that  line  the 
central  canal  of  the  spinal 
cord  and  the  ventricles  of 
the  brain,  and  diverge  con- 
stantly branching  towards 
the  surface  of  the  organ, 
where  they  end  by  slight 
enlargements     attached    to 


d  n(M-vo-fil)n',.'^,  which  differ 


203. — View  uf  tlie  ceiebro-.siiiual  axis  of  the  nervous 
system.  The  right  half  of  the  cranium  and  trunk  of 
the  body  lias  been  removed  by  a  vertical  section  ;  tlie 
membranes  of  the  brain  and  spinal  cord  have  also  been 
removeil,  and  the  roots  and  first  part  of  the  fifth  and 
ninth  cranial,  and  of  all  the  spinal  nerves  of  the  right 
side,  have  been  dissected  out  and  laid  separately  on  the 
wall  of  the  skull  and  on  the  several  vertebne  opposite 
to  the  place  of  their  natural  exit  from  the  cranio-spinal 
cavity.     (After  BourL;er)-.) 


192 


NERVE-CENTRES 


[CH.  XVII. 


the  pia  mater.  The  other  fibres  of  the  tissue  are  cell  processes  of 
the  neuroglia  or  glia  cells  proper,  or  spider  cells  as  they  are  some- 
times termed  (see  fig.  204). 

Xeuroglia  is  thus  a  connective  tissue  in  function,  but  it  is  not 
one  in  origin.  Like  the  rest  of  the  nervous  system,  it  originates 
from  the  outermost  layer  of  the  embryo,  the  epiblast.  All  true 
connective  tissues  are  mesoblastic. 

Chemicallv,  it  is  verv  different  from  connective  tissues.     It  con- 


FlG.  204.— Branched  neuroglia-cell.    (After  Stohr.) 

sists  of  an  insoluble  material  called  neuro-keratin,  or  nerve-horn, 
similar  to  the  horny  substance,  keratin,  which  is  found  in  the  surface 
layers  of  the  epidermis. 


Structure  of  Nerve-Cells. 

Xerve-cells  differ  a  good  deal  both  in  shape  and  size. 

In  the  early  embryonic  condition,  the  future  nerve-cell  is  a  small 
nucleated  mass  of  protoplasm  without  processes.  As  development 
progresses  branches  grow,  and  by  this  means  it  is  brought  into  con- 
tact with  the  branches  of  other  nerve-cells.  "\Mien  the  nerve-cells 
degenerate,  as  they  do  in  some  cases  of  brain  and  cord  disease,  there 
is  a  reversal  of  this  process ;  just  as  in  a  dying  tree  the  terminal 
branches,  those  most  distant  from  the  seat  of  nutrition,  are  the  first 
to  wither,  so  it  is  in  the  degenerating  nerve-celL  If  one  traces  the 
structure  of  nerve-cells  throughout  the  zoological  series,  there  is  also 
seen  an  increase  in  their  complexity,  and  the  number  of  points  of 
contact;  produced  by  an  increase  in  the  number  and  complexity  of  the 
branches,  multiplies  (fig.  205). 


CH.  XVTI.] 


NERVE-CELLS 


193 


The  simplest  nerve-cells  known  are  termed  bipolar.  In  the  lower 
animals  the  two  processes  come  off  from  the  opposite  ends  of  the 
cells ;  the  cell,  in  other  words,  appears  as  a  nucleated  enlargement  on 
the  course  of  a  nerve-fibre.  Fig.  206  (A)  shows  one  of  these  nerve- 
cells  from  the  Gasserian  ganglion  of  the  pike.  The  cells  of  the 
Gasserian  and  spinal  ganglia  in  the  mammalian  embryo  are  also 
bipolar,  but  as  development  progresses,  the  two  branches  become 
fused  for  a  considerable  distance,  so  that  in  the  fully  formed  animal 
each  cell  appears  to  be  unipolai\  This  is  shown  in  a  more  diagram- 
matic way  in  fig.  187,  p.  168.     The  bifurcation  of  the  nerve-fibre  is 


Fio.  205. — Diagram  after  Ramon  y  Cajal  to  show  the  ontogenetic  (or  embryological)  and  phylogenetic 
(i.e.  in  the  animal  series)  development  of  a  neuron,  a,  cerebral  cell  of  frog ;  b,  newt ;  c,  mouse  ;  d, 
man.  As  the  place  in  the  zoological  series  rises,  the  neuron  increases  in  complexity  and  in  the 
number  of  points  of  contact ;  this  is  produced  partly  by  an  increase  of  the  dendrons,  partly  by  an 
increase  in  the  side  branches  or  collaterals  of  the  axon,  a,  b,  c,  d,  e,  show  the  early  stages  in  the 
development  of  a  similar  cell  in  the  human  embrj'o  ;  the  first  branch  of  the  cell  to  appear  (in  a)  is 
the  axon  ;  the  dendrons  are  later  outgrowths.  The  reversal  of  this  process  takes  place  in  primary 
degeneration. 

spoken  of  as  a  T-shaped  junction.  As  will  be  seen  in  fig.  206  (C), 
the  nerve  process  has  a  convoluted  course  on  the  surface  of  the  cell 
before  it  bifurcates.  In  these  ganglia  it  should  be  also  noted  that 
each  cell  is  enclosed  within  a  connective  tissue  sheath,  and  the  nuclei 
seen  are  those  of  the  connective  tissue  corpuscles. 

In  the  8}Tnpathetic  ganglia,  the  cells  may  have  a  similar  structure, 
and  here  also  the  nucleated  sheath  is  seen.  In  some  cases,  however, 
when  there  appear  to  be  two  fibres  connected  to  a  cell,  one  of  them 
is  really  derived  from  another  cell,  and  is  passing  to  end  in  a  ramifi- 
cation which  envelopes  the  ganglion  cell ;  it  may  sometimes  be  coiled 
spirally  around  the  issuing  nerve-fibre. 

N 


194 


NERVE-CENTRES 


[CII.  XVII, 


The  majority  of  nerve-cells  found  in  the  body  are  multipolar. 
Here  the  cell  becomes  angular  or  stellate.  Fig.  207  shows  the  usual 
form  of  cell  present  in  sympathetic  ganglia.  From  the  angles  of  the 
cell,  branches  originate ;  the  majority  of  these  branches  divide  and 
subdivide  until  each  ends  in  an  arborescence  of  fine  twigs  or  fibrils ; 


N.S. 


Fig.  200. — Bipolar  nerve-cells.  A.  From  the  Gasserian  ganglion  of  the  pike  (after  Bidder).  B.  From  a 
spinal  ganglion  of  a  4A  weeks'  human  embryo  (after  His).  C.  Adult  condition  of  the  mammalian 
spinal  ganglion  cell :  N.  S.  nucleated  sheath  ;  only  the  nuclei  seen  in  prolile  are  represented.  T.  is 
the  T-shaped  junction  (after  Retzius). 


but  one  process,  and  one  process  only,  of  each  cell  becomes  the  axis 
cylinder  of  a  nerve-fibre. 

Passing  next  to  the  central  nervous  system,  we  here  again  find 
the  multipolar  cell  is  the  principal  kind  present. 

The  next  figure  (fig.  208)  shows  one  of  the  typical  multipolar  cells 
of  the  spinal  cord.  Here  again,  only  one  process  (a)  becomes  the 
axis  cylinder  of  a  nerve-fibre,  and  the  others  break  up  into  arborisa- 
tions of  fibrils.  The  cells  have  a  finely  fibrillar  structure,  and  the 
fibrils  can  be  traced  into  the  axis  cylinder  process  and  the  other 
branches  of  the  cell.     Between  the  fibrils  the  protoplasm  of  the  cell 


CM.  XVII.] 


NKRVE-CELLS 


195 


contains  a  number  of  angular  or  spindle-shaped  masses,  which  have 
a  great  affinity  of  basic  aniline  dyos  like  methylene  blue.     They  are 


Flii.  :207. — All  isolated  sympatliftic  t;anKl'oii  cell  of  man,  showing  sheath  with  nucleated  cell  lining,  Ji. 
A.  Ganglion  cell,  with  nucleus  and  nucleolus.  C.  Branched  process.  D.  Axis  cylinder  process 
(Key  and  Retzius.)     x  750. 

known  as  Nissl's  granules.  These  nerve-cells  often  contain,  especi- 
ally in  the  adult,  granules  of  pigment,  usually  yellow,  the  nature  of 
which  has  not  been  determined. 


V\Q.  208. — Multipolar  nerve-cell  from  anterior  horn  of  spinal  cord  ;  c,  axis  cylinder  process.     (Max 

Schultze.) 


196 


NERVE-CENTRES 


[CH.  XVII. 


In  preparations  made  by  Golgi's  chromate  of  silver  method,  the 
cells  and  their  processes  are  stained  an  intense  black  by  a  deposit  of 

silver.  The  various  structures 
in  the  cells  (nucleus,  granules, 
fibrils,  etc.),  are  not  visible  in 
such  preparations,  but  the  great 
advantage  of  the  method  is  that 
it  enables  one  to  follow  the 
branches  to  their  finest  ramifica- 
tions. It  is  thus  found  that  the 
axis  cylinder  process  is  not  un- 
branched,  as  represented  in  fig. 
208,  but  invariably  gives  off 
side-branches,  which  are  called 
collaterals ;  these  pass  into  the 
adjacent  nerve-tissue.  The  axis 
cylinder  then  acquires  the 
sheaths,  and  thus  is  converted 


Fig.  209. — Pyramidal  cell  of  human  cerebral  cortex. 
Golgi's  method. 

into  a  nerve-fibre.    This  nerve-fibre 

sometimes,  as  in  the  nerve-centres 

after   a    more    or    less    extended 

course,  breaks  up  into  a  terminal 

arborescence      enveloping      other 

nerve-cells ;    the    collaterals    also 

terminate  in  a  similar  way.     The 

longest   type    of   axis   cylinder   is 

that  which  passes  away  from  the  nerve-centre,  and  gets  bound  up 

with  other  similarly  sheathed  axis  cylinders  to  form  a  nerve;  but 


Fig.  210. — Cerebral  cortex  of  mammal,  prepared 
by  Golgi's  method,  a,  b,  c,  d,  k,  nerve-cells; 
E,  neuroglia-cell.    (Ramon  y  Cajal.) 


CII.  XVII.]  NERVE-CELLS  197 

all  ultimately  terminate  in  an  arborescence  of  fibrils  in  various  end 
organs  (end-plates,  muscle  spindles,  etc.). 

In  the  grey  matter  of  the  cerebrum  the  nerve-cells  are  various  in 
shape  and  size,  but  the  most  characteristic  cells  are  pyramidal  in 
shape.  They  are  especially  large  and  numerous  in  what  are  called 
the  motor  areas  of  the  brain.  The  apex  of  the  cell  is  directed  to  the 
surface ;  the  apical  process  is  long  and  tapering,  and  finally  breaks 
up  into  fibrils  that  lie  parallel  to  the  surface  of  the  brain  {tangential 
fibres).     From  the  lower  angles  and  other  parts  branching  processes 


Axon 


Fig.  211. — Cell  of  Purkinje  from  the  human  cerebellum.    Golgi's  method. 
(After  Szymonowicz.) 

originate ;  the  axis  cylinder  comes  off  from  the  base  of  the  pyramid. 
(Se^e  figs.  209,  210). 

The  grey  matter  of  the  cerebellum  contains  a  large  number  of 
small  nerve-cells,  and  one  layer  of  large  cells.  These  are  flask -shaped, 
and  are  called  the  cells  of  Purkinje.  The  neck  of  the  flask  breaks  up 
into  branches,  and  the  axis  cylinder  process  comes  off  from  the  base 
of  the  flask  (fig.  211). 

The  whole  nervous  system  consists  of  nerve-cells  and  their 
branches,  supported  by  neuroglia  in  the  central  nervous  system,  and 
by  connective  tissue  in  the  nerves.  Some  of  the  processes  of  a 
nerve-cell  break  up  almost  immediately  into  smaller  branches  ending 
in  arborescences  of  fine  twigs ;    these  branches,  which  used  to  be 


198 


NERVE-CENTRES 


[CH.  XVII. 


called  protoplasmic  processes,  are  now  termed  dendrons.  One  branch 
becomes  the  long  axis  cylinder  of  a  nerve-fibre,  but  it  also  ultimately 
terminates  in  an  arborisation ;  it  is  called  the  axis  cylinder  process, 
or,  more  briefly,  the  axon.  The  term  neuron  or  neurone  is  applied  to 
the  complete  nerve-unit,  that  is,  the  body  of  the  cell,  and  all  its 
branches.  Some  observers  have  supposed  that  the  axis  cylinder  pro- 
cess is  the  only  one  that  conducts  nerve  impulses,  the  dendrons 
being  rootlets  which  suck  up  nutriment  for  the  nerve-cell.  This 
view  has  not,  however,  been  accepted ;  the  dendrons  may  be  nutri- 
tive, but  there  is  no  doubt  that  they  also,  like  the  rest  of  the  nerve- 
unit,  are  concerned  in  the  conduction  of  nerve  impulses,  A  strong 
piece  of  evidence  in  this  direction  is  the  fact  that  the  fibrils  of  the 

axis  cylinder  may  be  traced 
through  the  body  of  the 
cell  into  the  dendrons. 

The  next  idea  which  it 
is  necessary  to  grasp  is,  that 
each  nerve-unit  (cell  plus 
branches  of  both  kinds)  is 
anatomically  independent 
of  every  other  nerve-unit. 
There  is  no  true  anasto- 
mosis of  the  branches  from 
one  nerve-cell  with  those  of 
another ;  the  arborisations 
interlace  and  intermingle, 
and  nerve  impulses  are 
transmitted  from  one  nerve- 
unit  to  another,  through 
contiguous,  but  not  through 
continuous  structures.  A 
convenient  expression  for  the  intermingling  of  arborisations  is 
synapse  (literally,  a  clasping). 

Fig.  212  is  a  diagram  of  the  nervous  path  in  a  reflex  action. 
Excitation  occurs  at  S,  the  skin  or  other  sensory  surface,  and  the 
impulse  is  transmitted  by  the  sensory  nerve-fibre  to  the  nerve- 
centre,  where  it  ends  not  in  a  cell-body,  but  by  arborising  around 
one  or  more  cell-bodies  and  their  dendrons.  The  only  cell-body  in 
actual  continuity  with  the  sensory  nerve-fibre  is  the  one  in  the  spinal 
ganglion  (G)  from  which  it  grew. 

The  terminal  arborisation  of  the  sensory  nerve-fibre  merely  inter- 
laces with  the  dendrons  of  the  motor  nerve-cell ;  yet  simply  by  this 
synapse,  the  motor  nerve-cell  (M  C)  is  affected  and  sends  an  impulse 
by  its  axis  cylinder  process  to  the  muscle  (M). 

A  very  rough  illustration  which  may  help  one  in  realising  this 


Fio.  212. — Reflex  action. 


CH.  XVII.] 


THE   NEURON   THEORY 


199 


s.c 


may  be  taken  as  follows :  Suppose  two  trees  standing  side  by  side ; 

their  stems  will  represent   the   axis  cylinders ;    their  branches  the 

dendrons.     If  the  trees  are  close  together  the 

branches  of  one  will  intermingle  with  those  of 

the  other :  there  is  no  actual  branch  from  the 

one  which  becomes  continuous  with  any  branch 

of  the  other;   but   yet   if   the  stem  of  one  is 

vigorously   shaken,  the   close   intermixture   of 

the  branches  will  affect  the  other  so  that  it  also 

moves. 

Another  very  important  general  idea  which 
we  must  next  get  •  hold  of,  is  that  a  nervous 
impulse  does  not  necessarily  travel  along  the 
same  nerve-fibre  all  the  way,  but  there  is  what 
we  may  term  a  system  of  relays.  The  nervous 
system  is  very  often  compared  to  a  telegraphic 
system  throughout  a  country.  The  telegraph 
offices  represent  the  nerve-centres,  the  afferent 
nerve-fibres  correspond  to  the  wires  that  carry 
the  messages  to  the  central  offices,  and  the 
efferent  nerve-fibres  are  represented  by  the  wires 
that  convey  messages  from  the  central  offices  to 
more  or  less  distant  parts  of  the  country.  This 
illustration  will  serve  us  very  well  for  our 
present  purpose,  provided  that  it  is  always  re- 
membered that  a  nervous  impulse  is  not  elec- 
tricity. Suppose,  now,  one  wishes  to  send  a 
message  from  the  metropolis,  which  will  repre- 
sent the  brain,  to  a  distant  house,  say  in  the 
Highlands  of  Scotland.  There  is  no  wire  straight 
from  London  to  that  house,  but  the  message 
ultimately  reaches  the  house;  one  wire  takes 
the  message  to  Edinburgh ;  another  wire  carries 
it  on  to  the  telegraph  station  in  the  town 
nearest  to  the  house  in  question ;  and  the  last 
part  of  the  journey  is  accomplished  by  a  mes- 
senger on  foot  or  horseback.  There  are  at  least 
two  relays  on  the  journey. 

It  is  just  the  same  with  the  nervous  system. 
Suppose  one  wishes  to  move  the  arm ;  the  im- 
pulse starts  in  the  nerve-cells  of  the  brain,  but 
there  are  no  fibres  that  go  straight  from  the 
brain  to  the  muscles  of  the  arm.  The  impulse 
travels  down  the  spinal  cord,  by  what  are  called  pyramidal  fibres, 
which  form  synapses  with  the  nerve-cells  of  the  spinal  cord,  and 


M 


Fig.  213. — Diagram  of  an  ele- 
ment of  the  motor  patli. 
U.S.,  upper  segment; 
L.S.,  lower  segment ; 
CO.,  cell  of  cerebral  cor- 
tex ;  S.C,  cell  of  spinal 
cord,  in  anterior  comu  ; 
M.,  the  muscle  ;  S.,  path 
from  senso^J'ne^^•e-root^■. 
(After  Gowers.) 


200  NERVE-CENTKES  [CH.  XVII. 

from  these  cells,  fresh  nerve-fibres  pass  on  the  impulse  to  the 
arm-muscles.  This  is  shown  in  the  accompanying  diagram  (fig. 
213).  The  cell  of  the  cerebral  grey  matter  is  represented  by  C.  C, 
the  pyi'amidal  nerve-fibre  arborises  aroimd  the  cell  of  the  spinal 
cord  (S.  C.)  from  which  the  motor  nerve-fibre  arises,  and  which 
carries  on  the  impulse.  The  spinal  cord  cells  are  thus  surrounded 
by  arliorisations  (synapses)  derived  not  only  from  the  sensory 
nerves  (S),  but  by  fibres  from  the  upper  part  of  the  nervous  system. 
"We  now  see  how  it  is  possible  that  reflex  actions  in  the  cord  may 
be  controlled  by  impulses  from  the  brain. 

The  system  of  relays  is  still  more  complicated  in  the  case  of 
sensory  impulses,  as  we  shall  see  later  on ;  the  s*me  is  true  for  the 
motor  path  to  involuntary  muscle,  accessory  ceU-stations  being  situated 
in  the  sympathetic  gangUa. 

We  may  now  return  for  a  moment  to  the  subject  of  degeneration. 
If  the  nerve-fibre  is  cut  off  from  its  connection  with  the  spinal  nerve- 
cell,  the  peripheral  end  degenerates  as  far  as  the  muscle. 

Suppose,  now,  the  pyramidal  fibre  were  cut  across,  the  piece  still 
attached  to  the  brain-cell  would  remain  in  a  comparatively  normal 
condition,  but  the  peripheral  end  would  degenerate  as  far  as  the 
synapse  round  the  spinal  cell  (S.  C),  but  not  beyond.  We  can  thus 
use  the  degeneration  method  to  trace  out  tracts  of  nerve-fibres  in 
the  white  matter  of  the  central  nervous  system.  The  histological 
change  in  the  fibres  is  here  the  same  as  that  already  described  in  the 
nerves,  except  that,  as  there  is  no  primitive  sheath,  there  can  be  no 
multiplication  of  its  nuclei ;  there  is  instead  an  over-growth  of  neuroglia. 
Degenerated  tracts  consequently  stain  differently  from  healthy  white 
matter,  and  can  be  by  tliis  means  easily  traced. 

Another  method  of  research  which  leads  to  the  same  results  as 
the  degeneration  method  is  called  the  embryological  method.  The 
nerve-fibres  which  grow  from  different  groups  of  nerve-cells  become 
fully  developed  at  different  dates,  and  so,  by  examining  brains  and 
cords  of  embryos  of  different  ages,  one  is  able  to  make  out  indi^'idual 
tracts  before  they  have  blended  in  the  general  mass  of  white  matter. 

We  shall,  however,  return  to  this  subject  when  later  on  we  are 
studying  the  physiology  of  the  central  nervous  system  in  detail. 

The  Significance  of  Nissl's  Granules. 

If  portions  of  the  brain  or  spinal  cord  are  fixed  in  absolute  alcohol, 
and  sections  obtained  from  the  hardened  pieces  are  stained  by  means 
of  methylene  blue,  the  nerve-ceUs  exhibit  a  characteristic  appearance. 
The  nucleus  and  nucleolus  take  up  the  blue  stain,  but  the  total 
amount  of  chromatin  present  in  the  nucleus  is  not  large,  except  in 
embryonic  nerve-cells ;  throughout  the  ceU  body  a  number  of  angular- 


cii.  XVII.]  nissl's  granules  201 

shaped  masses,  which  are  termed  Nissl's  granules,  are  also  stained 
blue.  These  extend  some  distance  into  the  dendrons,  but  not  into 
the  axon.  The  substance  of  which  they  are  composed  is  termed 
chromatoplasm,  or  chromophilic  material.  The  existence  of  granules 
in  cells  which  have  an  affinity  for  basic  dyes  like  methylene  blue 
is  not  at  all  common ;  the  granules  in  the  majority  of  the  white  l)lood 
corpuscles,  for  instance,  have  an  affinity  for  acid  dyes.  Micro- 
chemical  methods  have  shown  that  the  main  constituent  of  the  Nissl 
granules  is  an  iron -containing  nucleo-protein.  The  name  kineto- 
plasm  has  been  given  to  it  by  Marinesco  in  order  to  express  the  idea 
that  it  forms  a  source  of  energy  to  the  cell.  It  can  hardly  be  denied 
that  the  substance  of  which  the  granules  are  composed,  forming  as 
it  does  so  large  a  proportion  of  the  cell-contents,  and  made  of  a 
material  in  which  nuclein  forms  an  important  constituent,  is  intimately 
related  to  the  nutritional  condition  of  the  neuron.  Some  have  even 
compared  it  to  the  granular  material,  which  is  present  in  secreting 
cells ;  in  these  cells  before  secretion  occurs,  the  granules  accumulate, 
and  during  the  act  of  secretion  they  are  discharged  and  converted 
into  constituents  of  the  secretion.  It  is  stated  by  some  observers 
that  the  Nissl  granules  are  used  up  during  the  discharge  of  energy 
from  nerve-cells,  and  it  certainly  is  the  case  that  if  the  cells  are 
examined  after  an  epileptic  fit,  in  which  there  has  ])een  a  very  massive 
discharge  of  impulses,  the  Nissl  granules  have  disappeared,  or  at 
least  broken  up  into  fine  dust-like  particles,  so  that  the  cell  presents 
a  more  uniform  blue  staining  (see  fig.  214).  It  is,  however,  doubt- 
ful whether  this  is  due  to  a  transformation  associated  with  intense 
activity,  or  whether  it  may  not  be  caused  by  venosity  of  the  blood. 
The  cells  are  very  sensitive  to  altered  vascular  conditions ;  anaemia, 
for  instance,  produces  a  similar  change  accompanied  with  swelling  of 
the  cell,  and  swelling  and  in  extreme  cases  extrusion  of  the  nucleus. 
High  fever  (hyperpyrexia)  causes  a  very  similar  change,  which  is 
doubtless  associated  with  the  coagulation  of  the  proteins  of  the  cell- 
protoplasm  by  the  high  temperature. 

Since  attention  has  been  directed  towards  the  Nissl  granules,  a 
literature  which  has  become  alarmingly  vast  during  the  last  few  years 
has  sprung  up  in  relation  to  them.  This  is  quite  easy  to  understand, 
for  neurologists  have  by  this  sensitive  test  been  able  to  identify 
changes  in  the  cells  which  could  not  be  detected  by  the  previous 
methods  of  staining.  Thus  the  cells  have  been  examined  in  various 
diseases,  and  after  being  subjected  to  the  action  of  various  poisons. 
In  a  new  subject  of  this  kind  there  is,  as  would  be  expected,  consider- 
able divergence  of  views,  and  even  the  fundamental  question  has  not 
yet  been  answered  satisfactorily  whether  the  Nissl  granules  are  present 
as  such  in  the  living  cell,  or  whether  they  are  artifacts  produced  by 
the  fixative  action  of  strong  alcohol.     The  fact  that  they  cannot  be 


202 


NERVE-CENTRES 


[CH.  XVII. 


demonstrated  when  the  cells  are  stained  by  the  injection  of  methylene 
blue  into  the  circulation  before  the  animal  is  killed  is  a  very  strong 
piece  of  evidence  in  favour  of  the  latter  view.  But,  whichever 
view  is  correct,  the  method  is  a  valuable  one,  and  Nissl's  views  on 
this  question  appear  to  be  indisputable  :  they  are  briefly  as  follows  : — 
Healthy  cells  fixed  and  stained  in  a  constant  manner  will  appear  the 
same  under  constant  optical  conditions,  and  the  appearances  then 
seen  form  the  equivalent  of  such  healthy  cells  during  life.  It  follows 
that  if  the  cells  prepared  by  the  same  method  and  examined  under 
the  same  conditions  show  a  difference  from  the  equivalent  or  symbol 
of  healthy  cells,  the  difference  is  the  measure  of  some  change  that 
has  occurred  during  life. 

Chromatolysis  is  the  term  applied  to  designate  the  disappearance 


Fio.  214.— Nissl's  granules.  A.  Normal  pyramidal  cell  of  human  cerebral  cortex.  B.  Swollen  oede- 
matous  pyramidal  cell  from  a  case  of  status  epilepticus.  Notice  diffuse  staining,  and  absence  of 
Nissl's  granules  ;  the  nucleus  is  enlarged  and  eccentric.  The  lymph  space  around  the  cell  is 
dilated.  C.  Pyramidal  cell  of  dog  after  ligature  of  vessels  going  to  brain  and  consequent  anaemia. 
Notice  great  swelling  of  the  nucleus,  and  advanced  chromatolysis,  most  marked  at  the  periphery 
of  the  cell.     700  diameters.    (After  Mott.) 

or  disintegration  of  the  Nissl  granules.  The  process  generally  begins 
at  the  periphery  of  the  cell  and  in  the  dendrons,  but  in  advanced  cases 
the  whole  cell  may  be  affected.  We  have  already  alluded  to  the  fact 
that  chromatolysis  occurs  in  various  abnormal  states,  and  the  diminu- 
tion of  the  chromophilic  nucleo-protein  indicates  a  diminution  of  the 
vital  interaction  of  the  highly  phosphorised  nucleus  with  the  sur- 
rounding cell  protoplasm.  Chromatolysis  alone  is  not  indicative  of 
cell  destruction,  and  a  cell  may  recover  its  function  afterwards.  The 
integrity  of  the  nucleus  and  of  the  fibrils  between  which  the  Nissl 
substance  lies  is  much  more  important  to  the  actual  vitality  of  the  cell. 


CII.  XVir.]  CLASSIFICATION   OF   NERVE-CELLS  203 

When  a  nerve-fibre  is  cut  across,  the  distal  segment  undergoes 
Wallorian  degeneration ;  this  is  an  acute  change.  But  the  nerve-cell 
and  the  piece  of  the  nerve-fibre  still  attached  to  it  do  not  remain  un- 
affected. If  regeneration  of  the  fibre,  and  restoration  of  function 
takes  place,  no  change  is  observal^le.  But  if  regeneration  does  not 
occur  (and  it  never  takes  place  in  the  central  nervous  system),  the 
cell  and  its  processes  undergo  a  slow  chronic  wasting  ;  one  of  the 
earliest  signs  of  this  disuse  atrophy  is  chromatolysis.  "Warrington 
has  recently  stated  a  still  more  interesting  fact,  namely,  that  section 
of  the  posterior  roots  causes  chromatolysis  in  the  anterior  horn  cells 
of  the  same  side;  this  indicates  that  the  loss  of  sensory  stimuli 
•  produces  a  depression  of  the  activity  and  metabolic  functions  of 
the  spinal  motor  cells.  We  shall  see  later  on  that  this  accords 
quite  well  with  the  physiological  effects  observed  under  these  con- 
ditions. 


Classification  of  Nerve-cells  according  to  their  Function. 

In  addition  to  the  anatomical  classification  of  the  nerve-cells 
already  given,  Schiifer  separates  them  into  four  chief  classes  on  a 
physiological  basis : — 

1.  Afferent  or  sensory  root  cells. 

2.  Efferent  root  cells. 

3.  Intermediary  cells. 

4.  Distributing  cells. 

1.  Afferent  root  cells. — Originally  such  cells  are  situated  at  the 
periphery,  and  are  connected  with  a  process  or  afferent  fibre  which 
passes  to  and  arborises  among  the  nerve-cells  of  the  central  nervous 
system.  This  primitive  condition  is  well  seen  in  the  earthworm,  and 
persists  in  the  olfactory  cells  of  all  vertebrates. 

As  evolution  progresses,  the  peripheral  cell  sinks  below  the  in- 
tegument, leaving  a  process  at  the  surface ;  this  is  seen  in  the  worm 
jSTereis  (see  fig.  215).  Ultimately  the  body  of  the  cell  approaches 
close  to  the  central  nervous  system,  in  the  spinal  ganglion  of  the 
posterior  root,  and  the  peripheral  sensory  nerve-fibre  is  correspond- 
ingly longer. 

The  afferent  root  cells,  such  as  those  of  the  spinal  ganglia  and 
the  corresponding  ganglia  of  the  cranial  nerves,  are  peculiar  in 
possessing  no  dendrons. 

2.  Efferent  root  cells. — The  anterior  horn  cells  of  the  spinal  cord 
are  instances  of  these ;  their  axons  go  directly  to  muscle  fibres. 

3.  Intermediary  cells. — These  receive  impulses  from  afferent 
cells,  and  transmit  them  either  directly,  or  indirectly  through  other 
intermediary  cells  to  efferent  cells.  The  majority  of  the  cells  of  the 
brain  and  cord  come  under  this  heading ;  they  serve  the  purposes  of 


204  NERVE-CENTRES  [CII.  XVII. 

association    and   co-ordination,    and    form    the    basis    of    psychical 
phenomena. 

4.  Distributing  cells.— These  are  the  cells  of  the  sympathetic 
ganglia ;  they  are  situated  outside  the  central  nervous  system ;  they 
receive  impulses  from  efferent  cells  in  the  central  nervous  system, 
and  distribute  them  to  involuntary  muscles  and  secreting  glands. 


Earth-worm 


N 


ereis 


Vertebrate 


Fio.  215. — Diagram  to  illustrate  the  primitive  conditions  of  the  afferent  nerve-cf^ll,  and  the  manner  in 
which  it  becomes  altered  in  the  process  of  evolution.  (After  Retzius.)  I,  integument;  C,  central 
nervous  system  ;  the  arrows  show  the  direction  in  which  the  impulse  passes. 


The  Law  of  Axipetal  Conduction. 

A  general  law  has  been  laid  down  by  van  Gehuchten  and  Cajal, 
that  all  nerve  impulses  are  axipetal,  that  is,  they  pass  towards  the 
attachment  of  the  axon,  by  which  they  leave  the  body  of  the  cell. 
In  other  words,  the  direction  of  an  impulse  is  towards  the  body  of 
the  cell  in  the  dendrons,  and  away  from  it  in  the  axon.  When  we 
further  consider  that  every  nervous  pathway  is  formed  of  a  chain  of 
cells,  and  that  the  impulse  always  takes  the  "  forward  direction,"  we 
see  that  there  is  what  we  may  compare  to  a  valved  action  which 
permits  the  passage  of  impulses  in  one  direction  only.  The  synapses 
are  the  situations  of  these  so-called  valves. 

On  the  onward  propagation  of  a  nerve  impulse  through  a  chain 
of  neurons,  its  passage  is  delayed  at  each  synapse,  hence  there  is 
additional  "  lost  time  "  at  each  of  these  blocks.  The  relative  number 
of  the  blocks  furnishes  a  key  to  the  differences  found  in  reaction 
time  for  different  reflexes  and  psychical  processes.  This  we  may 
illustrate  by  two  examples,  one  taken  from  the  frog,  the  other  from 
man. 


CH.  XVII.]  AXIPETAL   CONDUCTION  205 

1.  If  a  frog's  posterior  root  is  stinmlated,  the  time  lost  in  the 
spinal  cord  when  the  gastrocnemius  of  the  same  side  contracts  is 
0"008  sec. ;  if  the  opposite  gastrocnemius  contracts,  the  additional 
lost  time  is  0"004  sec.  If  we  assume  that  in  the  latter  case,  two 
extra  synapses  have  to  be  jumped,  the  delay  at  each  is  0'002  sec. 

2.  In  the  case  of  the  eye  and  ear  in  man  the  total  length  of  the 
pathway  to  the  brain  is  approximately  the  same,  and  so  the  reaction 
times  might  be  expected  to  be  equal ;  but  this  is  not  the  case ;  the 
reaction  time  in  response  to  a  sudden  sound  is  0"150  sec,  in  response 
to  a  sudden  flash  of  light  0195  sec.  The  greater  delay  in  response 
to  a  visual  stimulus  directly  corresponds  to  the  greater  number  of 
synapses  through  which  it  has  to  travel  (see  later,  in  the  structure 
of  the  visual  and  auditory  mechanisms). 

The  valved  condition  of  nervous  paths  also  explains  another 
difficulty.  We  have  seen  in  p.  173  that  under  certain  circumstances 
a  nervous  impulse  will  travel  in  both  directions  along  a  nerve.  Yet 
when  we  stimulate  the  motor  fibres  in  an  anterior  spinal  root,  the 
only  effect  is  a  contraction  of  muscles ;  there  is  no  effect  propagated 
backwards  in  the  spinal  cord.  No  doubt  a  nervous  impulse  does 
travel  backwards  to  the  anterior  horn  cells,  but  it  is  there  extin- 
guished, it  cannot  jump  the  synapses  backwards,  and  there  is  no 
negative  variation  to  be  detected  in  a  galvanometer  connected  to  the 
pyramidal  tracts  in  the  cord. 

The  law  of  axipetal  conduction  is  no  doubt  true  for  the  majority 
of  neurons.  But  there  is  at  any  rate  one  very  striking  exception, 
namely,  in  the  typical  afferent  root  cells ;  here  the  impulse  passes 
to  the  body  of  the  cell  by  one  axon  from  the  periphery,  and  away 
from  it  to  the  spinal  cord  by  the  other.  To  say,  as  sonxe  do,  that  the 
peripheral  process  is  really  a  dendron  because  it  conducts  impulses 
centrifugally  is  simply  arguing  in  a  circle. 


CHAPTEK  XV 111 

THE   CIRCULATORY   SYSTEM 

The  circulatory  system  consists  of  the  heart,  the  arteries,  or  vessels 
that  carry  the  blood  from  the  heart  to  other  parts  of  the  body,  the 
veins,  or  vessels  that  carry  the  blood  back  to  the  heart  again,  and  the 
capillaries,  a  network  of  minute  tubes  which  connect  the  terminations 
of  the  smallest  arteries  to  the  commencements  of  the  smallest  veins. 
We  shall  also  have  to  consider  in  connection  with  the  circulatory 
system,  (1)  the  lymphatics,  which  are  vessels  that  convey  back  the 
h-mph  (the  fluid  which  exudes  through  the  thin  walls  of  the  blood- 
capillaries)  to  the  large  veins  near  to  their  entrance  into  the  heart, 
and  (2)  the  large  Ij-mph  spaces  contained  in  the  serous  membranes. 

The  Heart. 

This  is  the  great  central  pump  of  the  circulatory  system.  It  lies 
in  the  chest  between  the  right  and  left  lungs  (fig.  216),  and  is 
enclosed  in  a  covering  called  the  pericardium.  The  pericardium  is 
an  instance  of  a  serous  membrane.  Like  all  serous  membranes  it 
consists  of  two  layers ;  each  consists  of  fibrous  tissue  containing 
elastic  fibres ;  one  layer  envelopes  the  heart  and  forms  its  outer 
covering  or  epicardium ;  this  is  the  visceral  layer  of  the  pericardium ; 
the  other  layer  of  the  pericardium,  called  its  parietal  layer,  is  situ- 
ated at  some  little  distance  from  the  heart,  being  attached  below  to 
the  diaphragm,  the  partition  between  the  thorax  and  the  abdomen. 
The  \isceral  and  parietal  layers  are  continuous  for  a  short  distance 
along  the  great  vessels  at  the  base  of  the  heart,  and  so  form  a 
closed  sac.  This  sac  is  lined  by  endothehum ;  in  health  it  contains 
just  enough  hnnph  (pericardial  fluid)  to  lubricate  the  two  surfaces 
and  enable  them  to  glide  over  each  other  smoothly  during  the  move- 
ments of  the  heart.  The  presence  of  elastic  fibres  in  the  epicardium 
enables  it  to  follow  without  hindrance  the  changing  shape  of  the 
heart  itself ;  but  the  parietal  layer  of  the  pericardium  appears  to  be 
inextensible,  and  so  it  limits  the  dilatation  of  the  heart. 

The  pericardium  is  a  comparatively  simple  serous  membrane,  because  the 
organ  it  encloses  is  a  single  one  of  simple  external  form.     All  serous  membranes 


CH.  XVIII.] 


THE    HEART 


207 


Larynx 


art!  of  similar  structure  ;  tlius  tlie  pli'iira  wliicli  encloses  tlu-  lung,  and  the  iit-rilout'itm 
which  encloses  the  abdominal  viscera  differ  from  it  only  in  anatomical  arranj^ement. 
The  great  complexity  of  the  peritoneum  is  due  to  its  enclosing  so  many  organs. 
Kvery  serous  membrane  consists  of  a  visceral  layer  applied  to  the  organ  or  organs 
it  encloses  ;  and  a  parietal  layer  continuous  with  this  in  contiguity  with  the  parietes 
or  body-walls. 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is 
dividetl  by  a  longitudinal  partition  into  two  chief  cavities — right  and 
left.  Each  of  these  chambers  is  again  subdivided  transversely  into 
an  upper  and  a  lower  portion,  called  respectively,  auricle  and  ventricle, 
which  freely  communicate  one  with  the  other ;  the  aperture  of  com- 
munication, however,  is  guarded  by  valves,  so  disposed  as  to  allow 
blood  to  pass  freely  from 
the  auricle  into  the  \q\\- 
tricle,  but  not  in  the  oppo- 
site direction.  There  are 
thus  four  cavities  in  the 
heart — the  auricle  and  ven- 
tricle of  one  side  being 
quite  separate  from  those 
of  the  other  (figs.  217,  218). 

The  right  auricle  is  situ- 
ated at  the  right  part  of  the 
base  of  the  heart  in  front. 
It  is  a  thin  walled  cavity 
of  quadrilateral  shape,  pro- 
longed at  one  corner  into  a 
tongue-shaped  portion,  the 
right  auricular  appendix, 
which  slightly  overlaps  the 
exit  of  the  aorta,  from  the 
heart. 

The  interior  is  smooth, 
being  lined  with  the  general  lining  of  the  heart,  the  endocardium, 
and  into  it  open  the  superior  and  inferior  venae  cavse,  or  great  veins, 
which  convey  the  blood  from  all  parts  of  the  body  to  the  heart. 
The  opening  of  the  inferior  cava  is  protected  and  partly  covered  by 
a  membrane  called  the  Eustachian  valve.  In  the  posterior  wall  of 
the  auricle  is  a  slight  depression  called  the  fossa  ovalis,  which  corre- 
sponds to  an  opening  between  the  right  and  left  auricles  which 
exists  in  foetal  life.  The  coronary  sinus,  or  the  dilated  portion  of  the 
left  coronary  vein,  also  opens  into  this  chamber. 

The  right  ventricle  occupies  the  chief  part  of  the  anterior  surface 
of  the  heart,  as  well  as  a  small  part  of  the  posterior  surface ;  it  forms 
the  right  margin  of  the  heart.  It  takes  no  part  in  the  formation  of 
the  apex.     On  section  its  cavity,  in  consequence  of  the  encroachment 


Diaphragm. 


Fig.  216 


View  of  heart  and  lungs  in  situ.  The  front 
portion  of  the  chest-wall  and  the  outer  or  parietal 
layers  of  the  pleuni?  and  pericardium  have  been  re- 
moved.   The  lungs  are  partly  collapsed. 


208 


THE   CIRCULATORY   SYSTEM 


[CH.  XVIII. 


upon  it  of  the  septum  ventriculorum,  is  crescentic  (fig.  219) ;  into  it 
are  two  openings,  the  auriculo-ventricular  at  the  base  and  the  opening 
of  the  pulmonary  artery  also  at  the  base,  but  more  to  the  left ;  both 
orifices  are  guarded  by  valves,  the  former  called  tricuspid  and  the 


Fig.  217. — The  right  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  walls  removed, 
so  as  to  show  their  interior.  A. — 1,  superior  vena  cava;  2,  inferior  vena  cava;  2',  hepatic  veins  cut 
short ;  3,  right  auricle  ;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve  ;  3",  is 
placed  close  to  the  aperture  of  the  coronary  vein  ;  +  +,  placed  in  the  auriculo-ventricular  groove, 
where  a  narrow  portion  of  tlie  adjacent  walls  of  the  auricle  and  ventricle  lias  been  preserved  ;  4,  4, 
cavity  of  the  right  ventricle,  the  upper  tigure  is  immediately  below  the  semilunar  valves  ;  4',  large 
columna  carnea  or  musculus papillaris;  5,  5',  5",  tricuspid  valve  ;  6,  placed  in  the  interior  of  the 
pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed,  and  a  narrow 
portion  of  it  preserved  at  its  commencement,  where  the  semilunar  valves  are  attached  ;  7,  concavity 
of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus  ;  S,  ascending  part  or  sinus  of  the  arch 
covered  at  its  commencement  by  the  auricular  appendix  and  pulmonary  artery  ;  9,  placed  between 
the  innominate  and  left  carotid  arteries  ;  10,  appendix  of  the  left  auricle  ;  11,  11,  the  outside  of  the 
left  ventricle,  the  lower  tigure  near  the  apex.    (Allen  Thomson.) 

latter  semilunar.     In  this  ventricle  are  also  the  projections  of  the 
muscular  tissue  called  columnm  caimece  (described  at  length,  p.  212). 

The  left  auricle  is  situated  at  the  left  and  posterior  part  of  the 
base  of  the  heart,  and  is  best  seen  from  behind.  It  is  quadrilateral, 
and  receives  on  either  side   two   pulmonary  veins.     The   auricular 


CH.  XVIII.] 


THE    HEART 


209 


appendix   is   the   only  part  of  the  auricle  seen  from  the  front,  and 
corresponds   with   that  on    the   right  side,  but  is  thicker,  and  the 


Fig.  218. — The  left  auricle  and  ventricle  opened  and  a  part  of  their  anterior  and  left  walls  removed.  ^. 
— The  pulmonary  artery  has  been  divided  at  its  commencement ;  the  opening  into  the  left  ventricle 
is  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the  semilunar  valves  ;  and 
the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  The  right  auricle  is  out  of  view. 
1,  the  two  right  pulmonary  veins  cut  short ;  their  openings  are  seen  within  the  auricle  ;  1',  placed 
within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part  which  forms  the 
remains  of  the  valve  of  the  foramen  ovale,  of  which  the  crescentic  fold  is  seen  towards  the  left  hand 
of  1' ;  2,  a  narrow  portion  of  tlie  wall  of  the  auricle  and  ventricle  preserved  round  the  auriculo- 
ventricular  orifice ;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  become  very  much 
thinner  towards  3",  at  the  apex  ;  4,  a  small  part  of  the  anterior  wall  of  the  left  ventricle  which  has 
been  preserved  with  the  principal  anterior  columna  carnea  or  musculus  papillaris  attached  to  it ; 
5,  5,  musculi  papillares  ;  5',  the  left  side  of  the  septum,  between  the  two  ventricles,  within  the 
cavity  of  the  left  ventricle;  6,  6',  the  mitral  valve  ;  7,  placed  in  the  interior  of  the  aorta,  near  its 
commencement  and  above  the  three  segments  of  its  semilunar  valve  which  are  hanging  loosely 
together ;  T,  the  exterior  of  the  great  aortic  sinus ;  8,  the  root  of  the  pulmonary  artery  and  its 
semilunar  valves ;  8',  the  separated  portion  of  the  pulmonary  artery  remaining  attached  to  the 
aorta  by  9,  the  cord  of  the  ductus  arteriosus  ;  10,  the  arteries  rising  from  the  summit  of  the  aortic 
arch.    (Allen  Thomson.) 


interior  is  smoother.     The  left  auricle  is  only  slightly  thicker  than 
the  right.     The  left  auriculo-ventricular  orifice  is  oval,  and  a  little 

O 


210  THE   CIRCULATORY   SYSTEM  [CII.  XVIII. 

smaller  than  that  on  the  right  side.  There  is  a  depression  on  the 
septum  between  the  auricles,  which  is  a  vestige  of  the  foramen 
between  them,  that  exists  in  foetal  life. 

The  left  ventricle  occupies  the  chief  part  of  the  posterior  surface. 
In  it  are  two  openings  very  close  together,  viz.,  the  auriculo-ventri- 
cular  and  the  aortic,  guarded  by  the  valves  corresponding  to  those  of 
the  right  side  of  the  heart,  viz.,  the  bicuspid  or  mitral  and  the  semi- 
lunar. The  first  opening  is  at  the  left  and  back  part  of  the  base  of 
the  ventricle,  and  the  aortic  in  front  and  towards  the  right.  In  this 
ventricle,  as  in  the  right,  are  the  columnae  carnese,  which  are  smaller 
but  more  closely  reticulated.  They  are  chiefly  found  near  the  apex 
and  along  the  posterior  wall.  The  walls  of  the  left  ventricle,  which 
are  nearly  half  an  inch  in  thickness,  are,  with  the  exception  of  the 
apex,  about  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers.— During  life  each  ventricle  is 
capable  of  containing  about  three  ounces  of  blood.     The  capacity  of 


Cavity  of  right  ventricle.  _  __„  ^™-    „     .,       ,,  ,,         ... 

■  .«jHi  ■^^-  Cavity  of  left  ventricle. 


Fio.  219.— Transverse  section  of  bullock's  li'  ;    late  of  oadaveric  rigidity.    (Dalton.) 

the  auricles  is  rather  less  than  that  of  the  ventricles:  the  thick- 
ness of  their  walls  is  considerably  less.  The  latter  condition  is 
adapted  to  the  small  amount  of  force  which  the  auricles  require  in 
order  to  empty  themselves  into  their  adjoining  ventricles ;  the  former 
to  the  circumstance  of  the  ventricles  being  partly  filled  with  blood 
before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches 
long  (about  12'6  cm.),  3|  inches  (8  cm.)  greatest  width,  and  2|- 
inches  (6  "3  cm.)  in  its  extreme  thickness.  The  average  weight  of 
the  heart  in  the  adult  is  from  9  to  10  ounces  (about  300  grms.) ; 
its  weight  gradually  increases  throughout  life  till  middle  age;  it 
diminishes  in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost 
entirely  of  layers  of  muscular  fibres  (figs.  113  and  220);  but  a  ring 
of  connective  tissue,  to  which  some  of  the  muscular  fibres  are 
attached,  is  inserted  between  each  auricle  and  ventricle,  and  forms 
the  boundary  of  the  auriculo-ventricular  opening.  Fibrous  tissue  also 
exists  at  the  origins  of  the  pulmonary  artery  and  aorta. 


CH.  XVIII.] 


THE    IIEAUT 


211 


Tho  muscular  fibres  of  each  auricle  are  in  part  continuous  with 
those  of  tho  other,  and  partly  separate;  and  the  same  remark 
holds  true  for  the  ventricles.     Some  muscular  fibres  also  pass  across 


mmiMr' 


-/#» 


Fio.  220. — Network  uf  muscular  libres  from  the  heart  of  a  \nsi.     The  nuclei  are  well  shown,     x   450. 

(Klein  and  Noble  Smith.) 

the  tendinous  ring  which  separates  each  auricle  from  the  correspond- 
ing ventricle. 

Endocardium. — As  the  heart  is  clothed  on  the  outside  by  the 
epicardium,  so  its  cavities  are  lined  by  a  smooth  membrane,  the 
endocardium,  which  is  directly  continuous  with  the  internal  lining  of 
the  arteries  and  veins.  The 
endocardium  is  composed  of 
connective  tissue  with  a  large 
admixture  of  elastic  fibres ; 
its  inner  surface  is  covered 
by  endothelium.  Here  and 
there  muscular  fibres '  are 
sometimes  found  in  the  tissue 
of  the  endocardium. 

Valves.  —  The  arrange- 
ment of  the  heart's  valves  is 
such  that  the  blood  can  pass 
only  in  one  direction  (fig. 
221). 

The  tricuspid  valve  (5,  fig. 
217)  presents  three  principal 
cusps  or  subdivisions,  and  the 
mitral  or  bicuspid  valve  has 
two  such  portions  (6,  fig.  218). 
But  in  both  valves  there  is 
between  each  two  principal 
portions  a  smaller  one :  so  that  more  properly,  the  tricuspid  may  be 
described  as  consisting  of  six,  and  the  mitral  of  four,  portions.  Each 
portion  is  of  triangular  form.  Its  base  is  continuous  with  the  bases 
of  the  neighbouring  portions,  so  as  to  form  an  annular  membrane 


Fig.  221.— Diagram  of  the  circulation  through  the 
heart.    (Dal  ton.) 


212  THE   CIRCULATORY   SYSTEM  [CH.  XVIII. 

around  the  auriculo-ventricular  opening,  and  is  fixed  to  a  tendinous 
ring  which  encircles  the  orifice  between  the  auricle  and  ventricle, 
and  receives  the  insertions  of  the  muscular  fibres  of  both.  In  each 
principal  cusp  may  be  distinguished  a  central  part,  extending  from 
base  to  apex,  and  including  about  half  its  width.  It  is  thicker  and 
much  tougher  than  the  border  pieces  or  edges. 

While  the  bases  of  the  cusps  of  the  valves  are  fixed  to  the  tendinous 
rings,  their  ventricular  surface  and  borders  are  fastened  by  slender  ten- 
dinous fibres,  the  chordoe  tendinece,  to  the  internal  surface  of  the  walls 
of  the  ventricles,  the  muscular  fibres  of  which  project  into  the 
ventricular  cavity  in  the  form  of  bundles  or  columns — the  columnce 
carnece.  These  columns  are  not  all  alike,  for  while  some  are  attached 
along  their  whole  length  on  one  side,  and  by  their  extremities,  others 
are  attached  only  by  their  extremities ;  and  a  third  set,  to  which  the 
name  musculi  papillares  has  been  given,  are  attached  to  the  wall  of 
the  ventricle  by  one  extremity  only,  the  other  projecting,  papilla- 
like, into  the  cavity  of  the  ventricle  (5,  fig.  218),  and  having  attached 
to  it  chordae  tendineae.  Of  the  tendinous  cords,  besides  those  which 
pass  to  the  margins  of  the  valves,  there  are  some  of  especial  strength, 
which  pass  to  the  edges  of  the  middle  and  thicker  portions  of  the 
cusps  before  referred  to.  The  ends  of  these  cords  are  spread  out  in 
the  substance  of  the  valve,  giving  its  middle  piece  its  peculiar  strength 
and  toughness ;  and  from  the  sides  numerous  other  more  slender 
and  branching  cords  are  given  off,  which  are  attached  all  over  the 
ventricular  surface  of  the  adjacent  border-pieces  of  the  principal 
portions  of  the  valves,  as  well  as  to  those  smaller  portions  which 
have  been  mentioned  as  lying  one  between  each  two  principal  ones. 
Moreover,  the  musculi  papillares  are  so  placed  that,  from  the 
summit  of  each,  tendinous  cords  proceed  to  the  adjacent  halves  of 
two  of  the  principal  divisions,  and  to  one  intermediate  or  smaller 
division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and 
tricuspid  valve ;  but  it  should  be  added  that  the  mitral  is  considerably 
thicker  and  stronger  than  the  tricuspid,  in  accordance  with  the 
greater  force  which  it  is  called  upon  to  resist. 

The  semilunar  valves  guard  the  orifices  of  the  pulmonary  artery 
and  of  the  aorta.  They  are  nearly  alike  on  both  sides  of  the  heart ; 
but  the  aortic  valves  are  altogether  thicker  and  more  strongly  con- 
structed than  the  pulmonary  valves,  in  accordance  with  the  greater 
pressure  which  they  have  to  withstand.  Each  valve  consists  of  three 
parts  which  are  of  semilunar  shape,  the  convex  margin  of  each  being 
attached  to  a  fibrous  ring  at  the  place  of  junction  of  the  artery  to 
the  ventricle,  and  the  concave  or  nearly  straight  border  being  free, 
so  as  to  form  a  little  pouch  like  a  watch-pocket  (7,  fig.  218).  In 
the  centre  of  the  free  edge  of  the  pouch,  which  contains  a  fine  cord 


CH.  XVIII.] 


COURSE   OF  THE   CmCULATION 


218 


of  fibrous  tissue,  is  a  small  fibrous  nodule,  the  corpus  Arantii,  and 
from  this  and  from  the  attached  border  fine  fibres  extend  into  every 
part  of  the  mid  substance  of  the  valve,  except  a  small  lunated  space 
just  within  the  free  edge,  on  each  side  of  the  corpus  Arantii.  Here 
the  valve  is  thinnest,  and  composed  of  little  more  than  the  endo- 
cardium. Thus  constructed  and  attached,  the  three  semilunar 
pouches  are  placed  side  by  side  around  the  arterial  orifice  of  each 
ventricle;  they  are  separated  by  the  blood  passing  out  of  the 
ventricle,  but  immediately  afterwards  are  pressed  together  so  as  to 


Pulmonary  capillaries. 


Pulmonary  artery. 


Superior  cava  or  vein 
from  head  and  neck. 


Right  auricle. 
Inferior  vena  cava. 


Right  ventricle. 


Portal  circulation. 


Second  renal  circu- 
lation. 


Pulmonary  veins. 
Aorta. 

Arteries   to  head  and 
neck. 

Left  auricle. 


Left  ventricle. 


Gastric  and  intestinal 
vessels. 


First  renal  circulation. 


Systemic  capillaries. 


Fig.  222. — Diagram  of  the  circulation. 

prevent  any  return  (6,  fig.  217,  and  7,  fig.  218).  Opposite  each  of 
the  semilunar  cusps,  both  in  the  aorta  and  pulmonary  artery,  there 
is  a  bulging  outwards  of  the  wall  of  the  vessel :  these  bulgings  are 
called  the  simtses  of  Valsalva.  The  valves  of  the  heart  are  formed 
of  a  layer  of  closely  woven  connective  and  elastic  tissue,  over  which, 
on  every  part,  the  endocardium  is  reflected. 


Course  of  the  Circulation. 


The  blood  is  conveyed  away  from  the  left  ventricle  (as  in   the 
diagram,  fig.  222)  by  the  aorta  to  the  arteries,  and  returned  to  the 


214 


THE   CIRCULATORY   SYSTEM 


[CH.  XVIIl. 


right  auricle  by  the  veins,  the  arteries  and  veins  being  continuous 
with  each  other  at  the  far  end  by  means  of  the  capillaries. 

From  the  right  auricle  the  blood  passes  to  the  right  ventricle, 
then  by  the  pulmonary  artery,  which  divides  into  two,  one  for  each 
lung,  then  through  the  pulmonary  capillaries,  and  through  the 
pulmonary  veins  (two  from  each  lung)  to  the  left  auricle.  From 
here  it  passes  into  the  left  ventricle,  which  brings  us  back  to  where 
we  started  from. 

The  complete  circulation  is  thus  made  up  of  two  circuits,  the  one, 
a  shorter  circuit  from  the  right  side  of  the  heart  to  the  lungs  and 
back  again  to  the  left  side  of  the  heart ;  the  other 
and  larger  circuit,  from  the  left  side  of  the  heart 
to  all  parts  of  the  body  and  back  again  to  the 
right  side.  The  circulations  through  the  lungs 
and  through  the  system  generally  are  respectively 
named  the  Pulmonary  and  Systemic  or  lesser 
and  greater  circulations.  It  will  be  noticed  also 
in  the  same  figure  that  a  portion  of  the  stream 
of  blood  having  been  diverted  once  into  the 
capillaries  of  the  intestinal  canal,  and  some  other 
abdominal  organs,  and  gathered  up  again  into  a 
single  stream,  is  a  second  time  divided  in  its 
passage  through  the  liver,  before  it  finally  reaches 
the  heart  and  completes  a  revolution.  This  sub- 
ordinate stream  through  the  liver  is  called  the 
Portal  circulation.  A  somewhat  similar  accessory 
circulation  is  that  through  the  kidneys,  called  the 
Renal  circulation.  The  difference  of  colours  in 
fig.  222  indicates  roughly  the  difference  between 
arterial  and  venous  blood.  The  blood  is  oxygen- 
ated in  the  lungs,  and  the  formation  of  oxy- 
hsemoglobin  gives  to  the  blood  a  bright  red  colour. 
This  oxygenated  or  arterial  blood  (contained  in 
the  pulmonary  veins,  the  left  side  of  the  heart,  and  systemic  arteries) 
is  in  part  reduced  in  the  tissues,  and  the  deoxygenated  haemoglobin 
is  darker  in  tint  than  the  oxyhaemoglobin ;  this  venous  blood  passes 
by  the  systemic  veins  to  the  right  side  of  the  heart  and  pulmonary 
artery  to  the  lungs,  where  it  once  more  receives  a  fresh  supply  of 
oxygen. 

N.B. — It  should,  however,  be  noted  that  the  hings,  Hke  the  rest  of  the  body, 
are  also  supplied  with  arterial  blood,  which  reaches  them  by  the  bronchial  arteries. 


Fio.  223.— Minute  artery 
viewed  in  longitudinal 
section,  c.  Nucleated 
endotlielial  membrane, 
with  faint  nuclei  in 
lumen,  looked  at  from 
above,  i.  Elastic  mem- 
brane, m.  Muscular 
coat  or  tunica  media. 
a.  Tunica  adventitia. 
(Klein  and  Noble 
Smith.)     X  250. 


The  Arteries. 


The  arterial  system  begins  at  the  left  ventricle  in  a  single  large 
trunk,  the  aorta,  which  almost  immediately  after  its  origin  gives  off 


en.  XVIII.] 


THE   ARTERIES 


215 


in  the  thorax  three  large  branches  for  the  supply  of  the  head,  neck, 
and  upper  extremities ;  it  then  traverses  the  thorax  and  abdomen, 
giving  off  branches,  some  large  and  some  small,  for  the  supply  of  the 
various  organs  and  tissues  it  passes  on  its  way.  In  the  abdomen  it 
divides  into  two  chief  branches,  for  the  supply  of  the  lower  ex- 
tremities. The  arterial  branches  wherever  given  off  divide  and  sub- 
divide, until  the  calibre  of  each  subdivision  becomes  very  minute,  and 
these  minute  vessels  lead  into  capillaries.  Arteries  are,  as  a  rule, 
placed  in  situations  protected  from  pressure  and  other  dangers,  and 
are,  with  few  exceptions,  straight  in  their  course,  and  frequently 
communicate  (anastomose  or  inos- 
culate) with  other  arteries.  The 
branches  are  usually  given  off  at  an 
acute  angle,  and  the  sum  of  the  sec- 
tional areas  of  the  branches  of  an 
artery  generally  exceeds  that  of  the 
parent  trunk ;  and  as  the  distance 
from  the  origin  is  increased,  the  area 
of  the  combined  branches  is  increased 
also.  After  death,  arteries  are  usually 
found  dilated  (not  collapsed  as  the 
veins  are)  and  empty,  and  it  was  to 
this  fact  that  their  name  (aprtjpla,  the 
windpipe)  was  given  them,  as  the 
ancients  believed  that  they  conveyed 
air  to  the  various  parts  of  the  body. 
As  regards  the  arterial  system  of  the 
lungs,  the  pulmonary  artery  is  dis- 
tributed much  as  the  arteries  belong- 
ing to  the  general  systemic  circulation. 
Structure. — The  wall  of  an  artery 
is  composed  of  the  following  three 
coats : — 

(a)  The  external  coat  or  tunica  adventitia  (figs.  223  and  224,  a), 
the  strongest  part  of  the  wall  of  the  artery,  is  formed  of  areolar 
tissue,  with  which  is  mingled  throughout  a  network  of  elastic  fibres. 
At  the  inner  part  of  this  outer  coat  the  elastic  network  forms,  in 
some  arteries,  so  distinct  a  layer  as  to  be  sometimes  called  the 
external  elastic  coat  (fig.  224,  e). 

(b)  The  middle  coat  (fig.  224,  m)  is  composed  of  both  muscular 
and  elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the 
larger  arteries  (fig.  226)  its  thickness  is  comparatively  as  well  as 
absolutely  much  greater  than  in  the  small  ones ;  it  constitutes  the 
greater  part  of  the  arterial  wall.  The  muscular  fibres  are  unstriped 
(fig.  225),  and  are  arranged  for  the  most  part  transversely  to  the 


Fig.  224.— Transverse  section  through  a 
large  branch  of  the  inferior  mesenteric 
artery  of  a  pig.  e,  endothelial  mem- 
brane ;  i,  tunica  elastiea  interna,  no 
subendothelial  layer  Is  seen ;  m,  mus- 
cular tunica  media,  containing  only  a 
few  wa\-y  elastic  fibres ;  e,  e,  tunica 
elastiea  externa,  dividing  the  media 
from  the  connective-tissue  adventitia, 
a.    (Klein  and  Noble  Smith.)     x  350. 


216 


THE    CIRCULATORY   SYSTEM 


[CH.  XVIII. 


/i. 


long  axis  of  the  artery ;  while  the  elastic  element,  taking  also  a  trans- 
verse direction,  is  disposed  in  the  form  of  closely  interwoven  and 
branching  fibres,  which  intersect  in  aU  parts  the  layers  of  muscular 
fibres.  In  arteries  of  various  sizes  there  is  a  difference  in  the  pro- 
portion of  the  muscular  and  elastic  element,  elastic  tissue  prepon- 
derating in  the  largest  arteries,  and  unstriped  muscle  in  those  of 
medium  and  small  size. 

(c)  The  internal  coat  is  formed  by  a  layer  of  elastic  tissue,  called 
th.Q  fenestrated  membrane  of  Henle.  Its  inner  surface  is  lined  with  a 
delicate  layer  of  elongated  endothelial  cells  (fig.  224,  e),  which  make 
it  smooth,  so  that  the  blood  may  flow  with  the  smallest  possible 

amount  of  resistance  from  friction.  Imme- 
diately external  to  the  endothelial  Hning 
of  the  artery  is  fine  connective  tissue 
{suh- endothelial  layer)  with  branched  cor- 
puscles. Thus  the  internal  coat  consists 
of  three  parts,  (a)  an  endothelial  lining,  (Jb) 
the  sub-endothelial  layer,  and  {c)  elastic 
layer. 

Vasa.  Vasorurn.  —  The  walls  of  the 
arteries  are,  like  other  parts  of  the  body, 
supplied  with  little  arteries,  ending  in 
capillaries  and  veins,  which,  branching 
throughout  the  external  coat,  extend  for 
some  distance  into  the  middle,  but  do  not 
reach  the  internal  coat.  These  nutrient 
vessels  are  called  vasa  vasorurn. 

Serves. — Most  of   the  arteries  are  sur- 
rounded by  a  plexus  of  sympathetic  nerves, 
which  twine  around  the   vessel  very  much 
They  terminate  in  a  plexus  between  the 


'7 

// 


((' 


/ 


Fig.     225 


fibre-cells 


Moscolar 
from  haman  arteries,  magni- 
fied 350  diameters.  (Kolliker.) 
a.  Xucleus.  b.  A  fibre-cell 
treated  with  acetic  acid. 


like 


ivy 


round  a  tree. 


muscular  fibres  (fig.  227). 


The  Veins. 


The  venous  system  begms  in  smaU  vessels  which  are  slightly 
larger  than  the  capillaries  from  which  they  spring.  These  vessels 
are  gathered  up  into  larger  and  larger  trunks  until  they  terminate 
(as  regards  the  systemic  circulation)  in  the  two  vena  cavae  and  the 
coronary  veins,  which  enter  the  right  auricle,  and  (as  regards  the 
pulmonary  circulation)  in  four  pulmonary  veins,  which  enter  the  left 
auricle.  The  total  capacity  of  the  veins  diminishes  as  they  approach 
the  heart ;  but,  as  a  rule,  their  capacity  is  two  or  three  times  that 
of  the  corresponding  arteries.  The  pulmonary  veins,  however,  are 
an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the 
pulmonary  arteries.     The  veins  are  found  after  death  more  or  less 


CH.  XVIII.] 


THE   VEINS 


217 


collapsed,  owing  to  their  want  of  elasticity.  They  are  usually  dis- 
tributed in  a  superficial  and  a  deep  set  which  communicate  fre- 
quently in  their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general 
resemblance  to  those  of  arteries  (fig.  228).  Thus,  they  possess  outer, 
middle,  and  internal  coats. 

{a)  The  outer  coat  is  constructed  of  areolar  tissue  like  that  of  the 
arteries,  but  it  is  thicker.  In  some  veins  it  contains  muscular  fibres, 
which  are  arranged  longitudinally. 


fi-*j^* 


(«i-?..^  ^. 


Endothelium. 

'A 

Sub-endothelial  layer. 

% 

Elastic  Intima. 

Jliddle  coat. 


Fio.  226. — Transverse  section  of  aorta  tbrough  internal  and  about  half  the  middle  coat. 


(6)  The  middle  coat  is  considerably  thinner  than  that  of  the 
arteries ;  it  contains  circular  unstriped  muscular  fibres,  mingled  with 
a  few  elastic  fibres  and  a  large  proportion  of  white  fibrous  tissue. 
In  the  large  veins,  near  the  heart,  namely,  the  vence  cavce  and  pul- 
monary veins,  the  middle  coat  is  replaced,  for  some  distance  from 
the  heart,  by  circularly  arranged  striped  muscular  fibres,  continuous 
with  those  of  the  auricles.  The  veins  of  bones,  and  of  the  central 
nervous  system  and  its  membranes  have  no  muscular  tissue. 

(c)  The  internal  coat  of  veins  has  a  very  thin  fenestrated 
membrane,    which    may    be    absent    in    the    smaller    veins.     The 


218 


THE   CIRCULATORY  SYSTEM 


[CH.  XVIII. 


endothelium  is  made  up  of  cells  elongated  in  the  direction  of  the 
vessel,  but  wider  than  in  the  arteries. 

Valves. — The  chief  influence  which  the  veins  have  in  the  circu- 
lation is  effected  with  the  help  of  the  valves,  contained  in  all  veins 
subject  to  local  pressure  from  the  muscles  between  or  near  which 
they  run.  The  general  construction  of  these  valves  is  similar  to  that 
of  the  semilunar  valves  of  the  aorta  and  pulmondry  artery,  already 
described ;  but  their  free  margins  are  turned  in  the  opposite  direction, 
i.e.,  towards  the  heart,  so  as  to  prevent  any  movement  of  blood  back- 
ward. They  are  commonly  placed  in  pairs,  at  various  distances  in 
different  veins,  but  almost  uniformly  in  each  (fig,   229).      In  the 

smaller  veins  single  valves  are 
often  met  with ;  and  three  or 
four  are  sometimes  placed  to- 
gether, or  near  one  another,  in 
the  largest  veins,  such  as  the 
subclavian,  at  their  junction  with 
the  jugular  veins.  The  valves 
are  semilunar ;  the  unattached 
edge  is  in  some  examples  con- 
cave, in  others  straight.  They 
are  composed  of  an  outgrowth  of 
the  subendothelial  tissue  covered 
with  endothelium.  Their  situa- 
tion in  the  superficial  veins  of 
the  forearm  is  readily  discovered 
by  pressing  along  their  surface, 
in  the  direction  opposite  to  the 
venous  current,  i.e.,  from  the 
elbow  towards  the  wrist ;  when 
little  swellings  (fig.  229,  c)  appear 
in  the  position  of  each  pair  of 
valves.  These  swellings  at  once  disappear  when  the  pressure  is 
removed. 

Valves  are  not  equally  numerous  in  all  veins,  and  in  many  they 
are  absent  altogether.  They  are  most  numerous  in  the  veins  of  the 
extremities,  and  more  so  in  those  of  the  leg  than  the  arm.  They  are 
commoidy  absent  in  veins  of  less  than  a  line  in  diameter,  and,  as  a 
general  rule,  there  are  few  or  none  in  those  which  are  not  subject  to 
muscular  pressure.  Among  those  veins  which  have  no  valves  may 
be  mentioned  the  superior  and  inferior  vena  cava,  the  pulmonary 
veins,  the  veins  in  the  interior  of  the  cranium  and  vertebral  column, 
the  veins  of  bone,  and  the  umbilical  vein.  The  valves  of  the  portal 
tributaries  are  very  inefficient. 

Lymphatics  of  Arteries  and  Veins. — Lymphatic  spaces  are  present 


Fig.  227. — Ramification  of  nerves  and  termination 
in  the  muscular  coat  of  a  small  artery  of  the 
frog.     (Arnold.) 


CH.  XVIII.J 


THE   CAPILLARIES 


219 


in  the  coats  of  both  arteries  and  veins.  In  the  external  coat  of  large 
vessels  they  form  a  plexus  of  more  or  less  tubular  vessels.  In  smaller 
vessels  they  appear  as  spaces  lined  by  endothelium.  Sometimes,  as 
in  the  arteries  of  the  omentum,  mesentery,  and  membranes  of  the 
brain,  in  the  pulmonary,  hepatic,  and 
splenic  arteries,  the  spaces  are  con- 
tinuous with  vessels  which  distinctly 
ensheath  them — perivascular  lym- 
phatics (fig.  231). 

The  Capillaries. 

In  all  vascular  textures  except 
some  parts  of  the  corpora  cavernosa 
of  the  penis,  of  the  uterine  placenta, 
and  of  the  spleen,  the  transmission 
of  the  blood  from  the  minute  branches 
of  the  arteries  to  the  minute  veins  is 
affected  through  a  network  of  capil- 
laries. 

Their  walls  are  composed  of  endo- 
thelium— a  single  layer  of  elongated 
flattened  and  nucleated  cells,  so  joined 
and  dovetailed  together  as  to  form  a 
continuous  transparent  membrane 
(fig.  232).  Here  and  there  the  endo- 
thelial cells  do  not  fit  quite  accu- 
rately; the  space  is  filled  up  with 
cement  material ;  these  spots  are 
called  pseudo-stomata. 

The  diameter  of  the  capillary 
vessels  varies  somewhat  in  the 
different  tissues  of  the  body,  the 
most     common     size     beins;     about 


nVnth  of   an 


inch  (12  /jt).     Among 
may     be     mentioned 


,  228. — Transverse  section  througli  a 
small  artery  and  vein  of  the  mucous 
membrane  of  a  child's  epiglottis;  the 
artery  is  thick-walled  and  the  vein  thin- 
walled.  A.  Artery,  the  letter  is  placed 
in  the  lumen  of  the  vessel,  e.  Endo- 
thelial cells  with  nuclei  clearly  visible ; 
these  cells  appear  very  thick  from  the 
contracted  state  of  the  vessel.  Outside 
it  a  double  wavy  line  marks  the  elastic 
layer  of  the  tunica  intinia.  m.  Tunica 
media,  consisting  of  unstriped  muscular 
fibres  circularly  arranged  ;  their  nuclei 
are  well  seen.  a.  Part  of  the  tunica 
adventitia  showing  bundles  of  connec- 
tive-tissue libre  in  section,  with  the 
circular  nuclei  of  the  connective-tissue 
corpuscles.  This  coat  gradually  merges 
into  the  surrounding  connective  tissue. 
V.  In  the  lumen  of  the  vein.  The  other 
letters  indicate  the  same  as  in  the 
artery.  The  muscular  coat  of  the  vein 
(m)  is  seen  to  be  much  thinner  than 
that  of  the  artery.  x  350.  (Klein 
and  Noble  Smith.) 


2000 

the     smallest 

those   of  the    brain,  and  of   the  fol 

licles   of   the   mucous   membrane  of 

the    intestines ;    among   the   largest, 

those   of   the   skin,  lungs,  and  especially  those  of  the  medulla  of 

bones. 

The  size  of  capillaries  varies  necessarily  in  different  animals  in 
relation  to  the  size  of  their  blood  corpuscles :  thus,  in  the  Proteus, 
the  capillary  circulation  can  just  be  discerned  with  the  naked  eye. 

The  form  of  the  capillary  network  presents  considerable  variety 


220 


THE   CIRCULATORY   SYSTEM 


[CH.  xviir. 


in  the  different  tissues  of  the  body :  the  varieties  consist  principally 
of  modifications  of  two  chief  kinds  of  mesh,  the  rounded  and  the 
elongated.      That  kind  in  which  the  meshes  or  interspaces  have  a 


Pig.  229. — Diagram  showing  valves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out,  with  two  pairs 
of  valves,  b,  longitudinal  section  of  a  vein,  showing  the  apposition  of  the  edges  of  the  valves  in 
their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  swelling  in  the  situation  of  a  pair 
of  valves. 

roundish  or  polygonal  form  is  the  most  common,  and  prevails  in 
those  parts  in  which  the  capillary  network  is  most  dense,  such  as 
the  lungs  (fig.  233),  most  glands  and  mucous  membranes,  and  the 


Fig.  230. — a,  vein  with  valves   open 


1),  ^\■ith  valves  closed  ;   stream  of  blood  passing  off  by  lateral 
channel.    (Balton.) 


cutis.  The  capillary  network  with  elongated  meshes  is  observed  in 
parts  in  which  the  vessels  are  arranged  among  bundles  of  fine  tubes 
or  fibres,  as  in  muscles  and  nerves.  In  such  parts,  the  meshes  form 
parallelograms  (fig.  234),  the  short  sides  of  which  may  be  from  three 


CH.  XVIII.]  LYMPHATIC   VESSELS  221 

to  eight  or  ten  times  less  than  the  long  ones ;  the  long  sides  are 
more  or  less  parallel  to  the  long  axis  of  the  fihres. 

The  numher  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascularity  of  those  parts. 
The  capillary  network  is  closest  in  the  lungs  and  in  the  choroid 
coat  of  the  eye. 

It  may  be  held  as  a  general  rule,  that  the  more  active  the 
fimctions  of  an  organ  are,  the  more  vascular  it  is.  Hence  the 
narrowness  of   the  interspaces  in  all  glandular  organs,  in  mucous 


Fig.  231.— Surface  view  of  an  artery  from  the  mesentery  of  a  frog,  ensheathed  in  a  perivascular  lym- 
phatic vessel,  a,  the  arten',  with  its  circular  muscular  coat  (media)  indicated  by  broad  transverse 
markings,  with  an  indication  of  the  adventitia  outside.  I,  lymphatic  vessel ;  its  wall  is  a  simple 
endothelial  membrane.    (Klein  and  Noble  Smith.) 

membranes,  and  in  growing  parts,  and  their  much  greater  width  in 
bones,  ligaments,  and  other  comparatively  inactive  tissues. 

Lymphatic  Vessels. 

The  blood  leaves  the  heart  by  the  arteries  ;  it  returns  to  the  heart 
by  the  veins ;  but  this  last  statement  requires  modification,  for  in  the 
capillaries  some  of  the  blood-plasma  escapes  into  the  cell  spaces  of 
the  tissues  and  nourishes  the  tissue-elements.  This  fluid,  which  is 
called  lymph,  is  gathered  up  and  carried  back  again  into  the  blood  by 
a  system  of  vessels  called  lymphatics. 


222 


THE   CIRCULATORY   SYSTEM 


[CII.  XVIII. 


The  principal  vessels  of  the  lymphatic  system  are,  in  structure, 
like  small  thin-walled  veins,  provided  with  numerous  valves.  The 
beaded  appearance  of  the  lymphatic  vessels  shown  in  figs.  236  and 


Fio.  232.— Capillary  blood-vessels   from   the   omentum   of  rabbit,  showing  the  nucleated  endothelial 
membrane  of  which  they  are  composed.    (Klein  and  Noble  Smith.) 

237  is  due  to  the  presence  of  these  valves.  They  commence  in  fine 
microscopic  lymph-cainllaries,  in  the  organs  and  tissues  of  the  body, 
and  they  end  in  two  trunks  which  open  into  the  large  veins  near  the 


Fio,  233. — Network  of  capillai-y 
vessels  of  the  air-cells  of  the 
horse's  lung  magnified,  a,  a, 
capillaries  proceeding  from  h, 
h,  terminal  branches  of  the 
pulmonary  artery.    (Frey.) 


Fig.  234. — Injected  capil- 
lary vessels  of  muscle 
seen  with  a  low  mag- 
nifying power. 

(Sharpey. ) 


heart  (fig.  235).  The  fluid  which  they  contain,  unlike  the  blood, 
passes  only  in  one  direction,  namely,  from  the  fine  branches  to  the 
trunk,  and  so  to  the  large  veins,  on  entering  which  it  is  mingled  with 
the  stream  of  blood.     In  fig.  235  the  greater  part  of  the  contents  of 


CII.  XVIII.] 


THE   THORACIC    DUCT 


22i 


the  lympliatic  system  of  vessels  will  be  seen  to  pass  through  a  com- 
paratively large  trunk  called  the  thoracic  duct,  which  finally  empties 
its  contents  into  the  blooil-stream,  at  the  junction  of  the  internal 
jugular  and  subclavian  veins  of  the  left  side.  There  is  a  smaller 
duct  on  the  right  side.  The  lymphatic  vessels  of  the  intestinal  canal 
are  called  lacteals,  because  during  digestion  (especially  of  a  meal  con- 
taining fat)  the  fluid  contained  in  them  resembles  milk  in  appear- 


Lympliatics  of  lieail  ami 
neck,  right. 

Right    internal    jugular 

vein. 
Right  subclavian  vein. 

Lympliatics  uf  right  arm. 


Receptaculum  chyli. 


Lymphatics  of  lower  ex- 
tremities. 


Lymphatics  of  head  and 
neck,  left. 


Thoracic  iluct. 

Left  subclavian  vein. 


Thoracic  duct. 


Lacteals. 


Lymphatics  of  lower  ex- 
tremities. 


Fig.  23.5.— Diagram  of  the  principal  groups  of  lymphatic  vessels.     (From  Quain.) 


ance ;  and  the  lym2jh  in  the  lacteals  during  the  period  of  digestion 
is  called  chyle.  Chyle  is  lymph  containing  finely  divided  fat-globules. 
In  some  parts  of  its  course  the  lymph-stream  passes  through  lym- 
phatic glands,  to  be  described  later  on. 

Origin  of  Lymph  Capillaries. — The  lymphatic  capillaries  com- 
mence most  commonly  either  {a)  in  closely-meshed  networks,  or  (h) 
in  irregular  lacunar  spaces  between  the  various  structures  of  which 
the  different  organs  are  composed.     In  serous  membranes,  such  as  the 


224 


THE   CIRCULATORY   SYSTEM 


[CH.  XVIIl 


mesentery,  they   occur   as   a   connected    system    of   very   irregular 
branched  spaces  partly  occupied  by  connective-tissue  corpuscles,  and 


Fig.  236. — Lymphatic  vessels  of  the  head  and  neck  and  the 
upper  part  of  the  trunk  (Mascagni).  ^. — The  chest  and 
pericardium  have  been  opened  on  the  left  side,  and  the 
left  mamma  detached  and  thrown  outwards  over  the  left 
arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The 
principal  lymphatic  vessels  and  glands  are  shown  on  the 
side  of  the  head  and  face  and  in  the  neck,  axilla,  and  medi- 
astinum. Between  the  left  internal  jugular  vein  and  the 
common  carotid  artfry,  the  upper  ascending  part  of  the 
thoracic  duct  marked  1,  and  above  this,  and  descending 
to  2,  the  arch  and  last  part  of  the  duct.  The  termination 
of  the  upper  lymphatics  of  the  diaphragm  in  the  medias- 
tinal glands,  as  well  as  the  cardiac  and  the  deep  mammary 
lymphatics,  is  also  shown. 


Fio.  237. — Superficial  lymphatics 
of  the  forearm  and  palm  of 
the  hand.  i. — 5.  Two  small 
glands  at  the  bend  of  the 
arm.  G.  Radial  lymphatic 
vessels.  7.  Ulnar  lymphatic 
vessels.  S,  8'.  Palmar  arch 
of  lymphatics.  9,  0'.  Outer 
and  inner  sets  of  vessels. 
h.  Cephalic  vein.  d.  Radial 
vein.  p.  Median  vein.  /.Ulnar 
vein.  The  lymphatics  are  re- 
presented as  lying  on  the 
deep  fascia.    (Mascagni.) 


in  these  and  other  varieties  of  connective  tissue,  the  cell  spaces  com- 
municate freely  with   regular  lymphatic   vessels.     In   many  cases, 


Cll.  XVIII.] 


LYMPHATIC    CAPILLARIES 


225 


though  they  are  formed  mostly  by  the  chinks  and  crannies  between 
the  parts  whicli  may  happen  to  form  the  framework  of  the  organ  in 
which  they  exist,  they  are  lined  by  a  distinct  layer  of  endothelium. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin, 
namely,  as  blind  dilated  extremities  in  the  villi  of  the  small  intestine 
(see  fig.  38,  p.  27). 

Structure  of  Lymph  Capillaries. — The  structure  of  lymphatic 
capillaries  is  very  similar  to  that  of  blood  capillaries;  their  walls 
consist  of  a  single  layer  of  elongated  endothelial  cells  with  sinuous 
outline,  which  cohere  along  their  edges  to  form  a  delicate  membrane. 


Fig.  238.— Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate.  The 
shaded  background  is  composed  of  bundles  of  white  fibres,  between  which  the  lymphatics  lie. 
I,  Lymphatics  lined  by  long  narrow  endothelial  cells,  and  showing  v  valves  at  frequent  intervals. 
(Schofield.) 

They  differ  from  blood  capillaries  mainly  in  their  larger  and  very 
variable  calibre,  and  in  their  numerous  communications  with  the 
spaces  of  the  lymph-canalicular  system. 

In  certain  parts  of  the  body,  stomata  exist,  by  which  lymphatic 
capillaries  directly  communicate  with  parts  formerly  supposed  to  be 
closed  cavities.  They  have  been  found  in  the  pleura,  and  in  other 
serous  membranes ;  a  serous  cavity  thus  forms  a  large  lymph-sinus 
or  widening  out  of  the  lymph-capillary  system  with  which  it  directly 
communicates. 

A  very  typical  plexus  of  lymphatic  capillaries  is  seen  in  the 
central  tendon  of  the  diaphragm.  Fig.  238  represents  the  appearance 
presented  after  staining  with  silver  nitrate. 


CHAPTEE    XIX 

THE   CIRCULATION   OF   THE   BLOOD 

We  have  now  to  approach  the  physiological  side  of  the  subject, 
and  study  the  means  by  which  the  blood  is  kept  in  movement,  so 
that  it  may  convey  nutriment  to  all  parts,  and  remove  from  those 
parts  the  waste  products  of  their  acti^dty. 

Previous  to  the  time  of  Harvey,  the  vaguest  notions  prevailed 
regarding  the  use  and  movements  of  the  blood.  The  arteries  were 
supposed  by  some  to  contain  air,  by  others  to  contain  a  more  subtle 
essence  called  animal  spirits;  the  animal  spirits  were  supposed  to 
start  from  the  ventricles  of  the  brain,  and  they  were  controlled  by 
the  soul  which  was  situated  in  the  pineal  gland.  How  the  animal 
spirits  got  into  the  arteries  was  an  anatomical  detail  which  was 
bridged  across  by  the  imagination. 

There  was  an  idea  that  the  blood  moved,  but  this  was  considered 
to  be  a  haphazard,  to-and-fro  movement,  and  confined  to  the  veins. 
The  proofs  that  the  movement  is  in  a  circle  were  discovered  by 
William  Harvey,  and  to  this  eminent  discoverer  also  belongs  the 
credit  of  pointing  out  the  methods  by  which  every  physiological 
problem  must  be  studied.  In  the  first  place  there  must  be  correct 
anatomical  knowledge,  and  in  the  second  there  must  be  experiment, 
by  which  deductions  from  structure  can  be  tested;  moreover,  this 
second  method  is  by  far  the  more  important  of  the  two.  Harvey's 
proofs  of  the  circulation  came  under  both  these  heads.  The  structural 
or  anatomical  facts  upon  which  he  relied  were  the  following : — 

1.  The  existence  of  two  distinct  sets  of  tubes  in  connection  with 
the  heart,  namely,  the  arteries  and  the  veins. 

2.  The  existence  in  the  heart  and  also  in  the  veins,  of  valves 
which  would  only  allow  the  passage  of  the  blood  in  one  direction. 

His  experimental  facts  were  the  following: — 

3.  That  the  blood  spurts  with  great  force  and  in  a  jerky  manner 
from  an  artery  opened  during  life,  each  jerk  corresponding  with  a 
beat  of  the  heart, 

226 


CH.  XIX.]  HARVEY'S   WORK  227 

4.  That  if  the  large  veins  near  the  heart  are  tied,  the  heart 
becomes  pale,  flaccid,  and  bloodless,  and  on  removal  of  the  ligature 
the  blood  again  flows  into  the  heart. 

5.  If  the  aorta  is  tied,  the  heart  becomes  distended  with  blood, 
and  cannot  empty  itself  until  the  ligature  is  removed. 

6.  The  preceding  experiments  were  performed  on  animals,  but  by 
the  following  experiment  he  showed  that  the  circulation  is  a  fact  in 
man  also ;  if  a  ligature  is  drawn  tightly  round  a  limb,  no  blood  can 
enter  it,  and  it  becomes  pale  and  cold.  If  the  ligature  is  somewhat 
relaxed  so  that  blood  can  enter  but  cannot  leave  the  limb,  it  becomes 
swollen.  If  the  ligature  is  removed,  the  limb  soon  regains  its  normal 
appearance. 

7.  Harvey  also  drew  attention  to  the  fact  that  there  is  general 
constitutional  disturbance  resulting  from  the  introduction  of  a  poison 
at  a  single  point,  and  that  this  can  only  be  explained  by  a  movement 
of  the  circulating  fluid  all  over  the  body. 

Since  Harvey's  time  many  other  proofs  have  accumulated;  for 
instance : — 

8.  If  an  artery  is  wounded,  haemorrhage  may  be  stopped  by 
pressure  applied  between  the  heart  and  the  wound ;  but  in  the  case 
of  a  wound  in  a  vein,  the  pressure  must  be  applied  beyond  the  seat 
of  injury. 

9.  If  a  substance  which,  like  ferrocyanide  of  potassium,  can  be 
readily  detected,  is  injected  at  a  certain  point  into  a  blood-vessel,  it 
will  after  the  lapse  of  a  short  interval  have  entirely  traversed  the 
circulation  and  be  found  in  the  blood  collected  from  the  same  point. 

10.  Perhaps  the  most  satisfactory  proof  of  the  circulation  is  one 
now  within  the  reach  of  every  student,  though  beyond  that  of  Harvey. 
It  consists  in  actually  seeing  the  passage  of  the  blood  from  small 
arteries  through  capillaries  into  veins  in  the  transparent  parts  of 
animals,  such  as  the  tail  of  a  tadpole  or  the  web  of  a  frog's  foot. 
Harvey  could  not  follow  this  part  of  the  circulation,  for  he  had  no 
lenses  sufficiently  powerful  to  enable  him  to  see  it.  Harvey's  idea 
of  the  circulation  here  was  that  the  arteries  carried  the  blood  to  the 
tissues,  which  he  considered  to  be  of  the  nature  of  a  sponge,  and  the 
veins  collected  the  blood  again,  much  in  the  same  way  as  drainage 
pipes  would  collect  the  water  of  a  swamp.  The  discovery  that  the 
ends  of  the  arteries  are  connected  to  the  commencements  of  veins  by 
a  definite  system  of  small  tubes  we  now  call  capillaries,  was  made 
by  Malpighi,  in  the  year  1661.  He  first  observed  them  in  the  tail  of 
the  tadpole,  and  Leeuwenhoek,  seven  years  later,  saw  the  circulation 
in  the  lung  of  the  frog. 

We  can  now  proceed  to  study  some  of  the  principles  on  which 
the  circulation  depends : — 

The   simplest  possible   way   in  which   we   could   represent   the 


228 


THE   CIRCULATION    OF   THE   BLOOD 


[CH.  XIX. 


circulatory  system  is  shown  in  fig.  239  A.  Here  there  is  a  closed 
ring  containing  fluid,  and  upon  one  point  of  the  tube  is  an  enlarge- 
ment (H)  which  will  correspond  to  the  heart.  It  is  obvious  that  if 
such  a  ring  made  of  an  ordinary  Higginson's  sjTinge  and  a  tube  were 
placed  upon  the  table,  there  would  be  no  movement  of  the  fluid  in  it ; 
in  order  to  make  the  fluid  move  there  must  be  a  difference  of 
pressure  between  different  parts  of  the  fluid,  and  this  difference  of 
pressure  is  caused  in  the  fluid  by  the  pressure  on  it  of  the  heart 
walls.  If,  for  instance,  one  takes  the  syringe  in  one's  hand  and 
squeezes  it,  one  imitates  a  contraction  of  the  heart :  if  the  s}Tinge 
has  no  valves,  the  fluid  would  pass  out  of  each  end  of  it  in  the 
direction  of  the  two  arrows  placed  outside  the  ring.  When  the 
pressure  on  the  syringe  is  relaxed  (this  w^ould  correspond  to  the 
interval  between  the  heart  beats),  the  fluid  would  return  into  the 
heart  again  in  the  direction  of  the  two  arrows  placed  inside  the  ring. 


Fig.  239. — Simple  schema  of  the  circulation. 

This,  however,  would  be  merely  a  to-and-fro  movement,  not  a  circula- 
tion. Fig.  239  B  shows  how  this  to-and-fro  movement  could,  by  the 
presence  of  valves,  be  converted  into  a  circulation ;  when  the  heart 
contracts  the  fluid  could  pass  only  in  the  direction  of  the  outer 
arrow;  when  the  heart  relaxes  it  could  pass  only  in  the  direction 
of  the  inner  arrow;  the  direction  of  both  arrows  is  the  same,  and 
so  if  the  contraction  and  relaxation  of  the  heart  are  repeated  often 
enough  the  fluid  will  move  romid  and  round  within  the  tubular  ring. 

The  main  factor  in  the  circulation  is  difference  of  pressure.  In 
general  terms  fluid  flows  from  where  the  pressure  is  high  to  where  it 
is  lower.  This  difference  of  pressure  is  produced  in  the  first  instance 
by  the  contraction  of  the  heart,  but  we  shall  find  in  our  study  of  the 
vessels  that  some  of  this  pressure  is  stored  up  in  the  elastic  arterial 
walls,  and  keeps  up  the  circulation  during  the  periods  that  the  heart 
is  resting. 

Coming  to  different  groups  in  the  animal  kingdom  we  may  take 
the  crayfish  or  the  lobster  as  instances  of  animals  which  possess  a 


CH.  XIX.] 


THE    HEART   OF    WORM,    FISH,    AND    FROG 


229 


haemolymph  system,  that  is,  there  is  no  distinction  between  blood 
and  lyni])h.  The  heart  pumps  the  circulating  fluid  along  a  system 
of  vessels  which  distribute  it  over  the  body ;  there  are  no  capillaries, 
and  the  haemolymph  is  discharged  into  the  tissue  spaces  ;  it  is  thence 
drained  into  channels  which  convey  it  to  the  gills,  and  after  it  is 
aerated  there  in  a  set  of  irregular  vessels,  it  is  returned  to  the  peri- 
cardium. It  is  sucked  from  the  pericardium  into  the  heart  during 
diastole,  through  five  small  orifices  in  the  cardiac  wall ;  during 
systole  these  are  closed  by  valves.  In  these  animals  the  rate  of  flow 
of  haemolymph  is  necessarily  slow. 

In  worms,  the  circulatory  system  is  almost  as  simple  as  in  the 
schema  just  described ;  the  heart  is 
a  long  contractile  tube  provided 
with  valves,  which  contracts  peri- 
staltically  and  presses  the  blood 
forwards  into  the  aorta  at  its  an- 
terior end ;  this  divides  into  arteries 
for  the  supply  of  the  body;  the 
blood  passes  through  these  to  capil- 
laries, and  is  collected  by  veins 
which  converge  to  one  or  two  main 
trunks  that  enter  the  heart  at  its 
posterior  end. 

In  fishes,  the 
into  a  number  of 
in  single  file,  one 
other ;  the  most 
receives    the 


heart  is  divided 

chambers  placed 

in  front  of   the 

posterior    which 

veins    is    called    the 


Fig.  240. — The  heart  of  a  frog  (Kana  esculenla) 
from  the  front.  V,  ventricle;  Ad,  right 
auricle;  J  s,  left  auricle  ;  £,  bulbus  arteri- 
osus, dividing  into  right  and  left  aorta-. 
(Ecker.) 


sinus   venosus ;   this   contracts  and 

forces    the    blood    into    the    next 

chamber,   called    the    auricle ;    this 

forces    the    blood     into    the    next 

cavity,    that   of   the   ventricle,  and 

last  of  all  is  the  aortic  bulb.     From  the  bulb,  branches  pass  to  the 

gills,  where  they  break  up  into  capillaries,  and  the  blood  is  aerated : 

it  then  once  more  enters  larger  vessels  which  unite   to  form  the 

dorsal  aorta,  whence   the    blood   is    distributed    by  arteries    to   all 

parts  of  the  body;  here  it  enters  the  systemic  capillaries,  then  the 

veins  which  enter  the  sinus  (whence  we  started)  by  a  few"  large 

trunks. 

Taking  the  frog  as  an  instance  of  an  amphibian,  we  find  the 
heart  more  complex,  and  the  simple  peristaltic  action  of  the  heart 
muscle  as  we  have  described  it  in  the  hearts  of  worm  and  fish, 
becomes  correspondingly  modified.  There  is  only  one  ventricle,  but 
there  are  two  auricles,  right  and  left. 


230 


THE    CIRCULATION    OF    THE    BLOOD 


[Cn.  XIX. 


Ap.- 


The  ventricle  contains  mixed  blood,  since  it  receives  arterial 
blood  from  the  left  auricle  (which  is  the  smaller  of  the  two),  and 
venous  blood  from  the  right  auricle ;  the  right  auricle  receives  the 
venous  blood  from  the  sinus,  which  in  |  turn  receives  it  from  the 

systemic   veins.      The   left 
auricle,  as  in  man,  receives 
the  blood  from  the  pulmon- 
-^.s.d.     ary  veins. 

When  the  ventricle  con- 
tracts, it  forces  the  blood 
onward  into  the  aortic  bulb 
A.d.  which  divides  into  branches 
on  each  side  for  the  supply 
of  the  head  (fig.  240,  1), 
lungs  and  skin  (fig.  240,  3), 
and  the  third  branch  (fig. 
240,  2),  unites  with  its 
fellow  of  the  opposite  side 
to  form  the  dorsal  aorta  for 
the  supply  of  the  rest  of 
the  body. 

Passing  from  the  amphi- 
bians to  the  reptiles,  we 
find  the  division  of  the 
ventricle  into  two  beginning,  but  it  is  not  complete  till  we  reach 
the  birds.  The  heart  reaches  its  fullest  development  in  mammals, 
and  we  have  already  described  the  human  as  an  example  of  the 
mammalian  heart.  The  sinus  venosus  is  not  present  as  a  distinct 
chamber  in  the  mammalian  heart  (except  in  a  very  early  foetal  stage), 
but  is  represented  by  that  portion  of  the  right  auricle  at  which  the 
larsje  veins  enter. 


Fio.  241.— Tlie  linait  of  a  frog  (Rana  esculenta)  from  the 
back.  S.V.,  sinus  venosus  opened  ;  c.s.s.,  left  vena  cava 
superior;  c.s.d.,  right  vena  cava  superior;  c.i.,  vena 
cava  inferior;  v.p.,  vena  pulmonalis ;  A.d.,  right 
auricle  ;  A.s.,  left  auricle  ;  A.p.,  opening  of  communi- 
cation between  the  right  auricle  and  the  sinus  venosus. 
x2A— 3.     (Ecker.) 


CHAPTEK  XX 

PHYSIOLOGY   OF   THE    HEART 

The  Cardiac  Cycle. 

The  series  of  changes  that  occur  in  the  heart  constitutes  the  cardiac 
cycle.  This  must  be  distinguished  from  the  course  of  the  circulation. 
The  term  cycle  indicates  that  if  one  observes  the  heart  at  any 
particular  moment,  the  heart  from  that  moment  onwards  undergoes 
certain  changes  until  it  once  more  assumes  the  same  condition  that 
it  had  at  the  moment  when  the  observation  commenced,  when  the 
cycle  is  again  repeated,  and  so  on.  This  series  of  changes  consists  of 
alternate  contraction  and  relaxation.  Contraction  is  known  as 
systole,  and  relaxation  as  diastole. 

The  contraction  of  the  two  auricles  takes  place  simultaneously, 
and  constitutes  the  auricular  systole ;  this  is  followed  by  the  simul- 
taneous contraction  of  the  two  ventricles,  ventricular  systole,  and 
that  by  a  period  during  which  the  whole  of  the  heart  is  in  a  state  of 
relaxation  or  diastole;  then  the  cycle  again  commences  with  the 
auricular  systole. 

Taking  72  as  the  average  number  of  heart  beats  per  minute,  each 
cycle  will  occupy  -^  of  a  minute,  or  a  little  more  than  0'8  of  a 
second.  This  may  be  approximately  distributed  in  the  following 
way:— 

Auricular  systole  .  about  0*1  +  Auricular  diastole  .  0-7  =  0*8 
Ventricular  systole  .  ,,  0 'S  +  Ventricular  diastole  .  0-5  =  0*8 
Total  systole       .         .        ,,      0-4  +  Joint  diastole       .         .    0-4  =  0-8 

If  the  speed  of  the  heart  is  quickened,  the  time  occupied  by 
each  cycle  is  diminished,  but  the  diminution  affects  chiefly  the 
diastole.  These  different  parts  of  the  cycle  must  next  be  studied  in 
detail. 

The  Auricular  Diastole. — During  this  time,  the  blood  from  the 
large  veins  is  flowing  into  the  auricles,  the  pressure  in  the  veins 
though  very  low  being  greater  than  that  in  the  empty  auricles.  The 
blood  expands  the  auricles,  and  during  the  last  part  of  the  auricular 

231 


232  PHYSIOLOGY  OF  THE  HEART  [CH.  XX 

diastole  it  passes  on  into  the  ventricles.  The  dilatation  of  the 
auricles  is  assisted  by  the  elastic  traction  of  the  lungs.  The  lungs 
beincr  in  a  closed  cavity,  the  thorax,  and  being  distended  with  air, 
are  in  virtue  of  their  elasticity  always  tending  to  recoil  and  squeeze 
the  air  out  of  their  interior ;  in  so  doing  they  drag  upon  any  other 
organ  with  which  their  surface  is  in  contact:  this  elastic  traction 
will  be  greatest  when  the  lungs  are  most  distended,  that  is  during 
inspiration,  and  will  be  more  felt  by  the  thin-walled  auricles  than  by 
the  thick -walled  ventricles  of  the  heart. 

The  Auricular  Si/stole  is  sudden  and  very  rapid;  by  contracting, 
the  auricles  empty  themselves  into  the  ventricles.  The  contraction 
commences  at  the  entrance  of  the  great  veins,  and  is  thence  pro- 
pagated towards  the  auriculo-ventricular  opening.  The  reason  why 
the  blood  does  not  pass  backwards  into  the  veins,  but  onward  into 
the  ventricles,  is  again  a  question  of  pressure ;  the  pressure  in  the 
relaxed  ventricles,  which  is  so  small  as  to  exert  a  suction  action  on 
the  auricular  blood,  is  less  than  in  the  veins.  Moreover,  the 
auriculo-ventricular  orifice  is  large  and  widely  dilated,  whereas  the 
mouths  of  the  veins  are  constricted  by  the  contraction  of  their 
muscular  coats.  Though  there  is  no  regurgitation  of  the  blood 
backwards  into  the  veins,  there  is  a  stagnation  of  the  flow  of  blood 
onwards  to  the  auricles.  The  veins  have  no  valves  at  their  entrance 
into  the  auricles,  except  the  coronary  veLu  which  does  possess  a 
valve;  there  are  valves,  however,  at  the  junction  of  the  subclavian 
and  internal  jugular  veins. 

Ventricular  DiaMole ;  during  the  last  part  of  the  auricular  diastole 
and  the  whole  of  the  auricular  systole,  the  ventricles  have  been 
relaxed  and  then  filled  with  blood.  The  dilatation  of  the  ventricles 
is  chiefly  brought  about  in  virtue  of  their  elasticity ;  this  is  particu- 
larly evident  in  the  left  ventricle  with  its  thick  muscular  coat.  It 
is  equal  to  23  mm.  of  mercury,  and  is  quite  independent  of  the 
elastic  traction  of  the  lungs,  which,  however,  in  the  case  of  the 
thinner-walled  right  ventricle  comes  into  play. 

Tlie  Ventricular  Systole ;  this  is  the  contraction  of  the  ventricles, 
and  it  occupies  more  time  than  the  auricular  systole ;  when  it 
occurs  the  auriculo-ventricular  valves  are  closed  and  prevent  re- 
gurgitation into  the  auricles,  and  when  the  force  of  the  systole 
is  greatest,  and  the  pressure  within  the  ventricles  exceeds  that  in  the 
large  arteries  which  originate  from  them,  the  semilunar  valves  are 
opened,  and  the  ventricles  empty  themselves,  the  left  into  the  aorta, 
the  right  into  the  pulmonary  artery.  Each  ventricle  ejects  about 
3  ounces  of  blood  with  each  contraction ;  the  left  in  virtue  of  its 
thicker  walls  acts  much  more  forcibly  than  the  right.  The  greater 
force  of  the  left  ventricle  is  necessary,  as  it  has  to  overcome  the 
resistance  of  the  small  vessels  all  over  the  body ;  whereas  the  right 


CII.  XX.]  THE  VALVES  OF  THE  HEART  283 

ventricle  has  only  to  overcome  peripheral  resistance  in  the  pulmonary 
district. 

The  shape  of  both  ventricles  during  systole  has  been  described  as  under- 
going an  alteration,  the  diameters  in  the  plane  of  the  base  being  diminished,  and 
the  length  of  tlie  ventricles  slightly  lessened.  The  whole  heart,  moreover,  moves 
towards  tht-  right  and  forwards,  twisting  on  its  long  axis  and  exposing  more  of  the 
left  ventricle  anteriorly  than  wlien  it  is  at  rest.  These  movements,  which  were 
first  described  by  Harvey,  havi-  been  since  Harvey's  time  believed  to  be  the  cause 
of  the  cardiac  impulse  or  apex  beat  which  is  to  be  felt  in  the  fifth  intercostal 
space  about  tlnee  inches  from  the  middle  line.  It  has,  however,  been  shown  by 
Haycraft  that  these  changes  only  occur  when  the  chest  walls  are  open.  When  the 
heart  contracts  in  a  closed  thorax  it  undergoes  no  rotation,  and  the  contraction  is 
concentric,  that  is,  equal  in  all  directions.  The  diminution  of  the  heart's  volume 
which  occurs  in  systole  cannot  be  the  cause  of  the  apex  beat ;  it  would  rather  tend 
to  draw  the  chest  wall  inwards  than  push  it  outwards. 

The  apex  beat  is  caused  by  two  changes  in  the  physical  condition  of  the  heart. 
In  the  first  place,  on  systole  the  heart  becomes  hard  and  tense,  and  secondly,  its 
attachment  to  the  aorta  becomes  rigid  instead  of  being  flexible  as  it  is  in  diastole. 
Thus,  in  systole,  the  heart  becomes  rigidly  fixed  to  the  aorta,  and,  as  this  vessel  is 
curved,  it  tends  to  open  out  into  a  straight  line,  but  is  prevented  by  the  counter- 
resistance  at  the  two  ends  of  the  arch.  These  are  (a)  the  resistance  of  the  chest 
wall  against  the  heart,  and  (/')  that  of  the  vertebras  and  ribs  against  the  thoracic 
aorta.  The  pressure  of  the  heart  against  the  chest  wall  is  confined  to  a  small  area, 
situated  in  the  fifth  intercostal  space,  because  the  heart  surface  is  much  more  curved 
than  the  internal  thoracic  wall.  The  forward  movement  this  pressure  causes  is  the 
apex  beat.  It  must  be  noted  that  this  movement  is  not  over  the  actual  apex  of  the 
heart,  but  is  communicated  from  an  area  on  the  anterior  cardiac  surface. 

Action  of  the  Valves  of  the  Heart. 

1.  The  Auriculo-  Ventricular. — The  distension  of  the  ventricles 
with  blood  continues  throughout  the  whole  period  of  their  diastole. 
The  auriculo-ventricular  valves  are  gradually  brought  into  place  by 
some  of  the  blood  getting  behind  the  cusps  and  floating  them  up ; 
by  the  time  that  the  diastole  is  complete,  the  valves  are  in  appo- 
sition, and  they  are  firmly  closed  Ijy  the  reflux  current  caused 
by  the  systole  of  the  ventricles.  The  diminution  in  the  size  of  the 
auriculo-ventricular  rings  which  occurs  during  systole,  renders  the 
auriculo-ventricular  valves  competent  to  close  these  openings.  The 
margins  of  the  cusps  of  the  valves  are  still  more  secured  in  apposition 
with  one  another,  by  the  simultaneous  contraction  of  the  musculi 
papillares,  whose  chordae  tendinese  have  a  special  mode  of  attachment 
for  this  object.  The  cusps  of  the  auriculo-ventricular  valves  meet 
not  by  their  edges  only,  but  by  the  opposed  surfaces  of  their  thin 
outer  borders. 

The  musculi  papillares  prevent  the  auriculo-ventricular  valves 
from  being  everted  into  the  auricle.  For  the  chordae  tendinese  might 
allow  the  valves  to  be  pressed  back  into  the  auricle,  were  it  not  that 
when  the  wall  of  the  ventricle  is  brought  by  its  contraction  nearer 
to  the  auriculo-ventricular  orifice,  the  musculi  papillares  more  than 
compensate  for  this  by  their  own  contraction ;  they  hold  the  cords 


234  PHYSIOLOGY   OF   THE    HEART  [CH.  XX. 

tight,  and,  by  pulling  down  the  valves,  add  slightly  to  the  force  with 
which  the  blood  is  expelled. 

These  statements  apply  equally  to  the  auriculo-ventricular  valves 
on  both  sides  of  the  heart ;  the  closure  of  both  is  generally  complete 
every  time  the  ventricles  contract.  But  in  some  circumstances  the 
tricuspid  valve  does  not  completely  close,  and  a  certain  quantity  of 
blood  is  forced  back  into  the  auricle.  This  has  been  called  its  safety- 
valve  axtion.  The  circumstances  in  which  it  usually  happens  are  those 
in  which  the  vessels  of  the  lung  are  already  completely  full  when  the 
right  ventricle  contracts,  as,  e.g.,  in  certain  pulmonary  diseases,  and 
in  very  active  muscular  exertion.  In  these  cases,  the  tricuspid  valve 
does  not  completely  close,  and  the  regui'gitation  of  the  blood  may  be 
indicated  by  a  pulsation  in  the  jugular  veins  synchronous  with  that 
in  the  carotid  arteries. 

2.  The  Semilunar  Valves. — The  commencement  of  the  ventricular 
systole  precedes  the  opening  of  the  aortic  valves  by  a  fraction  of  a 
second,  as  is  proved  by  examining  records  of  the  intraventricular  and 
aortic  pressure  curves  taken  simultaneously.  The  first  result  of  the 
contraction  of  the  ventricles  is  the  closure  of  the  auriculo-ventricular 
valves,  and  as  soon  as  this  has  been  efifected  the  intraventricular 
pressui'e  begins  to  rise.  It  quickly  reaches  a  point  at  which  it  equals 
the  aortic  pressure,  and  then  exceeds  it,  and  as  soon  as  this  pressure 
difference  has  been  established  the  aortic  valves  are  opened  and  blood 
flows  from  the  ventricle  into  the  aorta.  The  valves  are  kept  open  as 
long  as  the  intraventricular  pressure  exceeds  the  aortic,  but  as  soon 
as  the  heart  has  emptied  itself,  the  ventricle  begins  to  relax,  its 
internal  pressure  consequently  begins  to  fall,  and  an  instant  is 
quickly  reached  at  which  it  is  exceeded  by  the  aortic.  The  blood, 
therefore,  tends  to  flow  back  from  the  aorta,  and  in  so  doing  fills  up 
the  pockets  of  the  semilunar  valves,  which  have  always  remained 
partly  fiUed,  and  brings  them  together  with  a  sharp  movement.  The 
movements  of  the  valves  are  therefore  effected  by  the  occurrence  of 
differences  of  pressure  upon  their  two  faces.  When  they  meet  they 
completely  close  the  orifice,  because  their  inner  edges,  which  are 
thinner  than  the  rest  of  the  valves,  are  brought  into  apposition 
and  held  so  by  the  high  pressure  acting  on  their  aortic  sm-faces 
only. 

The  Soxinds  of  the  Heart. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds 
may  be  heard  at  every  beat  of  the  heart,  which  follow  in  quick 
succession,  and  are  succeeded  by  a  paiLse  or  period  of  silence.  The 
first  or  systolic  soimd  is  dull  and  prolonged;  its  commencement 
coincides  with  the  impulse  of  the  heart  against  the  chest  wall,  and 
just  precedes  the  pulse  at  the  wrist.     The  second  or  diastolic  sound 


CH.  XX.] 


THE    HEART   SOUNDS 


235 


is  shorter  and  sharper,  with  a  somewhat  flapping  character,  and 
follows  close  after  the  arterial  pulse.  The  periods  of  time  occupied 
respectively  by  the  two  sounds  taken  together  and  by  the  pause,  are 
nearly  equal.  Thus,  according  to  Walshe,  if  the  cardiac  cycle  be 
divided  into  tenths,  the  first  sound  occupies  ^\ ;  the  second  sound, 
1% ;  the  first  pause  (almost  imperceptible),  -^^  ;  and  the  second  pause, 
1%.  The  sounds  are  often  but  somewhat  inaptly  compared  to  the 
syllables,  Ifibb — dap. 

The  events  wliich  correspond,  in  point  of  time,  with  the  Jirst 
soimd,  are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of 
the  dilatation  of  the  auricles,  (3)  the  tension  of  the  auriculo-ventricular 
valves,  (4)  the  opening  of  the  semilunar  valves,  and  (5)  the  propul- 
sion of  blood  into  the  arteries. 
The  sound  is  succeeded,  in 
about  one-thirtieth  of  a  second, 
by  the  pulsation  of  the  facial 
arteries,  and  in  about  one-sixth 
of  a  second,  by  the  pulsation 
of  the  arteries  at  the  wrist. 
The  second  sound,  in  point  of 
time,  immediately  follows  the 
cessation  of  the  ventricular 
contraction,  and  corresponds 
with  (a)  the  tension  of  the 
semilunar  valves,  (h)  the  con- 
tinued dilatation  of  the  auricles, 
(c)  the  commencing  dilatation 
of  the  ventricles,  and  (d)  the 
opening  of  the  auriculo-ventri- 
cular valves.  The  pause  imme- 
diately follows  the  second  sound, 
and  corresponds  in  its  first  part  with  the  completed  distension  of 
the  auricles,  and  in  its  second  with  their  contraction,  and  the  com- 
pleted distension  of  the  ventricles;  the  auriculo-ventricular  valves 
are  open,  and  the  arterial  valves  closed  during  the  whole  of  the 
pause. 

Causes. — The  exact  cause  of  the  first  sound  of  the  heart  is  a 
matter  of  discussion.  Two  factors  probably  enter  into  it,  viz.,  first, 
the  vibration  of  the  auriculo-ventricular  valves  and  the  chordce  tendinece. 
This  vibration  is  produced  by  the  increased  intraventricular  pressure 
set  up  when  the  ventricular  systole  commences,  which  puts  the  valves 
on  the  stretch.  It  is  not  unlikely,  too,  that  the  vibration  of  the 
ventricular  walls  themselves,  and  of  the  aorta  and  pulmonary  artery, 
all  of  which  parts  are  suddenly  put  into  a  state  of  tension 
at  the  moment  of  ventricular  contraction,  may  have  some  part  in 


Fig.  242. — Scheme  of  cardiac  cycle.  The  iuner  circle 
shows  the  events  which  occur  withiu  the  heart ; 
the  outer  the  relation  of  the  sounds  and  pauses  to 
these  events.    (Sharpey  and  Gairdner.) 


236  PHYSIOLOGY    OF    THE    HEART  [CH.  XX. 

producing  the  first  sound.  Secondly,  the  muscular  sound  produced 
by  contraction  of  the  mass  of  muscular  fibres  which  forms  the 
ventricle.  Looking  upon  the  contraction  of  the  heart  as  a  single 
contraction  and  not  as  a  series  of  contractions  or  tetanus,  it  is  at 
first  sight  difficult  to  see  why  there  should  be  any  muscular  sound 
at  all  when  the  heart  contracts,  as  a  single  muscular  contraction 
does  not  produce  sound.  It  has  been  suggested,  however,  that  it 
arises  from  the  repeated  unequal  tension  produced  when  the  wave 
of  muscular  contraction  passes  along  the  very  intricately  arranged 
fibres  of  the  ventricular  walls.  Many  regard  the  valvular  element  is 
the  more  important  of  the  two  factors,  because  the  sound  is  loudest 
at  first,  when  the  vibration  of  the  valves  commences,  and  fades 
away  as  the  vibrations  cease.  If  the  sound  was  mainly  muscular, 
it  would  be  loudest  when  the  muscular  contraction  was  most  powerful, 
which  is  approximately  about  the  middle  of  the  ventricular  systole. 
The  facts  of  disease  lend  support  to  the  theory  that  the  first  sound 
is  mainly  valvular ;  for  when  the  valves  are  incompetent,  the  first 
sound  is  largely  replaced  by  a  murmur  due  to  regurgitation  of  blood 
into  the  auricle.  After  the  removal  of  the  heart  from  the  body,  the 
muscular  contribution  to  the  first  sound  is  audible,  but  it  is  very 
faint.  It  is  stated  to  have  a  somewhat  lower  pitch  than  the  valvular 
sound. 

There  is,  on  the  other  hand,  much  to  be  said  against  the  view 
that  the  cause  of  the  first  sound  is  entirely  or  even  largely  due  to 
vibration  of  the  auriculo-ventricular  valves.  Any  sound  produced 
by  the  valves  must  be  very  quickly  damped  by  the  high  pressure 
acting  on  their  ventricular  surfaces  only.  The  sustained  character 
of  the  sound  (throughout  practically  the  whole  of  the  ventricular 
systole)  is  on  the  other  hand  exactly  what  is  to  be  expected  if  it  is 
of  muscular  origin.  The  argument  that  the  extent  to  which  the 
muscle  sound  contributes  to  the  production  of  the  first  sound  can 
be  judged  from  the  sound  heard  in  an  isolated  and  empty  heart  is 
quite  fallacious,  since  under  these  conditions  the  muscle  is  contract- 
ing against  no  resistance. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the 
first.  It  is  entirely  due  to  the  vibration  consequent  on  the  sudden 
stretching  of  the  semilunar  valves  when  they  are  pressed  down  across 
the  orifices  of  the  aorta  and  pulmonary  artery.  The  influence  of 
these  valves  in  producing  the  sound  was  first  demonstrated  by  Hope, 
who  experimented  with  the  hearts  of  calves.  In  these  experiments 
two  delicate  curved  needles  were  inserted,  one  into  the  aorta,  and 
another  into  the  pulmonary  artery,  below  the  line  of  attachment  of 
the  semilunar  valves,  and,  after  l)eing  carried  upwards  about  half  an 
inch,  were  brought  out  again  through  the  coats  of  the  respective 
vessels,  so  that  in  each  vessel  one  valve  was  included  between  the 


CII.  XX.]  THE   COUONAIIY    ARTERIES  237 

arterial  walls  and  the  wire.  Upon  applying  the  stethoscope  to  the 
vessels,  after  such  an  operation,  the  second  sound  ceased  to  be 
audible.  Disease  of  these  valves,  when  sufficient  to  interfere  with 
their  efficient  action,  also  demonstrates  the  same  fact  by  modifying 
the  second  sound  or  destroying  its  distinctness. 

The  contraction  of  the  auricles  is  inaudible. 

The  first  sound  is  heard  most  distinctly  at  the  apex  beat  in  the 
fifth  interspace ;  the  second  sound  is  best  heard  over  the  second  right 
costal  cartilage — that  is,  the  place  where  the  aorta  lies  nearest  to 
the  surface.  The  pulmonary  and  aortic  valves  generally  close  simul- 
taneously. In  some  cases,  however,  the  aortic  may  close  slightly 
before  the  pulmonary  valves,  giving  rise  to  a  "  reduplicated  second 
sound."  The  pulmonary  contribution  to  this  sound  is  best  heard  over 
the  second  left  cartilage. 

The  Coronary  Arteries. 

The  coronary  arteries  are  the  first  branches  of  the  aorta ;  they 
originate  from  the  sinuses  of  Valsalva,  and  are  destined  for  the  supply 
of  the  heart  itself;  the  entrance  of  the  coronary  vein,  into  the  right 
auricle,  we  have  already  seen  (p.  207). 

Ligature  of  the  coronary  arteries  causes  almost  immediate 
death ;  the  heart,  deprived  of  its  normal  blood-supply,  beats  irregu- 
larly, goes  into  fibrillary  twitchings,  and  then  ceases  to  contract 
altogether. 

In  fatty  degeneration  of  the  heart  in  man,  sudden  death  is  by 
no  means  infrequent.  This  is  in  many  cases  due  to  a  growth  in 
thickness  of  the  walls  of  the  coronary  arteries  called  atheroma,  which 
progresses  until  the  lumen  of  these  arteries  is  obliterated,  and  the 
man  dies  almost  as  if  they  had  been  ligatured. 

Self-steerinf/  Action  of  (he  Heart. — This  expression  was  originated  by  Briicke. 
He  supposed  that  the  semilunar  valves  closed  the  orifices  of  the  coronary  arteries 
during  the  systole  of  the  heart.  Unlike  all  the  other  arteries  of  the  body,  the 
coronary  arteries  would  therefore  fill  only  during  diastole,  and  this  increased  fulness 
of  the  vessels  in  the  heart  walls  during  diastole  would  assist  the  ventricle  to  dilate. 
This,  however,  is  incorrect ;  the  valves  do  not  cover  the  mouths  of  the  arteries;  and 
at  the  beginning  of  systole  the  velocity  and  pressure  in  the  coronary  arteries 
increase  ;  but  later  on  during  systole  the  ventricular  wall  is  so  strongly  contracted 
that  the  muscular  tension  becomes  greater  than  the  coronary  pressure,  and  so  the 
coronary  arteries  and  their  branches  are  compressed,  and  the  blood  driven  back 
into  the  aorta ;  the  coronary  arteries  are  then  again  filled  with  the  commencing 
diastole.  Self-steering  action  of  the  heart  therefore  exists,  but  it  is  brought  about  in 
a  different  way  from  what  Briicke  supposed. 

Cardiographs. 

A  cardiograph  is  an  instrument  for  obtaining  a  graphic  record 
of  the  heart's  movements.     In  animals  the  heart  may  be  exposed, 


238 


PHYSIOLOGY   OF   THE   HEART 


[CH.  XX. 


and   levers   placed   in   connection    with   its  various   parts  may  l»o 
employed  to  write  on  a  revolving  blackened  surface. 

A  simple  instrument  for  the  frog's  heart  is  the  following : — 

NF ^ 


"=^ 


Fif;.  243. — Simple  Cardiograph  for  frog's  heart. 

The  sternum  of  the  frog  having  been  removed,  the  pericardium 
opened,  and  the  frsenum  (a  small  band  from  the  back  of  the  heart 

to  the  pericardium)  divided,  the  heart  is 
pulled  through  the  opening,  a  minute  hook 
placed  in  its  apex,  and  this  is  fixed  by  a 
silk  thread  to  a  lever  pivoted  at  F  as  in 
the  figure.  The  cardiac  wave  of  contrac- 
tion starts  at  the  sinus,  this  is  followed 
by  the  auricular  systole,  and  that  by  the 
ventricular  systole  and  pause.  This  is 
recorded  as  in  the  next  figure  (fig.  244) 
by  movements  of  the  writing  point  at  the 
end  of  the  long  arm  of  the  lever.  Such 
apparatus  is,  however,  not  applicable  to 
the  human  heart,  and  all  the  various 
forms  of  cardiograph  devised  for  this  pur- 
pose are  modifications  of  Marey's  tambours. 
One  of  those  most  frequently  used  is 
depicted  in  the  next  two  diagrams. 

It  (fig.  245)  consists  of  a  cup-shaped  metal  box  over  the  open  front  of  which  is 
stretched  an  elastic  India  rubber  membrane,  upon  which  is  fixed  a  small  knob  of 
hard  wood  or  ivory.  This  knob,  however,  may  be  attached,  as  in  the  figure,  to  the 
side  of  the  box  by  means  of  a  spring,  and  may  be  made  to  act  upon  a  metal  disc 
attached  to  the  elastic  membrane. 

I The  knob  is  for  application  to  the  chest-wall  over  the  apex  beat.     The  box  or 

tambour  communicates  by  means  of  an  air-tight  tube  with  the  interior  of  a  second 
tambour,  in  connection  with  which  is  a  long  and  light  lever.  The  shock  of  the 
heart's  impulse  being  communicated  to  the  ivory  knob  and  through  it  to  the  first 
tambour,  the  effect  is  at  once  transmitted  by  the  column  of  air  in  the  elastic  tube 
to  the  interior  of  the  second  tambour,  also  closed,  and  through  the  elastic  and 
movable  lid  of  the  latter  to  the  lever,  which  is  placed  in  connection  with  a  register- 
ing apparatus,  which  consists  of  a  cylinder  covered  with  smoked  paper,  revolving 
with  a  definite  velocity.  The  point  of  the  lever  writes  upon  the  paper,  and  a  tracing 
of  the  heart's  impulse  or  cardiogram  is  thus  obtained. 


Fig.  244. — Cardiogram  of  frog's 
heart,  c,  showing  auricular, 
followed  by  ventricular  beat ; 
T,  time  in  half  seconds. 


CII.  XX.] 


CARDIOGRAPHS 


239 


Fig.  247  represents  a  typical  tracing  obtained  in  Lliis  way.     The 


Tube  to  communicate 
with  tambour. 


Tambour.  Ivory    Tape  to  attach  the  iiistru- 

kiiob.  ment  to  the  chest. 

Fin.  245. — Cardiograph.    (Sanderson's.) 

first  small  rise  of  the  lever  is  caused  by  the  auricular,  the  second 

Screw  to  re;?ulate  elevation  of  lever. 


Writing  lever. 


Tube  of  cardiograph. 


Fin.  246.— Marey's  Tambour,  to  which  the  movement  of  the  column  of  air  in  the  first  tambour  is  eon- 
ducted  by  a  tube,  and  from  which  it  is  communicated  by  the  lever  to  a  revolving  cylinder,  so  that 
the  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 

larger  rise  by  the  ventricular  systole ;  the  downstroke  represents  the 


Fig.  247. — Cardiogram  from  human  heart.    The  variations  in  the  individual  beats  are  due  to  the 
influence  of  the  respiratory  movements  on  the  heart.    To  be  read  from  left  to  right. 


240 


PHYSIOLOGY    OF    THE    HEART 


[CH.  XX. 


pause,  the  tremors  at  the  commencement  of  which  are  partly  instru- 
mental and  partly  caused  by  the  closure  of  the  semilunar  valves. 

Another  method  of  obtaining  a  tracing  from  one's  own  heart 
consists  in  dispensing  with  the  first  tambour,  and  placing  the  tube 
of  the  recording  tambour  in  one's  mouth,  and  holding  the  breath 
though  keeping  the  glottis  open.  The  chest  then  acts  as  the  first 
tambour,  and  the  movements  of  the  lever  (cardio-pneumatogram)  may 
be  written  in  the  usual  way. 

Intracardiac  Pressure, 

The  tracings  of  the  cardiograph  are,  however,  very  variable,  and 
their  interpretation  is  a  matter  of  discussion.  A  much  better  method 
of  obtaining  a  graphic  record  of  the  events  of  the  cardiac  cycle  con- 
sists in  connecting-  the  interior  of  an  animal's  heart  with  recording 


Fio.  248. — Apparatus  of  MM.  Chauveau  and  Marey  for  estimating  the  variations  of  endocardiac 
pressure,  and  the  production  of  the  impulse  of  the  lieart. 

apparatus.  There  are  several  methods  by  which  the  intracardiac 
pressure  may  be  recorded. 

By  placing  two  small  indiarubber  air-bags  or  cardiac  sounds  down 
the  jugular  vein  into  the  interior  respectively  of  the  right  auricle  and 
the  right  ventricle,  and  a  third  in  an  intercostal  space  in  front  of  the 
heart  of  a  living  animal  (horse),  and  placing  these  bags,  by  means  of 
long  narrow  tubes,  in  communication  with  three  tambours  with 
levers,  arranged  one  over  the  others  in  connection  with  a  registering 
apparatus  (fig.  248),  Chauveau  and  Marey  were  able  to  record  and 
measure  the  variations  of  the  intracardiac  pressure  and  the  compara- 
tive duration  of  the  contractions  of  the  auricles  and  ventricles.  By 
means  of  the  same  apparatus,  the  synchronism  of  the  impulse  with 
the  contraction  of  the  ventricles  is  also  shown. 

In  the  tracing  (fig.  249),  the  intervals  between  the  vertical  lines 
represent  periods  of  a  tenth  of  a  second.     The  parts  on  which  any 


CH.  XX.] 


INTRACARDIAC    PRESSURE 


241 


given  vertical  line  falls  represent  simultaneous  events.  It  will  be 
seen  that  the  contraction  of  the  auricle,  indicated  by  the  marked 
curve  at  a  in  the  first  tracing,  causes  a  slight  increase  of  pressure 
in  the  ventricle,  which  is  shown  at  a'  in  the  second  tracing,  and 
produces  also  a  slight  impulse,  which  is  indicated  by  a"  in  the 
third  tracing.  The  closure  of  the  semilunar  valves  causes  a 
momentarily  increased  pressure  in  the  ventricle  at  d',  affects  the 
pressure  in  the  auricle  D,  and  is  also  shown  in  the  tracing  of  the 
impulse  d".* 

The  large  curve  of  the  ventricular  and  the  impulse  tracings, 
between  a'  and  d',  and  a"  and  d",  are  caused  by  the  ventricular  con- 
traction ;  while  the  smaller  undulations,  between  B  and  c,  b'  and  c', 
b"  and  c",  are  caused  by  the  vibrations  consequent  on  the  tightening 
and  closure  of  the  auriculo-ventricular 
valves. 

Much  objection  has,  however,  been 
taken  to  this  method  of  investigation. 
First,  because  it  does  not  admit  of 
both  positive  and  negative  pressure 
being  recorded.  Secondly,  because  the 
method  is  only  applicable  to  large 
animals,  such  as  the  horse.  Tliirdly, 
because  the  intraventricvdar  changes 
of  pressure  are  communicated  to  the 
recording  tambour  by  a  long  elastic 
column  of  air;  and  fourthly,  because 
the  tambour  arrangement  has  a  ten- 
dency to  record  inertia  vibrations. 
Rolleston  reinvestigated  the  subject 
with  a  more  suitable  but  rather  com- 
plicated apparatus.  The  principle  of 
the  method  consisted  in  placing  the  cavity  of  a  heart-chamber  in 
communication  with  a  recording  apparatus  by  means  of  a  tube 
containing  saline  solution.  His  recording  apparatus  consisted  of  a 
lever  connected  to  a  piston ;  the  upward  and  downward  movements 
of  the  piston-rod  were  due  to  the  varying  pressures  exerted  on  the 
blood  by  the  contraction  and  dilatation  of  the  heart;  the  rise  and 
fall  of  the  lever  were  controlled  by  the  resistance  to  torsion  of  a 
steel  ribbon  to  which  it  was  attached.  The  following  figure  (fig. 
250)  shows  the  kind  of  tracing  he  obtained.     He  found : — 

1.  That  there  is  no  distinct  and  separate  auricular  contraction 
marked  in  the  curves  obtained  from  either  right  or  left  ventricles, 

*  There  can  be  no  doubt  that  the  point  d  which  Marey  considered  to  coincide 
with  the  closure  of  the  semilunar  valves  does  not  really  do  so.  The  closure  occurs 
much  earlier  (e  in  fig.  252). 


Fig.  249.— Tracings  of  (1),  Intra-auricular, 
and  (2),  Intra-ventricular  pressure, 
and  (3),  of  the  impulse  of  the  heart; 
to  be  read  from  left  to  right ;  ob- 
tained by  Chauveau  and  Marey's 
apparatus. 


242 


PHYSIOLOGY   OF   THE   HEART 


[CH.  XX. 


the  auricular  and  ventricular  rises  of  pressure  being  merged  into  one 
continuous  rise. 

2.  That  the  auriculo-ventricular  valves  are  closed  before  any 
great  rise  of  intraventricular  pressure  above  that  which  results  from 
the  auricular  systole  occurs  {a,  fig.  250).  The  closure  of  this  valve 
does  not  produce  any  notch  or  wave. 

3.  That  the  semilunar  valves  open  at  the  point  in  the  ventricular 


Fig.  250.— Curve  from  left  ventricle  obtained  by  RoUeston's  apparatus  ;  the  abscissa  shows 
atmospheric  pressure. 

systole,  situated  (at  c)  about  or  a  little  above  the  junction  of  the 
middle  and  upper  third  of  the  ascending  line  (a  b),  and  the  closure 
about  the  shoulder  (d). 

4.  That  the  minimum  pressure  in  the  ventricle  may  fall  below 
that  of  the  atmosphere,  but  that  the  amount  varies  considerably. 

Another  method  of  overcoming  the  imperfections  of  Marey's  tam- 
bour is  by  the  use  of  Hiirthle's  manometer  (fig.  244).  In  this  the  tam- 
bour is  very  small,  the  membrane  is  made  of  thick  rubber,  and  the 


Fig.  251. — Hiirthle's  Manometer. 


whole,  including  the  tube  that  connects  it  to  the  heart,  is  filled  with 
a  strong  saline  solution  (saturated  solution  of  sodium  sulphate). 

The  tracing  obtained  by  this  instrument,  when  connected  with 
the  interior  of  the  ventricle,  is  represented  in  the  next  figure. 

The  auricular  systole  causes  a  small  rise  of  pressure  A  b  ;  it  lasts 
about  '05  second.  It  is  immediately  followed  by  the  ventricular  con- 
traction, which  lasts  from  B  to  d.  From  b  to  c  the  ventricle  is 
getting  up  pressure,  so  that  at  c  it  equals  the  aortic  pressure.  This 
takes  '02  to  "04  second.  Just  beyond  c  the  aortic  valves  open,  and 
blood  is  driven  into  the  aorta ;    the  outflow  lasts  from  c  to  d  ('2 


CH.  X.\.] 


INTHACARDIAC    I'KESSUKE 


243 


secoiul).  At  D  the  ventricle  relaxes.  The  Hat  part  of  the  curve  is 
spoken  of  as  the  systolic  plateau,  and  according;  to  the  state  of  the 
lieart  and  the  })eripheral  resistance  may  present  a  gradual  ascent  or 
descent;  it  occupies  about  "18  second:     Almost  immediately  after  the 

D 


Fiii.  262.— Curve  of  intraventricular  pressure.     (After  Hiirlhlf.) 

relaxation  begins  the  intraventricular  pressure  falls  below  the  aortic, 
so  that  the  aortic  valves  close  near  the  upper  part  of  the  descent  at  E. 
The  amount  of  pressure  in  the  heart  is  measured  by  a  manometer, 
which  is  connected  to  the  heart  by  a  tube  containing  a  valve.  This 
was  first  used  by  Goltz  and  Gaule.  If  the  valve  permits  fluid  to  go 
only  from  the  heart,  the  manometer  will  indicate  the  maximum  pres- 
sure ever  attained  during  the  cycle.  If  it  is  turned  the  other  way, 
it  will  indicate  the  minimum  pressure.  The  following  are  some  of 
the  measurements  taken  from  the  dog's  heart  in  terms  of  millimetres 
of  mercury : — 

Left  ventricle 

Right  ventricle 

Right  auricle  .  ... 

By  a  negative  (  —  )  pressure  one  means  that  the  mercury  is  sucked  up 
in  the  limb  of  the  manometer  towards  the  heart. 

Another  valuable  instrument  introduced  by  Hiirthle  is  called  the  differential 
manometer.  In  this  instrument,  two  cannulse  are  brought  into  connection  with 
tambours  (a  and  b)  which  work  on  points  of  a  lever  at  equal  distances  from  and  on 


Maximum 
pressure. 
140  mm. 

Minimum 
pressure. 
-  30  to  40  mm. 

60  mm. 
20  mm. 

- 15  mm. 

-    7  to  8  mm. 

B  A 

F"iG.  253. — Diagram  of  Hiirthle '.s  differential  Manometer. 

opposite  sides  of  its  fulcrum  (f).  The  lever  sets  in  motion  a  writing  style  (s).  This 
instrument  enables  us  to  determine  the  relations  of  the  pressure  changes  in  any 
two  cavities.  For  instance,  suppose  a  is  connected  to  the  left  ventricle,  and  b  to 
the  aorta  ;  when  the  pressure  in  the  ventricle  is  greater  than  that  in  the  aorta,  the 
writing  style  will  be  raised ;  when  the  pressure  in  the  aorta  is  greater  than  that  in 
the  ventricle,  the  style  will  fall ;  when  the  two  pressures  are  equal,  it  will  be  in  the 
zero  position. 


2-44:  PHYSIOLOGY    OF    THE    HEART  [CH.  XX. 

Frequency  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  about  72  times  in  a 
minute;  but  many  circumstances  cause  this  rate,  which  of  course 
corresponds  with  that  of  the  arterial  pulse,  to  vary  even  in  health. 
The  chief  are  age,  temperament,  sex,  food  and  drink,  exercise,  time 
of  day,  posture,  atmospheric  pressure,  temperature.  Some  figures 
in  reference  to  the  influence  of  age  are  appended. 

The  frequency  of  the  heart's  action  gradually  diminishes  from  the 
commencement  to  near  the  end  of  life,  but  is  said  to  rise  again  some- 
what in  extreme  old  age,  thus  : — 


Before  birth  the  average  number 

of  pulsations  per  minute  is  .  150 
Just  after  birth  .  .  from  140  to  130 
During  the  first  year  .  ,,  130  to  115 
During  the  second  year  ,,  115  to  100 
During  the  third  year  .       „     100  to    90 


About  the  seventh  year  .  from  90  to  85 
About      the      fourteenth 

year      .         .         .         .  ,,     85  to  80 

In  adult  age     .         .         .  „     80  to  70 

In  old  age         .         .         .  ,,     70  to  60 

In  decrepitude          .         .  ,,     75  to  65 


In  health  there  is  observed  a  nearly  uniform  relation  between 
the  frequency  of  the  beats  of  the  heart  and  of  the  respirations ;  the 
proportion  being,  on  an  average,  1  respiration  to  3  or  4  beats.  The 
same  relation  is  generally  maintained  in  the  cases  in  which  the  action 
of  the  heart  is  naturally  accelerated,  as  after  food  or  exercise ;  but 
in  disease  this  relation  may  cease. 

Work  of  the  Heart. 

Waller  compares  the  work  performed  by  the  heart  in  the  day  to  that  done  by  an 
able-bodied  labourer  working  hard  for  two  hours.  The  heart's  work  consists  in  dis- 
charging blood  against  pressure,  and  in  imparting  velocity  to  it.  Thus,  if  V repre- 
sents the  output  of  the  heart  per  beat  measured  in  cubic  centimetres,  and  P  the 
mean  pressure  in  the  aorta,  m  the  mass  of  the  blood,  and  v  the  velocity  imparted  to 
it ;  the  work  W  is  given  by  the  equation  : — 

W=  VP  +  h  mv~ 
=  Vffdh  +  \  mv- 

where  h  is  the  mean  pressure    in    the   aorta   expressed  in   centimetres  of  blood, 
d  the  density  of  the  blood,  and  r/  the  acceleration  of  gravity  (981). 

If  now  a  is  the  transverse  section  of  the  aortic  orifice,  l>  that  of  the  aorta,  t  the 
duration  of  the  ventricular  systole,  and  t^  the  duration  of  the  cardiac  cycle,  then,  if 
«!  is  the  mean  velocity  of  the  blood  in  the  aorta, 

V  =  avt  =  hi\t^. 

Let  us  assume  that  the  output  of  the  heart  is  110  c.c.  per  beat.  The  duration 
of  the  cardiac  cycle  is  0-8  sec,  and  that  of  the  ventricular  systole  is  0-3  sec.  The 
diameter  of  the  aorta  is  about  3  cms.  and  that  of  the  aortic  orifice  2-6  cms.  Remem- 
bering that  the  radius  in  each  case  is  half  the  diameter,  we  have  :— 

110  =  7r(l-3)-  X  0-3  X  V  =  7r(l-5)-  x  0*8  x  v^ 
Therefore  v  =  86-03,  and  v^  =  19-45  cms.  per  second. 

That  is,  the  velocity  of  the  blood  as  it  is  discharged  from  the  heart  is  about  4-5  times 
greater  than  the  mean  velociti/  of  the  blood  in  the  aorta. 

If  //  represents  the  mean  intraventricular  pressure  during  the  time  blood  is 


CH.  XX.]  WORK    OF    THE    HRAItT  245 

biiii}:?  (lis(lKii<;e(l  intd  the  aorta,  iiuasimd  in  cms.  of  blood,  and  h  the  mean  aortic 
pressure  over  the  same  time,  then  :    - 

V-  =  2v(//     h). 

Or  /^      '"^) 

_  (86  •03)-' 
~  "  "*"  2  X  981 
=  /j  +  3-77  em.s.  of  blood. 

That  is,  the  mean  intraventrirular  pressure  during  the  time  the  semihmar  valves  are 
open  is  only  3 '7 7  cms.  of  blood  or  0'28  cms.  of  mercury  higher  than  the  mean  aortic 
pressure  during  the  same  time.  We  may  take  the  mean  aortic  pressure  during  the 
duration  of  systole  as  appro.vimately  12  cms.  of  mercury  or  156  cms.  of  blood,  if  vie 
take  the  deiisify  of  mercury  as  being  13  tiives  that  of  /he  blood. 

Now  if  Ep  rei)resents  the  total  potential  enerj^y  created  by  the  heart  per  beat, 
then, 

Ep  =  VgdH. 

A  part  of  this  energy,  Ek,  Is  converted  into  kinetic  energy  since  velocity  is 
imjiarted  to  the  blood.     This  amount  is  given  by  the  fornmla  : — 

Ek  =  iF^/r-. 
From  these  two  fornnihe 


Again 


Ep 

=  110  X  g  X  1-05  X  (156  +  3-77)  ergs 
=  110  X  1-05  X  (159-77)  grra.  cms. 
=  18453"4  grm.  cms. 

Ep       VgdH 
Ek  "  i  Vdv' 

V, 

H 
-H-h 

159-77 

-    3-77 

=  40  approximately. 

That  is,  Jff  of  the  total  energy  of  the  heart's  beat  is  used  in  imparting  velocity  to  the 
blood. 

When  the  blood  reaches  the  aorta  its  velocity  is  gradually  checked,  Z.^.,  some  of 
the  kinetic  energy  imparted  to  it  by  the  heart  is  reconverted  into  energy  of  pressure. 
The  remaining  kinetic  energy  is  given  by  the  equation  : — 

Ek^  =  I  mvi~ 

_  Vdv^^ 

=  22-275  grm.  cms. 

Hence,  the  kinetic  energy  of  the  blood  in  the  aorta  is  only  appro.rimcitely  ^^^  of  the 
total  enerqi^  imparted  to  the  blood  by  the  heart. 

The  Output  of  the  Heart.— The  first  estimations  of  the  work  of  the  heart,  made 
by  Volkmann  and  Vierordt,  gave  numbers  nearly  double  those  stated  in  the  preced- 
ing paragraph.  Recent  research  has  shown  that  their  estimate  of  the  output  of  the 
heart  was  excessive.  Direct  measurements  of  the  heart's  output  have  been  made 
by  Stolnikow  and  Tigerstedt.  The  former  cut  off  by  ligature  the  whole  of  the 
systemic  circulation  in  the  dog,  and  then  measured  the  amount  of  blood  passing 
through  the  simplified  circulation  which  consisted  only  of  the  pulmonary  and  coron- 
ary vessels  by  means  of  a  graduated  cylinder  interposed  on  the  course  of  the  vessels 
(see  fig.  254).'  Tigerstedt  made  his  observations  by  means  of  a  Stromuhr  (see  next 
chapter)  inserted  into  the  aorta.  Severe  operative  measures  of  this  kind,  however, 
interfere  with  the  circulation  a  good  deal. 


246 


PHYSIOLOGY    OF    THE    HEART 


[CH.   XX. 


A 


e 


f^^ 


e) 


B 


Grehant  and  Quinquand,  and  Zuntz  adopted  an  indirect  method  based  on  the 
comparison  of  tlie  amount  of  oxyjfen  absorbed  in  the  lungs  with  the  amount  added 
to  the  blood  in  its  passage  through  the  pulmonary  circulation. 

G.  N.  Stewart  has  introduced  an  ingenious  method,  the  principle  of  which  is 
the  following : — A  solution  of  an  innocuous  substance,  which  can  be  easily  recog- 
nised and  estimated,  is  allowed  to  flow  for  a  definite  time  and  at  a  uniform  rate  into 

the  heart :  the  substance  selected  was 
sodium  chloride.  This  mingles  with  the 
blood  and  passes  into  the  circulation. 
At  a  convenient  point  of  the  vascular 
system,  a  sample  of  blood  is  drawn  off 
just  before  the  injection,  and  an  equal 
amount  during  the  passage  of  the  salt ; 
the  quantity  of  the  sodium  chloride 
solution  which  must  be  added  to  the 
first  sample  in  order  that  it  may  contain 
as  much  as  the  second  sample  is  deter- 
mined. This  determination  gives  the 
extent  to  which  the  salt  solution  has 
been  mixed  with  the  blood  in  the  heart, 
and  knowing  the  quantity  of  the  solu- 
tion which  has  run  into  the  heart,  the 
output  in  a  given  time  can  be  calculated. 
All  these  experiments  have  been  on 
animals.  The  results  obtained  neces- 
sarily vary  with  the  size  of  the  animal 
used,  and  with  the  rate  at  which  the 
heart  is  beating.  If  the  same  relation- 
ship holds  for  man  as  for  animals, 
Stewart  calculates  that  in  a  man  weigh- 
ing 70  kilos,  the  output  of  each  ventric-le 
per  second  is  less  than  0"002  of  the  body 
weight,  i.e.,  about  105  grammes  of 
blood  per  second,  or  87  grammes  (about 
SO  c.c.)  per  heart  beat  with  a  pulse  rate 
of  72.  Zuntz  obtained  rather  smaller 
numbers  by  his  method. 

An  instrument  called  the  curd'to- 
meUr  was  invented  by  Roy  for  regis- 
tering the  output  of  the  "heart.  His 
instrument  was  made  of  metal,  and  oil 
was  used  as  the  transmitting  medium 
in  its  interior.  A  simple  modification 
of  this  applicable  to  the  heart  of  a  small 
mammal  like  a  cat  has  been  devised  by 
Barnard.  It  consists  of  an  indiarubber 
tennis  ball  with  a  circular  orifice  cut  in 
one  side  of  it  large  enough  to  admit  the 
heart ;  a  glass  tube  is  securely  fixed  into 
a  small  opening  on  the  opposite  side 
of  the  ball.  The  animal  is  anaesthetised, 
and  its  thorax  opened.  The  animal  is 
artificial 


Fig.  254. — Stolnikow's  apparatus.  A  and  B  are 
two  cylinders  fitted  with  floats  provided  with 
writing-points  at  their  upper  ends.  The  tube 
from  the  lower  end  of  each  bifurcates  into 
two,  a  and  v  from  A  ;  re'  and  v'  from  B.  o  and 
a  are  united  together  and  enter  the  right 
carotid  artery ;  v  and  v'  unite  and  are  inserted 
into  the  superior  vena  cava.  The  remaining 
branches  of  the  aorta  and  the  inferior  vena 
cava  are  tied.  B  is  hrst  filled  with  detibrin- 
ated  blood,  which  passes  down  v'  into  the 
right  auricle,  thence  to  the  right  ventricle, 
lungs  (where  it  is  oxygenated),  and  then 
enters  the  left  side  of  the  heart ;  the  left 
ventricle  expels  it  by  the  tube  a  into  A,  so 
that  the  float  in  A  rises  while  that  in  B  falls. 
As  soon  as  B  is  empty  the  tubes  v  and  n' 
which  were  previously  clamped  are  released, 
and  v'  and  a  are  clamped  instead.  The  left 
ventricle  now  expels  its  blood  by  the  tube  n' 
into  the  cylinder  B ;  simultaneously  A  empties 
itself  through  v  into  the  right  side  of  the 
heart.  Zigzag  lines  are  thus  traced  by  the 
writing-points  on  the  top  of  the  floats,  and 
their  frequency  enables  one  to  estimate  the 
output  of  the  left  ventricle  in  a  given  time. 
(After  Starling.) 


kept  alive  by  artificial  respiration. 
The  pericardium  is  then  opened  by  a  crucial  incision,  the  heart  is  slipped  into  the 
ball  ;  the  pericardium  overlaps  the  outside  of  the  ball,  and  the  apparatus  is 
rendered  air-tight  by  smearing  the  edges  of  the  hole  with  vaseline.  The  four 
corners  of  the  pericardium  are  then  tightly  tied  by  ligatures  round  the  glass  tube 
just  mentioned.  This  tube  is  connected  by  a  stout  indiarubber  tube  to  a  Marey's 
"tambour  or  a  piston-recorder,  the  writing-point  of  which  is  applied  to  a  moving 
blackened  cyhnder.     When  the  heart  contracts,  air  will  be  withdrawn  from  the 


CIl.  XX.]  INNEl;VAT10N    OK    TllK    IIKAUT  247 

tambour  to  tlu'  cardionii'ttr ;  wlun  tin-  luart  txjiaiuls,  the  air  will  move  in  tlie 
rovi-rsi-  (liri'ctioM.  Tlu'st-  luovcincnts  are  written  by  the  end  of  the  lever  of  the 
tambour,  and  variations  in  the  excursions  of  this  lever  correspond  with  variations 
in  the  amount  of  l)l()<)d  ex|)ellcd  from  or  drawn  into  the  lu'art  with  systole  and 
diastole  respectively.  By  calibratinfi,-  the  instrument  the  actual  volume  of  the 
blood  cxj>elied  I'an  be  ascertained. 

Innervation  of  the  Heart. 

The  nerves  of  the  heart,  which  under  normal  circumstances 
control  its  movements,  are: — 

1.  Cardiac  branches  of  the  vagus  (inhibitory  fibres). 

2.  Cardiac  branches  of  the  sympathetic  (augmentor  and  acceler- 
ator fibres). 

These  pass  to  the  heart  and  terminate  in  certain  collections  of 
ganglion  cells  in  its  wall ;  from  these  cells  fresh  fibres  are  distributed 
among  the  muscular  fibres.  In  addition  to  these  nerves,  which  are 
efferent,  we  have  to  mention  : — 

3.  The  sensory  or  afferent  nerves  of  the  heart,  the  best  known  of 
which  is  called  the  depressor  nerve.  This  nerve,  starting  from  the 
cardiac  tissue,  joins  the  vagus  trunk  ;  it  passes  to  the  bulb,  especially 
to  the  vaso-motor  centre.  We  shall  therefore  postpone  its  study 
until  we  are  considering  the  vaso-motor  nerves. 

The  Vagus. — The  ninth,  tenth,  and  eleventh  cranial  nerves  arise 
close  together  from  the  grey  matter  in  the  floor  of  the  fourth  ventricle, 
and  leave  the  bulb  by  a  number  of  rootlets.  These  rootlets  are 
divided  by  Grossmann  into  three  groups,  a,  h,  and  c ;  there  is  a  good 
deal  of  blending  of  the  rootlets  before  they  ultimately  emerge  from 
the  skull,  but  the  a  group  corresponds  fairly  well  with  the  fibres  of 
the  glossopharyngeal,  b  with  those  of  the  vagus,  and  c  with  those  of 
the  spinal  accessory.  The  rootlets  of  the  tenth  nerve  pass  through 
two  ganglia  called  respectively  the  jugular  ganglion,  and  the  ganglion 
trunci  vagi.  The  fibres  of  the  spinal  accessory  nerve  which  join  the 
vagus  are  chiefly  motor,  especially  to  the  larynx,  but  some  go  to  the 
heart.  The  vagus  gives  off  branches  to  many  organs,  pharynx,  larynx, 
heart,  lungs,  oesophagus,  and  various  abdominal  organs.  We  have, 
however,  in  this  place  only  to  deal  with  its  cardiac  fibres.  It  has 
been  known  since  the  experiments  of  the  Brothers  Weber  in  1845 
that  stimulation  of  one  or  both  vagi  j)roduces  slowing  or  stoppage  of 
the  beats  of  the  heart.  It  has  since  been  shown  that  in  all  vertebrate 
animals,  this  is  the  normal  result  of  vagus  stimulation  ;  the  pheno- 
menon is  called  inhibition,  and  the  nerve-fibres  cardio-inhibitory. 
Section  of  one  vagus  produces  slight  acceleration  of  the  heart ;  this 
result  is  better  marked  when  both  vagi  are  divided.  This  shows  that 
the  restraining  influence  of  the  vagus  is  being  continuously  exercised  ;  it 
is,  however,  found  that  the  amount  of  vagus  control  so  exercised  varies 
a  good  deal  in  different  animals.     The  most  potent  artificial  stimulus 


248 


PHYSIOLOGY   OF   THE    HEART 


[CH.  XX. 


which  can  be  applied  to  the  vagus  nerve  to  produce  inhibition  of  the 
heart  is  a  rapidly  interrupted  induction  current ;  severe  mechanical 
stimuli  have  a  slight  effect,  but  chemical  and  thermal  stimuli  are  in- 
eflfective. 

A  certain  amount  of  confusion  has  arisen  as  to  the  effect  of  vagus 


Fig.  255. — Tracing  showing  the  actions  of  the  vagus  on  the  heart.  Aur.,  auricular  ;  Vent.,  ventricular 
tracing.  The  part  between  the  perpendicular  lines  indicates  the  period  of  vagus  stimulation.  C.8 
indicates  that  the  secondary  coil  was  8  cm.  from  the  primary.  The  part  of  the  tracing  to  the  left 
shows  the  regular  contractions  of  moderate  height  before  stimulation.  During  stimulation,  and 
for  some  time  after,  the  beats  of  auricle  and  ventricle  are  arrested.  After  they  commence  again 
they  are  small  at  first,  but  soon  acquire  a  much  greater  amplitude  than  before  the  application  of 
the  stimulus.    (BYom  Brunton,  after  Gaskell.) 


stimulation,  because  so  many  experiments  have  been  made  on  the 
frog.  In  this  animal  the  sympathetic  fibres  join  the  vagus  after  it 
leaves  the  skull,  and  so  what  is  usually  called  the  vagus  in  this 
animal  should  more  properly  be  termed  the  vago-symimthetic.  It  will 
readily  be  understood  that  hj  stimulating  a  mixed  nerve,  one  obtains 
an  intermixture  of  effects.  If,  however,  one  stimulates  the  intra- 
cranial vagus  before  the  sympathetic  blends  with  it,  a  pure  inhibitory 


Fig.  256.— Tracing  showing  diminished  amplitude  and  slowing  of  the  pulsations  of  the  auricle  and 
ventricle  without  complete  stoppage  during  stimulation  of  the  vagus.  (From  Brunton,  after 
Gaskell.) 

efifect  is  obtained.  Figs.  255  and  256  show  the  common  effect  of 
stimulating  the  mixed  trunk ;  the  inhibitory  effect  is  usually  mani- 
fested first,  and  this  is  followed  by  the  augmentor  effect  due  to 
sympathetic  action.  But  it  is  by  no  means  infrequent  to  obtain  the 
phenomena  in  the  reverse  order.     It  is  often  stated  that  the  right 


CH.  XX.]  THE   CAKDIAC    SYMPATHETIC  249 

uorve  contains  more  inhibitory  fibres  than  the  left,  but  this  is  by  no 
means  a  constant  rule.  One  can  always  obtain  good  inhibition  if  the 
stimulus  is  applied  to  the  wall  of  the  sinus ;  here  one  stimulates 
the  post-ganglionic  fibres  which  originate  from  the  nerve-cells  in 
the  sinus  ganglion  around  which  the  vagi  terminate. 

The  effect  of  the  stimulus  is  not  immediately  seen ;  one  or  more 
beats  may  occur  before  stoppage  of  the  heart  takes  place,  and  slight 
stimulation  may  produce  only  slowing  and  not  complete  stoppage  of 
the  heart  (fig.  256).  The  stoppage  may  be  due  either  to  prolongation 
of  the  diastole,  as  is  usually  the  case,  or  to  diminution  of  the  systole. 
Vagus  stimulation  lessens  the  conductivity  of  the  cardiac  tissue, 
but  it  does  not  abolish  the  irritability  of  the  heart-muscle,  since 
mechanical  stimulation  may  bring  out  a  beat  during  the  stand-still 
caused  by  vagus  stimulation.  The  inhibition  of  the  beats  varies  in 
duration,  but  if  the  stimulation  is  a  prolonged  one,  the  beats  reappear 
before  the  current  is  shut  off.  This  is  known  as  "  vagus  escape,"  and 
occurs  in  all  animals ;  it  is  probably  due  to  fatigue  of  the  vagal 
endings. 

The  Sympathetic. — The  influence  of  the  sympathetic  is  the 
reverse  of  that  of  the  vagus.  Stimulation  of  the  sympathetic 
produces  acceleration  of  the  heart-beats,  and  according  to  most 
observers,  section  of  the  nerve  produces  no  slowing.  Hence  the 
nerve  is  not  in  constant  action  like  the  vagus.  The  acceleration 
produced  by  stimulation  of  the  sympathetic  fibres  is  accompanied  by 
increased  force,  and  so  the  action  of  the  nerve  is  also  termed 
augmentor.  It  is  probable  that  the  augmentor  fibres  are  distinct 
from  the  accelerator  fibres,  because  in  mammals  one  or  two  of  the 
small  nerves  leaving  the  stellate  ganglion  on  stimulation  produce 
augmentation  without  acceleration. 

The  fibres  of  the  sympathetic  system  which  influence  the  heart- 
beat in  the  frog,  leave  the  spinal  cord  by  the  anterior  root  of  the 
third  spinal  nerve,  and  pass  by  the  ramus  communicans  to  the  third 
sympathetic  ganglion,  then  to  the  second  sympathetic  ganglion,  then 
by  the  annulus  of  Vieussens  (round  the  subclavian  artery)  to  the  first 
sympathetic  ganglion,  and  finally  in  the  main  trunk  of  the  sympa- 
thetic, to  near  the  exit  of  the  vagus  from  the  cranium,  where  it  joins 
that  nerve  and  runs  down  to  the  heart  within  its  sheath,  forming  the 
joint  vago-sympathetic  trunk.  These  fibres  are  indicated  by  the  dark 
line  in  fig.  257.  The  fibres  of  the  sympathetic  seen  running  up  into 
the  skull  are  for  the  supply  of  blood-vessels  there.  It  should  be  noted 
that  the  frog  has  no  spinal  accessory  nerve. 

In  the  mammal  the  sympathetic  fibres  leave  the  cord  by  the 
second  and  third  dorsal  nerves,  and  possibly  by  anterior  roots  of  two 
or  more  lower  nerves ;  they  pass  by  the  rami  communicantes  to  the 
ganglion    stellatum,  or   first  thoracic  ganglion,  and   thence   by  the 


250 


niYSIOLOGY    OF    THE    IIEAKT 


[CI!.  XX. 


Roots  of 
Vagus 


aunulus  of  Vieussens  to  the  inferior  cervical  ganglion  of  the  sym- 
pathetic ;  fibres  from  the  annulus,  or  from  the  inferior  cervical 
ganglion,  proceed  to  the  heart  (see  fig.  258). 

In  man,  the  cardiac  branches  of  the  sympathetic  travel 
to  the  heart  from  the  annulus  of  Vieussens  and  cervical 
sympathetic  in  superior,  middle,  and  lower  bundles  of  fibres. 
These  pass  into  the  cardiac  plexus,  and  surrounding  the  coronary 

vessels  ultimately  reach 
the  heart.  They  probably 
contain  vaso-motor  fibres  for 
these  vessels,  as  well  as  the 
more  important  fibres  for  the 
heart  itself. 

By  stimulating  each  rootlet  in 
his  three  groups,  Grossmann  found 
the  cardio-inhibitory  fibres  in  the 
lower  two  or  three  rootlets  of  group  l> 
and  the  upper  rootlet  of  group  r. 
There  are  probably  differences  in 
different  animals.  In  the  cat  and  dog 
Cadman  finds  that  the  rootlets  in  the 
a  group  are  respiratory  and  afferent 
inhibitory,  and  that  all  the  efferent 
inhibitory  fibres  are  in  group  r. 

The  inhibitory  fibres  are  medul- 
lated,  and  only  measure  2^  to  o/jl  in 
diameter  ;  they  pass  to  the  heart  and 
have  their  cell-stations  in  the  ganglia 
of  that  organ.  The  sympathetic 
fibres,  on  the  other  hand,  reach  the 
heart  as  non-medullated  fibres  ;  they 
have  their  cell-stations  in  the  sym- 
pathetic (inferior  cervical  and  first 
thoracic)  ganglia.  The  augmentor 
and  accelerator  centres  in  the  central 
nervous  system  have  not  yet  been 
accurately  localised. 


Ant.  toot 


Post,  root 


Fig.  257. — Heart  nerves  of  frog.    (Diagrammatic.) 


Influence  of  Drugs. — The 
question  of  the  action  of  drugs 
on  the  heart  forms  a  large  branch  of  pharmacology.  We  shall  be 
content  here  with  mentioning  two  only,  as  they  are  largely  used  for 
experimental  purposes  by  physiologists.  Atropine  produces  consider- 
able augmentation  of  the  heart-beats  by  paralysing  the  inhibitor}- 
mechanism.  Ifuscarine  (obtained  from  poisonous  fungi)  produces 
marked  slowing,  and  in  larger  doses  temporary  stoppage  of  the 
heart.  Its  effect  is  a  prolonged  inhibition,  and  can  be  removed  by 
the  action  of  atropine.  The  action  of  atropine  cannot,  however,  be 
easily  antagonised  by  muscarine ;  a  large  dose  is  necessary.  That  these 
drugs  act  on  the  nerves,  and  not  the  muscular  substance  of  the 
heart,  is  shown  by  the  fact  that  in  the  hearts  of  early  embryos,  so 


CII.  XX.] 


i:efi.ex  ixiiiniTiox 


251 


Ganglion 
tninci 
Vagi 


Roots 
of 
Nerve 

Roots 

0/ 

XI   Nerue 


early  that  no  nerves  have  }-et  grown  to  the  heart,  these  drugs  have 
little  or  no  effect,     (rickering.) 

lic/Icx  Inhihltion. — Thus  there  is  no  doubt  that  the  vagi  nerves 
are  simply  the  media  of  an  inhibitory  or  restraining  influence  over 
the  action  of  the  heart,  which  is  conveyed  through  them  from  the 
centre  in  the  medulla  oblongata,  which  is  always  in  operation.  The 
restraining  induenco  of  the 

centre  in  "the  medulla  may  Juguiar^amjUon 

be  retlexly  increased  by 
stimulation  of  many  afferent 
nerves,  particularly  those 
from  the  nasal  mucous 
membrane,  the  larynx,  and 
the  lungs.  A  blow  on  the 
abdomen  causes  inhibition 
and  fainting;  a  blow  on  the 
larynx,  even  a  moderate  one, 
will  kill.  There  is  no  com- 
parison between  the  ease 
with  which  stimulation  of 
the  laryngeal  or  pulmonary 
fibres  produces  inhibition,  as 
compared  to  the  difficulty  of 
obtaining  inhibition  from  the 
alimentary  tract.  Chloro- 
form vapour  *  and  tobacco 
smoke  in  some  people  and 
animals,  by  acting  on  the 
terminations  of  the  vagi  or 
their  branches  in  the  respi- 
ratory system,  may  also  pro- 
duce reflex  inhibition  of  the 
heart.  Some  very  remark- 
able facts  concerning  the 
readiness  by  which  reflex 
inhibition  of  the  fish's  heart 
may  be  produced  were  made 
out     by     M'William ;     any 

irritation  of  the  tail,  gills,  mucous  membrane  of  mouth  and  pharynx, 
or  of  the  parietal  peritoneum,  causes  the  heart  to  stop  beating. 

In  connection  with  the  subject  of  reflex  inhibition,  it  may  be 
mentioned  in  conclusion  that  though  we  have  no  voluntary  control 

*  Embley,  however,  considers  that  the  usual  cause  of  sudden  death  during 
the  early  stages  of  chloroform  narcosis  is  the  direct  action  of  the  drug  on  the  vagus 
centre.     In  animals,  cutting  the  vagi  immediately  sets  the  heart  going  again. 


Fig.  258. — Heart  nerves  of  mammal.    (Diagrammatic.) 


252  PHYSIOLOOY   OF   THE   HEART  [CH.  XX. 

over  the  heart's  movements,  yet  cerebral  excitement  will  produce  an 
effect  on  the  rate  of  the  heart,  as  in  certain  emotional  conditions. 

Gaseous  exclaanges  during  Inhibition. — The  mammalian  heart 
is  more  difficult  to  stop  by  stimulation  of  the  vagus  than  the  frog's 
heart ;  commonly  it  is  only  slowed,  and  the  amplitude  of  the  beat 
reduced,  yet  it  is  most  important  for  the  student  of  medicine  to 
recollect  that  vagus  inhibition  may  have  far-reaching  results.  An 
overdose  of  chloroform  at  the  onset  of  anaesthesia  may  so  stimulate 
the  vagus  centre  in  the  brain  so  as  to  produce  heart-stoppage  which 
may  end  fatally.  (This  is  quite  different  to  the  stoppage  caused  by 
the  direct  action  of  chloroform  on  the  cardiac  tissue  as  the  result  of 
the  continued  action  of  the  drug,  and  the  word  inhibition  is  not 
properly  applied  in  this  case.)  In  true  inhibition,  the  metabolism  of 
the  heart  tissue  is  reduced  :  this  is  followed  by  increased  metabolism 
during  the  subsequent  period,  and  this  corresponds  with  the  increase 
of  visible  activity  which  then  occurs  and  which  is  seen  in  the 
tracings  given  in  figs.  255  and  256.  This  is  well  illustrated  by  the 
following  data  of  the  gaseous  exchanges  in  the  heart  of  the  cat, 
which  were  obtained  by  analysing  the  blood  in  the  coronary  vessels. 
(Barcroft  and  Dixon.) 


Oxygen  used  up  per  minute 
Carbonic  acid  given  out  per  minute 

Normal  Heart.     Dartog  Vagus       Aft<>r  Vagus 
Inhibition.           Inhibition. 

0-21  C.C.            0-13  c.c.            0-34  c.c. 
0-4.T  c.c.            0-07  c.c.            0-22  c.c. 

The  Excised  Heart, 

The  heart  beats  after  its  removal  from  the  body;  in  the  case  of 
the  frog  and  other  cold-blooded  animals,  this  will  go  on  for  hours, 
and  under  favourable  circumstances  for  days.  In  the  case  of  the 
mammal,  it  is  more  a  question  of  minutes  unless  the  heart  is  artifi- 
cially fed  through  the  coronary  artery  with  arterial  blood.  If  this 
is  done,  especially  in  an  atmosphere  of  oxygen,  the  dog's  heart,  or 
even  strips  of  the  dog's  heart,  can  be  kept  beating  for  hours.  (Porter.) 
Einger's  salt  solution  (see  p.  256),  if  well  oxygenated,  will  also  keep 
an  excised  mammal's  heart  beating  for  hours,  especially  if  a  little 
dextrose  is  added  to  the  solution.     (Locke.) 

At  one  time  the  rhythm  was  supposed  to  originate  from  the 
intrinsic  nervous  system  of  the  heart;  but  we  now  know  that  the 
power  of  rhythmical  peristalsis  resides  in  the  muscular  tissue  itself, 
though  normally  during  life  it  is  controlled  and  regulated  by  the 
nerves  that  supply  it  (see  p.  159). 

The  intracardiac  nerves  have  been  chiefly  studied  in  the  frog ;  the 


cn.  XX.] 


CONDUCTION    IN    THE    HEART 


253 


two  Viigo-sympathetic  nerves  terminate  in  various  groups  of  ganglion 
cells ;  of  these  the  most  important  are  Remalcs  ganglion,  situated  at 
the  junction  of  the  sinus  with  the  right  auricle ;  and  Bidders  ganglion, 
at  the  junction  of  the  auricles  and  ventricle.  A  third  collection  of 
ganglion  cells  {von  Bezold's  ganglion)  is 
situated  in  the  inter-auricular  septum. 
From  the  ganglion  cells,  fibres  spread 
out  over  the  walls  of  the  sinus,  auricles, 
and  upper  part  of  the  ventricle. 
Eemak's  ganglion  used  to  be  called 
the  local  inhibitory  centre  of  the  heart ; 
it  is  really  the  cell-station  of  the 
inhibitory  fibres,  and  stimulation  of 
the  heart  at  the  sino-auricular  junction 
is  the  most  certain  way  of  obtain- 
ing stoppage  of  the  heart.  Bidder's 
ganglion  was  called  the  local  accelerator 
centre  for  a  corresponding  reason. 

The  accompanying  figures  show  the 
vagal  terminations  in  Remak's  ganglion 
(fig.  259),  some  isolated  nerve-cells 
from  this  ganglion  (fig.  260) ;  and  fig. 
261  is  a  rough  diagram  to  indicate  the 
positions  of  the  two  principal  ganglia. 

Conduction  in  the  Heart. — The  question  has  been  discussed 
whether  the  wave  of  contraction  is  propagated  along  the  heart-wall 
by  nervous  or  muscular  connection.  The  slow  rate  of  propagation 
of  the  wave  points  to  the  link  being  a  muscular  one,  and  it  will  be 


Fig.  259.— Course  of  the  iierve.s  in  the 
auricular  partition  wall  of  the  heart 
of  a  frog,  d,  dorsal  branch  ;  v,  ventral 
branch.     (Ecker.) 


Aorta 


Fn;.  260.— Isolated  nerve-cells  from  the  frog's  heart.  I.  Usual 
form.  1 1.  Twin  cell.  C,  capsule  ;  J\',  nucleus  ;  iV,  nucleolus  ; 
1',  i)rocess.    (From  Ecker.) 


Fig.  261. — Diagram  of  ganglia  in  frog's 
heart.  R.  Remak's,  B,  Bidder's 
ganglion  ;  S,  sinus;  A,  right  auricle; 
V,  ventricle. 


remembered  that  histology  lends  support  to  this  view,  the  muscular 
fibres  being  connected  to  each  other  by  intercellular  bridges  of  proto- 
plasm (see  p.  87).  An  experimental  proof  of  the  same  view  is  the 
following:  if  a  strip  of  the  heart  wall  is  taken  and  a  number  of 


254  PHYSIOLOGY    OF    THE    HEART  [CIT.  XX. 

cuts  going  nearly  completely  across  it,  be  made  first  from  one  side, 
then  from  the  other,  all  the  nerves  must  be  cut  through  at  least  once, 
and  the  only  remaining  tissue  not  severed  is  muscular,  yet  the  strip 
still  continues  to  beat ;  in  other  words,  the  propagation  is  myodromic. 
The  passage  of  the  wave  from  one  chamber  to  another  is  also  myo- 
dromic. The  slow  rate  of  propagation  indicates  that  this  is  so,  and 
the  view  has  been  fully  proved  by  the  discovery  of  muscular  fibres 
passing  across  from  one  chamber  to  the  next. 

Blocking.^This  phenomenon  has  been  chiefly  studied  by  Gaskell. 
It  appears  that  under  normal  conditions  the  wave  of  contraction  in 
the  heart  starts  at  the  sinus,  and  travels  over  the  auricles  to  the 
ventricle ;  the  irritability  of  the  muscle  and  the  power  of  rhythmic 
contractility  is  greatest  in  the  sinus,  less  in  the  auricles,  and  still  less 
in  the  ventricles.  Under  ordinary  conditions  the  apical  portion  of 
the  ventricles  exhibits  very  slight  power  of  spontaneous  contraction. 
The  importance  of  the  sinus  as  the  starting-point  of  the  peristalsis 
can  be  shown  by  warming  it.  If  a  frog's  heart  is  warmed  by  bathing 
it  in  warm  salt  solution  at  about  body  temperature,  it  beats  faster ; 
this  is  due  to  the  sinus  starting  a  larger  number  of  peristaltic  waves ; 
that  this  is  the  case  may  be  demonstrated  by  warming  localised  portions 
of  the  heart  by  a  small  galvano-cautery ;  if  the  sinus  is  warmed  the 
heart  beats  faster,  but  if  the  auricles  or  ventricles  are  warmed  there 
is  no  alteration  in  the  heart's  rate.  The  sinus  in  the  frog's  heart, 
and  that  portion  of  the  right  auricle  in  the  mammal's  heart  which 
corresponds  to  the  sinus,  is  always  the  last  portion  of  the  heart  to 
cease  beating  on  death,  or  after  removal  from  the  body  (ultima 
moriens,  Harvey).  This  is  an  additional  proof  of  the  superior  rhyth- 
mical power  which  it  possesses. 

But  to  continue  our  description  of  the  phenomenon  known  as 
blocking ;  it  is  supposed  that  the  wave  starting  at  the  sinus  is  more 
or  less  blocked  by  a  ring  of  lower  irritabihty  at  its  junction  with  the 
auricle ;  again,  the  wave  in  the  auricle  is  similarly  delayed  in  its 
passage  over  to  the  ventricle  by  a  ring  of  lesser  irritability,  and  thus  the 
wave  of  contraction  is  delayed  at  its  entrance  into  both  auricular  and 
ventricular  tissue.  By  an  arrangement  of  ligatures,  or,  better,  of 
clamps,  one  part  of  the  heart  may  be  isolated  from  the  other  portions, 
and  the  contraction  when  aroused  by  an  induction  shock  may  be 
made  to  stop  in  the  portion  of  the  heart  muscle  in  which  it  begins. 
It  is  not  unlikely  that  the  contraction  of  one  portion  of  the  heart  acts 
as  a  stimulus  to  the  next  portion,  and  that  clamps  and  ligatures  prevent 
this  normal  propagation  of  stimuli.  It  must  not,  however,  be  thought 
that  the  wave  of  contraction  is  incapable  of  passing  over  the  heart  in 
any  other  direction  than  from  the  sinus  onwards;  for  it  has  been 
shown  that  by  the  application  of  appropriate  stimuli  at  appropriate 
instants,  the  natural  sequence  of  beats  may  be  reversed,  and  the  con- 


CII.  XX.]  THE   STANNIUS    HEART  255 

traction  starting  at  the  arterial  part  of  the  ventricle  may  pass  to  the 
auricles  and  then  to  the  sinus. 

If  Gaskell's  clamps  or  ligatures  are  not  ap[)lied  sufficiently  tight 
one  often  sees  partial  blocking,  a  few  waves  get  through  but  not  all ; 
in  the  experiment  descril)ed  on  the  preceding  page,  in  which  the 
heart  wall  is  left  connected  with  other  parts  by  a  small  portion  of 
undivided  muscular  tissue,  the  effect  is  much  thelsame,  the  wave  is 
only  able  to  pass  the  block  every  second  or  third  beat. 

TJie  Stannius  Experimeyit. — This  consists  in  applying  a  tight  ligature 
to  the  heart  between  the  sinus  and  the  right  auricle  ;  the  sinus 
continues  to  beat,  but  the  rest  of  the  heart  is  quiescent.  The  quiescent 
parts  of  the  heart  may  be  made  to  contract  in  response  to  mechanical 
or  electrical  stimulation.  If  a  second  ligature  is  applied  to  the 
junction  of  the  auricles  with  the  ventricle,  the  ventricle  begins  to 
beat  again ;  the  auricles  may  also  beat,  but  they  usually  do  not. 
According  to  Gaskell,  the  effect  of  the  first  ligature  is  simply  an 
example  of  blocking;  it  is,  however,  difficult  to  wholly  accept  this 
view,  for  if  instead  of  applying  a  ligature  at  the  sino-auricular 
junction,  the  heart  wall  is  simply  cut  through  at  this  spot,  the 
auricles  and  ventricle  are  not  thereby  always  rendered  quiescent.  It 
appears  probable,  therefore,  that  there  is  some  truth  in  the  older 
view  that  the  ligature  acts  as  a  stimulus  irritating  the  vagal  termi- 
nations in  Remak's  ganglion,  and  so  eliciting  a  condition  of  prolonged 
inhibition ;  this,  however,  passes  off  after  a  variable  time,  and  the 
auricles  and  ventricle  once  more  beat  rhythmically.  It  is  impossible 
to  explain  the  effect  of  the  second  Stannius  ligature  except  on  the 
hypothesis  that  it  acts  as  a  stimulus,  and  there  is  no  a  priori  reason 
why  the  two  ligatures  should  act  in  opposite  ways. 

The  fact  that  the  Stannius  heart  is  quiescent  has  enabled 
physiologists  to  study  the  effects  of  stimuli  upon  heart  muscle.  A 
single  stimulus  produces  a  single  contraction,  which  has  a  long  latent 
period,  is  slow,  and  propagated  as  a  wave  over  the  heart  at  the  rate 
of  f  to  f  inch,  or  10 — 15  mm.  a  second.  A  second  stimulus  causes 
a  rather  larger  contraction,  a  third  one  larger  still,  and  so  on  for 
some  four  or  five  beats,  when  the  size  of  the  contraction  becomes 
constant.  This  staircase  phenomenon,  as  it  is  called,  is  also  seen  in 
voluntary  muscle  (see  p.  117),  but  it  is  more  marked  in  the  heart. 
The  following  tracing  shows  the  result  of  an  actual  experiment : — 

There  are,  however,  more  marked  differences  than  this  between 
voluntary  and  heart  muscle.  The  first  of  these  is,  that  the  amount 
of  contraction  does  not  vary  with  the  strength  of  the  stimulation.  A 
stimulus  strong  enough  to  produce  a  contraction  at  all  brings  out  as 
big  a  beat  as  the  strongest.  The  second  is,  that  the  heart  muscle 
has  a  long  refractory  period ;  that  is  to  say,  after  the  application  of 
a  stimulus,  a  second  stimulus  will  not  cause  a  second  contraction 


256  PHYSIOLOGY   OF   THE   HEART  [CH.  XX. 

until  after  the  lapse  of  a  certain  interval  called  the  refractory  period. 
The  refractory  period  lasts  as  long  as  the  contraction  period.  The 
third  difference  depends  on  the  second,  and  consists  in  the  fact  that 
the  heart  muscle  can  never  be  thrown  into  complete  tetanus  by  a  rapid 


Fic.  262. — Staircase  from  frog's  heart.  This  was  obtained  from  a  Stannius  preparation;  an  induction 
shock  being  sent  into  it  with  every  revolution  of  the  cylinder  (rapid  rate).  The  contractions 
became  larger  with  every  beat.    To  be  read  from  right  to  left. 

series  of  stimulations ;  with  a  strong  current  there  is  a  partial  fusion 
of  the  beats,  but  this  is  entirely  independent  of  the  rate  of  faradisa- 
tion. Indeed,  as  a  rule,  the  heart  responds  by  fewer  beats  to  a  rapid 
than  to  a  slow  rate  of  stimulation. 

In  spite  of  these  differences  there  are  many  and  important  re- 
semblances between  heart  muscle  and  voluntary  muscle. 

The  thermal  and  chemical  changes  are  similar ;  there  is  a  using- 
up  of  oxygen  and  a  production  of  carbonic  acid  and  sarco-lactic  acid. 
The  using-up  of  oxygen  was  well  illustrated  by  an  experiment  of 
Yeo's.  He  passed  a  weak  solution  of  oxy-haemoglobin  through  an 
excised  beating  frog's  heart,  and  found  that  after  it  had  passed 
through  the  heart,  the  solution  became  less  oxygenated  and  venous 
in  colour. 

The  electrical  changes  are  also  similar,  and  have  already  been 
dwelt  upon  in  Chapters  XII.  and  XIV. 

Instruments  for  Studying  the  Excised  Heart. 

If  a  frog's  heart  is  simply  excised  and  allowed  to  remain  without 
being  fed,  it  ceases  to  beat  after  a  time  varying  from  a  few  minutes 
to  an  hour  or  so ;  but  if  it  is  fed  with  a  nutritive  fluid,  it  will  continue 
to  beat  for  many  hours.  A  very  good  nutritive  fluid  is  defibrinated 
blood  diluted  with  twice  its  volume  of  physiological  saline  solution. 
Einger  has,  however,  shown  that  nearly  as  good  results  are  obtained 
with  physiological  saline  solution  to  which  minute  quantities  of 
calcium  and  potassium  salts  have  been  added ;  in  other  words,  the 
inorganic  salts  of  the  blood  will  maintain  cardiac  activity  for  a  time 
without  the  addition  of  any  organic  material.  Howell  has  shown 
that  such  an  inorganic  mixture  is  especially  efficacious  in  throwing 


CH.  XX.] 


ROYS   TONOMETER 


257 


the  sinus  or  venous  end  of  the  heart  into  rhythmical  action.  The 
normal  stimulus  for  the  starting  of  the  heart-heat  is  therefore  to  be 
sought  in  the  mineral  constituents  of  the  Mood.  These  mineral 
constituents  in  solutions  are  broken  up  into  their  constituent  ions ; 
and  of  these  the  sodium  ions  are  the  most  potent  in  producing 
rhythmical  activity.     (Loeb.) 

The  fluid  is  passed  through  the  heart  by  means  of  a  perfusion 
cannula  (fig.  263).  The  heart  is  tied  on  to  the  end  of  the  cannula; 
the  fluid  enters  by  one  and  leaves  by  the  other  tube.  Numerous 
instruments  have  been  devised  for  obtaining  graphic  records  of  the 
heart's  movements  under  these  circumstances,  but  we  shall  be  content 
with  describing  a  few  of  the  best.  They  have  been  much  used  in  the 
investigation  of  the  effects  of  drugs  on  the  heart,  and  the  results 
obtained  have  been  of  much  service  to  physicians. 

(1)  The  heart  having  been  securely  tied  on  to  the  perfusion  cannula,  the 
circulating  fluid  is  passed  through  it.  One  stem  of  the  cannula  is  then  attached 
by  the  small  side  branch  on  the  left  in  fig.  263  by  a  tube  containing  salt  solution  to 
a  small  mercurial  manometer,  provided  with  a  float,  on  the  top  of  which  is  a  writing 
style.     The  apparatus  is  arranged  so  that  the  movements  of  the  mercury  can  be 


Fig.  263. — Kronecker's  Perfusion 
Cannula,  for  supplying  fluids 
to  the  interior  of  the  frog's 
heart. 

It  consists  of  a  double  tube, 
one  outside  the  other.  The  inner 
tube  branches  out  to  the  right; 
thus,  when  the  ventricle  is  tied 
to  the  outer  tube  of  the  cannula, 
a  current  of  liquid  can  be  made 
to  pass  into  the  heart  by  one  tube 
and  out  through  the  other. 


Fio.  264 


Tonometer. 


recorded  by  the  float  and  the  writing  style  on  a  slowly  revolving  drum.     The  move- 
ments of  the  mercury  are  due  to  changes  in  the  intracardiac  pressure. 

(•2)  Roifa  Tonometer  (fig.  264) :  A  small  bell-jar,  open  above,  but  provided  with 
a  firmly  fitting  stopper,  in  which  is  fixed  a  double  cannula,  is  adjustable  by  a 
smoothly  ground  base  upon  a  circular  brass  plate,  about  2  to  3  inches  in  diameter. 
The  junction  is  made  complete  by  greasing  the  base  with  lard.  In  the  plate,  which 
is  fixed  to  a  stand  adjustable  on  an  upright,  are  two  holes,  one  in  the  centre,  a  large 

R 


258  PHYSIOLOGY   OF   THE    HEART  [CII.  XX. 

one  about  one-third  of  an  inch  in  diameter,  to  which  is  fixed  below  a  brass  grooved 
collar,  about  half  an  inch  deep  ;  the  other  hole  is  the  opening  into  a  pipe  provided 
with  a  stop-cock.  The  opening  provided  with  the  collar  is  closed  at  the  lower  part 
with  a  membrane,  which  is  closely  tied  by  means  of  a  ligature  around  the  groove 
at  the  lower  edge  of  the  collar.  To  this  membrane  a  piece  of  cork  is  fastened  by 
sealing-wax,  from  which  passes  a  wire,  which  is  attached  to  a  lever  (cut  short  in 
the  diagram)  fixed  on  a  stage  below  the  ajiparatus. 

When  using  the  apparatus,  the  bell-jar  is  filled  with  olive-oil.  The  heart  of  a 
large  frog  is  prepared  and  the  cannula  fixed  in  the  stopper  is  firmly  tied  into  it; 
the  tubes  of  the  cannula  communicate  with  the  reservoir  of  circulating  fluid  on  the 
one  hand,  and  with  a  vessel  to  receive  it  after  it  has  rim  through  the  heart  on  the 
other.  The  cannula  with  heart  attached  is  passed  into  the  oil,  and  the  stopper 
firmly  secured.  Every  time  the  heart  enlarges,  the  membrane  is  pressed  down  ; 
every  time  the  heart  contracts  the  membrane  is  pulled  up  ;  the  lever  follows  and 
magnifies  these  movements.  The  lever  is  adjusted  to  a  convenient  elevation  and 
allowed  to  write  on  a  moving  drum.  After  a  short  time  the  heart  may  stop  beating  ; 
hut  two  wires  are  arranged,  the  one  in  the  cannula,  the  other  projecting  from  the 
jilate  in  such  a  way  that  the  heart  can  be  moved  against  them  by  shifting  the  posi- 
tion of  the  bell-jar  a  little.  The  wires  act  as  electrodes,  and  can  be  made  to  com- 
municate with  an  induction  apparatus,  so  that  induction  shocks  can  be  sent  into 
the  heart  to  produce  contractions.  After  a  time  the  heart  ceases  to  beat  altogether  ; 
and  before  doing  so  it  becomes  irregular.  A  frequent  form  of  irregularity  seen  con- 
sists of  groups  of  contractions  each  showing  a  staircase,  separated  by  long  intervals  of 
quiescence  (Luciani's  Groups). 

(3)  Schafers  Hecvt-plethj/smof/raph. — The  principle  of  this  apparatus  is  the 
same  as  Roy's.  A  diagrammatic  sketch  of  it  is  given  in  fig.  265.  The  heart,  tied 
on  to  a  double  cannula,  is  inserted  into  an  air-tight  vessel  containing  oil.  On  one 
side  of  the  vessel  is  a  tube,  in  which  a  lightly  moving  piston  is  fitted  ;  to  this  a 


Fig.  ii'ij. — Schiifer's  Heart-plethysmogra] 


writing-point  is  attached.  The  piston  is  moved  backwards  and  forwards  by  the 
changes  of  volume  in  the  heart  causing  the  oil  to  alternately  recede  from  and  pass 
into  this  side  tube.  The  corresponding  tube  on  the  other  side  can  be  opened  and 
the  tube  with  the  piston  closed  when  one  wishes  to  cease  recording  the  movements. 
(4)  In  order  to  obtain  a  beating  heart  after  excising  it  from  a  mammal,  the 
following  procedure  should  be  adopted.  A  rabbit  is  killed  by  bleeding  or  pithing ; 
the  heart  enclosed  in  the  pericardium  is  then  quickly  cut  out,  and  gently  kneaded 
to  free  it  from  blood,  in  some  warm  Ringer's  solution.  The  pericardium  is  then 
dissected  off,  and  a  cannula  tied  into  the  aorta  ;  this  is  connected  to  a  burette  which 
is  kept  full  of  Ringer's  solution.  The  Ringer's  solution  must  be  maintained  at  body 
temperature,  by  a  warm  water  jacket,  and  must  be  well  oxygenated  by  letting  oxygen 
bubble  through  it.  The  fluid  is  then  allowed  to  flow,  and  it  enters  the  coronary 
arteries,  and  escapes  from  the  right  auricle,  which  should  be  freely  opened.  Under 
these  circumstances  the  heart  will  continue  to  beat  for  many  hours,  especially  if  a 
little  dextrose  is  added  to  the  circulating  fluid.  A  graphic  record  may  be  obtained 
by  putting  a  small  hook  into  the  apex,  and  attaching  this  by  a  thread  to  a  recording 
lever  beneath  it.  A  very  good  illustration  of  the  usefulness  of  the  method  for 
demonstrating  the  action  of  drugs  consists  in  adding  a  small  amount  of  chloroform 
to  the  circulating  fluid,  and  one  notices  its  immediate  depressant  effect ;  on  the  other 
hand,  a  minute  dose  of  adrenaline  markedly  increases  the  rate  and  force  of  the  heart. 


CHAPTEK  XXI 

THE    CIliCULATION    IN    THE   BLOOD-VESSELS 

The  movement  of  the  blood  from  the  heart  through  the  arteries, 
capillaries,  and  veins  back  to  the  heart  again,  depends  on  a  number 
of  physical  factors;  and  in  the  consideration  of  this  important  subject 
we  shall  have  to  take  into  account  the  general  laws  which  regulate 
the  movement  of  fluids  in  tubes,  as  well  as  their  special  application 
to  the  flow  of  the  blood  in  the  blood-vessels. 

The  contraction  of  the  heart  is  the  primary  propelling  force,  and 
the  increase  of  pressm-e  which  is  thus  communicated  to  the  blood  it 
contains  causes  that  blood  to  enter  the  arteries ;  the  arterial  blood 
pressure  is  higher  than  that  in  the  capillaries,  and  the  capillary 
pressure  is  higher  than  that  in  the  veins;  the  venous  pressure 
gradually  falls  as  we  approach  the  heart ;  it  is  lowest  of  all  in  the 
heart  cavities  during  diastole  ;  fluid  moves  in  the  direction  of  lower 
pressure,  hence  the  flow  of  blood  is  from  the  heart  through  the 
vessels  back  to  the  heart  again. 

The  vessels  are  not  rigid  tubes,  but  possess  marked  elasticity ;  it 
is  owing  to  this  that  the  intermittent  force  of  the  heart  is  modified 
in  such  a  way  that  the  stream  of  blood  in  the  capillaries  is  a  constant 
one,  and  under  normal  circumstances  exhibits  no  pulsation  ;  the  pulse 
is  one  of  the  main  characters  of  the  arterial  flow.  A  further  com- 
plication is  due  to  the  fact  that  the  vessels  through  which  the  blood 
flows  are  of  varying  calibre,  and  this  is  the  main  factor  in  determin- 
ing its  velocity.  Every  time  an  artery  divides,  the  united  sectional 
area  of  its  branches  is  greater  than  that  of  the  parent  artery,  although, 
of  course,  each  of  the  individual  branches  is  of  smaller  calibre.  The 
total  bed  of  the  stream  is  thus  becoming  greater,  until  when  we 
reach  the  capillaries  the  bed  is  increased  suddenly  and  enormously, 
being  several  hundred  times  greater  than  that  of  the  aorta  from 
which  they  all  ultimately  spring.  In  the  case  of  the  veins  the  same 
is  true  in  the  reverse  direction ;  the  sectional  area  of  a  vein  is  less 
than  that  of  the  total  sectional  area  of  its  tributaries ;  hence  as  we 

259 


260  THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CH.  XXL 

approach  the  heart  the  total  bed  of  the  stream  is  becoming  continually 
smaller,  but  never  so  small  as  in  the  corresponding  arteries ;  a  vein 
is  always  twice  the  size,  often  more  than  twice  the  size  of  the  cor- 
responding artery.  Velocity  of  flow  varies  inversely  with  the  bed 
of  the  stream,  the  velocity  is  therefore  greatest  in  the  aorta,  slows 
down  in  the  small  arteries,  and  becomes  slowest  of  all  in  the  capil- 
laries where  the  total  bed  is  widest ;  we  may  compare  the  combined 
capillaries  to  a  vast  lake  into  which  the  arterial  river  flows.  On 
leaving  the  capillaries,  the  blood,  in  traversing  the  veins  once  more, 
becomes  accelerated  because  the  bed  of  the  stream  becomes  narrower, 
but  its  speed  in  a  vein  is  only  about  half  that  in  the  corresponding 
artery  because  the  bed  is  twice  as  great. 

In  connection  with  the  variation  in  the  bed  of  the  stream  we 
must  also  consider  the  question  of  resistance.  If  the  increase  in 
sectional  area  took  place  without  division  of  the  stream  into  numerous 
branches,  the  main  effect  would  be  to  lower  resistance  to  the  flow  of 
fluid ;  but  the  friction-lowering  effect  of  increased  area  is  much  more 
than  counterbalanced  by  the  increased  surface  of  the  numerous 
branches,  and  there  is  increased  friction  on  this  account.  The  resist- 
ance of  the  capillaries  would  be  large  even  for  a  stream  of  water, 
and  when  we  consider  that  the  blood  is  much  more  viscid  than  water, 
we  see  the  effect  must  be  much  greater.  The  resistance  to  the  flow 
of  fluid  along  a  small  tube  is  in  inverse  proportion  to  the  fourth 
power  of  the  diameter,  i.e.,  if  the  diameter  of  the  tube  is  halved,  the 
resistance  is  increased  sixteen-fold.  Between  the  arteries  and  the 
capillaries  are  the  small  arteries  or  arterioles;  these  vessels  are 
always  in  a  state  of  moderate  or  tonic  constriction ;  they  may  roughly 
be  compared  to  narrow  inlets  into  the  wide  capillary  lake.  The 
main  resistance  to  the  passage  of  blood  through  the  tissues  is  situated 
in  the  arterioles,  and  not  in  the  capillaries ;  this  is  usually  spoken 
of  as  the  peripheral  resistance,  and  it  is  variable  by  alterations  in  the 
calibre  of  the  arterioles,  their  muscular  tissue  being  under  the  control 
of  nerves  which  are  termed  vaso-motor. 

The  main  resistance  is  in  the  arterioles  and  not  in  the  capillaries 
for  the  following  reason :  each  individual  capillary  is  small,  and  its 
resistance  therefore  great,  but  their  number  is  so  immense,  and  the 
tqtal  bed  so  large  that  the  resultant  resistance  offered  is  com- 
paratively small.  This  is  well  brought  out  by  a  comparison  of  the 
velocity  in  the  two  cases ;  in  the  arterioles  the  velocity  has  to  be 
high  in  order  to  supply  with  blood  the  large  capillary  areas  spring- 
ing from  them;  in  the  capillaries,  as  we  have  already  seen,  the 
velocity  is  low. 

After  this  general  account  of  the  main  features  of  the  circulation, 
we  can  now  pass  to  a  detailed  description  of  the  various  points 
raised. 


en.  XXI.]  ELASTICITY   OF   THE    RLOOD-VESSELS  261 

Use  of  the  Elasticity  of  the  Vessels. 

If  a  pump  is  connected  to  a  rigid  tube,  such  as  a  glass  tube, 
filled  witii  water,  and  a  certain  amount  of  water  is  forced  into  the 
tube,  an  exactly  equal  amount  of  water  is  driven  out  from  the  open 
end.  During  the  intervals  of  pumping  the  flow  ceases,  accurately  at 
the  instant  the  inflow  stops.  If  in  the  next  place  the  open  orifice  is 
constricted  and  the  pumping  continued  as  before,  the  outflow  is  still 
restricted  to  the  time  during  which  water  is  being  driven  into  the 
tube.  The  only  difference  is  that  a  greater  force  of  pumping  will  be 
required  if  the  pump  is  to  empty  itself  in  the  same  time  as  before, 
and  the  force  required  will  increase  in  proportion  to  the  degree  of 
constriction  of  the  orifice,  until  with  a  fairly  considerable  constriction 
the  force  required  will  be  enormous. 

If  the  rigid  tube  is  replaced  by  an  elastic  one  with  a  wide  free 
opening,  the  outflow  will  again  be  intermittent  but  not  quite  restricted 
to  the  time  of  the  pumping.  This  latter  difference  is  because  the 
elastic  wall  of  the  tube  will  stretch  a  little  at  each  output  of  the 
pump,  and  this  continues  after  the  pump  has  ceased  to  discharge,  and 
will  then  recover,  at  the  same  time  driving  out  the  extra  small  amount 
of  fluid  it  contained,  after  the  pump  has  ceased  to  act.  The  flow  will 
thus  be  intermittent,  but  the  outflow  will  last  for  a  short  time 
longer  than  the  inflow.  This  persistence  will  increase  with  the 
resistance  of  the  tube,  with  the  velocity  of  the  inflow,  and  lastly  with 
the  mass  of  the  column  of  fluid  lying  in  the  tube.  If  now  the 
orifice  be  diminished,  the  duration  of  the  outflow  will  begin  to 
increase  still  further,  and,  as  the  constriction  is  increased  more  and 
more,  will  gradually  extend  over  the  diastolic  period  of  the  pumping. 
The  amount  of  work  required  to  drive  the  fixed  volume  of  fluid 
through  the  constricted  orifice  is  the  same  with  a  rigid  and  with  an 
elastic  tube.  In  the  former  case,  however,  the  duration  of  the  out- 
flow is  of  necessity  the  same  as  that  of  the  inflow,  whereas  in  the 
second  case  this  time  is  prolonged.  Consequently  the  rate  of  working 
in  the  first  case  must  exceed  that  in  the  second  in  proportion  to  this 
difference  of  time,  or  the  maximum  pressure  set  up  in  the  former 
case  is  far  greater  than  in  the  latter.  If  the  constriction  of  the 
orifice  of  the  elastic  tube  is  still  further  increased,  a  point  is  at  last 
reached  at  which  the  outflow  lasts  throughout  the  whole  cycle  of  the 
pump,  and  here  therefore  the  energy  imparted  to  the  fluid  by  the 
pump  is  converted  into  a  pressure  energy  represented  by  the  tension 
of  the  elastic  walls  of  the  tube,  and  this  energy  is  given  out  again 
after  the  fluid  has  ceased  to  enter  the  tube  and  is  just  sufficient  to 
exactly  drive  out  the  stored  fluid  during  the  resting  period.  If  the 
constriction  be  carried  still  further,  the  tube  will  not  be  able  to  empty 
itself  during  the  diastolic  period,  and  when  the  second  inflow  begins, 


262  THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CII.  XXI. 

some  of  the  fluid  will  Le  still  distending  the  tube,  i.e.,  the  pressure 
will  not  have  fallen  to  zero.  With  the  second  inflow  the  maximum 
pressure  reached  will  be  higher  than  before,  but  still  the  force  acting 
throughout  the  whole  of  the  cycle  may  not  be  sufficient  to  empty  the 
tube  to  the  extent  found  at  the  commencement  of  that  inflow,  and  we 
may  find  a  further  volume  of  fluid  retained  within  the  tube,  and  the 
pressure  just  before  the  next  inflow  still  higher  than  in  the  preceding 
instance.  This  summation  will  continue,  until  at  last  a  point  is 
reached  at  which  the  mean  pressure  during  a  complete  cycle  will  Ije 
just  sufficient  to  drive  out  exactly  the  same  volume  of  fluid  as  is  sent 
in  at  each  pumping.  When  this  point  is  reached,  the  pressure  will 
simply  oscillate  about  this  mean  position,  and  the  outflow  from  the 
tube  will  therefore  be  continuous,  but  not  necessarily  constant.  If 
we  still  further  constrict  the  orifice,  the  result  is  that  the  mean 
pressure  will  rise  still  further,  and  the  outflow  will  be  of  a  less 
remittent  character.  The  latter  because  the  input  of  the  same 
volujne  of  fluid  into  the  distended  tube  will  produce  less  marked 
fluctuations  in  the  driving  pressure,  since  at  the  end  of  diastole  the 
pressure  still  driving  the  fluid  will  be  high  and  nor  nearly  zero,  as  in 
the  former  instance.  If  the  constriction  is  sufficiently  increased,  a 
point  will  ultimately  be  reached  at  which  the  outflow  will  become 
not  only  continuous  but  also  constant.  The  degree  of  constriction 
necessary  to  produce  this  effect  will  depend  upon  the  distensibility 
of  the  elastic  tube.  The  more  distensible  this  is,  the  earlier  will  this 
stage  be  reached,  and  the  lower  will  be  the  mean  pressure.  This  is 
the  condition  we  find  in  the  circulatory  system. 

Let  us  now  apply  this  to  the  body. 

At  each  beat  the  left  ventricle  forces  about  three  ounces  of  blood 
into  the  already  full  arterial  system.  The  arteries  are  elastic  tubes, 
and  the  amount  of  elastic  tissue  is  greatest  in  the  large  arteries. 
The  first  effect  of  the  extra  three  ounces  is  to  distend  the  aorta  still 
further ;  the  elastic  recoil  of  the  walls  drives  on  another  portion  of 
blood,  which  distends  the  next  section  of  the  arterial  wall,  and  this 
distension  is  transmitted  as  a  wave  along  the  arteries,  but  with 
graduallv  diminishins:  force  as  the  total  arterial  stream  becomes 
larger.  This  wave  constitutes  the  pulse-wave.  Between  the  strokes 
of  the  pump,  or,  in  other  words,  during  the  periods  of  diastole,  the 
arteries  drive  the  blood  on  and  so  return  to  their  original  size.  The 
flow,  therefore,  does  not  cease  during  the  heart's  inactivity,  so  that 
although  the  force  of  the  heart  is  an  intermittent  one,  the  flow 
through  the  capillaries  and  -the  veins  beyond  is  a  constant  one,  all 
trace  of  pulsation  having  disappeared.  The  peripheral  resistance 
which  keeps  up  the  blood-pressure  in  the  arteries,  and  like  the  con- 
striction at  the  end  of  our  india-rubber  tube,  assists  in  the  conversion 
of  the  intermittent  into  a  continuous  and  constant  stream,  is  to  be 


CII.  XXI.] 


BLOOD-PRESSURE 


263 


found  in  the  arterioles  or  small  arteries,  just  before  the  blood  passes 
into  what  we  have  termed  the  vast  capillary  lake.  These  small 
arteries  with  their  relative  excess  of  muscular  tissue,  are  in  health 
always  in  a  state  of  moderate  tonic  contraction. 

The  large  arteries  contain  a  considerable  amount  of  muscular  as 
well  as  elastic  tissue.  This  co-operates  with  the  elastic  tissue  in 
adapting  the  calibre  of  the  vessels  to  the  quantity  of  blood  they 
contain.  For  the  amount  of  blood  in  the  vessels  is  never  quite 
constant,  and  were  elastic  tissue  only  present,  the  pressure  exercised 
by  the  walls  of  the  containing  vessels  on  the  contained  blood  would 
be  sometimes  very  small,  sometimes  too  great.  The  presence  of  a 
contractile  element,  however,  provides  for  a  certain  uniformity  in  the 
amount  of  pressure  exercised.  There  is  no  reason  to  suppose  that 
the  muscular  coat  assists  in  propelling  the  onward  current  of  blood, 
except  in  virtue  of  the  fact  that  muscular  tissue  is  elastic,  and  there- 
fore co-operates  in  the  large  arteries  with  the  elastic  tissue  in  keeping 
up  the  constant  flow  in  the  way  already  described. 

The  contractility  of  the  arterial  walls  fulfils  a  useful  purpose  in 
checking  haemorrhage  should  a  small  vessel  be  cut,  as  it  assists  in  the 
closure  of  the  cut  end,  and  this  in  conjunction  with  the  coagulation 
of  the  blood  arrests  the  escape  of  blood. 


Blood-pressure. 

The  circulation  of  the  blood  depends  on  the  existence  of  different 
degrees  of  pressure  in  different  parts  of  the  circulatory  system ; 
there  is  a  diminution  of  pressure  from  the  heart  onwards  through 
arteries,  capillaries,  and  ^-eins,  back  to  the  heart  again. 


Fig.  266.— Height  of  blood-pressure  (bp)  in  lv,  left  ventricle,    a,  arteries ;  c,  capillaries  ;  v,  veins  ;  ra, 
right  auricle  ;  oo,  line  of  no  pressure.    (After  Starling.) 

Fig.  266  represents  roughly  the  fall  of  pressure  along  the  systemic 
vascular  system. 

It  falls  slowly  in  the  great  arteries ;  at  the  end  of  the  arterial 
system  it  falls  suddenly  and  extensively  in  the  course  of  the 
arterioles ;  it  again  falls  gradually  through  the  capillaries  and  veins 
till  in  the  large  veins  near  the  heart  it  is  negative.     Such  a  diagram 


264  THE   CIRCULATION   IN   THE '  BLOOD-VESSELS  [CH.  XXL 

of  blood-pressure  is  thus  very  different  from  one  of  velocity;  the 
velocity  like  the  pressure  falls  from  the  arteries  to  the  capillaries, 
but  unlike  it,  rises  again  in  the  veins. 

We  must  now  study  the  methods  by  which  blood-pressure  is 
measured  and  recorded,  and  the  main  causes  that  produce  variations 
in  its  amount. 

In  order  that  we  may  understand  the  methods  that  are  used  for 
this  purpose,  it  v»ill  be  first  necessary  for  us  to  consider  some  of  the 
general  laws  of  fluid  pressure,  and  then  to  study  the  methods  that 
are  employed  in  an  artificial  schema  of  the  circulation. 

Fluid  pressure  is  a  different  thing  from  the  pressure  of  a  solid, 
and  is  exercised  equally  in  all  directions.  If  a  cylindrical  vessel, 
placed  vertically,  is  filled  with  a  cylinder  of  ice,  the  pressure  of  the 
ice  will  be  exercised  on  the  bottom  of  the  cylinder,  but  not  on  its 
sides.  When  the  ice  melts,  the  water  presses  on  the  sides  also,  and 
if  a  hole  is  made  in  the  cylinder  below  the  level  of  the  upper  surface 
of  the  water,  the  water  will  flow  out  of  the  hole,  and  the  force  with 
which  it  escapes  will  be  proj)ortional  to  the  depth  of  the  hole  beneath 
the  surface.  If  we  take  a  square  centimetre  as  the  unit  of  area,  the 
actual  pressure  excited  onitis  hxdxg,  where  h  is  the  height  of  the 
free  surface  above  the  level  where  we  are  measuring  the  pressure,  d 
its  density,  and  g  the  acceleration  of  gravity  (981).  Suppose  a 
gramme  of  water  to  flow  out,  we  may  consider  that  this  gramme  has 
fallen  through  a  height  or  head  h  in  centimetres  from  the  free  surface 
to  the  opening ;  it  comes  practically  from  the  top,  because  it  is  there 
that  the  liquid  disappears  from  inside  the  vessel.  In  falling  the 
height  h,  it  gives  out  hg  ergs  of  work. 

The  unit  of  force  is  called  a  di/ne  ;  a  moving  body  is  said  to  possess 
viomentum  :  this  is  measured  by  the  product  of  its  mass  and  its  velocity  ;  thus  the 
eifective  quantity  of  motion  of  a  body  may  be  large  on  account  of  its  having  a  large 
mass  (for  instance,  a  heavy  waggon  rolling  down  a  hill),  or  large  velocity  (for  instance, 
a  bullet  speeding  through  the  air).  A  force  continuously  applied  to  a  moving  mass 
produces  a  continuous  increase  in  its  rate  of  movement ;  this  is  termed  acceleration, 
and  force  may  be  defined  as  the  rate  of  change  of  momentum  ;  it  can  be  measured, 
therefore,  by  observing  the  amoimt  of  momentum  it  generates  in  a  measured  time, 
and  dividing  by  that  time.  If  a  gramme  is  taken  as  the  unit  of  mass,  a  centimetre 
as  the  unit  of  length,  and  a  second  as  the  unit  of  time,  the  unit  of  force 

=  momentum  =  gramme-centimetre  per  second 
Time.  Time  in  seconds. 

—  gramme-centimetre  per  second,  per  second  =  1  dyne. 

The  unit  which  corresponds  to  the  dyne  in  the  measurement  of  work  is  called  an 
e.rg,  that  is,  the  work  done  in  lifting  a  gramme  weight  through  the  height  of  one 
centimetre ;  the  weight  of  a  gramme  is  981  dynes,  and  the  work  done  in  lifting  it 
one  centimetre  is  981  ergs. 

The  kinetic  energy  of  a  body  moving  with  velocity  -z;  is  J  x  mass 
X  v^,  or  for  one  gramme  i  v"- ;  hence  if  all  the  work  that  liquid  can  do 
is  spent  in  giving  kinetic  energy  to  it,  the  velocity  with  which  it  will 


CH.  XXl] 


FLUID   PRESSURE 


265 


flow  out  is  given  l)y  putting  the  kinetic  energy  =  work  done.     In 
other  terms : — 

]v-  =  g/i ;  hence  r  =  J2gh  or  /'  =  ^ 

A  lii|uiJ,  however,  has  not  necessarily  a  free  surface,  but  may  be 
completely  enclosed,  as  is  the  water  in  a  system  of  hydraulic  pressure 
mains,  or  the  blood  in  the  circulatory  system.  The  pressure  in  such 
a  system  at  any  point  may  be  measured  by  inserting  at  that  point 
a  vertical  tube  at  right  angles  to  the  blood-vessel ;  the  blood  would 
rise  in  it  to  a  point,  and  would  form  a  free  surface  a  certain  distance 
up  this  tube ;  the  head  h  in  the  above  calculation  must  be  reckoned 


Fig.  267. — Schema  to  illustrate  blood-pressure. 

from  this  free  surface  downwards.  If,  instead  of  using  a  tube  of  fine 
bore  for  this  purpose,  we  employ  a  wider  tube,  say  of  ten  times 
greater  area,  the  height  or  head  to  which  the  fluid  rises  will  be  the 
same  as  in  the  narrow  tube,  though  naturally  the  actual  weight  of 
fluid  supported  will  be  ten  times  greater ;  but  the  weight  per  unit  of 
area  is  the  same  in  both  cases.  When,  therefore,  we  measure  the 
pressure  of  fluid  in  terms  of  the  height  of  a  column  of  fluid,  like 
mercury,  which  it  will  balance,  we  really  mean  that  the  force  of  the 
blood  is  equal  to  the  weight  of  the  mercury  it  supports  per  unit  of 
area,  and  this  will  naturally  be  proportional  to  the  height  of  the 
column. 

Let  us  next  consider  the  simple  case  of  a  fluid  flowing  from  a 
reservoir,  E  (fig.  267),  along  a  tube,  which  we  will  imagine  is  open  at 
the  other  end. 


2G6  THE    CIRCULATION    IN    THE    BLOOD-VESSELS  [CIl.  XXI. 

Ill  the  course  of  the  tube  we  will  suppose  three  upright  glass 
tubes  (A,  B,  and  D)  are  inserted  at  equal  distances.  Between  B  and 
D  there  is  a  bladder,  which  may  be  divided  into  a  number  of  channels 
by  packing  it  with  tow  to  represent  the  capillaries,  and  between  B  and 
C,  a  clip  E,  which  can  be  tightened  or  loosened  at  will,  and  which 
will  roughly  represent  the  peripheral  resistance  produced  by  the 
arterioles.  The  far  end  of  the  tube  is  provided  with  a  stop-cock.  If 
this  stop-cock  is  closed  there  will  naturally  be  no  flow  of  fluid,  and 
the  fluid  will  rise  to  equal  heights  indicated  by  the  dotted  line  in  all 
the  upright  tubes.  This  shows  that  the  pressure  in  all  parts  of  the 
tube  is  the  same.  The  upright  tubes  which  measure  the  lateral 
pressure  exerted  by  the  fluid  on  the  wall  of  the  main  tube,  are  called 
pizometers,  manojneters,  oy  pressure  measurers. 

If  now  the  stop-cock  is  opened,  the  fluid  flows  on  account  of  the 
difference  of  pressure  brought  about  by  gravitation ;  the  height  of  the 
fluid  in  the  manometers  indicates  that  the  pressure  is  greatest  in  R, 
less  in  A,  less  still  in  B,  and  least  of  all  in  D. 

On  account  of  the  peripheral  resistance  of  the  arterioles  and 
capillaries,  the  pressure  is  very  small  in  the  veins,  as  indicated  by  the 
height  of  the  fluid  in  the  manometer  D.  The  difference  between  D 
and  B  is  much  more  marked  than  the  difference  between  B  and  A. 
If  the  fluid  which  flows  out  of  the  end  of  the  tube  is  collected  in  a 
jug  and  poured  back  into  R,  we  complete  the  circulation.  But  the 
schema  is  an  extremely  rough  one,  and  is  especially  faulty  in  that  the 
pressure  which  starts  at  R  is  nearly  constant  and  not  intermittent. 
This  may  be  remedied  by  taking  R  in  the  hand,  and  raising  and  lower- 
ing it  alternately.  The  fluid  in  the  manometers  bobs  up  and  down 
with  every  rise  and  fall  of  R :  this  is  least  marked  in  D.  The  greater 
and  the  faster  the  movement  of  R,  the  greater  is  the  rise  of  arterial 
pressure.  This  is  a  rough  illustration  of  the  fact  that  increase  in 
the  force  and  frequency  of  the  heart's  beat  causes  a  rise  of  arterial 
pressure. 

Again,  if  more  fluid  is  poured  into  R,  there  is  a  correspond- 
ing rise  in  fluid  in  the  manometers.  This  illustrates  the  rise  of 
pressure  produced  by  an  increase  in  the  contents  of  the  vascular 
system. 

And  this  schema,  rough  though  it  is,  also  serves  to  illustrate  the 
third  important  factor  in  the  maintenance  of  the  blood-pressure, 
namely,  the  peripheral  resistance.  This  is  done  by  means  of  the  clip 
E ;  if  the  clip  is  tightened,  one  imitates  increased  constriction  of  the 
arterioles ;  if  it  is  loosened,  one  imitates  dilatation  of  the  arterioles. 
If  it  is  closed  entirely,  the  fluid  in  A  and  B  rises  to  the  same  level  as 
that  in  R ;  the  pressure  of  R  is  not  felt  at  all  by  C  and  D,  which 
empty  themselves,  and  the  flow  ceases.  If  the  clip  E  is  only  tightened 
so  as  not  to  be  quite  closed,  the  arterial  pressure  (in  A  and  B)  rises, 


CU.   XXI.] 


sen  KM  A  OF  THE  CIRCULATION 


2G7 


and  the  venous  pressure  (in  D)  falls ;  if  the  clip  is  freely  opened,  the 
arterial  pressure  falls,  and  the  venous  pressure  rises. 

These  same  facts  can  be  demonstrated  by  a  more  perfect  circula- 
tion schema,  such  as  is  represented  in  fitj.  268. 

The  heart  (H)  is  represented  by  a  Higginson's  syringe,  which  is 
worked  with  the  hand  ;  the  tube  from  it  represents  the  arterial  system, 
the  clip  E  the  resistance  of  the  arterioles ;  C  is  the  capillary  lake, 
from  which  the  vein  (larger  than  the  artery)  leads  back  to  the  heart 
H.  A  and  B  are  two  manometers  which  respectively  indicate  arterial 
and  venous  pressures.  Only  in  place  of  straight  tubes  mercurial 
manometers  are  used.  Each  of  these  is  a  [J -tube  about  half  filled 
with  mercury,  and  united  to  the  artery  or  vein  by  a  tube  containing 
fluid.     If  the  mercury  in  the  two  limbs  of  the  (J  is  at  the  same  level, 


Fig.  26S. — Schema  of  the  circulation. 


the  pressure  of  the  fluid  in  connection  with  one  limb  is  exactly  equal  to 
that  exerted  by  the  atmospheric  pressure  on  the  other.  The  mercury, 
however,  is  pushed  up  in  the  far  limb  of  the  manometer  connected  to 
the  artery,  the  pressure  there  being  greater  than  that  of  the  atmos- 
phere ;  this  is  therefore  called  positive  pressure,  and  the  total  amount 
of  pressure  is  measured  by  the  difference  between  the  levels  a  and  a'. 
The  manometer  B  attached  to  the  vein,  however,  indicates  a  negative 
pressure  (h  b'),  that  is  a  pressure  less  than  that  of  the  atmosphere,  so 
that  the  mercury  in  the  limb  nearest  the  vein  is  sucked  up. 

Anderson  Stuart's  kymoscope  (fig.  269)  is  a  more  complete  schema. 
It  consists  of  a  long  leaden  tube  filled  with  fluid,  the  two  ends  of 
wliich  are  connected  by  an  india-rubber  tube  on  which  is  a  valved 
syringe  to  represent  the  heart.  On  the  course  of  the  tube  are  a  large 
number  of  open-mouthed  upright  manometers  which  indicate  the  pres- 
sure when  the  syringe  is  worked,  and  confer  on  the  tube  the  elasticity 


2GS 


THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CIL  XXL 


necessary  to  cause  the  disappearance  of  the  pulse  in  the  middle  region 
which  represents  the  capillaries.  The  long  leaden  tube  is  twisted 
round  a  cylinder,  so  that  the  manometers  are  placed  closely  side  by 
side. 

We  can  now  pass  on  to  the  methods  adopted  in  the  investigations 
of  lilood-pressure  in  animals. 

The  fact  that  the  blood  exerts  considerable  pressure  on  the 
arterial  walls  may  be  readily  shown  by  puncturing  any  artery ;  the 
blood  is  propelled  with  great  force  through  the  opening,  and  the  jet 
rises  to  a  considerable  height ;  in  the  case  of  a  small  artery,  where 

the  pressure  is  lower,  the  jet  is  not  so 

^^T'i!M~M'^!!nf!^^  ^^o^  ^^  ^^  ^  ^^^o®  artery:   the  jerky 

■(iinnnlilinniinnnnnnniiiiiiiiiiiliiiiiiiB-'J  character  of  the  outflow  due  to  the 

intermittent  action  of  the  heart  is 
also  seen.  If  a  vein  is  similarly  in- 
jured, the  blood  is  expelled  with  much 
less  force,  and  the  flow  is  continuous, 
not  intermittent. 

The  first  to  make  an  advance  on 
this  very  rough  method  of  demon- 
strating blood-pressure  was  the  Rev. 
Stephen  Hales,  "Vicar  of  Teddington 
(1702).  He  inserted,  using  a  small 
brass  tube  as  a  cannula,  a  glass  tube 
at  right  angles  to  the  femoral  artery 
of  a  horse,  and  noted  the  height  to 
which  the  blood  rose  in  it.  This  is  a 
method  like  that  which  we  used  in 
the  first  schema  described  (fig.  267). 
The  blood  rose  to  the  height  of  about 
8  feet,  and  having  reached  its  highest 
point,  it  oscillated  with  the  heart- 
beats, each  cardiac  systole  causing  a 
rise,  each  diastole  a  fall.  Hales  also 
noted  a  general  rise  during  each  inspiration.  The  method  taught 
Hales  these  primary  truths  in  connection  with  arterial  pressure,  but 
it  possesses  many  disadvantages ;  in  the  first  place,  the  blood  in 
the  glass  tube  very  soon  clots,  and  in  the  second  place,  a  column  of 
liquid  eight  feet  high  is  an  inconvenient  one  to  work  with. 

The  first  of  these  disadvantages  was  overcome  to  a  great  extent 
by  Vierordt,  who  attached  a  tube  filled  with  saturated  solution  of 
sodium  carbonate  to  the  artery,  and  the  blood-pressure  was  measured 
by  the  height  of  the  column  of  this  saline  solution  which  the  blood 
would  support. 

The  second  disadvantage  was  overcome  by  Poiseuille,  who  iutro- 


FiG.  2G9. — Anderson  Stuart': 
Kymoscope. 


cn.  XXI.] 


THE  kymo(;raph 


269 


duced  the  heavy  liquid,  mercury,  as  the  substance  on  which  the  blood 
exerted  its  pressure;  and  the  U-shaped  mercurial  manometer  was 
connected  to  the  artery  by  a  tube  filled  with  sodium  carbonate 
solution  to  delay  clotting. 

The  study  of  blood-pressure  cannot,  however,  be  considered  to 
have  been  in  a  satisfactory  condition  until  the  introduction  by  Carl 
Ludwig  of  the  Kymograph ;  that  is  to  say,  Poiseuille's  hcemodynamo- 
meter  was  coml)ined  with  apparatus  for  obtaining  a  graphic  record 
of  the  oscillations  of  the  mercury.  The  name  kymograph  or  wave- 
writer,  we  shall  see  immediately,  is  a  very  suitable  one. 

A  skeleton  sketch  of  the  apparatus  is  given  in  fig.  270. 


Flo.  270. — Diagram  uf  mercurial  Kymograph. 

The  artery  is  exposed  and  clamped,  so  that  no  haemorrhage 
occurs ;  it  is  then  opened,  and  a  glass  cannula  is  inserted  and  firmly 
tied  in.  The  form  of  cannula  usually  employed  (Franc^ois  Franck's) 
is  shown  on  a  larger  scale  at  A ;  the  narrow  part  with  the  neck  in  it 
is  tied  into  the  artery  towards  the  heart ;  the  cross  piece  of  the  T  is 
united  to  the  manometer;  the  third  limb  is  provided  with  a  short 
piece  of  indiarubber  tubing  which  is  kept  closed  by  a  clip  and  only 
opened  on  emergencies,  such  as  to  clear  out  a  clot  with  a  feather 
should  one  form  in  the  cannula  during  the  progress  of  an 
experiment. 

The  tube  by  means  of  which  the  cannula  is  united  to  the  mano- 
meter is  not  an  elastic  one,  but  is  made  of  flexible  metal,  so  that  none 


270 


THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CIL  XXL 


of  the  arterial  force  may  be  wasted  in  expanding  it.  The  tube, 
cannula,  and  proximal  liml)  of  the  manometer  are  all  filled  with  a 
saturated  solution  of  sodium  carbonate,  sodium  sulphate,  or  other  salt 
which  will  mix  with  blood  and  delay  its  clotting.  Before  the  clip  is 
removed  from  the  artery,  the  pressure  is  first  got  up  by  a  syringe  (or 
pressure  bottle  containing  the  same  saline  solution  suspended  at  a 
good  height  above  the  apparatus  and  connected  to  it  by  a  tube),  so 
that  the  mercury  rises  in  the  distal  limb  to  a  height  greater  than  that 
of  the  anticipated  blood-pressure ;  this  prevents  Ijlood  passing  into 
the  cannula  when  the  arterial  clip  is  removed. 

In  the  distal  limb  of  the  (J't^^^Q)  floating  on  the  surface  of  the 


Fio.  1!71.  -The  manometer  uf  Ludwij;'s  Kymograph.  It  is  also  shown  in  fij;.  272,  d,  v,  e.  The 
mercury  whicli  partially  tills  the  tube  supports  a  float  in  the  form  of  a  piston,  nearly  filling  the 
tube ;  a  wire  is  tixerl  to  the  float,  and  the  writing  style  or  pen  fixed  to  the  wire  is  guided  by  passing 
through  the  brass  cap  of  the  tube;  the  pressure  is  communicated  to  the  mercury  by  means  of  a 
flexible  metal  tube  filled  with  fluid. 


mercury,  is  an  ivory  float,  from  which  a  long  steel  wire  extends 
upwards,  and  terminates  in  a  writing-point.  The  writing-point  may 
be  a  stiff  piece  of  parchment  or  a  bristle  which  writes  on  a  moving 
surface  covered  with  smoked  paper,  or  a  small  brush  kept  full  of  ink 
which  writes  on  a  long  strip  of  white  paper  made  to  travel  by  clock- 
work in  front  of  it.  When  the  two  limbs  of  the  mercury  are  at  rest, 
the  writing-point  inscribes  a  base  line  or  abscissa  on  the  travelling 
surface ;  when  the  pressure  is  got  up  by  the  syringe  it  writes  a  line 
at  a  higher  level.  When  the  arterial  clip  is  removed  it  writes  waves 
as  shown  in  the  diagram  (fig.  270),  the  large  waves  corresponding  to 
respiration   (the   rise   of   pressure   in   most  animals   accompanying 


CII.  XXI. J  THE    KYMOGRAPH  271 

inspiration),*  Lho  sniallor  ones  to  tho  individual  hoait-l)eats.  The 
blood-pvossure  is  really  twice  as  great  as  that  indicated  by  the  height 
of  tho  tracing  above  tho  abscissa,  because  if  tho  nianoniotor  is  of  equal 
bore  throughout,  the  mercury  falls  in  one  limb  tho  same  distance  that 
it  rises  in  the  other;  the  true  pressure  is  measured  by  tho  difference 
of  level  between  a  and  a  (fig.  270). 

Fig.  271  shows  a  more  complete   view  of   the   manometer,  and 


Fig.  272.— Diagram  of  mercurial  Kymograph,  a,  Revolving  cylinder,  worked  by  a  clockwork  arrange- 
ment contained  in  the  box  (b),  the  speed  being  regulated  by  a  fan  above  the  box ;  the  cylinder  is 
supported  by  an  upright  (h),  and  is  capable  of  being  raised  or  lowered  by  a  screw  (re),  by  a  handle 
attached  to  it ;  d,  c,  e,  represent  the  mercurial  manometer,  which  is  shown  on  a  larger  scale  in 
tig.  271. 

fig.  272  is  a  diagram  of  the  arrangement  by  means  of  which  it  is 
made  into  a  kymograph. 

Fig.  273  shows  a  typical  normal  arterial  blood-pressure  tracing  on 
a  larger  scale. 

In  taking  a  tracing  of  venous  blood-pressure,  the  pressure  is  so  low 
and  corresponds  to  so  few  millimetres  of  mercury,  that  a  saline 
solution  is  usually  employed  instead  of  mercury.     If  the  vein  which 

*  The  explanation  of  the  respiratory  curves  on  the  tracing  is  postponed  till 
after  we  have  studied  Respiration. 


272 


THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CH.  XXI. 


is  investigated  is  near  the  heart,  a  venous  pulse  is  exliibited  on  the 
tracing,  with  small  waves  as  before  corresponding  to  heart-beats,  and 


Fli;.  273.  Normal  tracing,  somewb^t  magiiilied,  of  arterial  pressure  in  tlie  rabljit  obtained  with  the 
mercurial  kymograph.  The  smaller  undulations  correspuud  with  the  heart-beats,  the  larger  curves 
with  the  respiratory  movements.  The  abscissa  or  base  line,  which  on  this  scale  would  be  several 
inches  below  the  tracing,  is  not  shown.     (Burdon-Sanderson.) 

laro-er  waves  to  respiration,  only  the  respiratory  rise  in  pressure  now 
accompanies  expiration. 

The  capillary  pressure  is  estimated  Ijy  the  amount  of  pressure 


Fir    •'74  —A  form  of  Kick's  Spring  Kymograph.     «,  Tube  to  be  connected  with  artery ;  c,  hollow  spring, 
"the  movement  of  which  moves  /-,  the  writing  lever;  c,  screw  to  regulate  height  of  fc;  </,  outside 
protective  spring ;  jf,  screw  to  fix  on  the  upright  of  the  support. 

necessary  to  blanch  the  skin  ;  this  has  been  done  in  animals  and  men 
(v.  Kries,  Roy  and  Brown). 

Other  manometers  are  often  employed  instead  of  the  mercurial 
one.  Fick's  is  one  of  these.  The  blood-vessel  is  connected  as  before 
with  the  manometer,  and  the  pressure  got  up  by  the  use  of  a  s}Tinge 


Cll.  XXI.] 


FICK  S    KYMOintAl'll 


273 


(whicii  is  seen  in  fig.  275,  (j),  l)cfuio  the  clip  is  removed  from  the 
artery.  The  manometer  itself  is  a  hollow  C-shapcd  spring  filled  with 
liquid  ;  this  opens  with  increase,  and  closes  with  decrease  of  pressure, 
and  the  movements  of  the  spring  are  communicated  to  a  lever  pro- 
vided with  a  writing-point. 

Hiirthle's  manometer  (see  p.  242)  is  also  very  much  used.     The 
advantage  of  these  forms  of  manometer  is  that  the  character  and 


Fig.  275.— Kick's  Kymograph,  improved  by  Bering  (after  M'Keiifirick).  a,  Hollow  spring  tilled  with 
alcohol,  bearing  lever  arrangement  h,  d,  c,  to  which  is  attached  the  marker  e  ;  the  rod  c  passe.s 
downwards  into  the  tube/,  containing  castor  oil,  which  oflers  resistance  to  the  oscillations  of  c; 
g,  syringe  for  filling  the  leaden  tube  h  with  saturated  sulphate  of  sodium  solution,  and  to  apply 
sufficient  pressure  as  to  prevent  the  blood  from  pa.ssing  into  the  tube  h  at  i,  the  cannula  inserted 
into  the  vessel;  I,  abscissa-marker,  which  can  be  applied  to  the  moving  surface  by  turning  the 
screw  111 ;  k,  screw  for  adjusting  the  whole  apparatus  to  the  moving  surface  ;  o,  screw  for  elevating 
or  depressing  the  Kymograph  by  a  rack-and-pinion  movement;  n,  screw  for  adjusting  the  position 
of  the  tube/. 


extent  of  each  pressure  change  is  much  better  seen.  In  a  mercury 
manometer  the  inertia  is  so  great  that  it  cannot  respond  to  the  very 
rapid  variations  in  pressure  which  occur  within  an  artery  during  each 
cardiac  cycle.  If  Tick's  or  Hiirthle's  manometer  is  employed,  and 
the  surface  travels  sufficiently  fast,  these  can  be  recorded  (see  fig. 
276).  These  instruments,  though  useful  for  recording  the  complete 
changes  in  pressure,  require  calibration :  that  is,  the  extent  of  move- 
ment that  corresponds  to  known  pressures  must  be  ascertained  by 

s 


274  THE   CIRCULATION    IN    THE    BLOOD-VESSELS  [CH.  XXL 

actual  experiment.  They  teach  us  that  the  highest  pressure  reached 
during  systole  may  be  twice  or  thrice  the  lowest  attained  during 
diastole. 


Fig.  276. — Xomial  arterial  tracing  obtained  with  Pick's  Kymograph  in  the  dog. 
(Burdon-Sanderson.) 

The  following  table  gives  the  probable  average  height  of  blood- 
pressure  in  various  parts  of  the  vascular  system  in  man.  They  have 
been  very  largely  inferred  from  experiments  on  animals : — 

T  .     ■      /  i.-j\  I  +  1  to  mm.  (about  6  inches) 

Larsre  arteries  (e.cr-  carotid)       .       ,  ^  '' 

°  ^   '^  ■'  \  mercury. 

Medium  arteries  (e.g.  radial)      .         +110  mm.  mercury. 

Capillaries  .  .  .   +  15  to  +      20     „ 

Small  veins  of  arm    .  .  .         +        9     „ 

Portal  vein         .  .  .  .         +      10     „ 

Inferior  vena  cava     .  .  .         +        3     „ 

Large  veins  of  neck  from  0  to  -        8     ,, 

(Starling.) 

These  pressures  are,  however,  subject  to  considerable  variations ; 
the  principal  factors  that  cause  variation  are  the  following : — 
Increase  of  arterial  blood-pressure  is  produced  by — 

1.  Increase  in  the  rate  and  power  of  the  heart-beat. 

2.  Increase  in  the  contraction  of  the  arterioles. 

3.  Increase  in  the  total  quantity  of  blood  (plethora,  after  a  meal, 

after  transfusion). 
Decrease  in  the  arterial  blood-pressure  is  produced  by — 

1.  Decrease  in  the  rate  and  force  of  the  heart-beat. 

2.  Decrease  in  the  contraction  of  the  arterioles. 

3.  Decrease  in  the  quantity  of  blood  {e.g.  after  haemorrhage). 

The  above  is  true  for  general  arterial  pressure;  but  if  we  are 
investigating  local  arterial  pressure  in  any  organ,  the  increase  or 
decrease  in  the  size  of  the  arterioles  of  other  areas  may  make  its 
effect  felt  in  the  special  area  under  investigation. 

Venous  pressure  varies  directly  with  the  volume  of  the  blood  ;  in 
the  arteries  the  effect  of  increase  of  fluid  is  sHght  and  temporary, 
owing  to  the  rapid  adaptability  of  the  peripheral  resistance;  the 
excess  of  fluid  collects  in  and  distends  the  easily  dilatable  venous 
reservoir.  With  regard  to  the  first  and  second  factors  in  the  foregoing 
table,  venous  pressure  varies  in  the  opposite  way  to  arterial  pressure. 


CII.  XXI.]  VENOUS    I'KESSUHE  275 

It  is  easy  to  undorstand  Ikjw  this  is ;  when  the  rate  of  tlie  heart 
increases,  the  total  vohinie  of  blood  dischar^red  into  the  aorta  per 
second  is  increased ;  similarly,  an  increase  in  the  force  of  the  Ijeat 
also  results  in  an  increase  in  the  cardiac  output,  and  in  both  cases 
a  more  rapid  and  complete  emptying  of  the  auricle  is  produced.  This 
is  felt  throughout  the  whole  of  the  pulmonary  circulation,  and  the 
accelerated  flow  therefore  causes  a  fall  in  the  venous  pressure.  If, 
however,  the  rise  of  pressure  is  due  to  a  contraction  of  the  arterioles, 
a  stage  may  be  reached  in  which  the  heart  is  no  longer  able  to  over- 
come the  high  pressure  produced.     It  then  fails  to  empty  itself,  and 


Fir..  277.— Effect  of  weak  stimulation  of  the  perii/heral  end  of  vagus  un  arterial  blood -pressure  (carotid 
of  rabbit),  bp,  Blood-pressure;  a,  abscissa  or  base  line;  t,  time  in  seconds.  Note  fall  of  blood- 
pressure  and  slow  heart-beats. 

the  blood  is  dammed  up  on  the  venous  side,  i.e.  the  venous  pressure 
rises. 

With  regard  to  the  arterioles,  contraction  means  a  rise  in  arterial 
pressure,  because  while  the  amount  sent  into  the  arteries  remains  the 
same  the  outflow  is  cut  down.  More  blood  is  therefore  retained  in 
them ;  they  become  more  distended  and  the  pressure  rises.  The  first 
effect  of  this  upon  the  venous  pressure  will  be  to  diminish  it,  because 
if  more  blood  is  retained  in  the  arteries  there  is  less  for  the  veins 
and  capillaries.  Also  the  rate  of  flow  into  the  veins  is  at  first 
decreased,  and  the  venous  pressure  therefore  falls.  Moreover,  the 
heart  usually  responds  to  a  rise  in  pressure  by  increasing  its  force 
and  rate,  and  consequently  more  blood  is  taken  from  the  veins  near 


276  THE    CIRCULATION    IN    THE   BLOOD-VESSELS  [CH.  XXI. 

the  heart.     For  both  reasons,  then,  the  venous  pressin-e  will  fall,  but 
that  fall  is  limited,  as  pointed  out  above,  to  such  an  increase  only  as 
the  heart  is  capable  of  overcoming  successfully. 
Capillary  jjressure  is  increased  by — 

1.  Dilatation  of  the  arterioles;  the  blood-pressure  of  the  large 
arteries  is  then  more  readily  propagated  into  them. 

2.  The  size  of  the  arterioles  remaining  the  same,  increase  of 
arterial  pressure  from  any  other  cause  will  produce  a  rise  of  capillary 
pressure. 

3.  By  narrowing  the  veins  leading  from  the  capillary  area ;  com- 
plete closure  of  the  veins  may  quadruple  the  capillary  pressure. 
This  leads  secondarily  to  an  increased  formation  of  lymph  (dropsy) ; 
as  when  a  tumour  presses  on  the  veins  coming  from  the  legs. 

4.  Any  circumstance  that  leads  to  increased  pressure  in  the  veins 
will  act  similarly;  this  is  illustrated  by  the  effects  produced  by 
gravity  on  the  circulation,  as  in  alterations  of  posture. 

Capillary  pressure  is  decreased  by  the  opposite  conditions. 

Capillary  pressure  is  much  more  influenced  by  changes  in  the 
venous  pressure,  than  by  changes  in  the  arterial  pressure,  since  there 
is  between  the  arteries  and  capillaries  the  variable  and  usually  un- 
known peripheral  resistance  of  the  arterioles. 

Effect  of  gravity  on  the  circulation. — The  main  effect  of  gravity  is 
that  the  veins  are  filled  with  blood  in  the  part  which  is  placed  down. 
Thus,  if  an  animal  is  placed  suddenly  with  its  legs  hanging  down,  less 
blood  will  go  to  the  heart,  and  the  blood-pressure  in  the  arteries  will 
fall  temporarily  in  consequence.  This  hydrostatic  effect  of  gravity  is 
soon  overcome  by  an  increased  constriction  of  the  vessels  of  the 
splanchnic  area,  when  the  vaso-motor  mechanism  is  working  normally. 
The  efficient  action  of  the  "  respiratory  pump  "  is  also  of  importance 
in  counteracting  gravity. 

A  very  striking  illustration  of  the  effect  of  gravity  on  the  circula- 
tion can  be  demonstrated  on  the  eel.  The  animal  is  ansesthetised, 
and  a  small  window  is  made  in  the  body  wall  to  expose  the  heart. 
If  the  animal  is  then  suspended  tail  downwards,  the  beating  heart  is 
seen  to  be  empty  of  blood ;  all  the  blood  accumulates  in  the  tail  and 
lower  part  of  the  body ;  the  animal  has  no  "  respiratory  pump,"  such 
as  a  mammal  possesses,  to  overcome  the  effects  of  gravity.  If,  how- 
ever, the  animal,  still  with  its  tail  downwards,  be  suspended  in  a  tall 
vessel  of  water,  the  pressure  of  the  water  outside  its  body  enables  it 
to  overcome  the  hydrostatic  effect  of  gravitation,  and  the  heart-cavi- 
ties once  more  fill  with  blood  during  every  diastole.  Another  experi- 
ment originally  performed  by  Salathe,  can  be  demonstrated  on  a 
"hutch"  rabbit.  If  the  animal  is  held  by  the  ears  with  its  legs 
hanging  down,  it  soon  becomes  unconscious,  and  if  left  in  that  position 
for  about  half  an  hour  it  will  die.     This  is  due  to  anaemia  of  the 


CU.  XXI.] 


CARDIAC    NERVES    AND    BLOOD-PRESSURE 


277 


brain ;  the  blood  accumulates  in  the  very  pendulous  abdomen  which 
such  domesticated  animals  acquire,  and  the  vaso-motor  mechanism  of 
the  splanchnic  area  is  deficient  in  tone,  and  cannot  be  set  into  such 
vigorous  action  as  is  necessary  to  overcome  the  bad  effects  of  gravity. 
Consciousness  is,  however,  soon  restored  if  the  animal  is  placed  in  a 
horizontal  position,  or  if  while  it  is  still  hanging  vertically  the  abdomen 
is  squeezed  or  bandaged.  A  wild  rabbit,  on  the  other  hand,  suffers  no 
inconvenience  from  a  vertical  position ;  it  is  a  more  healthy  animal  in 
every  respect;  its  abdomen  is  not  pendulous,  and  its  vaso-motor 
power  is  intact.     (Leonard  Hill.) 


t^io.  278. — Effect  of  strong  stimulation  of  tlio  periplieral  end  of  vagus  on  arterial  blood -pressure  (carotid 
of  rabbit).  Note  stoppage  of  heart  and  fall  of  blood-pressure  nearly  to  zero  ;  after  the  recoTumence- 
ment  of  the  heart,  the  blood-pressure  rises,  as  in  fig.  277,  above  the  normal  for  a  short  time. 


The  pressure  in  the  Pulmonary  Circulation  varies  from  \  to  ^ 
(mean  \)  of  that  in  the  systemic  vessels. 

The  influence  of  the  Cardiac  Nerves  on  blood-pressure.  The 
importance  of  the  heart's  action  in  the  maintenance  of  blood-pressure 
is  well  shown  by  the  effect  that  stimulation  of  the  vagus  nerve  has 
on  the  blood-pressure  curve.  If  the  vagus  of  an  animal  is  exposed 
and  cut  through,  and  the  peripheral  end  stimulated,  the  result  is  that 
the  heart  is  slowed  or  stopped ;  the  arterial  Ijlood-pressure  conse- 
quently falls ;  the  fall  is  especially  sudden  and  great  if  the  heart  is 
completely  stopped.     There  is  a  rise  in  venous  pressure.     The  effect 


278  THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CH.  XXI. 

on  arterial  pressure  is  shown  in  the  two  accompanying  tracings  ;  fig. 
277  representing  the  effect  of  partial,  and  fig.  278  of  complete 
stoppage  of  the  heart ;  in  both  cases  the  animal  used  was  a  rabbit, 
and  the  artery  the  carotid. 

On  stimidating  the  cardiac  sympathetic  (accelerator  and  augmentor 
fibres)  the  increased  action  of  the  heart  causes  a  rise  of  arterial  pres- 
sure. 

The  effects  of  stimulating  the  central  end  of  the  vagus  and  other 
nerves  cannot  be  understood  until  we  have  studied  the  vaso-motor 
nervous  system. 

The  Velocity  of  the  Blood-flow. 

We  have  already  seen  that  the  velocity  of  the  current  of  blood  is 
inversely  proportional  to  the  sectional  area  of  the  bed  through  which 
it  flows.  The  flow  is,  therefore,  swiftest  in  the  aorta  and  arteries,  and 
slowest  in  the  capillaries.  In  very  round  numbers,  the  rate  is  about 
a  foot  per  second  in  the  aorta,  and  about  an  inch  per  minute  in  the 
capillaries.  The  capacity  of  the  veins  is  about  twice  or  thrice  that  of 
the  arteries ;  so  the  velocity  in  the  veins  is  from  a  half  to  a  third  of 
that  in  the  corresponding  arteries.  The  rate  in  the  veins  increases  as 
we  approach  the  heart,  as  the  total  sectional  area  of  the  venous  trunks 
becomes  less  and  less. 

The  question  of  velocity  is  one  of  great  importance,  for  it  is  on 
velocity  that  the  actual  amount  of  blood  supplying  the  tissues  mainly 
depends.  In  the  capillaries  the  rate  can  Ije  measured  by  direct  micro- 
scopic investigation  of  the  transparent  portions  of  animals.  E.  H. 
Weber  and  Valentin  were  among  the  earliest  to  make  these  measure- 
ments in  the  frog,  and  the  mean  of  their  estimates  gives  the  velocity 
as  25  mms.  per  minute  in  the  systemic  capillaries.  In  warm-blooded 
animals  the  velocity  is  somewhat  greater ;  in  the  dog  it  is  -^  to  ^-^ 
inch  (O'o  to  0'75  mm.)  per  second.  It  must  be  remembered  that  the 
total  length  of  capillary  vessels  through  which  any  given  portion  of 
blood  has  to  pass  probably  does  not  exceed  from  w  to  ^  inch 
(0'5  mm.),  and  therefore  the  time  required  for  each  quantity  of  blood 
to  traverse  its  own  appointed  portion  of  the  general  capillary  system 
will  scarcely  amount  to  a  second.  It  is  during  this  time  that  the 
blood  does  its  duties  in  reference  to  nutrition. 

In  the  larger  vessels  direct  observations  of  this  kind  are  not 
possible,  and  it  is  necessary  to  have  recourse  to  some  instrumental 
method. 

Volkinann  was  the  first  to  make  more  or  less  accurate  measure- 
ments by  introducing  a  long  (J -shaped  glass  tube  into  the  course  of 
an  artery.  A  diagram  of  this  hcemodromometer,  as  it  was  termed,  is 
shown  in  the  accompanying  diagram  (fig.  279);  this  is  filled  with 
salt  solution,  and  provided  with  a  stop-cock  a  ;  this  tap  is  so  arranged 


en.  XXI. J 


THE   STROMUHR 


279 


that  the  blood  can  flow  straight  across  from  ono  section  of  the  artery 
to  the  other ;  then  at  a  given  instant  it  is  turned  into  the  position 
shown  in  the  diagram,  and  the  blood  has  to  traverse  the  long  (J -tube, 
and  the  time  that  it  takes  to  traverse  the  tube,  the  length  of  which 
is  known,  is  accurately  observed.  If  the  sectional  area  of  the  tube  is 
the  same  as  that  of  the  artery,  the  velocity  is  obtained  without 
further  correction;  but  the  difhculty  of  obtaining  glass  tubes  with 
the  exact  calibre  of  every  blood-vessel  which  one  desires  to  experi- 
ment with  led  to  the  abandonment  of  this  method,  and  Ludwig's 
Stromuhr  (literally  stream-clock)  took  its  place.  This  consists  of  a 
U-shaped  glass  tul)e  dilated  at  a  and  a,  the  ends  of  which,  h  and  i, 


(r^ 


]iiiiu^uu\>    *w^    -wwm 


Fig.  27y.— Volkmann's 
Haemodromompter. 


Pig.  280.— Ludwig'i 
Stromuhr. 


are  of  known  calibre.  The  bulbs  can  be  filled  by  a  common  opening 
at  k.  The  instrument  is  so  contrived  that  at  h  and  h',  the  glass  part 
is  firmly  fixed  into  metal  cylinders,  attached  to  a  circular  horizontal 
table  c  c,  capable  of  horizontal  movement  on  a  similar  table  d  d', 
about  the  vertical  axis  marked  in  the  figure  by  a  dotted  line.  The 
openings  in  c  c',  when  the  instrument  is  in  position,  as  in  fig.  280, 
corresponds  exactly  with  those  in  d  d'  ]  but  if  c  c  is  turned  at  right 
angles  to  its  present  position,  there  is  no  communication  between  h 
and  a  and  i  and  a,  but  h  communicates  directly  with  i ;  and  if  turned 
through  two  right  angles  c'  communicates  with  d,  and  c  with  d',  and 
there  is  no  direct  communication  between  h  and  i.  The  experiment 
is  performed  in  the  following  way : — The  artery  to  be  investigated 


280  THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CH.  XXJ. 

is  divided  and  connected  with  two  cannulse  and  tubes  which  fit  it 
accurately  with  h  and  i\  h  \q  the  central  end,  and  i  the  peri- 
pheral ;  the  bulb  a  is  filled  with  olive  oil  up  to  a  point  rather  lower 
than  h,  and  a  and  the  remainder  of  a  is  filled  with  defibrinated 
blood ;  the  tube  on  k  is  then  carefully  clamped ;  the  tubes  d  and  d' 
are  also  filled  with  defibrinated  blood.  When  everything  is  ready, 
the  blood  is  allowed  to  flow  into  a  through  h,  thus  driving  the  oil 
over  into  a  and  displacing  the  defibrinated  blood  through  i  into  the 
peripheral  end  of  the  artery ;  a  is  then  full  of  oil ;  when  the  blood 
reaches  the  former  level  of  the  oil  in  a,  the  disc  c  c  is  turned  rapidly 
through  two  right  angles,  and  the  blood  flowing  through  d  into  a 
again  displaces  the  oil,  which  is  driven  into  a.  This  is  repeated 
several  times,  and  the  duration  of  the  experiment  noted.  The 
capacity  of  a  and  a  is  known ;  the  diameter  of  the  artery  is  then 
measured,  and  as  the  number  of  times  a  has  been  filled  in  a  given 
time  is  known,  the  velocity  of  the  current  can  be  calculated. 
We  may  take  an  example  to  illustrate  this : — 

volume  per  second       V 

Velocity  = , =  -^. 

•'  sectional  area  s 

If  the  capacity  of  the  bulb  is  5  c.c,  and  it  required  100  seconds  to 
fill  it  10  times,  then  the  amount  of  blood  passing  through  the  instru- 
ment would  be  50  c.c.  in  100  seconds,  or  0"5  c.c.  in  1  second.  Next, 
suppose  the  diameter  of  the  artery  is  4  mm.  The  sectional  area  is 
TT?--;  r  is  the  radius  (2  mm.),  and  7r  =  31416.  From  these  data  we 
get 

,^  ,               V           05  c.c.          500  cubic  millimetres 
Velocity  =-g  =  3.1416^2,= 3all6^r4 =  ^^"^  ™™-  ^'^'  ^""- 

Many   modifications    of    Ludwig's    original    instrument    have    been  • 
devised.     Fig.  281  shows  Tigerstedt's. 

The  tubes  A  and  B  are  placed  in  connection  with  the  two  ends 
of  the  cut  artery  as  before;  there  is  also  a  turn-table  arrangement  at 
F,  by  means  of  which  the  two  upper  tubes  C  and  D  may  be  connected 
as  in  the  figure ;  or  by  twisting  it  through  two  right  angles,  D  can  be 
made  to  communicate  with  A,  and  C  with  B.  In  place  of  the  two 
bulbs  of  Ludwig's  instrument  there  is  a  glass  cylinder  H  which 
contains  a  metal  ball  E.  The  whole  instrument  is  washed  out  with 
oil  to  delay  clotting,  and  filled  with  defibrinated  blood.  As  soon  as 
blood  is  allowed  to  flow  from  the  artery,  the  ball  E  is  driven  over  by 
the  current  till  it  reaches  the  other  end  of  the  cylinder ;  the  instru- 
ment is  then  rapidly  rotated  through  two  right  angles,  and  once 
more  the  ball  is  driven  to  the  opposite  end.  This  is  repeated  several 
times,  and  the  number  of  revolutions  during  a  given  period  is  noted. 
The  capacity  of  the  cylinder  minus  that  of  the  ball  is  ascertained, 


CFI.  XXI.] 


THE    VRF,OriTY    PULSE 


281 


and  the  velocity  is  calculatod  l)y  the  same  fonuula  as  that  already 
given. 

The  Stromuhr  has  one  advantage  over  the  hsemodromometer,  in 
that  it  enables  one  to  note  changes  in  mean  velocity  during  the 
course  of  an  experiment.  The  mean  velocity  varies  very  greatly 
even  during  a  short  experiment.  Thus,  in  the  carotid  artery  of  a 
dog,  the  velocity  of  the  stream  varied  from  350  to  730  mm.  per 
second  in  the  course  of  eighty  seconds ;  in  the  same  artery  of  the 
rabbit  the  variations  were  still  more  extensive  (94  to  226  mm.  per 
second — Dogiel). 

Other  instruments  have  been  devised  which  give  the  variations 
in  the  velocity  during  the  phases  of  the  heart-beat;  and  some  of 
these  lend  themselves  to  the  graphic  method,  and  give  tracings  of 
what  is  called  the  velocity  pulse.  Before  we  can  understand  these,  it 
is  necessary  first  to  study  the 
relationship  of  velocity  to  blood- 
pressure.  Mere  records  of  blood - 
pressure  give  us  no  indication  of 
the  velocity  of  the  blood-stream ; 
the  latter  depends,  not  on  the 
absolute  amount  of  pressure,  but 
on  the  differences  of  pressure 
l)etween  successive  points  of  the 
vascular  system.  When  a  fluid 
is  in  movement  along  a  tube  the 
forces  maintaining  the  flow  are 
two  in  number,  the  one  hydro- 
kinetic,  the  other  hydro  -  static. 
Thus,  if  we  consider  the  flow  from 

one  point  in  the  tube  to  another  (say,  for  example,  at  1  cm.  dis- 
tance), the  force  producing  the  flow  are  (1)  the  kinetic  energy  pos- 

sessed  by  the  blood  when  it   enters   the  first  spot  {i.e.   -^  dynes 

or    _-    gramme-centimetres) ;  and  (2)  the  difference  between  the  two 

lateral  pressures  at  the  two  points  in  question.  The  important 
point  to  remember  with  respect  to  the  part  the  pressure  plays,  is 
that  the  actual  value  of  the  lateral  pressure  does  not  matter,  but 
that  the  resulting  velocity,  so  far  as  pressure  is  concerned,  depends 
only  upon  the  fall  of  pressure  between  the  two  points.  Therefore, 
the  measurement  to  be  determined  is  the  rate  of  fall  of  pressure, 
or,  as  it  is  usually  expressed,  the  pressure  gradient.  The  steeper 
this  gradient  is,  the  more  rapid  is  the  flow.  Thus,  if  an  artery 
is  suddenly  cut  across,  the  blood  will  spurt  out  at  a  far  greater 
velocity  than    it  possessed   when   flowing  along   the  intact  artery. 


Fig.  2S1. — Tijierstedt's  Stromuhr. 


282  THE   CIKCULATION    IN    THE    BLOOD-VESSELS  [CH.  XXI. 

because  the  pressure  gradient  has  been  enormously  increased  in 
steepness.  If,  on  the  other  hand,  we  suddenly  cut  across  a  vein 
along  which  the  blood  had  been  flowing  at  the  same  pace  as  in  the 
intact  artery  first  investigated,  the  flow  will  not  be  markedly 
accelerated,  because  the  change  in  pressure  gradient  has  not  been 
increased  to  nearly  so  great  an  extent. 

Again,  the  flow  along  a  vein  is  just  as  rapid  as  along  an  artery 
of  the  same  size,  for  although  the  actual  pressure  in  the  vein  is  much 
less,  the  pressure  gradient  is  just  as  steep. 

The  influence  of  the  kinetic  factor  is  also  of  great  importance  in 
the  consideration  of  the  flow  of  blood  along  the  arteries  and  veins. 
In  the  first  place,  it  is  obviously  possible  for  the  blood  to  flow  from 
one  point  to  another  at  a  higher  pressure  if  the  kinetic  energy  at  the 
first  point  is  more  than  enough  to  comj)ensate  for  the  pressure 
increase.  Under  such  circumstances  the  velocity  at  the  second 
point  must  of  course  be  less  than  that  at  the  first.  This  implies, 
therefore,  that  the  bed  of  the  stream  has  widened,  and  under  such 
circumstances  the  blood  could  actually  flow  uphill.  In  the  case  of 
the  veins,  as  we  have  previously  seen,  the  bed  continuously  narrows, 
so  that  this  cannot  take  place ;  still  it  is  possible  to  conceive  such 
a  condition  to  occur  as  that  in  which  the  blood  from  a  well-filled 
vein  empties  into  a  more  collapsed  larger  vein  situated  at  a  higher 
level.  The  one  instance  in  which  this  effect  is  produced  and  is  of 
great  importance  is  in  the  filling  of  the  auricles  and  ventricles.  As 
these  cavities  fill,  the  blood  comes  to  rest  and  so  loses  all  kinetic 
energy;  consequently  the  whole  of  the  kinetic  energy  possessed 
by  the  blood  flowing  in  the  veins  is  converted  into  static  energy, 
that  is,  into  a  pressure-head ;  in  this  way  the  cavities  are  distended 
to  a  much  higher  pressure  than  that  in  the  great  veins.  The 
acute  distension  of  the  right  auricle  which  follows  any  sudden 
failure  of  the  right  ventricle  is  brought  about  chiefly  in  this 
way. 

It  is  usual  to  speak  of  the  lateral  pressure  of  the  blood  on  the 
vessel  wall  as  the  pressure-head,  and  of  the  kinetic  energy  measured 
in  terms  of  a  pressure  as  the  velocity -head.  We  could  then  say  that 
the  velocity  between  any  two  points  is  determined  by  the  difference 
between  the  two  pressure-heads  j^/t^  the  velocity -head  at  the  first 
point.  One  method  of  recording  the  velocity-head  is  by  the  use  of 
a  tube  (Pitot's  tube)  shaped  as  in  the  accompanying  figure  (fig.  282). 
The  blood  is  made  to  enter  at  A,  and  leave  through  B ;  in  the  same 
straight  line  as  A  is  a  tube  C,  and  a  second  tube  D  is  placed  at  right 
angles  to  the  tube  B.  If  the  tubes  C  and  D  are  placed  vertically 
and  were  sufficiently  long,  the  blood  would  flow  up  C  until  it 
reached  a  height  which  would  balance  the  pressure-head  plus  the 
velocity -head ;  in  D  it  would  only  reach  a  height  sufficient  to  balance 


CII.  XXI. ] 


PITOT  S    TUBE 


283 


r~\ 


D 


the  pressure-head ;  the  difference  in  height  between  the  two  would 
therefore  give  the  velocity-head.  As  the  tubes  would  in  this  way 
be  inconveniently  long,  it  is  better  to  use  short  tubes  connected  at 
the  top  by  glass  or  rubber-tubing.  The  air  contained  will  be  com- 
pressed, and  the  two  pressure-heads  will  balance  one  another,  so  that 
the  difference  in  height  will  again  represent  the  velocity-head ;  the 
velocity  will  be  directly  proportional  to  the  square  root  of  this 
velocity-head.  This  is  the  principle  of  one  of  the  best  instruments 
we  possess  for  determining  velocity,  namely,  Cybulski's  photo-hsemato- 
chometer.  The  meniscus  of  the  fluid  in  each  tube  is  photographed 
on  a  moving  sensitive  plate,  and  in  this 
way  a  graphic  record  is  obtained  of  the 
changes  in  velocity  at  times  corresponding 
to  different  parts  of  the  cardiac  cycle.  If 
one  wishes  to  determine  the  velocity  in 
absolute  measures,  the  instrument  must  be 
previously  calibrated  by  passing  through 
it  fluids  flowing  at  known  rates.  It  will 
be  sufficient  to  give  the  results  of  one 
experiment;  in  the  carotid  artery  during 
the  ventricular  systole  the  flow  was  at  the 
rate  of  238-248  mm.  per  second;  during 
the  diastole  it  sank  to  127-156;  in  the 
femoral  artery  of  the  same  animal,  these 
numbers  were  356  and  177  respectively. 

To  determine  the  pressure  gradient  in 
arteries,  simultaneous  measurements  of 
the  lateral  pressures  in  two  vessels  at 
different  distances  from  the  heart  must  be 
recorded. 

It  has  been  found  that  the  diastolic 
pressures  in  the  crural  and  carotid  are 
practically  identical,  but  that  the  maximum 
systolic  pressure  is  actually  higher  in  the 

crural  than  in  the  carotid;  in  the  dog  the  difference  may  amount 
to  as  much  as  60  mm.  mercury.  This  difference  is  partly  to  be 
explained  in  that  the  carotid  arises  from  the  aorta  at  a  right  angle, 
and  therefore  gives  the  true  pressure-head,  while  the  crural,  to  a  con- 
siderable extent,  faces  the  stream,  and  therefore  gives  both  pressure- 
head  and  velocity -head. 

Unfortunately,  at  present  no  really  satisfactory  measurements  are 
at  hand  from  which  the  pressure  gradient  can  be  determined. 

Cybulski's  instrument  is  not  the  only  one  we  possess  for  obtaining 
records  of  the  velocity -pidse.  Vierordt  invented  a  haemo-taehometer, 
employing  the  principle  of  the  hydrometric  pendulum  ;  his  instrument 


Fig.  282. — Diagram  to  illustrate 
the  principle  of  Pitot's  Tube 
and  Cybulski's  Photo-hsemato- 
chometer. 


284 


THE   CIRCULATION    IN    THE    BLOOD-VESSELS  [CH.  XXI. 


was  improved   by  Chauveaii. 
fig.  283. 

It  consists  of  a  thin  brass  tube,  a, 
closed  by  thin  vuU-anised  indiarubber. 
one  end  of  which,  slightly  flattened, 
extends  into  the  lumen  of  the  tube, 
while  the  other  moves  over  the  face 
of  a  dial.  The  tube  is  inserted  into 
the  interior  of  an  artery,  and  liga- 
tures applied  to  fix  it,  so  that  the 
'■'■  vdocifif  pulse,'"  i.e.,  the  change  of 
velocity  with  each  heart-beat,  may 
be  indicated  by  the  movement  of 
the  outer  extremity  of  the  lever  on 
the  face  of  the  dial. 

In  order  to  obtain  the 
actual  value  of  these  move- 
ments in  terms  of  velocity,  the 
instrument  must  be  calibrated 


Chauveau's   instrument  is  shown  in 


in  one  side  of  which  is  a  small  perforation 
Passing  through  the  rubber  is  a  fine  lever, 


Fig.  283.— Diagrani  of  Chauveau's  Droniograph.  a.  Brass 
tube  for  introduction  into  the  lumen  of  the  artery, 
and  containing  an  index  needle,  which  passes 
through  the  elastic  membrane  in  its  side,  and 
moves  by  the  impulse  of  the  blood  current ; 
c,  graduated  scale,  for  measuring  the  extent  of  the 
oscillations  of  the  needle. 


beforehand.  The  next  dia- 
gram, fig.  284,  shows  how  the 
instrument  may  be  adapted 
to  give  a  graphic  record. 
The  movements  of  the  pen- 
dulum are  brought  to  bear  upon  a  tambour  B,  which  communicates 
by  a  tube  with  the  recording  tambour  C.  If  the  mass  of  the  pen- 
dulum is  small,  the  accuracy  of  the  instrument  is  considerable. 
Fig.  285  shows  the  tracing  obtained  from  the  carotid  artery  of 
the  horse.  The  pressure  curve  is  placed  below  it  for  purpose  of 
comparison.  The  tracing  shows  the  effects  during  the  time  corre- 
sponding to  one  cardiac  cycle.     On  both  curves  the  upstroke  is  the 


Fig.  284.— Chauveau's  Dromograph  connected  with  tambours  to  give  a  graphic  record. 

effect  of  the  ventricular  systole ;  this  terminates  at  the  apex  of  the 
first  small  curve  (between  the  vertical  lines  3  and  4)  on  the  down- 
stroke  of  the  pressure  curve,  the  rest  of  the  downstroke  until  the 
commencement  of  the  next  systole  (line  5)  corresponds  with  the 
ventricular  diastole.  Beyond  the  line  4  is  a  larger  secondary  wave, 
which  is  known  as  the  dicrotic  wave ;  the  smaller  post-dicrotic  waves 


CH.  XXI.] 


TIME   OF    A    COMPLETE   CIRCULATION 


285 


are  due  to  elastic  vibrations.  We  shall  be  studying  all  those  points 
more  in  detail  when  we  come  to  the  pulse.  When  we  compare  the 
two  curves  together  we  note  that  the  velocity  curve  reaches  its  maxi- 
mum before  the  pressure  curve ;  this  is  because,  as  the  arteries  become 
overfilled,  the  heart  cannot  maintain  the  initial  velocity  of  output.  The 
blood  is  thus  forced  along  the  arteries ;  then  comes  the  diastole,  and 
the  recoil  of  the  elastic  arteries  not  only  forces  the  blood  onwards, 
but  also  produces  a  back-swing  against  the  closed  aortic  valves ;  this 
produces  the  notch  before  the  dicrotic  wave ;  the  blood  is  reflected 
from  the  aortic  valves,  once  more  producing  a  positive  wave  (the 
dicrotic  wave).  This  affects  both  speed  and  pressure.  It  will  bo 
noticed  that  during  the  dicrotic  notch  the  pressure  falls  comparatively 
little,  but  in  the  velocity  curve  the  fall  is  considerable,  and  the  curve 
sinks  below  the  base  line  oo.     This  negative  effect  is  naturally  much 


Fio.  285. Velocity  curve  (V),  and  pressure  curve  (P)  from  the  oarotiil  artery  of  the  horse  ;  on,  abscissa 

of  velocity  curse;  1,  2,  3,  4  show  simultaneous  points  on  both  curves.    (Chauveau  and  Marey.) 

more  marked  in  the  aorta  and  its  first  large  branches  than  in  situa- 
tions further  from  the  heart. 

In  actual  values  Chauveau  found  that  the  velocity  in  the  horse's 
carotid  reached  520  mm.  per  second  during  systole ;  it  sank  to  220 
at  the  time  of  the  dicrotic  wave,  and  to  150  during  diastole. 

The  effect  on  the  blood-flow  of  functional  activity  or  vaso-motor 
changes  has  also  been  observed.  Thus  Lortet  found  that  the  carotid 
flow  is  five  or  six  times  greater  when  the  horse  is  actively  masticating 
than  when  it  is  at  rest.  After  section  of  the  cervical  sympathetic, 
the  lessening  of  the  peripheral  resistance  raised  the  velocity  from 
540  to  750  mm.  per  second. 

The  Time  of  a  Complete  Circulation. 

Among  the  earliest  investigators  of  the  question  how  long  an 
entire  circulation  takes,  was  Hering.  He  injected  a  solution  of 
potassium  ferrocyanide  into  the  central  end  of  a  divided  jugular 
vein,  and  collected  the  blood  either  from  the  other  end  of  the  same 


286  THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CIL  XXI. 

vein,  or  from  the  corresponding  vein  of  the  other  side.  The  sub- 
stance injected  is  one  that  can  be  readily  detected  by  a  chemical 
test  (the  Prussian  blue  reaction).  Vierordt  improved  this  method 
by  collecting  the  blood  as  it  flowed  out,  in  a  rotating  disc  divided 
into  a  number  of  compartments.  The  blood  was  tested  in  each  com- 
partment, and  the  ferrocyanide  discovered  in  one  which  in  the  case  of 
the  horse  received  the  blood  about  half  a  minute  after  the  injection 
had  been  made.  The  experiment  was  performed  in  a  large  number 
of  animals,  and  the  following  were  a  few  of  the  results  obtained : — 

In  the  horse  .  .  .  .31  seconds. 

„       dog  .  .  .  .         16 

„       cat  ....  6'5     „ 

„       fowl  .  .  .  .  5        „ 

At  first  sight  these  numbers  show  no  agreement,  but  in  each  case 
it  was  found  that  the  time  occupied  was  27  heart-beats.  The  dog's 
heart,  for  instance,  beats  twice  as  fast  as  the  horse's,  and  so  the  time 
of  the  entire  circulation  only  occupies  half  as  much  time. 

The  question  has  recently  been  re-investigated  by  Stewart  by 
improved  methods,  which  have  shown  that  the  circulation  time  is 
considerably  less  than  was  found  by  the  researches  of  Hering  and 
Vierordt.  The  great  objection  to  the  older  method  is  the  fact  that 
haemorrhage  is  occurring  throughout  the  experiment,  and  this  would 
materially  weaken  the  heart  and  slow  down  the  circulation.  Stewart 
has  employed  two  methods.  In  the  first,  the  carotid  artery  is  exposed, 
and  non-polarisable  electrodes  applied  to  it.  These  are  placed  in 
circuit  with  a  cell,  a  galvanometer  and  one  arm  of  a  Wheatstone's 
bridge.  After  the  resistances  in  the  bridge  have  been  balanced,  and 
the  galvanometer  needle  brought  to  rest,  a  small  quantity  of  strong 
sodium  chloride  solution  is  injected  into  the  opposite  jugular  vein. 
As  soon  as  the  salt  reaches  the  carotid  artery,  the  resistance  of  the 
blood  is  altered,  the  balance  of  the  Wheatstone's  bridge  is  upset,  and 
the  galvanometer  needle  moves.  The  period  between  the  injection 
and  the  swing  of  the  needle  is  accurately  noted. 

The  second  method  used  is  even  simpler,  and  gives  practically  the 
same  results ;  a  solution  of  methylene  blue  is  injected  into  the 
jugular  vein.  The  carotid  artery  on  the  opposite  side  is  exposed, 
placed  upon  a  sheet  of  white  paper,  and  strongly  illuminated.  The 
time  is  noted  between  the  injection  and  the  moment  when  the  blue 
colour  is  seen  to  appear  in  the  artery.  Stewart  has  appUed  these 
methods  also  for  determining  the  time  occupied  by  the  passage  of 
blood  through  various  districts  of  the  circulation ;  the  longest  circula- 
tion times  were  found  in  the  kidney,  the  portal  system,  and  the 
lower  limbs.  He  calculates  that  the  total  circulation  time  in  man 
is  about  15  seconds. 


CII.  XXI.] 


THE    PULSE 


287 


None  of  these  methods,  however,  i^ive  the  true  time  of  the  entire 
circulation ;  they  give  merely  the  shortest  possible  time  in  which  any 
particle  of  blood  can  travel  through  the  shortest  pathway.  The 
blood  that  travels  in  the  axial  current,  or  whicli  takes  a  broad  path- 
way through  wide  capillaries,  will  arrive  far  more  sjjeodily  at  its 
destination  than  that  which  creeps  through  tortuous  or  constricted 
vessels.  The  direct  observations  of  Tigerstedt  on  the  output  of  the 
left  ventricle  show  that  the  circulation  time  of  the  whole  blood  is  at 
least  five  times  as  long  as  the  period  arrived  at  by  the  Hering 
method.  It  is  therefore  fallacious  to  use  the  circulation  times 
arrived  at  by  Hering's  or  Stewart's  methods  as  a  basis  for  calculating 
the  total  amount  of  the  blood  in  the  body. 

The  Pulse. 

Tliis  is  the  most  characteristic  feature  of  the  arterial  flow.  It  is 
the  response  of  the  arterial  wall  to  the  changes  in  lateral  pressure 
caused  by  each  heart-beat. 

A  physician  usually  feels  the  pulse  in  the  radial  artery,  since  this 
is  near  the  surface,  and  supported  by  bone.     It  is  a  most  valuable 


Fig.  280.  — Marey's  Sphygmograpli,  moditied  by  Mahomed. 


indication  of  the  condition  of  the  patient's  heart  and  vessels.     It  is 
necessary  in  feeling  a  pulse  to  note  the  following  points : — 

1.  Its  frequency ;  that  is  the  number  of  pulse-beats  per  minute. 

This  gives  the  rate  of  the  heart-beats. 

2.  Its  strength ;  whether  it  is  a  strong,  bounding  pulse,  or  a  feeble 

beat ;    this    indicates    the   force   with   which    the    heart   is 
beating. 


288 


THE   CIRCULATION    IN    THE   BLOOD-VESSELS  [CII.  XXL 


3.  Its  refjularity  or  irregularity ;  irregularity  may  occur  owing  to 

irregular  cardiac  action  either  in  force  or  in  rhythm. 

4.  Its  tension ;  that  is  the  force  necessary  to  obliterate  it.     This 

gives  an  indication  of  the  state  of  the  arterial  walls  and  the 
peripheral  resistance. 
In  disease  there  are  certain  variations  in  the  pulse,  of  which  we 
shall  mention  only  two ;  namely,  the  intermittent  pulse,  due  to  the 


Fig.  287.  -  Diagram  of  the  lever  of  the  SphygrnoLTaph. 

heart  missing  a  beat  every  now  and  then ;  and  the  vjater  hammer 
pulse,  due  either  to  aortic  regurgitation  or  to  a  loss  of  elasticity  of 
the  arterial  walls;  either  of  these  circumstances  diminishes  the 
onward  flow  of  blood  during  the  heart's  diastole,  and  thus  the  sudden- 
ness of  the  impact  of  the  blood  on  the  arterial  wall  during  systole  is 
increased.  When  this  condition  is  due  to  arterial  disease,  such  as 
atheroma  or  calcification,  this  sudden  pulse,  combined  with  the 
decreased  extensibility  of  the  arteries,  may  lead  to  rupture  of   the 


Fig.  2SS.— The  Sphygmograph  applied  to  the  arm. 

walls,  and  this  is  especially  serious  if  it  occurs  in  the  arteries  of  the 
brain  (one  cause  of  apoplexy). 

In  order  to  study  the  pulse  more  fully,  it  is  neces.sary  to  obtain 
a  graphic  record  of  the  pulse-beat,  and  this  is  accomplished  by  the 
use  of  an  instrument  called  the  sphygmograph.  This  instrument 
consists  of  a  series  of  levers,  at  one  end  of  which  is  a  button  placed 
over  the  artery ;  the  other  end  is  provided  with  a  writing-point  to 
inscribe  the  magnified  record  of  the  arterial  movement  on  a  travelling 
surface. 


CH.  XXI.] 


SPHYGMOGRAPHS 


289 


The  instruments  most  frequently  used  are  those  of  Marey,  one  of 
the  numerous  modifications  of  which  is  represented  in  figures  286, 
287,  and  288,  and  of  Dudgeon  (fig.  289). 


Fig.  289. — Dudgeon's  Sphygmograph.    The  dotted  outline  represents  the  piece  of  blackened  paper  on 
which  the  sphygmogram  is  written. 

Each  instrmnent  is  provided  with  an  arrangement  by  which  the 
pressure  can  be  adjusted  so  as  to  obtain  the  best  record.  The 
measurement  of  the  pressure  is,  however,  rough,  and  both  instruments 
have  the  disadvantage  of  giving  oscillations  of  their  own  to  the 
sphygmogram ;  this  is  specially  notice- 
able in  Dudgeon's  sphygmograph. 
But  these  defects  may  be  overcome 
by  the  use  of  some  form  of  sphyg- 
mometer. (See  later,  p.  292.)  It  is 
also  important  to  remember  that  the 
pad  or  button  placed  upon  the  artery 
rests  partly  on  the  vense  comites,  so 
that  not  only  arterial  tension  but  any 
turgidity  arising  from  venous  conges- 
tion, will  affect  the  height  and  form 
of  the  sphygmographic  record. 

Fig.  290  represents  a  typical  sphyg- 
mographic tracing  obtained  from  the  radial  artery.     It  consists  of 
an  upstroke  due  to  the  expansion  of  the  artery,  and  a  downstroke 
due  to  its  retraction.     The   descent  is  more  gradual  than  the  up- 
stroke, because  the  elastic  recoil  acts  more  constantly  and  steadily 

T 


Fig.  290. — Diagram  of  pulse-tracing,  a,  up- 
stroke ;  B,  downstroke ;  c,  pre-dicrotic 
wave;  d,  dicrotic;  E.post-dicroticwave. 


290 


THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CH.  XXI. 


than  the  heart-beat.  On  the  descent  are  several  secondary  (kata- 
crotic)  elevations. 

A  is  the  primary,  or  percussion  wave ;  C  is  the  pre-dicrotic,  or 
tidal  wave;  D  is  the  dicrotic  wave,  and  E  the  post-dicrotic  wave, 
and  of  these  there  may  be  several.  In  some  rare  cases  there  is  a 
secondary  wave  on  the  upstroke,  which  is  called  an  anacrotic  wave 
(fig.  291). 

These  various  secondary  waves  have  received  different  inter- 
pretations, but  the  best  way  of  explaining  them  is  derived  from 
information  obtained  by  taking  simultaneous  tracings  of  the  pulse, 
aortic  pressure,  apex  beat,  and  intraventricular  pressure,  as  in  the 
researches  of  Hiirthle.  By  this  means  it  is  found  that  the  percussion 
and  tidal  waves  occur  during  the  systole  of  the  heart,  and  the  other 
waves  during  the  diastole.  The  closure  of  the  aortic  valves  occurs 
just  before  the  dicrotic  wave.  The  secondary  waves  on  the  down- 
stroke  other  than  the  dicrotic  are  due  to  the  elastic  tension  of  the 
arteries,  and  are  increased  in  number  when  the  tension  of  the  arteries 


Fio.  201. — Anacrotic  pulse. 

is  greatest.  Some  of  the  post-dicrotic  waves  are  also  doubtless 
instrumental  in  origin.  The  dicrotic  wave  has  a  different  origin.  It 
was  at  one  time  thought  that  this  wave  was  due  to  a  wave  of  pressure 
reflected  from  the  periphery,  but  this  view  is  at  once  excluded  by  the 
fact  that  wherever  we  take  the  pulse-tracing,  whether  from  the  aorta, 
carotid,  radial,  dorsalis  pedis,  or  elsewhere,  this  secondary  elevation 
always  follows  the  percussion  wave  after  the  same  interval,  showing 
that  it  has  its  origin  in  the  commencement  of  the  arterial  system. 
Moreover,  a  single  pressure-wave  reflected  from  the  periphery  would 
be  impossible,  as  such  a  wave  reflected  from  one  part  would  be  inter- 
fered with  by  those  from  other  parts  ;  moreover,  a  dicrotic  elevation 
]3roduced  by  a  pressure-wave  reflected  from  the  periphery,  would  be 
increased  by  high  peripheral  resistance,  and  not  diminished  as  is 
actually  the  case. 

The  primary  cause  of  the  dicrotic  wave  is  the  closure  of  the  semi- 
lunar valves;  as  already  explained  when  we  were  considering  the 
velocity  pulse  (p.  285),  the  inflow  of  blood  into  the  aorta  suddenly 
ceases,  and  the  blood  is  driven  back  against  the  closed  aortic  doors 
by  the  elastic  recoil  of  the  aorta;  the  wave  rebounds  from  these 
and   is   propagated   through   the   arterial   system    as    the    dicrotic 


CH.  XXI.]  THE   PULSE-TRACING  291 

olovation.  Tho  production  of  the  dicrotic  wave  is  favoured  by  a 
low  blood-pressure  when  the  heart  is  beating  forcibly,  as  in  fever. 
Such  a  pulse  is  called  a  dicrotic  pulse  (fi^.  292),  and  the  second  beat 
can  be  easily  felt  by  the  finger  on  the  radial  artery. 

The  percussion  wave  is  produced  by  the  ventricular  systole 
expanding  tho  artery.  The  sharp  top  at  its  summit  is  due  to  the 
sudden  upward  spring  of  the  light  lover  of  the  s])hygmograph.  If  it 
were  possible  to  obtain  a  true  record 
of  what  really  occurs,  we  should 
doubtless  have  a  tracing  as  shown 
by  the  continuous  line  in  tho 
accompanying  figure  (fig.  293).  The 
apex  of  the  tidal  wave,  B,  marks  the  fig.  292.— Dicrotic  puise. 

end  of  the  ventricular  systole. 

In  our  study  of  intra-cardiac  pressure,  we  saw  that  the  systolic 
plateau  sometimes  has  an  ascending,  sometimes  a  descending,  slope 
(see  p.  243) ;  we  now  come  to  the  explanation  of  this  fact.  If  after 
the  first  sudden  rise  of  pressure  in  the  aorta  the  peripheral  resistance 
is  low,  and  the  blood  can  be  driven  on  from  the  aorta  more  rapidly 
than  it  is  thrown  in,  the  plateau  will  sink.  If,  on  the  other  hand, 
the  paripheral  resistance  is  high,  the  aortic  pressure  will  rise  as  long 
as  the  blood  is  flowing  in,  and  we  get  an  ascending  systolic  plateau 
and  an  anacrotic  pulse.  Thus  an  anacrotic  pulse 
is  seen  in  Bright's  disease,  where  the  peripheral 
resistance  is  very  high. 

If  a  long  pulse-tracing  is  taken,  the  effect  of 
the  respiration  can  be  seen  causing  an  increase  of 
pressure,  and  a  slight  acceleration  of  the  heart's 
beats  during  inspiration. 
^"^uise^rTcUigf'Arpe?-  Tho  main  waves  of  the  pulse  can  be  demon- 

cussion;  b  tidal ;  r,      stratcd  without  the  use  of  any  instrument  at  all 

dicrotic ;  and  d,  post-  1 1         •  ^         ^  t         ^  p 

dicrotic  waves.  by  ailowmg  the  blood  to  spurt  from  a  cut  artery 

on  to  the  surface  of  a  large  sheet  of  white  paper 
travelling  past  it.  We  thus  obtain  what  is  very  appropriately  called 
a  hccmautograjjh  (fig.  294). 

A  distinction  must  be  drawn  between  the  pulse  as  felt  at  any 
one  spot  in  the  course  of  an  artery,  and  the  pulse-wave  which  is 
propagated  throughout  the  arterial  system.  This  wave  of  expansion 
travels  along  the  arteries,  and  is  started  by  the  propulsion  of  the 
contents  of  the  left  ventricle  into  the  already  full  arterial  system. 
The  more  distant  the  artery  from  the  heart,  the  longer  the  interval 
that  elapses  between  the  ventricular  beat  and  the  arrival  of  the 
pulse-wave.  Thus  it  is  felt  in  the  carotid  earlier  than  in  the  radial 
artery,  and  is  still  later  in  the  dorsal  artery  of  the  foot.  The 
difference  of  time  is,  however,  very  slight ;  it  is  only  a  minute  frac- 


292 


THE   CIRCULATION   IN   THE   BLOOD-VESSELS 


[CH.  XXL 


Fig.   294 


Hfemaiito- 
graph,  to  be  read 
from  right  to  left. 


tion  of  a  second;  the  wave  travels  at  the  rate  of  from  5  to  10  metres 
a  second,  that  is  twenty  to  thirty  times  the  rate  of  the  blood  current. 

The  Rate  of  Propac/ation  of  the  Pulse-Ware. — The  method  of  asfertaining  this 
may  be  illustrated  b}'  the  use  of  a  long  elastic  tube  into  which  fluid  is  forced  by 
the  sudden  stroke  of  a  pump.  If  a  series  of  levers  are  placed 
along  the  tube  at  measured  distances  those  nearest  the  pump 
will  rise  first,  those  farthest  from  it  last.  If  these  are  arranged 
to  write  on  a  revolving  cylinder  under  one  another,  this  will 
be  shown  graphically,  and  the  time  interval  between  their 
movements  can  be  measured  by  a  time  tracing.  The  same 
principle  is  applied  to  the  arteries  of  the  body ;  a  series  of 
Marey's  tambours  are  applied  to  the  heart  and  to  various 
arteries  at  known  distances  from  the  heart ;  their  levers  are 
arranged  to  write  immediately  under  one  another,  as  in  fig.  248. 
The  difference  in  time  between  the  commencement  of  their  up- 
strokes is  measured  by  a  time  tracing  in  the  usual  way. 

The  tracing  taken  with  a  sphygmograph  is  that 
of  the  pressure  pulse ;  we  may  regard  it  as  a  blood- 
pressure  tracing  without  a  base  line.  The  actual 
measurement  of  the  blood-pressure  in  the  human 
subject  cannot  obviously  be  effected  by  the  apparatus 
employed  on  animals,  and  numerous  instruments 
have  been  invented  for  the  purpose  which  may  be 
applied  to  the  vessels  without;  any  dissection. 
These  instruments  are  termed  sphygmometers,  and  the  best  of 
them  are  modifications  of  one  originally  introduced  by  Eiva  Rocci. 
C.  J.  Martin's  pattern  consists  of  a  four-sided  elastic  bag  about  four 
and  a  half  inches  wide,  and  long  enough  to  encircle  the  arm.  It  is 
wrapped  round  the  arm,  and  outside  of  it  a  cuff  of  strong  canvas  is 
firmly  strapped.  Air  is  forced  into  the  bag  by  a  tube  leading  from 
a  ball  syringe;  this  tube  is  also  connected  by  a  side  branch  to  a 
mercury  manometer.  As  one  continues  to  pump  and  distend  the 
bag,  the  pulse  beats  are  transmitted  to  the  mercury  which  is  seen  to 
rise  in  the  manometer  and  oscillate  with  the  pulse  beats.  As  the 
pressure  rises  the  oscillations  become  more  pronounced,  and  at  a 
certain  point  they  exhibit  more  a  greater  excursion  than  they  do  at 
any  other  height ;  beyond  this  point  of  maximal  pulsation,  the 
oscillations  diminish  in  amplitude,  and  as  the  distension  of  the  bag 
is  increased  still  more,  the  pressure  is  at  last  reached,  when  it  is 
sufficient  to  obliterate  the  pulse,  and  the  oscillations  of  the  mercurial 
column  cease,  and  the  pulse  is  no  longer  to  be  felt  at  the  wrist.  The 
pressure  necessary  to  do  this  is  equal  to  the  systolic  ^Jressurc,  and  the 
height  of  the  mercurial  column  should  be  noted  when  the  pulse  just 
disappears.  The  point  of  maximal  pulsation  gives  a  reading  of  the 
diastolic  pressure.  The  systolic  pressure  is  more  easily  read  than  the 
diastolic  pressure,  for  it  is  by  no  means  easy  to  judge  accurately 
where  the  pulsations  are  greatest.     Moreover,  the  amount  of  systolic 


CH.  XXI.j 


BLOOD-PRESSURE   IN   MAN 


2^3 


pressure  gives  one  moro  useful  information  of  the  condition  of  the 
circulation  than  does  the  diastolic  pressure. 


Martin's  Sphygmometer  (made  by  Hawskley,  357  Oxford  Street). 


The  normal  pressure  in  the  radial  artery  of  healthy  young  adults 
is  110  to  120  mm.  Hg.  It  appears  to  be  as  constant  as  the  body 
temperature.  In  the  recumbent  posture  the  pressure  is  slightly 
lower  than  in  the  erect  position.  This  relation  is  reversed  in  condi- 
tions of  exhaustion.  During  muscular  exertion  the  pressure  is  raised, 
while  in  the  subsequent  period  of  rest  it  is  subnormal.  Mental 
work  raises  the  pressure ;  during  rest  and  sleep  it  is  lowered.  The 
taking  of  food  produces  no  noteworthy  effect.  In  disease  there  are 
naturally  variations  in  different  directions,  and  the  study  of  these 
has  already  yielded  valuable  results. 

The  Capillary  Flo-w. 

When  the  capillary  circulation  is  examined  in  any  transparent 
part  of  a  living  animal  by  means  of  the  microscope  the  blood  is  seen 
to  flow  with  a  constant  equable  motion;  the  red  blood-corpuscles 
move  along,  mostly  in  single  file,  and  bend  in  various  ways  to 
accommodate  themselves  to  the  tortuous  course  of  the  capillary,  but 
instantly  recover  their  normal  outline  on  reaching  a  wider  vessel. 

At  the  circumference  of  the  stream  in  the  larger  capillaries,  and 
in  the  small  arteries  and  veins,  there  is  a  layer  of  blood-plasma  in 
contact  with  the  walls  of  the  vessel,  and  adhering  to  them,  which 
moves  more  slowly  than  the  blood  in  the  centre.  Anyone  who  has 
rowed   on   a   river  will   know  that   the    swiftest  current   is   in  the 


294  THE   CIRCULATION   IN   THE   BLOOD-VESSELS  [cH.  XXL 

middle  of  the  stream.  The  red  corpuscles  occupy  the  middle  of  the 
stream  and  move  with  comparative  rapidity  ;  the  colourless  corpuscles 
run  much  more  slowly  by  the  walls  of  the  vessel ;  while  next  to  the 
wall  there  is  a  transparent  space  in  which  the  fluid  is  at  comparative 
rest  (the  so-called  "  still  layer  ") ;  if  any  of  the  corpuscles  happen  to 
be  forced  within  it,  they  move  more  slowly  than  before,  rolling  lazily 
along  the  side  of  the  vessel,  and  often  adhering  to  its  wall.  Some- 
times, when  the  motion  of  the  blood  is  not  strong,  many  of  the  white 
corpuscles  collect  in  a  capillary  vessel,  and  for  a  time  entirely  prevent 
the  passage  of  the  red  corpuscles. 

When  the  peripheral  resistance  is  greatly  diminished  by  the 
dilatation  of  the  small  arteries,  so  much  blood  passes  on  from  the 
arteries  into  the  capillaries  at  each  stroke  of  the  heart,  that  there  is 
not  sufficient  remaining  in  the  arteries  to  distend  them.  Thus,  the 
intermittent  current  of  the  ventricular  systole  is  not  converted  into 
a  continuous  stream  by  the  elasticity  of  the  arteries  before  the  capil- 
laries are  reached ;  and  so  intermittency  of  the  flow  occurs  both  in 
capillaries  and  veins,  and  a  pulse  is  produced  there.  The  same  pheno- 
menon may  occur  when  the  arteries  become  rigid  from  disease,  and 
when  the  beat  of  the  heart  is  so  slow  or  so  feeble  that  the  blood  at 
each  cardiac  systole  has  time  to  pass  on  to  the  capillaries  before  the 
next  stroke  occurs ;  the  amount  of  blood  sent  out  at  each  stroke  is 
then  insufficient  to  properly  distend  the  elastic  arteries. 

It  was  formerly  supposed  that  the  occurrence  of  any  transudation 
from  the  interior  of  the  capillaries  into  the  midst  of  the  surrounding 
tissues  was  confined,  in  the  absence  of  injury,  strictly  to  the  fluid 
part  of  the  blood ;  in  other  words,  that  the  corpuscles  could  not 
escape  from  the  circulating  stream,  unless  the  wall  of  the  containing 
blood-vessel  was  ruptured.  Augustus  Waller  afi&rmed,  in  1846,  that 
he  had  seen  blood-corpuscles,  both  red  and  white,  pass  bodily  through 
the  wall  of  the  capillary  vessel  in  which  they  were  contained ;  and 
that,  as  no  opening  could  be  seen  before  their  escape,  so  none  could 
be  observed  afterwards — so  rapidly  was  the  part  healed.  But  these 
observations  did  not  attract  much  notice  until  the  phenomenon  was 
rediscovered  by  Cohnheim  in  1867. 

Cohnheim's  experiment  was  performed  in  the  following  manner : 
A  frog  is  curarised ;  and  the  abdomen  having  been  opened,  a  portion 
of  small  intestine  is  drawn  out,  and  its  transparent  mesentery  spread 
out  under  a  microscope.  After  a  variable  time,  occupied  by  dilatation, 
following  contraction  of  the  minute  vessels  and  accompanying 
quickening  of  the  blood-stream,  there  ensues  a  retardation  of  the 
current,  and  blood-corpuscles  begin  to  make  their  way  through  the 
capillaries  and  small  vessels. 

Diapedesis,  or  emigration  of  the  white  corpuscles,  occurs  to  a  small 
extent  in  health.     But  it  is  much  increased  in  inflammation,  and  may 


CH.  XXI.] 


DIAPEDESIS 


295 


go  on  so  as  to  form  a  large  collection  of  leucocytes  (i.e.  white  cor- 
puscles) outside  the  vessels. 

The  emigration  of  red  corpuscles  is  only  seen  in  inflammation,  and 
is  a  passive  process ;  it  occurs  when  the  holes 
made  by  the  emigrating  leucocytes  do  not  close 
up   immediately,   and    so   the   red   corpuscles 
escape  too. 

The  real  meaning  of  the  process  of  inflam- 
mation is  a  subject  which  is  being  much  dis- 
cussed now,  but  it  may  be  interesting  to  state 
briefly  the  views  of  Metschnikoff,  who  has  in 
recent  years  been  a  prominent  investigator  of 
the  subject.  Even  if  these  views  do  not  repre- 
sent the  whole  truth,  it  can  hardly  be  doubted 
that  the  phenomena  described  play  a  very 
important  part  in  the  process.  Metschnikoff 
teaches  that  the  vascular  phenomena  of  inflam- 
mation have  for  their  object  an  increase  in  the 
emigration  of  leucocytes,  which  have  the  power 
of  devouring  the  irritant  substance,  and  re- 
moving the  tissues  killed  by  the  lesion.  They 
are  therefore  called  phagocytes  (devouring  or 
scavenging  corpuscles).  It  may  be  that  the 
microbic  influence,  or  the  influence  of  the 
chemical  poisons  they  produce,  is  too  powerful 
for  the  leucocytes ;  then  they  are  destroyed, 
and  the  dead  leucocytes  become  pus  corpuscles;  but  if  the  leuco- 
cytes are  successful  in  destroying  the  foreign  body,  micro-organisms, 
and  disintegrated  tissues,  they  disappear,  wandering  back  to  the 
blood-vessels,  and  the  lost  tissue  is  replaced  by  a  regeneration  of 
the  surrounding  tissues.* 

The  circulation  through  the  capillaries  must,  of  necessity,  be 
largely  influenced  by  that  which  occurs  in  the  vessels  on  either  side 
of  them  in  the  arteries  or  the  veins;  their  intermediate  position 
causes  them  to  feel  at  once  any  alteration  in  the  size,  rate,  or  pres- 
sure of  the  arterial,  and  more  especially  of  the  venous  blood-stream. 
The  apparent  contraction  of  the  capillaries,  on  the  application  of 
certain  irritating  substances,  and  during  fear,  and  their  dilatation  in 
blushing,  may  be  referred  primarily  to  the  action  of  the  small  arteries. 


J.  296.— A  large  capillary 
from  the  frog's  mesentery 
eight  hours  after  irrita- 
tion had  been  set  up, 
showing  emigration  of 
leucocytes,  a.  Cells  in 
the  act  of  traversing  the 
capillary  wall ;  6,  some 
already  escaped.     (Frey.) 


The  Venous  Plo-w. 

The  blood-current  in  the  veins  is  maintained  primarily  by  the 
vis  a  tergo,  that  is,  the  force  behind,  which  is   the  blood-pressure 

*  This  question  is  closely  related  to  that  of  immunity,  which  is  discussed  in  the 
chapter  on  the  Blood  (Chapter  XXVI). 


296  THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CH.  XXI. 

transmitted  from  the  heart  and  arteries ;  but  very  effectual  assist- 
ance to  the  flow  is  afforded  by  the  action  of  the  muscles  capable  of 
pressing  on  the  veins  with  valves,  as  well  as  by  the  suction  action 
of  the  heart,  and  the  aspiratory  action  of  the  thorax  (vis  a 
fronte). 

The  effect  of  muscular  pressure  upon  the  circulation  may  be  thus 
explained.  When  pressure  is  applied  to  any  part  of  a  vein  and  the 
current  of  blood  in  it  is  obstructed,  the  portion  behind  the  seat  of 
pressure  becomes  swollen  and  distended  as  far  back  as  the  next  pair 
of  valves,  which  are  in  consequence  closed  (fig.  230,  B,  p.  220).  Thus, 
whatever  force  is  exercised  by  the  pressure  of  the  muscles  on  the 
veins,  is  distributed  partly  in  pressing  the  blood  onwards  in  the 
proper  course  of  the  circulation,  and  partly  in  pressing  it  backwards 
and  closing  the  valves  behind. 

The  circulation  might  lose  as  much  as  it  gains  by  such  an  action, 
if  it  were  not  for  the  numerous  communications  which  the  veins  make 
with  one  another ;  through  these,  the  closing  up  of  the  venous 
channel  by  the  backward  pressure  is  prevented  from  being  any  serious 
hindrance  to  the  circulation,  since  the  blood,  the  onward  course  of 
which  is  arrested  by  the  closed  valves,  can  at  once  pass  through 
some  anastomosing  channel,  and  proceed  on  its  way  by  another 
vein.  Thus,  the  effect  of  muscular  pressure  upon  veins  which  have 
valves,  is  turned  almost  entirely  to  the  advantage  of  the  circula- 
tion. 

In  the  web  of  the  bat's  wing,  the  veins  are  furnished  with  valves, 
and  possess  the  remarkable  property  of  rhythmical  contraction  and 
dilatation,  whereby  the  current  of  blood  within  them  is  distinctly 
accelerated  (Wharton  Jones).  The  contraction  occurs,  on  an  average, 
about  ten  times  in  a  minute ;  the  existence  of  valves  prevents  regur- 
gitation, so  the  entire  effect  of  the  contractions  is  auxiliary  to  the 
onward  current  of  blood.  Analogous  phenomena  have  been  observed 
in  other  animals. 

A  venous  pulse  is  observed  under  the  conditions  previously 
described  (p.  294),  when  the  arterioles  are  dilated  so  that  the  arterial 
pulse  passes  through  the  capillaries  to  the  veins. 

A  venous  pulse  is  also  seen  in  the  superior  and  inferior  vena 
cava  near  to  their  entrance  into  the  heart ;  this  corresponds  to  varia- 
tions of  the  pressure  in  the  right  auricle.  When  the  ventricle  is  con- 
tracting there  is  a  slow  rise  due  to  the  fact  that  the  blood  cannot  get 
into  the  ventricle,  and  so  distends  the  auricle;  a  second  short,  sharp 
elevation  of  pressure  is  produced  by  the  auricular  systole.  Altera- 
tions of  venous  pressure  are  also  produced  in  the  great  veins  by  the 
respiratory  movements,  the  pressure  sinking  during  inspiration,  and 
rising  during  expiration. 


CH.  XXI.]  THE   VASO-MOTOR   NERVOUS    SYSTEM  297 

The  Vaso-Motor  Nervous  System. 

Tho  vaso-motor  nervous  system  consists  of  the  vaso-motor  centre 
situated  in  the  bulb,  of  certain  subsidiary  vaso-motor  centres  in  the 
spinal  cord,  and  of  vaso-motor  nerves,  which  are  of  two  kinds — (a) 
those  the  stimulation  of  which  causes  constriction  of  the  vessels ; 
these  are  called  vaso-constridor  nerves ;  (h)  those  the  stimulation  of 
which  causes  dilatation  of  the  vessels ;  these  are  called  vaso-dilator 
nerves. 

The  following  names  are  associated  with  the  history  of  the  subject. 
The  muscular  structure  of  arteries  was  first  described  by  Henle  in 
1841 ;  in  1852  Brown  Sequard  made  a  study  of  the  vaso-constrictor, 
or,  as  he  termed  them,  tonic  nerves.  The  vaso-motor  centre  was  dis- 
covered by  Schiff  (1855),  and  more  accurately  localised  by  Ludwig 
(1871).  The  dilator  nerves  were  also  discovered  by  Schiff;  at  first 
they  were  termed  paretic  nerves.  Other  names  which  must  be 
mentioned  in  connection  with  the  subject  are  those  of  Claude  Bernard, 
Heidenhain,  and,  in  more  recent  years,  Gaskell,  Langley,  and  Ramon 
y  Cajal. 

The  nerves  supply  the  muscular  tissue  in  the  walls  of  the  blood- 
vessels and  regulate  their  calibre,  but  exert  their  most  important 
action  in  the  vessels  which  contain  relatively  the  greatest  amount  of 
muscular  tissue,  namely,  the  small  arteries  or  arterioles. 

Under  ordinary  circumstances,  the  arterioles  are  maintained  in 
a  state  of  moderate  or  tonic  contraction,  and  this  constitutes  the 
peripheral  resistance,  the  use  of  which  is  to  keep  up  the  arterial 
pressure,  which  must  be  high  enough  to  force  the  blood  through  the 
capillaries  and  veins  in  a  continuous  stream  back  to  the  heart. 

Another  function  which  is  served  by  this  muscular  tissue  is  to 
regulate  the  amount  of  blood  which  flows  through  the  capillaries  of 
any  organ  in  proportion  to  its  needs.  During  digestion,  for  instance, 
it  is  necessary  that  the  digestive  organs  should  be  supplied  with  a 
large  quantity  of  blood :  for  this  purpose  the  arterioles  of  the 
splanchnic  area  are  relaxed,  and  there  is  a  vast  amount  of  blood  in  this 
area,  and  therefore  a  correspondingly  small  amount  in  other  areas,  such 
as  the  skin ;  this  accounts  for  the  sensation  of  chilliness  experienced 
after  a  full  meal.  The  skin  vessels  form  another  good  example ;  one 
of  the  most  important  uses  of  the  skin  is  to  get  rid  of  the  heat  of 
the  body  in  such  a  way  that  the  body  temperature  shall  remain 
constant ;  when  excess  of  heat  is  produced  there  is  also  an  increase 
in  the  loss  of  heat ;  the  skin  vessels  are  then  dilated,  and  so  more 
blood  is  exposed  on  the  surface,  and  thus  an  increase  in  the  radiation 
of  heat  from  the  surface  is  brought  about.  On  the  other  hand,  when 
it  is  necessary  that  the  heat  produced  should  be  kept  in  the  body, 
the  loss  of  heat  is  diminished  by  a  constriction  of  the  skin  vessels, 


298  THE  CIRCULATION   IN   THE   BLOOD-VESSELS  [CH.  XXI. 

as  in  cold  weather.  The  alteration  of  the  calibre  of  the  vessels  is 
brought  about  by  the  action  of  the  vaso-motor  nervous  system  on 
the  muscular  tissue  of  the  arterioles. 

There  are  certain  organs  of  the  body  in  which  the  necessity  for 
alterations  in  their  blood-supply  does  not  exist.  Such  organs  are 
the  lungs  and  the  brain.  It  is  in  the  vessels  of  these  organs  that  the 
influence  of  vaso-motor  nerves  is  at  a  minimum.  The  pulmonary 
vessels  are  stated  by  Bradford  and  Dean  to  be  supplied  by  nerves 
which  leave  the  cord  in  the  upper  thoracic  region ;  but  on  stimulating 
these  the  rise  of  pressure  produced  is  extremely  small;  it  is  very 
doubtful  if  the  fibres  in  question  are  really  vaso-constrictors ;  the 
small  rise  observed  may  be  partly  or  even  wholly  due  to  the  accelera- 
tion of  the  heart,  which  is  another  result  of  stimulating  these  nerve- 
roots. 

The  vaso-motor  centre  lies  in  the  grey  matter  of  the  floor  of  the 
fourth  ventricle ;  it  is  a  few  millimetres  in  length,  reaching  from  the 
upper  part  of  the  floor  to  within  about  4  mm.  of  the  calamus  scrip- 
torius.  The  position  of  this  centre  has  been  discovered  by  the 
following  means :  when  it  is  destroyed  the  tone  of  the  small  vessels 
is  no  longer  kept  up,  and  in  consequence  there  is  a  great  and  universal 
fall  in  arterial  blood-pressure;  when  it  is  stimulated  there  is  an 
increase  in  the  constriction  of  the  arterioles  all  over  the  body,  and 
therefore  a  rise  of  arterial  blood-pressure.  Its  upper  and  lower 
limits  have  been  accurately  determined  in  the  following  way :  a  series 
of  animals  is  taken,  and  the  central  nervous  system  divided  in  a 
different  place  in  each;  the  cerebrum  and  cerebellum  may  be  cut 
off  without  affecting  blood -pressure,  the  vaso-motor  centre  must 
therefore  be  below  these ;  if  the  section  is  made  just  above  the 
medulla,  the  blood-pressure  still  remains  high,  and  it  is  not  till  the 
upper  limit  of  the  centre  is  passed  that  the  blood-pressure  falls. 
Similarly,  in  another  series  of  animals,  if  the  cervical  cord  is  cut 
through,  and  the  animal  kept  alive  by  artificial  respiration,  there  is 
an  enormous  fall  of  pressure  due  to  the  influence  of  the  centre  being 
removed  from  the  vessels ;  in  other  experiments  the  section  is  made 
higher  and  higher,  and  the  same  result  noted,  until  at  last  the  lower 
limit  of  the  centre  is  passed,  and  the  fall  of  pressure  is  less  and  less 
marked  the  higher  one  goes  there,  until  in  the  animal  in  which  the 
section  is  made  at  the  upper  boundary  of  the  centre  the  blood- 
pressure  is  not  affected  at  all,  and  the  centre  can  be  influenced 
reflexly  by  the  stimulation  of  afferent  nerves,  the  pressor  and 
depressor  nerves,  which  we  shall  be  considering  immediately. 

After  the  destruction  of  the  vaso-motor  centre  in  the  bulb,  there 
is  a  fall  of  pressure.  If  the  animal  is  kept  alive,  the  vessels  after  a 
time  recover  their  tone,  and  the  arterial  pressure  rises ;  it  rises  still 
more  on  stimulating  the  central  end  of  a  sensory  nerve ;  this  is  due 


Cn.  XXI.]  VASO-MOTOR   NERVES  299 

to  the  existence  of  subsidiary  vaso-motor  centres  in  the  spinal  cord ; 
for  on  the  subsequent  destruction  of  the  spinal  cord  the  vessels  again 
lose  their  tone  and  the  blood-pressure  sinks. 

The  vaso-motor  path  is  down  the  lateral  column  of  the  spinal 
cord,  and  the  fibres  terminate  by  arborising  around  the  cells  in  the 
grey  matter  of  the  subsidiary  vaso-motor  centres,  the  anatomical 
position  of  which  is  uncertain,  though  it  is  probably  in  the  cells  of 
the  intermedio-lateral  tract.  From  these  cells  fresh  axis-cylinder 
processes  originate,  which  pass  out  as  the  small  meduUated  nerve- 
fibres  in  the  anterior  roots  of  the  spinal  nerves. 

The  vaso-constrictor  nerves  for  the  whole  body  leave  the  spinal 
cord  by  the  anterior  roots  of  the  spinal  nerves  from  the  second 
thoracic  to  the  second  lumbar,  both  inclusive.  They  leave  the  roots 
by  the  white  rami  communicantes,  and  pass  into  the  ganglia  of  the 
sympathetic  chain,  which  lies  on  each  side  along  the  front  of  the 
vertebral  column.  The  ganglia  on  this  chain  (the  lateral  ganglia  of 
Gaskell)  may  also  be  called  the  chain  of  vaso-motor  ganglia,  because 
here  are  situated  cell  stations  on  the  course  of  the  vaso-constrictor 
nerves  for  the  head,  trunk  and  limbs.  That  is  to  say,  the  small 
medullated  nerve-fibres  terminate  by  arborising  around  the  cells  of 
these  ganglia,  and  a  fresh  relay  of  axis-cylinder  processes  from  these 
cells  carry  on  the  impulses. 

The  next  figure  (fig.  297)  represents  diagrammatically  how  this 
occurs.     The  sheaths  of  the  fibres  are  not  represented. 

The  cell  station  of  any  particular  fibre  is  not  necessarily  situated 
in  the  first  ganglion  to  which  it  passes ;  the  fibres  of  the  white  ramus 
communicans  of  the  second,  thoracic  do  not,  for  instance,  all  have  their 
cell  stations  in  the  corresponding  thoracic  ganglion,  but  may  pass 
upwards  or  downwards  in  the  chain  to  a  more  or  less  distant  ganglion 
before  they  terminate  by  arborising  around  a  cell  or  cells. 

The  vaso-constrictor  nerves,  however,  have  all  cell  stations  some- 
where in  the  sympathetic  system,  and  the  new  axis-cylinders  that 
arise  from  the  cells  of  the  ganglia  differ  from  those  which  terminate 
there  in  the  circumstance  that  they  do  not  possess  a  medullary  sheath, 
but  they  are  pale,  grey,  or  non-medullated  fibres.  Those  which  are 
destined  for  the  supply  of  the  vessels  of  the  head  and  neck  pass  into 
the  ganglion  stellatum  or  first  thoracic  ganglion,  thence  through  the 
annulus  of  Vieussens  to  the  inferior  cervical  ganglion,  and  thence 
along  the  sympathetic  trunk  to  their  destination.  Their  cell  station 
is  in  the  superior  cervical  ganglion. 

Those  for  the  body  wall  and  limbs  pass  back  from  the  sympathetic 
ganglia  to  the  spinal  nerves  by  the  grey  rami  communicantes,  and  are 
distributed  with  the  other  spinal  nerve-fibres.  The  cell  stations  for 
the  upper  limb  fibres  are  in  the  ganglion  stellatum,  and  for  the  lower 
limb  fibres  in  the  lower  lumbar  and  upper  sacral  ganglia. 


300 


THE   CIRCULAtlON   IN   TliE   BLOOD-VESSELS  [CH.  XXL 


Those  for  the  interior  of  the  body  pass  into  the  various  plexuses 
of  sympathetic  nerves  in  the  thorax  and  abdomen,  and  are  distributed 
to  the  vessels  of  the  thoracic  and  abdominal  viscera.     This  set  includes 


Fig.  297.— Transverse  section  through  half  the  spmal  cord,  showing  the  ganglia.  A,  anterior  cornual 
cells ;  B,  axis-cylinder  process  of  one  of  these  going  to  posterior  root ;  C,  anterior  (motor)  root ;  D, 
posterior  (sensory)  root ;  E,  spinal  ganglion  on  posterior  root  ;  F,  sympathetic  ganglion ;  G,  ramus 
communicans ;  H,  posterior  branch  of  spinal  nerve ;  I,  anterior  branch  of  spinal  nerve ;  o,  long 
collaterals  from  posterior  root  fibres  reaching  to  anterior  horn;  '),  short  collaterals  passing  to 
Clarke's  column ;  c,  cell  in  Clark's  column  sending  an  axis-cylinder  (d)  process  to  the  direct  cere- 
bellar tract ;  e,  fibre  of  the  anterior  root ;  /,  axis-cylinder  from  sympathetic  ganglion  cell,  dividing 
into  two  branches,  one  to  the  periphery,  the  other  towards  the  cord ;  g,  fibre  of  the  anterior  root 
terminating  by  an  arborisation  in  the  sympathetic  ganglion  ;  h,  sympathetic  fibre  passing  to  peri- 
phery.   (Ramon  y  Cajal.) 

the  most  important  vaso-motor  nerves  of  the  body,  the  splanchnics. 
Their  cell  stations  are  situated  in  the  various  ganglia  of  the  abdominal 
plexuses. 

The  vaso-dilator  nerves  in  part  accompany  those  just  described, 
but  they  are  not  limited  to  the  outflow  from  the  second  thoracic  to 
the  second  lumbar.  Thus,  the  nervi  erigentes  originate  as  white 
rami  communicantes  from  the  second  and  third  sacral  nerves,  and 
the  chorda  tympani,  another  good  example  of  a  vaso-dilator  nerve, 
is  a  branch  of  the  seventh  cranial  nerve.  Bayliss  has  also  shown 
that  the  posterior  root  fibres  may  act  as  vaso-dilators  (see  p.  303). 

All  vaso-motor  nerves,  whether  they  are  constrictor  or  dilator, 
differ  very  markedly  from  the  spinal  nerve-fibres  which  are  distri- 
buted to  voluntary  muscles  in  being  ganghonated ;  that  is,  in  having 


CH.  XXI.]  VASO-MOTOR    NERVES  301 

cell  stations  ui*  positions  of  relay  on  their  course  from  the  central 
nervous  system  to  the  muscular  fibres  they  supply. 

The  existence  of  cell  stations  between  the  central  nervous 
system  and  the  muscular  fibres  is  not  confined  to  the  nerves  of 
blood-vessels,  but  is  found  also  in  the  nerves  which  supply  the 
heart  and  other  viscera. 

Moreover,  the  nerves  which  supply  the  voluntary  muscles  are 
motor  in  function ;  inhibitory  fibres  to  the  voluntary  muscles  of 
vertebrates  do  not  exist.  But  in  the  case  of  the  involuntary  muscles 
there  are  usually  the  two  sets  of  nerve-fibres  with  opposite 
functions. 

In  the  case  of  the  heart,  we  have  an  accelerator  set  which  course 
through  the  sympathetic,  and  an  inhibitory  set  which  course  through 
the  vagus. 

In  the  case  of  the  vessels,  we  have  an  accelerator  set,  which  we 
have  hitherto  called  vaso-constrictors,  and  an  inhibitory  set  we  have 
been  calling  vaso-dilators. 

In  the  case  of  the  other  contractile  viscera,  we  have  also  viscero- 
accelerator  and  viscero-inhibitory,  which  respectively  hasten  and 
lessen  their  peristaltic  movements. 

Adopting  Gaskell's  nomenclature,  we  may  further  term  the 
accelerator  groups  of  nerves  katabolic,  as  they  increase  the  activity 
of  the  muscles  they  supply,  bringing  about  an  increase  of  wear  and 
tear,  and  an  increase  in  the  discharge  of  waste  material.  The 
inhibitory  nerves,  on  the  other  hand,  are  anabolic,  as  they  produce  a 
condition  of  rest  in  the  tissues  they  supply,  and  so  give  an  oppor- 
tunity for  repair  or  constructive  metabolism. 

The  distribution  of  the  vaso-motor  nerves  and  the  viscero-motor 
nerves  has  been  within  recent  years  very  thoroughly  worked  out 
by  Langley.  The  nerves  of  the  various  viscera  we  shaU  take  with 
the  individual  organs.  In  all  these  cases,  there  is  a  cell  station 
somewhere  in  the  sympathetic  system,  and  only  one  for  each  nerve- 
fibre.  T\iQ  preganglionic  fibres  {i.e.,  the  fibres  from  the  spinal  cord  to 
the  sympathetic  cell  station)  are  usually  medullated ;  the  postgang- 
lionic fibres  {i.e.,  those  that  leave  the  gangHon)  are  usually  non- 
medullated.  But  this  histological  distinction,  so  much  emphasised 
by  Gaskell,  is  not  without  exceptions,  and  the  localisation  of  cell 
stations  is  made  with  far  greater  certainty  by  Langley's  nicotine 
method.  Nicotine  in  small  doses  paralyses  nerve-cells,*  but  not 
nerve-fibres;  if  the  drug  is  injected  into  an  animal,  stimulation  of 
the  anterior  nerve-roots  produces  no  movements  of  the  involuntary 

*  It  is  still  a  matter  of  uncertainty  whether  this  drug  acts  upon  the  nerve-cells 
themselves,  or  the  terminal  arborisations  (synapses)  of  the  nerve-fibres  that 
surround  them.  Before  the  paralytic  effect  of  nicotine  comes  on,  it  excites  the 
nerve-cells,  and  thus  in  the  case  of  the  blood-vessels  causes  a  general  constriction 
of  the  arterioles  and  a  rise  of  arterial  pressure. 


302  THE   CIRCULATION    IN   THE   BLOOD-VESSELS  [CH.  XXL 

muscles,  because  the  paralysed  cell  stations  on  the  course  of  the 
nerve-fibres  act  as  blocks  to  the  propagation  of  the  impulses.  If  the 
nicotine  is  applied  locally  by  painting  it  over  one  or  more  ganglia, 
there  will  be  a  block  in  those  fibres  only  which  have  their  cell 
stations  in  those  particular  ganglia.  Thus,  in  the  lateral  chain  of 
ganglia  we  find  the  cells  on  the  course  of  the  pilo-motor  nerves  {i.e., 
to  the  muscles  of  the  hairs),  of  the  vaso-constrictors  of  the  head, 
limbs,  and  body  walls,  and  possibly  of  the  splenic  nerves.  In  the  col- 
lateral ganglia  {i.e.,  coehac,  mesenteric,  etc.)  are  found,  amongst  others, 
the  ceils  on  the  course  of  the  splanchnic  nerves,  of  the  nerves  to 
sweat  glands,  of  the  cardiac  accelerators,  and  of  the  inhibitory 
fibres  of  the  alimentary  canal;  while  in  the  terminal  gangha  are 
placed,  among  others,  the  cells  on  the  course  of  the  cardiac  inhibi- 
tory nerves,  of  the  motor  fibres  to  the  lower  part  of  the  intestine 
and  bladder,  and  of  the  inhibitory  fibres  to  the  external  genital 
organs. 

We  may  now  ask  what  is  the  object  that  is  served  by  the  existence  of  ganglia 
on  the  course  of  these  nerves.  It  appears  to  be  a  means  of  distributing  nerve- 
fibres  to  a  vast  area  of  muscular  tissue  by  means  of  a  comparatively  small  number 
of  nerve-fibres  that  leave  the  central  nervous  system  ;  for  each  fibre  that  leaves  the 
central  nervous  system  arborises  around  a  number  of  cells,  and  thus  the  impulse  it 
carries  is  transferred  to  a  large  number  of  new  axis-cylinder  processes. 

In  some  cases,  it  is  true,  a  single  nerve-fibre  will  divide  into  multitudinous 
branches  to  accomplish  the  same  object  (as  in  the  supply  of  the  electric  organ  of 
Malapterurus,  the  fibres  to  the  millions  of  its  subdivisions  all  originating  from  a 
single  axis-cylinder),  but  the  usual  way  appears  to  be  a  combination  of  this  method 
with  that  of  subsidiary  cell-stations. 

At  one  time  a  ganglion  was  supposed  to  be  the  normal  centre  for  reflex  action. 
The  submaxillary  ganglion  was  the  battle-field  in  which  this  question  was  fought 
out  in  Claud  Bernard's  time.  In  the  later  researches  of  Langley  and  Anderson, 
the  only  instances  where  such  a  thing  seemed  possible  were  the  following : — When 
all  the  nervous  connections  of  the  inferior  mesenteric  ganglion  are  divided  except 
the  hypogastric  nerves,  stimulation  of  the  central  end  of  one  hj^jogastric  causes 
contraction  of  the  bladder,  the  efferent  path  to  which  is  the  other  hypogastric 
nerve.  In  addition,  they  observed  an  apparent  reflex  excitation  of  the  nerve  sup- 
plying the  erector  muscles  of  the  hairs  (pilo-motor  nerves)  through  other  sympa- 
thetic ganglia.  In  neither  case  is  the  action  truly  reflex,  but  is  caused  by  the 
stimulation  of  the  central  ends  of  motor-fibres  which  issue  from  the  spinal  cord, 
and  which  after  passing  through  the  ganglion  send  branches  down  each  hypogastric 
nerve.     The  experiment  is  in  fact  similar  to  Kiihne's  gracilis  experiment  (p.  173). 

It  certainly  is  the  case  that  under  normal  circumstances,  the  centres  for  reflex 
action  are  in  the  central  nervous  system.  But  there  do  appear  to  be  some  condi- 
tions in  which  it  is  possible  for  ganglia  to  assume  this  function.  The  recovery 
of  vaso-motor  tone,  and  of  tone  in  certain  viscera  after  destruction  of  extensive 
tracts  of  the  spinal  cord,  or  the  persistence  of  peristaltic  action  in  the  intestine 
after  cutting  through  all  its  nerves,  are  cases  in  point.  (See  further,  under 
Intestinal  Movements,  and  Spinal  Visceral  Reflexes). 

The  observations  of  W.  M.  Bayliss  on  the  vaso-diiator  nerves  of  dogs  are  of 
considerable  interest.  He  could  find  no  vaso-dilator  fibres  to  the  hind  limb  in  the 
abdominal  sympathetic  chain  ;  but  the  only  fibres  excitation  of  which  produced 
vascular  dilatation  there,  are  contained  in  the  posterior  roots.  He  also  found  fibres 
in  the  posterior  roots  of  the  12th  and  1.3th  thoracic  nerves,  which  act  as  vaso-dilators 
of  the  small  intestine.  Not  only  is  vaso-diiatation  the  result  of  mechanical,  electri- 
cal, or  thermal  stimulation  of  these  roots,  but  experiments  are  adduced  which  show 


CH.  XXT.]  THE    VASO-MOTOR    CENTRE  303 

that  in  normal  reflexes,  such  as  occur  when  the  depressor  nerve  is  stimulated,  the 
dilator  impulses  travel  by  the  same  nmte.  This  raises  tiie  qu<stion  whether  the 
posterior  roots  conbiin  true  efferent  fibres.  The  facts  of  defreneration  show  that 
they  do  nt)t.  Bayliss  is  therefore  driven  to  the  conclusion  that  the  same  nerve 
terminations  in  the  periphery  serve  both  to  take  up  sensory  impressions,  and  to 
convey  inhibitory  impulses  to  the  muscular  structures  in  which  they  end.  In  other 
words,  we  have  here  another  example  which  may  be  added  to  those  previously 
mentioned  (p.  173),  that  nervc-fibrae  may  convey  impulses  in  both  directions.  The 
term  (tntidromir  is  used  by  Bayliss  to  express  the  fact  that  impulses  may  travel  in 
the  reverse  direction  to  that  in  which  they  usually  pass. 

The  Vaso-motor  centre  can  be  excited  directly,  as  by  induc- 
tion currents;  the  result  is  an  increase  of  arterial  blood -pressure 
owing  to  an  increase  of  the  contraction  of  the  peripheral  arterioles. 

It  can  also  be  excited  by  the  action  of  poisons  in  the  blood  which 
circulates  through  it ;  thus,  strophanthus  or  digitalis  causes  a  marked 
rise  of  general  arterial  pressure  due  to  the  constriction  of  the  peri- 
pheral vessels  brought  about  by  impulses  from  the  centre. 

It  is  also  excited  by  venous  blood,  as  in  asphyxia;  the  rise  of 
blood-pressure  which  occurs  during  the  first  part  of  asphyxia  is  due 
to  constriction  of  peripheral  vessels ;  the  fall  during  the  last  stage  of 
asphyxia  is  largely  due  to  heart  failure.  We  shall  study  asphyxia 
more  at  length  in  connection  with  respiration.  During  the  period  of 
decreased  pressure,  waves  are  often  observed  on  the  blood-pressure 
curve  which  arise  from  a  slow  rhythmic  action  of  the  vaso-motor 
centre.  The  centre  alternately  sends  out  stronger  and  weaker  con- 
strictor impulses.  They  are  known  as  the  Trauhe-Hering  waves,  and 
are  much  slower  in  their  rhvthm  than  the  waves  on  the  tracing 
which  are  due  to  respiration.  They  are  not  peculiar  to  asphyxia,  but 
are  frequently  seen  in  tracings  from  normal  animals.  Fig.  298 
represents  a  tracing  obtained  from  a  dog  under  the  influence  of 
an  anaesthetic.  This  tracing  shows  the  three  sets  of  waves,  first  the 
oscillations  due  to  the  heart-beats,  next  in  size  those  due  to  the 
respiratory  movements,  which  in  their  turn  are  superposed  on  the 
prolonged  Traube-Hering  waves. 

The  Vaso-motor  centre  may  be  excited  reflexly. — The  afferent 
impulses  to  the  vaso-motor  centre  may  be  divided  into  pressor  and 
depressor. 

Most  sensory  nerves  are  pressor  nerves.  The  sciatic  or  the  vagus 
nerves  may  be  taken  as  instances ;  when  they  are  divided  and  their 
central  ends  stimulated,  the  result  is  a  rise  of  blood-pressure  due  to 
the  stimulation  of  the  vaso-motor  centre,  and  a  consequent  constric- 
tion of  the  arterioles  all  over  the  body,  but  especially  in  the 
splanchnic  area.  Fig.  299  shows  the  result  of  such  an  experiment. 
It  is  necessary  in  performing  such  an  experiment  to  administer  curare 
as  well  as  an  anaesthetic  to  the  animal,  in  order  to  obviate  reflex 
muscular  struggles,  which  would  themselves  produce  a  rise  in  arterial 
pressure. 


304 


THE   CIRCULATION    IX   THE    BLOOD-VESSELS 


[CH.  XXI. 


Fig.  298. — Arterial  blood-pressure  tracing  from  dog  showing  Tranbe-Hering  waves.    (Sherrington.) 


Fig.  2yy. — Kise  in  arterial  blo<'ja-pressure  produced  by  stiinuiating  the  central  tad  of  a  .sensory  nerve  (external  popliteal) 
in  a  cat  under  the  influence  of  morphine  and  curare,  bp,  blood-pressure ;  a,  abscissa  or  base  line ;  t,  time  inters'als 
of  5  seconds  ;  e  ,  signal  line,  the  lowering  of  which  indicates  the  period  of  stimulation  of  the  nerve.  The  size  of  the  figure 
is  slightly  reduced  in  reproduction.    (.Sherrington.) 


CH.  XXI.]  PRESSOR   AND   DEPRESSOR   NERVES  305 

Many  sensory  nerves  also  contain  depressor  i'lbres  which  produce 
the  opposite  effect.  The  most  marked  bundle  of  these  is  known  as 
the  depressor  nerve.  In  most  animals  this  is  bound  up  in  the  trunk 
of  the  vagus ;  but  in  some,  like  the  rabbit,  cat,  and  horse,  the  nerve 
runs  up  as  a  separate  branch  from  the  heart  (or,  according  to  some 
recent  observations,  from  the  commencement  of  the  aorta),  and  joins 
the  vagus  or  its  superior  laryngeal  branch,  and  ultimately  reaches  the 
vaso-motor  centre.  When  this  nerve  is  stimulated  (the  vagi  having 
been  previously  divided  to  prevent  reflex  inhibition  of  the  heart),  a 
marked  fall  of  arterial  blood -pressure  is  produced  (see  fig.  300). 
Stimulation  of  this  nerve  affects  the  vaso-motor  centre  in  such  a  way 
that  the  normal  constrictor  impulses  that  pass  down  the  vaso-con- 
strictor  nerves  are  inhibited.  The  fall  of  pressure  is  very  slight  after 
section  of  the  splanchnic  nerves,  showing  that  the  splanchnic  area  is 
the  part  of  the  body  most  affected.  The  normal  function  of  this 
nerve  is  to  adapt  the  peripheral  resistance  to  the  heart's  action :  if 
the  constriction  of  the  arterioles  is  too  high  for  the  heart  to  overcome, 
an  impulse  by  this  nerve  to  the  vaso-motor  centre  produces  reflexly 
a  lessening  of  the  peripheral  resistance. 

N.B.— The  term  depressor  should  be  carefully  distinguished  from  inhibitory; 
stimulation  of  the  peripheral  end  of  the  vagus  produces  a  fall  of  blood-pressure  due 
to  inhibition  (slowing  or  stoppage)  of  the  heart  (see  figs.  277  and  278) ;  stimulation 
of  the  central  end  of  the  depressor  nerve  produces  a  lowering  of  blood-pressure  for 
a  different  reason,  namely,  a  reflex  relaxation  of  the  splanchnic  arterioles. 

Experiments  on  Vaso-motor  nerves. — The  experiments  on  the 
vaso-motor  nerves  are  similar  to  those  performed  on  other  nerves 
when  one  wishes  to  ascertain  their  functions.  They  consist  of 
section  and  excitation. 

Section  of  a  vaso-constrictor  nerve,  such  as  the  splanchnic,  causes 
a  loss  of  normal  arterial  tone,  and  consequently  the  part  supplied  by 
the  nerve  becomes  flushed  with  blood.  Stimulation  of  the  peripheral 
end  causes  the  vessels  to  contract  and  the  part  to  become  compara- 
tively pale  and  bloodless.  This  can  be  very  readily  demonstrated  on 
the  ear  of  the  rabbit.  This  is  a  classical  experiment  associated  with 
the  name  of  Claude  Bernard.  Division  of  the  cervical  sympathetic 
produces  an  increased  redness  of  the  side  of  the  head,  and  looking  at 
the  ear,  the  transparency  of  which  enables  one  to  follow  the  phenomena 
easily,  the  central  artery  with  its  branches  is  seen  to  become  larger, 
and  many  small  branches  not  previously  visible  come  into  view.  The 
ear  feels  hotter,  though  this  effect  soon  passes  off  as  the  exposure  of  a 
large  quantity  of  blood  to  the  air  causes  a  rapid  loss  of  heat.  On 
stimulating  the  peripheral  end  of  the  cut  nerve,  the  ear  resumes  its 
normal  condition,  and  then  becomes  paler  than  usual  owing  to  exces- 
sive constriction  of  the  vessels. 

The  first  part  of  the  experiment,  the  dilatation  following  section, 

U 


306 


THE   CIRCULATION   IN   THE   BLOOD-VESSELS  [CH.  XXL 


can  be  demonstrated  in  a  very  simple  way,  by  pressing  the  thumb- 
nail forcibly  on  the  nerve  where  it  lies  by  the  side  of  the  central 
artery  of  the  ear. 

Section  of  a  vaso-dilator  nerve,  such  as  the  chorda  tympani,  pro- 
duces no  effect  on  the  vessels,  but  stimulation  of  its  peripheral  end 


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Fig.  300. — Tracing  of  arterial  blood-pressure  showing  the  effect  of  stimulating  the  central  end  of  the  Depressor  nerve  in 
ii  cat.     The  letters  prelixed  to  the  various  lines  have  the  same  meaning  as  in  lig.  299.     (Sherrington.) 

causes  great  enlargement  of  all  the  arterioles,  so  that  the  submaxillary 
gland  and  the  neighbouring  parts  supplied  by  the  nerve  become  red 
and  gorged  with  blood,  and  the  pulse  is  propagated  through  to  the 
veins ;  the  circulation  through  the  capillaries  is  so  rapid  that  the  blood 
loses  very  little  of  its  oxygen,  and  is  therefore  arterial  in  colour  in 
the  veins.  Another  effect,  free  secretion  of  saliva,  we  shall  study  in 
connection  with  that  subject. 

Other  examples  of  vaso-dilator  nerves  are  the  nervi  erigentes  to 


CH.  XXI.]  PLETHYSMOGRAPHY  307 

the  erectile  tissue  of  the  penis,  etc.,  and  of  the  lingual  nerve  to  the 
vessels  of  the  tongue. 

It  is,  however,  probable  that  all  the  vessels  of  the  body  receive 
both  constrictor  and  dilator  nerves.  But  the  presence  of  the  latter 
is  difficult  to  determine  unless  they  are  present  in  excess ;  if  they 
are  not,  stimulation  affects  the  constrictors  most.  The  effect  of 
section  is  also  inconclusive ;  for  if  a  mixed  nerve  is  cut,  the  only  effect 
observed  is  a  dilatation  due  to  removal  of  the  tonic  constrictor  influence. 

To  solve  this  difficult  problem,  three  methods  are  in  use : — 

1.  Tlie  method  of  degeneration. — If  the  sciatic  nerve  is  cut,  the 
vessels 'of  the  limb  dilate.  This  passes  off  in  a  day  or  two.  If  the 
peripheral  end  of  the  nerve  is  then  stimulated,  the  vessels  are  dilated, 
as  the  constrictor  fibres  degenerate  earliest,  and  so  one  gets  a  result 
due  to  the  stimulation  of  the  still  intact  dilator  fibres. 

2.  The  method  of  slowly  interrupted  shocks. — If  a  mixed  nerve  is 
stimulated  with  the  usual  rapidly  interrupted  faradic  current,  the 
effect  is  constriction ;  but  if  the  induction  shocks  are  sent  in  at  long 
intervals  {e.g.,  at  intervals  of  a  second),  vaso-dilator  effects  are 
obtained.  This  can  be  readily  demonstrated  on  the  kidney  vessels 
by  stimulation  of  the  anterior  root  of  the  eleventh  thoracic  nerve  in 
the  two  ways  just  indicated. 

By  studying  the  rate  of  flow  of  the  blood  through  the  submaxillary 
gland,  in  which  the  vaso-constrictor  and  dilator  fibres  run  separate 
courses,  it  has  been  shown  that  if  both  sets  of  fibres  are  simultane- 
ously excited,  constriction  is  produced  during  the  stimulation,  while 
marked  dilatation  follows  after  the  stimulation  has  ceased.  Excitation 
of  the  constrictors  alone  is  not  followed  by  dilatation.  These  results 
explain  the  mode  of  action  of  slowly  interrupted  shocks,  for  with  each 
there  will  only  be  a  very  slight  constriction,  while  the  dilator  effects 
which  run  a  much  slower  course  will  be  summed  up  to  produce  a 
marked  effect. 

3.  The  influence  of  temperature. — Exposure  to  a  low  temperature 
depresses  the  constrictors  more  than  the  dilators.  If  the  leg  is 
placed  in  ice-cold  water,  stimulation  of  the  sciatic,  even  if  it  has  only 
been  recently  divided,  produces  a  flushing  of  the  skin  with  blood. 

Plethysmography. 

The  action  of  vaso-motor  nerves  can  be  studied  in  another  way 
than  by  the  use  of  various  forms  of  manometer,  which  is  the  only 
method  we  have  considered  so  far.  The  second  method,  which  is 
often  used  together  with  the  manometer,  consists  in  the  use  of  an 
instrument  which  records  variations  in  the  volume  of  any  limb,  or 
organ  of  an  animal.  Such  an  instrument  is  called  a  plethy sinograph. 
One  of  these  instruments  applied  to  the  human  arm  is  shown  in  the 
accompanying  figure  (fig.  301). 


308  The  ciRcuLAtioN  in  the  blood-vessels  [ch.  xxt. 

Every  time  the  arm  expands  with  every  heart's  systole,  a  little 
of  the  fluid  in  the  plethysmograph  is  expelled  and  raises  the  lever. 
Variations  in  volume  due  to  respiration  are  also  seen  in  the  tracing. 
An  air  plethysmograph  connected  to  a  sensitive  recorder  gives  equally 
good  results. 

The  same  instrument  in  a  modified  form  applied  to  such  organs 
as  the  spleen  and  kidney  is  generally  called  an  oncometer,  and  the 
recording  part  of  the  apparatus,  the  oncograph.  These  instruments 
we  owe  to  Eoy,  and  the  next  two  figures  represent  respectively 
sections  of  the  kidney  oncometer  and  oncograph. 

An  oncometer  consists  of  a  metal  capsule,  of  shape  suitable  to 
enclose  the  organ:  its  two  halves  are  jointed  together,  and  fit 
accurately  except  at  one  opening  which  is  left  for  the  vessels  of  the 
organ.     A  delicate  membrane  is  attached  to  the  rim  of  each  half,  the 


Fig.  301. — Pletliysmograph.  By  means  of  this  apparatus,  the  alteration  in  vohime  of  the  arm,  e,  which 
is  enclosed  in  a  glass  tube,  a,  tilled  with  fluid,  the  opening  through  which  it  passes  being  firmly 
closed  by  a  thick  gutta.percha  band,F,  is  communicated  to  the  lever,  d,  and  registered  by  a  recording 
apparatus.  The  fluid  in  a  communicates  with  that  in  b,  the  upper  limit  of  which  is  above  that  in 
A.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the  arm.  When 
the  volume  is  increased,  fluid  passes  out  of  the  glass  cylinder,  and  the  lever,  d,  also  is  raised,  and 
when  a  decrease  takes  place  the  fluid  returns  again  from  n  to  a.  It  will  therefore  be  evident  that 
the  apparatus  is  capable  of  recording  alterations  of  the  volume  of  blood  in  the  arm. 

space  between  which  and  the  metal  is  filled  with  warm  oil.  The 
tube  from  the  oncometer  is  connected  to  the  oil-containing  cavity  of 
the  oncograph  by  a  tube  also  containing  oil.  An  increase  in  the 
volume  of  the  organ  squeezes  the  oil  out  of  the  oncometer  into  the 
oncograph,  and  so  produces  a  rise  of  the  oncograph  piston  and  lever ; 
a  contraction  of  the  organ  produces  a  fall  of  the  lever. 

Very  good  results  are  obtained  by  using  saline  solution  instead  of 
oil;  and  Schafer  has  shown  in  connection  with  the  spleen  that  a 
spleen  box  of  simple  shape  covered  with  a  glass  plate,  made  air-tight 
with  vaseline,  and  communicating  by  a  tube  with  a  Marey's  tambour, 
gives  a  far  more  delicate  record  of  the  splenic  alterations  of  volume 
than  the  oil  oncometer.  Similar  air  oncometers  are  now  used  in  the 
-investigation  of  many  organs. 


CH.  XXI.] 


THE  ONCOMETER 


309 


If  now  wo  aro  invosti^atiiit;'  tho  action  of    the  anterior  root  of 
eleventh  thoracic  norvoon  (ho  vessels  of  thekidiiov.a  tracinf^  is  taken 


Fio.  302. — Diagram  of  Roy's  Oiicometiir.  o,  represents  the  kidney  enclosed  in  a  metal  box,  which  opens 
by  hinge  /;  b,  the  renal  vessels  and  duct.  Surrounding  the  kidney  are  two  chambers  formed  by 
membranes,  the  edges  of  which  are  firmly  fixed  by  being  clamped  between  the  outside  metal  capsule, 
and  one  (not  represented  in  the  figure)  inside,  the  two  being  firmly  screwed  together  by  screws  at  h, 
and  below.  The  membranous  chamber  below  is  filled  with  a  varying  amount  of  warm  oil,  according 
to  the  size  of  the  kidney  experimented  with,  through  the  opening,  then  closed  with  the  plug  i. 
After  the  kidney  has  been  enclosed  in  the  capsule,  the  membranous  chamber  above  is  filled  with 
warm  oil  through  the  tube  c,  which  is  then  closed  by  a  tap  (not  represented  in  the  diagram) ;  the 
tube  d  communicates  with  a  recording  apparatus,  and  any  alteration  in  the  volume  of  the  kidney 
is  communicated  by  the  oil  in  the  tube  to  the  chamber  d  of  the  Oncograph,  fig.  303. 


Fio.  303. — Roy's  Oncograph,  or  apparatus  for  recording  alterations  in  the  volume  of  the  kidney,  etc., 
as  shown  by  the  oncometer— n,  upright,  supporting  recording  lever  I,  which  is  raised  or  lowered  by 
needle  ft,  which  works  through  /,  and  which  is  attached  to  the  piston  e,  working  in  the  chamber  d, 
with  which  the  tube  from  the  oncometer  communicates.  The  oil  is  prevented  from  being  squeezed 
out  as  the  piston  descends  by  a  membrane,  which  is  clamped  between  the  ring-shaped  surfaces  of 
cylinder  by  the  screw  i  working  upwards  ;  the  tube  h  is  for  filling  the  instrument. 

simultaneously  of  the  arterial  blood-pressure  in  the  carotid,  and  of 
the  volume  of  the  kidney  by  the  oncometer.     On  stimulating  the 


310  THE   CIKCULATION    IN   THE   BLOOD-VESSELS  [CH.  XXL 

nerve  rapidly,  there  is  a  slight  rise  of  arterial  pressure,  but  a  large 
fall  of  the  oncograph  lever,  showing  tliat  the  kidney  has  diminished 
in  volume.  It  is  evident  that  there  must  be  an  active  contraction  of 
the  arterioles  of  the  kidney,  causing  it  to  diminish  in  size,  for  the 
blood-pressure  tracing  (which  is  taken  as  a  control  to  be  sure  the 
changes  are  not  otherwise  produced)  shows  that  there  is  no  failure  of 
the  heart's  activity  to  account  for  it. 

We  shall  return  to  the  subject  of  the  oncometer  in  connection 
with  the  spleen  and  the  kidney.     We  may,  however,  say  in  passing 
what   a  very  important  experimental   method   plethysmography  is 
becoming.     Since  the  introduction  of  air  oncometers,  the  method  is 
remarkably  easy  to  apply,  and  it  is  now  part  of  the  routine  practice 
of  physiologists,  when  they  are  investigating  the  action  of  a  drug, 
or  of  a  nerve,  on  any  organ,  to  record  its  volume  changes  by  the 
plethysmographic  method.     Thus,  the  salivary  glands,  lobes  of  the 
liver  or  lung,  the  limbs,  the  kidney,  spleen,  a  coil  of  intestine,  etc., 
can  all  be  easily  enclosed  in  an  appropriately  shaped  gutta-percha 
box,  covered  with  a  glass  plate  made  air-tight  with  vaseline.     There 
are  always  two  openings  to  such  a  box,  one  to  allow  the  vessels  and 
nerves  to  enter  (leakage  of  air  around  these  is  prevented  by  packing 
with  cotton-wool  soaked  in  vaseline) ;  the  other  opening  is  filled  up 
with  a  piece  of  glass  tubing  which  is  connected  by  an  indiarubber 
tube  to  the  recording  apparatus.     The  most  delicate  of  the  volume 
recorders  is  the   bellows-recorder   of   Brodie   (see  p.  152)   and   the 
piston  recorder  of  Hilrthle ;  a  Marey's  tambour  is  not  so  sensitive, 
and,  moreover,  it  is  a  recorder  of  pressure  rather  than  of  volume  only. 
Of  all  the  oncometers,  I  am  inclined  to  believe  that  the  intestinal 
oncometer  is  the  most  instructive,  because  the  coil  of  intestine  under 
observation  gives  a  truer  record  of  what  is  occurring  in  that  important 
area  called  the  splanchnic  area,  than  any  other  abdominal  organ. 

Pathological  Conditions. 

The  vaso-motor  nervous  system  is  influenced  to  some  extent  by 
conditions  of  the  cerebrum,  some  emotions,  such  as  fear,  causing 
pallor  (vaso-constriction),  and  others  causing  blushing  (vaso- 
dilatation). 

It  is  almost  impossible  to  over-estimate  the  importance  of  the 
study  of  vaso-motor  phenomena  as  a  means  of  explaining  certain 
pathological  conditions;  our  knowledge  of  the  processes  concerned 
in  inflammation  is  a  case  in  point. 

Disorders  of  the  vessels  due  to  vaso-motor  disturbances  are 
generally  called  angio -neuroses.  Of  these  we  may  mention  the 
following : — 

Tache  cerebrale  is  due  to  abnormal  sensitiveness  of  the  vascular 
nerves ;  drawing  the  finger-nail  across  the  skin  causes  an  immediate 


en.  XXI.]  CIRCULATION    IN   THE   BRAIN  311 

wheal,  ur  at  least  a  rod  mark  that  lasts  a  considerable  time.  At  one 
time  this  was  considered  characteristic  of  affections  of  the  cerebral 
meninges  like  tubercular  meningitis,  and  was  consequently  called  the 
"  meningeal  streak."  It,  however,  occurs  in  a  variety  of  pathological 
conditions  of  the  nervous  system,  both  cerebral  and  spinal. 

In  certain  conditions  which  lead  to  angina  pectoris  the  pain  in 
the  heart  is  in  part  due  to  its  being  unable  to  overcome  an  immense 
peripheral  resistance,  and  the  condition  is  relieved  by  the  adminis- 
tration of  drugs  like  amyl-nitrite  or  nitro-glycerin,  which  relax  the 
vessels  and  cause  universal  blushing. 

Raynaud's  disease  is  one  in  which  there  is  a  localised  constriction 
of  the  vessels  which  is  so  effectual  as  to  entirely  cut  off  the  blood 
supply  to  the  capillary  areas  beyond,  and  if  this  lasts  any  considerable 
time  may  lead  to  gangrene  of  the  parts  in  question. 

Local  Peculiarities  of  the  Circulation. 

The  most  remarkable  peculiarities  attending  the  circulation  of  blood  through 
different  organs  are  observed  in  the  cases  of  the  brain,  erectile  organs,  lungs,  liver, 
spleen,  and  kidneys. 

In  the  Brain. — The  brain  must  always  be  supplied  with  blood,  for  otherwise  im- 
mediate loss  of  consciousness  would  follow.  Hence,  to  render  accidental  oblitera- 
tion almost  impossible,  four  large  arteries  are  supplied  to  the  brain,  and  these  anas- 
tomose together  in  the  circle  of  Willis.  The  two  vertebral  arteries  are,  moreover, 
protected  in  bony  canals.  Two  of  the  brain  arteries  can  be  tied  in  monkeys,  and 
three  or  even  all  four  in  dogs,  without  the  production  of  serious  symptoms.  In  the 
last  case  enough  blood  reaches  the  brain  by  branches  from  the  superior  intercostal 
arteries  to  the  anterior  spinal  artery.  The  sudden  obliteration  of  one  carotid  artery 
in  man  may  in  some  cases  produce  epileptiform  spasms ;  the  sudden  occlusion  of 
both  occasions  loss  of  consciousness.  Uniformity  of  supply  is  further  ensured  by 
the  arrangement  of  the  vessels  in  the  pia  mater,  in  which,  previous  to  their  distribu- 
tion to  the  substance  of  the  brain,  the  large  arteries  break  up  and  divide  into 
innumerable  minute  branches  ending  in  capillaries,  which,  after  frequent  communi- 
cation with  one  another,  enter  the  brain  and  carry  into  nearly  every  part  of  it  uni- 
form and  equable  streams  of  blood.  The  arteries  are  enveloped  in  a  special 
lymphatic  sheath.  The  arrangement  of  the  veins  within  the  cranium  is  also  peculiar. 
The  large  venous  trunks  or  sinuses  are  formed  so  as  to  be  scarcely  capable  of  change 
of  size ;  and  composed,  as  they  are,  of  the  tough  tissue  of  the  dura  mater,  and,  in 
some  instances,  bounded  on  one  side  by  the  bony  cranium,  they  are  not  compres- 
sible by  any  force  which  the  fulness  of  the  arteries  might  exercise  through  the  sub- 
stance of  the  brain  ;  nor  do  they  admit  of  distension  when  the  flow  of  venous  blood 
from  the  brain  is  obstructed.  No  valves  are  placed  between  the  vertebral  veins  and 
the  vena  cava  ;  the  vertebral  veins  anastomose  with  the  cerebral  sinuses.  Hence  on 
squeezing  the  thorax  and  abdomen,  venous  blood  can  be  pressed  from  those 
parts  out  of  any  opening  made  into  the  longitudinal  sinus.  Expiration  acts  in  the 
same  way  ;  it  raises  the  cerebral  venous  pressure  ;  if  the  skull  wall  is  defective  the 
brain  expands  owing  to  the  distension  of  its  capillaries  during  the  expiratory  act. 
The  exposed  brain  also  expands  with  each  systole  of  the  heart.  Owing  to  the  fact 
that  the  brain  lies  enclosed  in  the  cranium,  the  arterial  pulse  is  transmitted  through 
the  brain  substance  to  the  cerebral  veins,  and  so  the  blood  issues  from  these  in  pulses. 

Since  the  brain  is  enclosed  in  the  rigid  cranium  the  volume  of  blood  in  the 
cerebral  vessels  cannot  alter  unless  the  volume  of  the  other  cranial  contents  alters  in 
the  opposite  sense. 

These  conditions  of  the  brain  and  skull  led  Monro  and  Kellie  many  years  ago 
to  advance  the  opinion  that  the  quantity  of  blood  in  the  brain  must  be  the  same  at 


312  THE   CIRCULATION   IN   THE   BLOOD-VESSELS  [CH.  XXL 

all  times.  This  doctrine  has  been  frequently  disputed,  and  many  have  advanced 
the  theory  that  increase  or  diminution  of  the  blood  is  accompanied  with  simidtane- 
ous  diminution  or  increase  of  the  cerebro-spinal  fluid,  so  that  the  contents  of  the 
cranium  are  kept  uniform  in  volume.  But  the  recent  work  of  Leonard  Hill  has 
shown  that  the  Monro-Kellie  doctrine  is  in  the  main  true.  Histological  evidence 
has  recently  been  obtained  of  the  existence  of  nerve  plexuses  round  the  pial 
arteries.  The  arteries  are  muscular,  and  the  nerves  therefore  are  most  probably 
vaso-motor  in  function.  Experimental  evidence  so  far,  however,  has  not  estab- 
lished that  the  action  of  these  nerves  is  a  marked  one* ;  the  cerebral  circulation 
passively  follows  the  slightest  changes  in  aortic  and,  more  especially,  vena  cava 
pressure,  and  no  active  vaso-motor  change  has  been  conclusively  proved.  The 
velocity  of  blood-flow  through  the  brain  is  thus  influenced  markedly  by  the  con- 
dition of  the  vessels  of  the  splanchnic  area.  If  the  tone  of  the  skeletal  muscles  and 
that  of  the  vessels  be  suddenly  inhibited  by  fear,  or  temporarily  destroyed  by  shock, 
the  blood  will  drop  owing  to  its  weight  into  the  dilated  and  supported  vessels  in  the 
most  dependent  parts  of  the  body.  The  flow  of  blood  through  the  brain  will,  under 
these  conditions,  cease,  that  is  to  say,  so  long  as  the  body  is  in  the  erect  posture. 
Thus,  to  restore  a  fainting  person  the  head  must  be  lowered  between  the  knees. 
Muscular  exercise,  by  returning  blood  to  the  heart  from  the  veins  of  the  lower  parts 
of  the  body,  conduces  to  the  maintenance  of  an  efficient  cerebral  circulation. 

It  is  not  the  volume  of  the  blood  but  the  velocity  of  flow  which  is  altered  in 
the  brain  by  changes  in  the  general  circulation.  The  brain  with  its  circulating 
blood  almost  entirely  fills  the  cranial  cavity  in  the  living  animal ;  that  is,  there  is 
no  more  cerebro-spinal  fluid  there  than  is  sufficient  to  moisten  the  membranes. 
Cerebro-spinal  fluid  escapes  into  the  veins  at  any  pressure  above  the  cerebral 
venous  pressure  ;  the  tension  of  this  fluid  and  the  pressure  in  the  veins  are  therefore 
always  the  same.  The  fluid  probably  transudes  from  the  vascular  fringes  of  the 
choroid  plexuses  in  the  ventricles  of  the  brain,  and  is  absorbed  by  the  pial  veins. 
There  is  not  enough  of  this  absorbable  fluid  present  to  allow  of  more  than  a  slight 
increase  of  the  volume  of  blood  in  the  brain.  If  the  aortic  pressure  rises  and  the 
vena  cava  pressure  remains  constant  the  conditions  in  the  brain  are  as  follows  :— 

More  blood  in  the  arteries,  less  in  the  veins,  increased  velocity  of  flow. 

While  if  the  aortic  pressure  remains  constant  and  the  vena  cava  pressure  rises, 
the  conditions  are  : — 

Less  blood  in  the  arteries,  more  in  the  veins,  diminished  velocity  of  flow. 

The  brain  presses  against  the  cranial  wall  with  a  pressure  equal  to  that  in  the 
cerebral  capillaries.  A  foreign  body  introduced  within  the  cranium,  such  as  a 
blood-clot  or  depressed  bone,  produces  local  anaemia  of  the  brain,  by  occupying  the 
room  of  the  blood.  So  soon  as  the  capillaries  are  thus  obliterated  the  pressure  is 
raised  to  arterial  pressure.  This  local  increase  of  cerebral  tension  cannot  be  trans- 
mitted by  the  cerebro-spinal  fluid,  because  this  fluid  can  never  be  retained  in  the 
meningeal  spaces  at  a  tension  higher  than  that  of  the  cerebral  veins,  but  is 
immediately  re-absorbed.  The  anatomical  arrangements  of  the  tentorium  cerebelli 
and  the  falciform  ligaments  are  such  as  to  largely  prevent  the  transmission  through 
the  brain-substance  of  a  local  increase  of  pressure.  There  is  complete  pressure 
discontinuity  between  the  cranial  and  vertebral  cavities.  The  serious  results  that 
follow  cerebral  compression  are  primarily  due  to  obliteration  of  the  blood-vessels, 
and  consequent  anaemia  of  the  brain.  A  very  small  foreign  body  will,  if  situated 
in  the  region  of  the  bulb,  produce  the  gravest  symptoms.  For  the  centres  which 
control  the  vascular  and  respiratory  systems  are  rendered  anaemic  thereby.  The 
cerebral  hemispheres  may,  on  the  other  hand,  be  compressed  to  a  large  extent 
without  causing  a  fatal  result.  The  major  symptoms  of  compression  arise  as  soon 
as  any  local  increase  of  pressure  is  transmitted  to  the  bulb  and  causes  anaemia 
there. 

In  Erectile  StrucUires. — The  instances  of  greatest  variation  in  the  quantity  of 
blood  contained,  at  different  times,   in   the  same  organs,  are  found   in   certain 

*  The  only  experimental  evidence  yet  adduced  as  to  the  functional  activity  of  these  nerves  is  con- 
tained in  the  work  of  Ferrier  and  Brodie.  They  perfused  defibrlnaled  blood  through  a  recently  excised 
brain,  and  found  that  the  addition  of  adrenalin  to  the  blood  always  produced  constriction  of  the  vessel^ 
and  a  lessened  blood  flow, 


CH.  XXI.]  ERECTILE   STRUCTURES  313 

structures  which,  under  ordinary  circumstances,  are  soft  and  llaccid,  but,  at  certain 
times,  receive  an  unusually  iarj^e  quantity  of  blood,  become  distended  and  swollen 
by  it,  and  pass  into  the  state  which  has  been  termed  trrrfion.  Such  structures  are 
the  corpora  rarernoxa  and  ror/>iis  upoTujiosinn  of  the  penis  in  the  male,  and  the 
clitoris  in  the  female ;  and,  to  a  less  degree,  the  iiipfili'  of  the  mammary  gland  in 
both  sexes.  The  corpus  cavernosum  penis,  which  is  the  best  example  of  an  erectile 
structure,  has  an  external  fibrous  membrane  or  sheath  ;  and  from  the  iiuier  surface 
of  the  latter  are  prolonged  numerous  fine  laiuelhe  which  divide  its  cavity  into  small 
compartments.  Within  these  is  situated  the  plexus  of  veins  upon  which  the 
peculiar  erectile  property  of  the  organ  mainly  depends.  It  consists  of  short  veins 
which  very  closely  interlace  and  anastomose  with  each  other  in  all  directions,  and 
admit  of  great  variations  of  size,  collapsing  in  the  passive  state  of  the  organ,  but 
capable  of  an  amount  of  dilatation  which  exceeds  beyond  comparison  that  of  the 
arteries  and  veins  which  convey  the  blood  to  and  from  them.  The  strong  fibrous 
tissue  lying  in  the  intervals  of  the  venous  plexuses,  and  the  external  fibrous 
membrane  or  sheath  with  which  it  is  connected,  limit  the  distension  of  the  vessels, 
and  during  the  state  of  erection,  give  to  the  penis  its  condition  of  tension  and  firm- 
ness. The  same  general  condition  of  vessels  exists  in  the  corpus  spongiosum 
urethrcTp,  but  around  the  urethra  the  fibrous  tissue  is  much  weaker  than  around  the 
body  of  the  penis,  and  around  the  glans  there  is  none.  The  venous  blood  is 
returned  from  the  plexuses  by  comparatively  small  veins.  For  all  these  veins  one 
condition  is  the  same  ;  namely,  that  they  are  liable  to  the  pressure  of  muscles  when 
they  leave  the  penis.  The  muscles  chiefly  concerned  in  this  action  are  the  erector 
penis  and  accelerator  urinae.  Erection  residts  from  the  distension  of  the  venous 
plexuses  with  blood.  The  principal  exciting  cause  in  the  erection  of  the  penis  is 
nervous  irritation,  originating  in  the  part  itself,  and  derived  reflexly  from  the  brain 
and  spinal  cord.  The  nervous  influence  is  communicated  to  the  penis  by  the  pudic 
nerves,  which  ramify  in  its  vascular  tissue ;  and  after  their  division  the  penis  is 
no  longer  capable  of  erection. 

Erection  is  not  complete,  nor  maintained  for  any  time  except  when,  together 
with  the  influx  of  blood,  the  muscles  mentioned  contract,  and  by  compressing  the 
veins,  stop  the  efflux  of  blood,  or  prevent  it  from  being  as  great  as  the  influx. 

Tlifi  circulation  in  the  Liim/s,  Liver,  Spleen  and  Kidnei/s  will  be  described  in  our 
study  of  those  organs. 


CHAPTEE  XXII 

LYMPH   AND   LYMPHATIC    GLANDS 

As  the  blood  circulates  through  the  capillary  blood-vessels,  some  of 
its  liquid  constituents  exude  through  the  thin  walls  of  these  vessels, 
carrying  nutriment  to  the  tissue  elements.  This  exudation  is  called 
lymph ;  it  receives  from  the  tissues  the  products  of  their  activity, 
and  is  collected  by  the  lymph  channels,  which  converge  to  the  thoracic 
duct — the  main  lymphatic  vessel — and  thus  the  lymph  once  more 
re-enters  the  blood-stream  near  to  the  entrance  of  the  large  systemic 
veins  into  the  right  auricle. 

Lymph  is  a  fluid,  which  comes  into  much  more  intimate  relation- 
ship with  metabolic  processes  in  the  tissues  than  the  blood ;  in  fact, 
there  is  only  one  situation — the  spleen — where  the  blood  comes  into 
actual  contact  with  the  elements — that  is,  cells,  fibres,  etc. — of  a 
tissue. 

Composition  of  Lymph. 

Lymph  is  alkaline;  its  specific  gravity  is  about  1015,  and  after 
it  leaves  the  vessels  it  clots,  forming  a  colourless  coagulum  of  fibrin. 
It  is  like  blood-plasma  in  composition,  only  diluted  so  far  as  its 
protein  constituents  are  concerned.  This  is  due  to  the  fact  that 
proteins  do  not  pass  readily  through  membranes.  The  proteins 
present  are  called  fihrinogen,  serum  globulin,  and  serum  albumin ; 
these  we  shall  study  with  the  blood-plasma.  The  salts  are  similar 
to  those  of  blood-plasma,  and  are  present  in  the  same  proportions. 
The  waste  products,  like  carbonic  acid  and  urea,  are  more  abun- 
dant in  lymph  than  in  blood.  The  amount  of  solids  dissolved  in 
lymph  is  about  6  per  cent.,  more  than  half  of  which  is  protein  in 
nature. 

When  examined  with  the  microscope  the  transparent  lymph  is 
found  to  contain  colourless  corpuscles,  which  are  called  lymphocytes ; 
these  are  cells  with  large  nuclei  and  comparatively  little  protoplasm. 
They  pass  with  the  lymph  into  the  blood,  where  they  undergo 
growth,  and  become  converted  into  certain  varieties  of  leucocytes. 


CH.  XXII.]  LYMPHATIC    GLANDS  315 

All  tho  lym])haiics  pass  at  some  point  of  their  course  through 
lymphatic  glands,  which  are  the  factories  of  these  corpuscles.  Lym- 
phocytes also  pass  into  the  lymph  stream  wherever  lymphoid  tissue 
is  found,  as  in  the  tonsils,  thymus,  Malpighian  bodies  of  the  spleen, 
Peyer's  patches,  and  the  solitary  glands  of  the  intestine.  The  lymph 
that  leaves  these  tissues  is  richer  in  lymph-cells  than  that  which 
enters  them. 

When  lymph  is  collected  from  the  thoracic  duct  after  a  meal 
containing  fat,  it  is  found  to  be  milky.  This  is  due  to  the  presence 
in  the  lymph  of  minutely  subdivided  fat  particles  absorbed  from  the 
interior  of  the  alimentary  canal.  The  lymph  is  then  called  chyle. 
The  fat  particles  constitute  what  used  to  be  called  the  molecular  basis 
of  chyle.  If  the  abdomen  is  opened  during  the  process  of  fat  absorp- 
tion, the  lymphatics  are  seen  as  white  lines,  due  to  their  containing 
this  milky  fluid.     They  are  consequently  called  lacteals. 

The  structure  and  arrangement  of  the  lymphatic  vessels  are  given 
in  Chapter  XVIII.,  and  we  have  now  to  study  the  structure  of 

The  Lymphatic  Glands. 

Lymphatic  glands  are  romid  or  oval  bodies  varying  in  size  from 
a  hemp-seed  to  a  bean,  interposed  in  the  course  of  the  lymphatic 
vessels,  and  through  which  the  lymph  passes  in  its  course  to  be  dis- 
charged into  the  blood-vessels.  They  are  found  in  great  numbers  in 
the  mesentery,  and  along  the  great 
vessels  of  the  abdomen,  thorax,  and 
neck ;  in  the  axilla  and  groin ;  a 
few  in  the  popliteal  space,  but  not 
further  down  the  leg,  and  in  the 
arm  as  far  as  the  elbow. 

A  lymphatic  gland  is  covered 
externally  by  a  capsule  of  con- 
nective-tissue, generally  containing 
some    unstriped    muscle.      At   the 

inner     side    of     the    gland,  which    is  Fig.  304.— section  of  a  mesenteric  gland  from 

1      .                          /7   -7      \  /!-.       nr\A\  the  ox,  slightly  magnltied.     a,  Hllus ;  b  (in 

somewhat  concave  {hllus),  (ng.  o04),  the  central  part  of  the  figure),  meduUarj- 

*-l,^  „^..^^,,1^  r,^^j„  ,•„ .J„ „    „    „  substance;  c,  cortical  substance  with  Indls- 

the  capsule  sends  m wards  processes  tinct  aiveoii ;  rf,  capsule.  (Kouiker.) 
called  trdbeculce  in  which  the  blood- 
vessels are  contained,  and  these  join  with  other  processes  prolonged 
from  the  inner  surface  of  the  part  of  the  capsule  covering  the 
convex  or  outer  part  of  the  gland  ;  they  have  a  structure  similar 
to  that  of  the  capsule,  and  entering  the  gland  from  all  sides,  and 
freely  communicating,  form  a  fibrous  scaffolding.  The  interior  of  the 
gland  is  seen  on  section,  even  when  examined  with  the  naked  eye,  to 
be  made  up  of  two  parts,  an  outer  or  cortical^  which  is  light  coloured. 


316 


LYMPH   AND   LYMPHATIC   GLANDS 


[CH.  XXIL 


and  an  inner  or  medullary  portion  of  redder  appearance  (figs.  30-4, 
305).  In  the  outer  part,  or  cortex,  of  the  ghmd  (tig.  305),  the 
intervals  between  the  trabeculae  are  large  and  regular ;  they  are 
termed  alveoli ;  whilst  in  the  more  central  or  medullary  part  is  a 
finer  meshwork  formed  by  an  irregular  anastomosis  of  the  trabecular 
processes.  Within  the  alveoli  of  the  cortex  and  in  the  meshwork 
formed  by  the  trabeculae  in  the  medulla,  is  contained  lymphoid 
tissue ;  this  occupies  the  central  part  of  each  alveolus ;  but  at  the 
periphery,  surrounding  the  central  portion  and  immediately  next  the 
capsule  and  trabeculae,  is  a  more  open  meshwork  of  retiform  tissue 


Fig.  305. — Diagrammatic  section  of  lymphatic  gland,  a.l.,  afferent;  e.l.,  efferent  lymphatics;  C, 
cortical  substance ;  /./i.,  lymphoid  tissue;  i.s.,  Ij'mph-path  ;  c,  fibrous  capsule  sending  in  trabeculae 
tr.  into  the  substance  of  the  gland.    (Shai-pey.) 

constituting  the  lym'ph-'path,  and  containing  but  few  lymph-corpuscles. 
At  the  inner  part  of  the  alveolus,  the  central  mass  divides  into  two 
or  more  smaller  rounded  or  cord -like  masses  which,  joining  with 
those  from  the  other  alveoli,  form  a  much  closer  arrangement  than 
in  the  cortex ;  spaces  (fig.  306,  5)  are  left  within  those  anastomosing 
cords,  in  which  are  found  portions  of  the  trabecular  meshwork  and 
the  continuation  of  the  lymph-path. 

The  lymph  enters  the  gland  by  several  afferent  vessels,  which 
pierce  the  capsule  and  open  into  the  lymph-path ;  at  the  same  time 
they  lay  aside  all  their  coats  except  the  endothelial  lining,  which  is 
continuous  with  the  lining  of  the  lymph-path.  The  efferent  vessels 
begin  in  the  medullary  part  of  the  gland,  and  are  continuous  with 


CH.'XXII.] 


THE    FLOW   OF   LYMPH 


317 


the  lymph-path  here  as  the  afferent   vessels  are  with  the  cortical 
portion. 

The  efferent  vessels  leave  the  gland  at  the  hilus,  and  either  at 
once,  or  very  soon  after,  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are 
freely  distributed    to  the  trabe- 
cular and  lymphoid  tissues. 

The  Lymph  PIotv. 

The  flow  of  the  lymph  towards 
the  point  of  its  discharge  into  the 
veins  is  brought  about  by  several 
agencies.  With  the  help  of  the 
valvular  mechanism  all  occasional 
pressure  on  the  exterior  of  the 
lymphatic  and  lacteal  vessels  pro- 
pels the  lymph  onward;  thus 
muscular  and  other  external 
pressure  accelerates  the  flow  of 
the  lymph  as  it  does  that  of  the 
blood  in  the  veins.  The  action 
of  the  muscular  fibres  of  the 
small  intestine,  and  the  layer  of 
unstriped  muscle  present  in  each 
intestinal  villus,  assist  m  propel- 
ling the  chyle;  in  the  small  in- 
testine of  a  mouse,  the  chyle  has 
been  seen  moving  with  intermit- 
tent propulsions  that  correspond 
with  the  peristaltic  movements 
of  the  intestine.  But,  for  the 
general  propulsion  of  the  lymph 
and  chyle,  it  is  probable  that,  together  with  the  vis  a  tergo  resulting 
from  external  pressure,  some  of  the  force  is  derived  from  the  con- 
tractility of  the  vessel's  own  walls.  The  respiratory  movements, 
also,  favour  the  current  of  lymph  through  the  thoracic  duct  as  they 
do  the  current  of  blood  in  the  thoracic  veins. 

Lsrmph-Hearts. — In  amphibia,  reptiles  and  some  birds,  an  important  auxiliary 
to  the  movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular  sacs,  named 
lymph-hearts,  and  it  has  been  shown  that  the  caudal  heart  of  the  eel  is  a  lymph- 
heart  also.  The  number  and  positions  of  these  organs  vary.  In  frogs  and  toads, 
there  are  usually  four,  two  anterior  and  two  posterior.  Into  each  of  these  cavities 
several  lymphatics  open,  the  orifices  of  the  vessels  being  guarded  by  valves,  which 
prevent  the  retrograde  passage  of  the  lymph.  From  each  heart  a  single  vessel 
proceeds,  and  conveys  the  lymph  directly  into  the  venous  system.  Blood  is  pre- 
vented from  passing  into  the  lymphatic  heart  by  a  valve  at  its  orifice. 


Fig.  300 


A  small  portion  of  medullary  substance 
from  a  mesenteric  gland  of  the  ox.  d,  d,  trabe- 
culee  ;  a,  part  of  a  cord  of  lymphoid  tissue  from 
which  all  but  a  "few  of  the  lymph<'orpuscles 
have  been  washed  out  to  show  its  supporting 
meshwork  of  retiform  tissue  and  its  capillary 
blood-vessels  (which  have  been  injected,  and 
are  dark  in  the  figure);  &,  h,  lymph-path,  of 
which  the  retiform  tissue  is  represented  only 
at  c,  c.    X  300.    (KoUiker.) 


318  LYMPH   AND   LYMPHATIC   GLANDS  [CH.  XXIL 

The  muscular  coat  of  these  hearts  is  of  variable  thickness  ;  in  some  cases  it  can 
only  be  discovered  by  means  of  the  microscope  ;  but  in  every  case  it  is  composed  of 
striped  fibres.  The  contractions  of  the  hearts  are  rhythmical,  occurring  about 
sixty  times  in  a  minute.  The  pulsations  of  the  cervical  pair  are  not  always 
synchronous  with  those  of  the  pair  in  the  ischiatic  region,  and  even  the  correspond- 
ing sacs  of  opposite  sides  are  not  always  synchronous  in  their  action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart  appear  to 
be  directly  dependent  upon  a  certain  limited  portion  of  the  spinal  cord.  For 
Volkmann  found  that  so  long  as  the  portion  of  spinal  cord  corresponding  to  the 
third  vertebra  of  the  frog  was  uninjured,  the  cervical  pair  of  lymphatic  hearts 
continued  pulsating  after  all  the  rest  of  the  spinal  cord  and  the  brain  were  destroyed  ; 
while  destruction  of  this  portion,  even  though  all  other  parts  of  the  nervous  centres 
were  uninjured,  instantly  arrested  the  hearts'  movements.  The  posterior,  or 
ischiatic,  pair  of  lymph-hearts  were  found  to  be  governed,  in  like  manner,  by  the 
portion  of  spinal  cord  corresponding  to  the  eighth  vertebra.  Division  of  the 
posterior  spinal  roots  did  not  arrest  the  movements ;  but  division  of  the  anterior 
roots  caused  them  to  cease  at  once. 

Innervation  of  the  Thoracic  Duct, — By  determining  the  rate  of  outflow  of  a 
fluid  at  constant  pressure  passing  through  the  thoracic  duct,  Camus  and  Gley  have 
obtained  evidence  of  the  presence  of  nerves,  causing  both  dilatation  and  constric- 
tion of  the  duct.  These  are  contained  in  the  sympathetic-  chain  below  the  first 
thoracic  ganghon.     The  eflfect  of  stimulation  is  principally  dilatation. 


Relation  of  Lymph  and  Blood. 

The  volume  of  blood  in  the  body  remains  remarkably  constant. 
If  the  amount  is  increased  by  injection  of  fluids,  at  first  its  specific 
gravity  is  lessened,  but  in  a  short  time,  often  in  a  few  minutes,  it 
returns  to  the  normal.  The  excess  of  fluid  is  got  rid  of  in  two  ways : 
(1)  by  the  kidneys,  which  secrete  profusely ;  and  (2)  by  the  tissues, 
which  become  more  watery  in  consequence.  After  the  renal  arteries 
are  ligatured,  and  the  kidney  is  consequently  thrown  out  of  action, 
the  excess  of  water  passes  only  into  the  tissues. 

On  the  other  hand,  a  deficiency  of  blood  (for  instance,  after 
hsemorrhage)  is  soon  remedied  by  a  transfer  of  water  from  the 
tissues  to  the  blood  through  the  intermediation  of  the  lymph. 

In  severe  haemorrhage  life  has  often  been  saved  by  injection  of 
saline  solution  into  the  vessels,  or  by  transfusion  from  another 
person.  The  transfer  of  the  blood  of  another  animal  to  the  human 
vascular  system  is  usually  dangerous,  especially  if  the  blood  has  been 
defibrinated,  for  the  serum  of  one  animal  is  usually  poisonous  to 
another,  producing  various  changes,  of  which  a  breakdown  of  the 
corpuscles  (hsemolysis)  is  the  most  constant  sign. 

Formation  of  Lymph. 

Carl  Ludwig  taught  that  the  lymph  flow  is  conditioned  by  two 
factors :  first,  differences  in  the  pressure  of  the  blood  in  the  capillaries 
and  of  the  fluid  in  the  tissue  spaces,  giving  rise  to  n,  filtration  of  fluid 
through   the   capillary   walls;    and    secondly,   chemical    differences 


CH.  XXII.]  FORMATION    OF   LYMPH  319 

between  these  two  fluids,  setting  up  osmotic  interchanges  through  the 
wall  of  the  blood-vessel. 

The  accurate  meaning  of  these  terms  is  explained  in  the  section  in  small  print 
at  the  end  of  this  chapter. 

If  the  lymph  is  produced  by  a  simple  act  of  tiltration,  then  the 
amount  of  lymph  must  rise  and  sink  with  the  value  of  D — d;  D 
representing  the  capillary  blood-pressure,  and  d  the  pressure  in  the 
tissue  spaces. 

In  support  of  this  mechanical  theory,  various  workers  in  Ludwig's 
laboratory  showed  that  increased  capillary  pressure  due  to  obstruction 
of  the  venous  outflow  increases  the  amount  of  lymph  formed ;  and 
that  diminution  of  the  pressure  in  the  lymph  spaces,  by  squeezing 
out  the  lymph  previously  contained  in  them,  leads  to  an  increase  in 
the  transudation. 

On  the  other  hand,  there  were  some  facts  which  could  not  be  well 
explained  by  the  filtration  theory,  among  which  may  be  mentioned 
the  action  of  curare  in  causing  an  increase  of  lymph  flow. 

Heidenhain  was  the  first  to  fully  recognise  that  the  laws  of 
filtration  and  osmosis  as  applied  to  dead  membranes  may  be  con- 
siderably modified  when  the  membranes  are  composed  of  living  cells  ; 
and  he  considered  that  the  formation  of  lymph  is  due  to  the  selective 
or  secretory  activity  of  the  endothelial  walls  of  the  capillaries.  This 
so-called  vital  action  of  the  endothelial  cells  is  seen  in  the  fact  that 
after  the  injection  of  sugar  into  the  blood,  in  a  short  time  the  per- 
centage of  sugar  in  the  lymph  becomes  higher  than  that  in  the 
blood.  There  must,  therefore,  be  some  activity  of  the  endothelial 
cells  in  picking  out  the  sugar  from  the  blood  and  passing  it  on  to 
the  lymph. 

Heidenhain  is  also  the  inventor  of  the  term  lymphagogues 
(literally,  lymph  drivers).  These  are  substances  like  curare,  which 
have  a  specific  action  in  causing  an  increased  lymph  flow.  Heiden- 
hain considers  the  majority  of  these  act  by  stimulating  the  endothelial 
cells  to  activity.  This  conclusion,  however,  has  been  subjected  to 
much  criticism.  In  this  country  the  question  has  been  taken  up  by 
Starling,  who  has  shown  that  the  influence  of  vital  action  is  not 
so  marked  as  Heidenhain  supposes  it  to  be,  but  that  most  of  the 
phenomena  in  connection  with  lymph  formation  can  be  explained  by 
the  simpler  mechanical  theory.  Starling's  views  may  be  briefly 
stated  as  follows  : — 

The  amount  of  lymph  produced  in  any  part  depends  on  two 
factors : — 

1.  The  pressure  at  which  the  blood  is  flowing  through  the  capil- 
laries. Heidenhain  took  the  arterial  pressure  in  his  experiments  as 
the  measure   of   the   capillary  pressure;    Starling  points  out,  very 


320  LYMPH  AND  LYMPHATIC  GLANDS  [CH.  XXIL 

justly,  that  this  is  incorrect,  as  there  is  between  the  arteries  and  the 
caj)illaries  the  peripheral  resistance  in  the  arterioles. 

2.  The  permeability  of  the  capillary  wall.  This  varies  enormously 
in  different  regions;  it  is  greatest  in  the  liver,  so  that  an  intra- 
capillary  pressure  which  would  cause  IjTuph  to  flow  here  is  without 
effect  on  the  production  of  IjTnph  in  the  limbs. 

The  flow  of  lymph  may  therefore  be  increased  in  two  ways : — 

1.  By  increasing  the  intracapillary  pressure.  This  may  be  done 
locally  by  ligaturing  the  veins  of  an  organ ;  or  generally  by  injecting 
a  large  amount  of  fluid  into  the  circulation,  or  by  the  injection  of 
such  substances  as  sugar  and  salt  (Heidenhain's  first  class  of 
lymphagogues)  into  the  blood.  These  attract  water  from  the  tissues 
into  the  blood,  and  thus  increase  the  volume  of  the  circulating  fluid 
and  raise  the  intracapillary  pressure. 

2.  By  increasing  the  permeability  of  the  capillary  wall  by  injuring 
its  vitality.  This  may  be  done  locally  by  scalding  a  part ;  or 
generally,  by  injecting  certain  poisonous  substances,  such  as  peptone, 
leech  extract,  decoction  of  mussels,  etc.  (Heidenhain's  second  class 
of  lymphagogues).  These  act  chiefly  on  the  liver  capillaries ;  curare 
acts  chiefly  on  the  limb  capillaries. 

In  the  light  of  our  present  knowledge  on  this  question,  it  is 
impossible  to  pronounce  any  absolutely  positive  opinion.  But  facts 
appear  to  me  to  be  accumidating  which  tell  in  favour  of  the  secretion 
theory.  If  the  endothelial  wall  were  a  non-livmg  membrane,  physical 
processes  would  obviously  explain  all  the  phenomena  of  lymph  forma- 
tion. But  we  must  recognise  that  the  endothelial  cells  are  alive, 
and  that  like  other  cells  they  are  capable  of  a  selective  action  which 
may  mask  or  counteract  or  assist  the  purely  physical  processes.  If 
the  action  of  poisons  was  simply  to  injure  the  vessel  wall  and  increase 
its  permeability,  the  amount  of  lymph  should  be  proportional  to  the 
intensity  of  the  injury;  but  this  is  not  found  to  be  the  case. 
Heidenhain  no  doubt  went  too  far  when  he  attributed  lymph  forma- 
tion almost  exclusively  to  endothelial  activity ;  and  Starling  has  gone 
too  far  in  the  other  direction.  My  own  opinion  is  that  lymph 
formation  is  mainly  influenced  by  the  physical  conditions  present, 
for  the  action  of  such  thin  cells  as  those  of  the  capillary  wall  cannot 
be  sufficiently  great  to  entirely  counteract  these  conditions ;  at  the 
same  time  it  is  impossible  to  deny  that  there  is  some  such  action 
as  may  be  described  by  the  terms  "  selective "  or  "  secretory."  The 
question  is  closely  related  to  that  of  absorption  from  the  alimen- 
tary canal,  and  we  shall  find  in  studying  that  subject  that  there 
is  a  similar  difference  of  opinion,  and  that  recently  published 
researches  confirm  the  theory  of  selective  activity  of  the  absorptive 
epithelium. 


CH.  XXII.]  THEORY   OF   SOLUTIONS  321 

Osmotic  Phenomena. 

The  investigations  of  physical  eheniists  (hirinji:  recent  years  have  given  us  new 
conceptions  of  the  nature  of  solutions,  anil  thest-  have  important  bearings  on  the 
explanation  of  osmotic  phenomena,  and  so  are  interesting  to  the  physiologist. 

Water  is  the  tluid  in  which  soluble  materials  are  usually  dissolved,  and  at 
ordinary  temperatures  it  is  a  fluid  the  molecules  of  which  are  in  constant  movement ; 
the  hotter  the  water  the  more  active  are  the  movements  of  its  molecules,  until  when 
at  last  it  is  converted  into  steam,  the  molecular  movements  become  much  more 
energetic.  Perfectly  pure  water  consists  of  molecules  with  the  formula  H.,0,  and 
these  molecules  undergo  practically  no  dissociation  into  their  constituent  ions,  and 
it  is  for  this  reason  that  pure  water  is  not  a  conductor  of  electricity. 

If  a  substance  like  sugar  is  dissolved  in  the  water,  the  solution  still  remains 
incai)able  of  conducting  an  electrical  current.  The  sugar  molecules  in  solution  are 
still  sugar  molecules  ;  they  do  not  undergo  dissociation. 

But  if  a  substance  like  salt  is  dissolved  in  the  water,  the  solution  is  then  capable 
of  conducting  electrical  currents,  and  the  same  is  true  for  most  acids,  bases,  and  salts. 
These  substances  do  undergo  dissociation,  and  the  simpler  materials  into  which 
they  are  broken  up  in  the  water  are  called  ions.  Thus,  if  sodium  chloride  is  dissolved 
in  water  a  certain  number  of  its  molecules  become  dissociated  into  sodium  ions, 
which  are  charged  with  positive  electricity,  and  chlorine  ions,  which  are  charged 
with  negative  electricity.  Similarly  a  solution  of  hydrochloric  acid  in  water  con- 
tains free  hydrogen  ions  and  free  chlorine  ions.  Sulphuric  acid  is  decomposed  into 
hydrogen  ions  and  ions  of  SO4.  The  term  ion  is  thus  not  equivalent  to  atom,  for 
an  ion  may  be  a  group  of  atoms,  like  SO4,  in  the  example  just  given. 

Further,  in  the  case  of  hydrochloric  acid,  the  negative  charge  of  the  chlorine 
ion  is  equal  to  the  positive  charge  of  the  hydrogen  ion  ;  but  in  the  case  of  the 
sulphuric  acid,  the  negative  charge  of  the  SO4  ion  is  equal  to  the  positive  charge  of 
two  hydrogen  ions.  We  can  thus  speak  of  monovalent,  divalent,  trivalent,  etc., 
ions. 

Ions  positively  charged  are  called  kat-ions  because  they  move  towards  the  kathode 
or  negative  pole  ;  those  which  are  negatively  charged  are  called  an-ions  because  they 
move  towards  the  anode  or  positive  pole.  The  following  are  some  examples  of  each 
class  : — 

Kat-ions.     Monovalent : — H,  Na,  K,  NHj,  etc. 

Divalent : — Ca,  Ba,  Fe  (in  ferrous  salts),  etc. 

Trivalent :— Al,  Bi,  Sb,  Fe  (in  ferric  salts),  etc. 
An-ions.       Monovalent :— CI,  Br,  I,  OH,  NO.,  etc. 

Divalent  : — S,  Se,  SO4,  etc. 

Roughly  speaking,  the  greater  the  dilution  the  more  nearly  complete  is  the 
dissociation,  and  in  a  very  dilute  solution  of  such  a  substance  as  sodium  chloride 
we  may  consider  that  the  number  of  ions  is  double  the  number  of  molecules  of  the 
salt  present. 

The  ions  liberated  by  the  act  of  dissociation  are,  as  we  have  seen,  charged  with 
electricity,  and  when  an  electrical  current  is  led  into  such  a  solution,  it  is  conducted 
through  the  solution  by  the  movement  of  the  ions.  Substances  which  exhibit  the 
property  of  dissociation  are  known  as  electrol}i;es. 

The  liquids  of  the  body  contain  electrolytes  in  solution,  and  it  is  owing  to  this 
fact  that  they  are  able  to  conduct  electrical  currents. 

This  conception  of  electrolytes  which  we  owe  to  Arrhenius  is  extremely  impor- 
tant in  view  of  the  question  of  osmotic  pressure,  because  the  act  of  dissociation 
increases  the  number  of  particles  moving  in  the  solution,  and  so  increases  the 
osmotic  pressure,  for  in  this  relation  an  ion  plays  the  same  part  as  a  molecule. 

Another  physiological  aspect  of  the  subject  is  seen  in  a  study  of  the  actions  of 
mineral  salts  in  solution  on  living  organisms  and  parts  of  organisms.  Many  years 
ago  Ringer  showed  that  contractile  tissues  (heart,  cilia,  etc.)  continue  to  manifest 
their  activity  in  certain  saline  solutions.  We  have  already  seen  (p.  256)  that  Howell 
considers  the  cause  of  rhythmical  action  in  the  heart  is  the  presence  of  these 
inorganic  substances  in  the  blood  or  lymph  which  bathes  it. 


322  LYMPH  AND  LYMPHATIC  GLANDS  [CH.  XXIL 

Loeb  and  his  fellow-workers  have  confirmed  these  statements,  but  interpret  them 
now  as  ionic  action.  Contractile  tissues  will  not  contract  in  pure  solutions  of  non- 
electroljiies  (such  as  sugar,  urea,  albumin).  But  different  contractile  tissues  differ 
in  the  nature  of  the  ions  which  are  most  favourable  stimuli.  Thus  cardiac  muscle, 
cilia,  amoeboid  movement,  karyokinesis,  cell  division,  are  all  alike  in  requiring  a 
proper  adjustment  of  ions  in  their  surroundings  if  they  are  to  continue  to  act,  but 
the  proportions  must  be  different  in  individual  cases.  Ions  affecting  the  rhythmical 
contractions  may  be  divided  into  three  classes  :  (1)  Those  which  produce  such  con- 
tractions ;  of  these  the  most  efficacious  is  Na.  (2)  Those  which  retard  or  inhibit 
rhythmical  contractions  ;  for  instance,  Ca  and  K.  (3)  Those  which  act  catalytically, 
that  is,  they  accelerate  the  action  of  Na,  though  they  do  not  themselves  produce 
rhythmical  contractions  directly  :  for  instance,  H  and  OH.  In  spite  of  the 
antagonistic  effect  of  Ca,  a  certain  minimal  amount  of  it  must  be  present  if  contrac- 
tions are  to  continue  for  any  length  of  time.  Ions  produce  rhythmical  contrac-tion 
only  because  they  affect  either  the  physical  condition  of  the  colloidal  substances 
(protein,  etc.)  in  protoplasm,  or  the  rapidity  of  chemical  processes. 

Loeb  has  even  gone  so  far  as  to  consider  that  the  process  of  fertilisation  is 
mainly  ionic  action.  He  denies  that  the  nuclein  in  the  head  of  the  spermatozoon  is 
essential,  but  asserts  that  all  the  spermatozoon  does  is  to  act  as  the  stimulus  in  the 
due  adjustment  of  the  proportions  of  the  surrounding  ions.  He  supports  this  view 
by  numerous  experiments  on  ova,  in  which,  without  the  presence  of  spermatozoa, 
he  has  produced  larvae  (generally  imperfect  ones,  it  is  true)  by  merely  altering  the 
saline  constituents  of  the  fiuidthat  bathes  them.  Whether  such  a  sweeping  and 
almost  revolutionary  notion  will  stand  the  test  of  further  verification  must  be  left  to 
the  future.  So  also  must  the  equally  important  idea  that  the  basis  of  a  nerve- 
impulse  is  electrohi:ic  action. 

Gramme-molecular  Solutions. — From  the  point  of  view  of  osmotic  pressure  a 
convenient  unit  is  the  gramme-molecule.  A  gramme-molecule  of  any  substance  is 
the  quantity  in  grammes  of  that  substance  equal  to  its  molecular  weight.  A 
gramme-molecular  solution  is  one  which  contains  a  gramme-molecule  of  the  sub- 
stance per  litre.  Thus  a  gramme-molecular  solution  of  sodium  chloride  is  one  which 
contains  58'o  grammes  of  sodium  chloride  (Na  =  23"0.0:  Cl  =  35"4.'))  in  a  litre.  A 
gramme-molecular  solution  of  grape  sugar  (QHj.jOJ  is  one  which  contains  179 '58 
grammes  of  grape  sugar  in  a  litre.  A  gramme-molecule  of  hydrogen  (H.,)  is  2 
grammes  by  weight  of  hydrogen,  and  if  this  was  compressed  to  the  volume  of  a 
litre,  it  would  be  comparable  to  a  gramme-molecular  solution.  It  therefore  follows 
that  a  litre  containing  2  grammes  of  hydrogen  contains  the  same  number  of 
molecules  of  hydrogen  in  it  as  a  litre  of  a  solution  containing  .'iSo  grammes  of 
sodium  chloride,  or  one  containing  179*.")S  grammes  of  grape  sugar,  has  in  it  of  salt 
or  sugar  molecules  respectively.  To  put  it  another  way,  the  heavier  the  weight  of 
a  molecule  of  any  substance,  the  more  of  that  substance  must  be  dissolved  in  the 
litre  to  obtain  its  gramme-molecular  solution.  Or  .still  another  way  :  if  solutions  of 
various  substances  are  made  all  of  the  same  strength  per  cent. ,  the  solutions  of  the 
materials  of  small  molecular  weight  will  contain  more  molecules  of  those  materials 
than  the  solutions  of  the  materials  which  have  heavy  molecules.  We  shall  see  that 
the  calculation  of  osmotic  pressure  depends  upon  these  facts. 

Diflfusion,  Dialysis,  Osmosis. — If  two  gases  are  brought  together  within  a 
closed  space,  a  homogeneous  mixture  of  the  two  is  soon  obtained.  This  is  due 
to  the  movements  of  the  gaseous  molecules  within  the  confining  space,  and  the 
process  is  called  di fusion.  In  a  similar  way  diffusion  will  effect  in  time  a  homo- 
geneous mixture  of  two  liquids  or  solutions.  If  water  is  carefully  poured  on  to  the 
surface  of  a  solution  of  salt,  the  salt  or  its  ions  will  soon  be  equally  distributed 
throughout  the  whole.  If  a  solution  of  albumin  or  any  other  colloidal  ,sub.stance  is 
used  instead  of  salt  in  the  experiment,  diffusion  will  be  found  to  occur  much  more 
slowly.  If,  instead  of  pouring  the  water  on  to  the  surface  of  a  solution  of  salt  or 
sugar,  the  two  are  separated  by  a  membrane  made  of  such  a  material  as  parchment 
paper,  a  similar  diffusion  will  occur,  though  more  slowly  than  in  cases  where  the 
membrane  is  absent.  In  time,  the  water  on  each  side  of  the  membrane  will  contain 
the  same  quantity  of  sugar  or  salt.  Substances  which  pass  through  such  membranes 
are  called  crystalloids.     Substances  which  have  such  large  molecules  (starch,  pro- 


CH.  XXII.] 


OSMOSIS 


323 


M 


toin,  etc.)  tli.it  tiny  will  not  p.iss  tlirotigli  sucli  membranes  are  called  ro//o»V/.v. 
DilVusioM  (tf  substancfs  in  solution  which  havt;  to  dt-al  with  an  intervcninj;^  membrane 
is  usually  called  didli/sis-.  The  ]irocess  of  Ji/fni/ion  (i.e.,  the  ])assafre  of  materials 
throujih  the  pores  of  a  meuibraiie  under  tlu-  influence  of  nieehanical  pressure)  may 
be  excluded  in  such  expcrinients  by  plaeiiif;'  the  membrane  (m)  vertically  as  shown 
in  the  diagram  (lii;-.  :il)7).  and  tlu'  two  fluids  a  and  ii  on  each  side  of  it.  Diffusion 
throiii;h  .1  nieinhrane  is  not  limited  to  the  molecules  of  water,  but  it  may  occur  also 
in  the  molecules  of  certain  substances  dissolved  in  the  water.  Hut  verj'  few  or  no 
membranes  are  (-(jually  permeable  to  water  and  to  molecules  of  the  substances  dis- 
solved in  the  water.  If  in  the  accom|)anyinf::  diagram  the  compartment  a  is  filled 
with  juire  water,  and  n  with  a  sodium  chloridt;  solution,  the  liquids  in  the  two  com- 
partnicnts  will  ultimately  be  found  to  be  equal  in  bulk  as  they  were  at  the  start,  and 
each  will  be  a  solution  of  salt  of  half  the  original  strength  of  that  in  the  compart- 
ment II.  But  at  first  the  volume  of  the  liquid  in  compartment  h  increases,  because 
more  wati-r  moU'cuIes  ])ass  into  it  from  a  than  salt  molecules  pass  from  it  to  a.  The 
term  osnioals  is  generally  limited  to  the  stream  of  water  molecules  passing  through  a 
membrane,  while  the  term  ilia/i/ds  is  applied  to  the  passage  of  the  molecules  in  solu- 
tion in  the  water.  The  osmotic  stream  of  water  is  esjiecially  important,  and  in  con- 
nection with  this  it  is  necessary  to  explain  the  term  osmoiic  prenntny.  At  first,  then, 
osmosis  (the  diffusion  of  water)  is  more  rapid  than  the  dialysis  (the  diffusion  of  the 
salt  molecules  or  ions).  The  older  explanation  of  this  was  that  salt  attracted  the 
water,  but  we  now  express  the  fact  differently  by  saying 
that  the  salt  in  solution  exerts  a  certain  osmotic  pressure  : 
the  result  of  the  osmotic  pressure  is  that  more  water  flows 
from  the  water  side  to  the  side  of  the  solution  than  in  the 
contrary  direction.  The  osmotic  pressure  varies  with  the 
amount  of  substance  in  solution,  and  is  also  altered  by 
variations  of  temperature  occurring  more  rapidly  at  high 
than  at  low  temperatures. 

If  we  imagine  two  masses  of  water  separated  by  a 
permeable  membrane,  as  many  water  molecules  will  pass 
through  from  one  side  as  from  the  other,  and  so  the 
volumes  of  the  two  masses  of  water  will  remain  un- 
changed. If  now  we  imagine  the  membrane  m  is  not  per- 
meable except  to  water,  and  the  compartment  a  contains 
water,  and  the  compartment  n  contains  a  solution  of  salt 
or  sugar  ;  under  these  circumstances  water  will  pass  through  into  it,  and  the 
volume  of  it  will  increase  in  proportion  to  the  osmotic  pressure  of  the  sugar  or 
salt  in  solution  in  it,  but  no  molecules  of  sugar  or  salt  can  get  through  into  a  from  it, 
so  the  volume  of  fluid  in  a  will  continue  to  decrease,  until  at  last  a  limit  is  reached. 
The  determination  of  this  limit,  as  measured  by  the  height  of  a  column  of  fluid 
or  mercury  which  it  will  support,  will  give  us  a  measurement  of  the  osmotic 
pressure. 

If  a  bladder  containing  strong  salt  solution  is  placed  in  a  vessel  of  distilled 
water,  water  passes  into  the  bladder  by  osmosis,  so  that  the  bladder  is  swollen, 
and  a  manometer  connected  with  its  interior  will  show  a  rise  of  pressure  (osmotic 
pressure).  But  the  total  rise  of  pressure  cannot  be  measured  in  this  way  for  two 
reasons  :  (1)  because  the  salt  diffuses  out  as  the  water  diffuses  in  ;  and  (2)  because 
the  membrane  of  the  bladder  leaks  ;  that  is,  permits  of  filtration  when  the  pressure 
within  it  has  attained  a  certain  height. 

It  is  therefore  necessary  to  use  a  membrane  which  will  not  allow  salt  to  pass 
out  either  by  dialysis  or  filtration,  though  it  will  let  the  water  pass  in.  Such 
membranes  are  called  semipermeahk  membranes,  and  one  of  the  best  of  these  is 
ferrocyanide  of  copper.  This  may  be  made  by  taking  a  cell  of  porous  earthenware 
and  washing  it  out  first  with  copper  sulphate  and  then  with  potassium  ferrocyanide. 
An  insoluble  precipitate  of  copper  ferrocyanide  is  thus  deposited  in  the  pores  of  the 
earthenware. 

If  such  a  cell  is  arranged  as  in  fig.  308,  and  filled  with  a  1  per  cent,  solution  of 
sodium  chloride,  water  diffuses  in,  till  the  pressure  registered  by  the  manometer 
reaches  the  enormous  height  of  5000  mm.  of  mercury.     If  the  pressure  in  the  cell 


324 


LYMPH    AND    LYMPHATIC    GLANDS 


[cH.  xxn. 


M 


rt^ 


is  increased  beyond  this  artificially,  water  will  be  pressed  through  the  semi-perme- 
able walls  of  the  cell  and  the  solution  will  become  more  concentrated. 

In  other  words,  in  order  to  make  a  solution  of  sodium  chloride  of  greater  con- 
centration than  1  per  cent.,  a  pressure  greater  than  5000  mm.  of  mercury  must  be 
employed.  The  osmotic  pressure  exerted  by  a  2  per  cent,  solution  would  be  twice 
as  great. 

Though  it  is  theoretically  possible  to  measure  osmotic  pressure  by  a  manometer 
in  this  direct  way,  practically  it  is  hardly  ever  done,  and  some  of  the  indirect 
methods  of  measurement  described  later  are  used  instead.  The  reason  for  this  is 
that  it  has  been  found  difficult  to  construct  a  membrane  which  is  absolutely  semi- 
permeable ;  they  are  nearly  all  permeable  in  some  degree  to  the  molecules  of  the 
dissolved  crystalloid.  In  course  of  time,  therefore, 
the  dissolved  crystalloid  will  be  equally  distributed 
on  both  sides  of  the  membrane,  and  osmosis  of  water 
will  cease  to  be  apparent,  since  it  will  be  equal  in 
both  directions. 

Many  explanations  of  the  nature  of  osmotic 
pressure  have  been  brought  forward,  but  none  is 
perfectly  satisfactory.  The  following  simple  ex- 
planation is  perhaps  the  best,  and  may  be  rendered 
most  intelligible  by  an  illustration.  Suppose  we 
have  a  solution  of  sugar  separated  by  a  semi-per- 
meable membrane  from  water ;  that  is,  the  mem- 
brane is  permeable  to  water  molecules,  but  not  to 
sugar  molecules.  The  streams  of  water  from  the  two 
sides  will  then  be  unequal ;  on  one  side  we  have 
water  molecules  striking  against  the  membrane  in 
what  we  may  call  normal  numbers,  while  on  the 
other  side  both  water  molecules  and  sugar  molecules 
are  striking  against  it.  On  this  side,  therefore,  the 
sugar  molecules  take  up  a  certain  amount  of  room, 
and  do  not  allow  the  water  molecules  to  get  to  the 
membrane ;  the  membrane  is,  as  it  were,  screened 
against  the  water  by  the  sugar,  therefore  fewer 
water  molecules  will  get  through  from  the  screened 
to  the  unscreened  side  than  vice  versa.  This  comes 
to  the  same  thing  as  saying  that  the  osmotic  stream 
of  water  is  greater  from  the  unscreened  water  side  to 
the  screened  sugar  side  than  it  is  in  the  reverse 
direction.  The  more  sugar  molecules  that  are 
present,  the  greater  will  be  their  screening  action, 
and  thus  we  see  that  the  osmotic  pressure  is  pro- 
portional to  the  number  of  sugar  moleciJes  in  the 
solution,  that  is,  to  the  concentration  of  the  solution. 

Osmotic  pressure  is,  in  fact,  equal  to  that  whicli 
the  dissolved  substance  would  exert  if  it  occupied  the 
same  space  in  the  form  of  a  gas  (Van't  HoiFs  hypo- 
thesis). The  nature  of  the  substance  makes  no  differ- 
ence ;  it  is  only  the  number  of  molecules  which  causes  osmotic  pressure  to  vary. 
The  osmotic  pressure,  however,  of  substances  like  sodium  chloride,  which  are  elec- 
trolytes, is  greater  than  what  one  would  expect  from  the  number  of  molecules  present. 
This  is  because  the  molecules  in  solution  are  split  into  their  constituent  ions,  and 
an  ion  plays  the  same  part  as  a  molecule,  in  questions  of  osmotic  pressure.  In  dilute 
solutions  of  sodium  chloride  ionisation  is  more  complete,  and  as  the  total  number  of 
ions  is  then  nearly  double  the  number  of  original  molecules,  the  osmotic  pressure  is 
nearly  double  what  would  have  been  calculated  from  the  number  of  molecules. 

The  analogy  between  osmotic  pressure  and  the  pressure  of  gases  is  very  com- 
plete, as  may  be  seen  from  the  following  statements  : — 

1.  At  a  constant  temperature  osmotic  pressure  is  proportional  to  the  concentra- 
tion of  the  solution  (Boyle-Mariotte's  law  for  gases). 


B 


Fig.  308. — A,  outer  vessel,  con- 
taining distilled  water ;  B, 
inner  semi-permeable  vessel, 
containing  1  per  cent,  salt 
solution  ;  M,  mercurial 
manometer.  (After  Star- 
ling.) 


en.  XXII.]  OSMOTIC    PRESSURE  325 

2.  With  constant  concentration,  the  osmotic  pressure  risrs  with  and  is  pro])or- 
tional  to  the  ti-rapirature  (Gay-Lussac"s  law  for  gases). 

3.  The  osmotic  pressure  of  a  sohition  of  different  substances  is  equal  to  the  sum 
of  the  pressures  which  tlie  individual  sul)stances  would  exert  if  they  were  alone  in 
the  solution  (Ilenry-naltoii  law  for  partial  pressure  of  gases). 

I.  The  osmotic  pressure  is  independent  of  the  nature  of  the  substance  in 
solution,  and  depends  only  on  the  number  of  molecules  or  ions  in  solution 
(Avogadro's  law  for  gases). 

Calculation  of  Osmotic  Pressure. — We  may  best  Illustrate  this  by  an  example, 
and  to  sim|)lify  matters  we  will  take  an  example  in  the  case  of  a  non-electrolyte 
such  as  sugar.  We  shall  then  not  have  to  take  into  account  any  electrolytic  dissocia- 
tion of  the  molecules  into  ions.  We  wiU  suppose  we  want  to  calculate  the  osmotic 
pressure  of  a  1  per  cent,  solution  of  cane  sugar. 

One  gramme  of  hydrogen  at  atmospheric  pressure  and  0'  C.  occupies  a  volume 
of  11 '2  litres;  two  grammes  of  hydrogen  will  therefore  occupy  a  volume  of  22*4 
litres.  A  gramme-molecule  of  hydrogen — that  is,  '1  grammes  of  hydrogen — when 
brought  to  tiie  vohime  of  1  litre,  will  exert  a  gas  pressure  equal  to  that  of  22*4  litres 
compressed  to  1  litre — that  is,  a  pressure  of  22  4  atmospheres.  A  gramme-mole- 
cular solution  of  cane  sugar,  since  it  contains  the  same  number  of  molecules  in  a 
litre,  must  therefore  exert  an  osmotic  pressure  of  22  4  atmospheres  also.  A 
gramme-molecular  solution  of  cane  sugar  (C,.jH.j.jO,,)  contains  342  grammes  of  cane 
sugar  in  a  litre  of  water.  A  1  per  cent,  solution  of  cane  sugar  contains  only  10 
grammes  of  cane  sugar  in  a  litre ;   hence  the  osmotic  pressure  of  a  1  per  cent. 

solution   of  cane  sugar  is  ■;r-~    x    22*4   atmospheres,   or   0"65   of  an   atmosphere, 

o42 

which  in  terms  of  a  column  of  mercury  =  760  x  0"65  =  494  mm. 

It  would  not  be  possible  to  make  such  a  calculation  in  the  case  of  an  electro- 
lyte, because  we  should  not  know  how  many  molecules  had  been  ionised.  In  the 
liquids  of  the  body,  both  electrolytes  and  non-electrolytes  are  present,  and  so  a 
calculation  is  here  also  impossible. 

We  have  seen  that  for  such  liquids  the  osmotic  pressure  is  seldom  directly 
measured  by  a  manometer,  because  of  the  difficulty  in  obtaining  perfect  semi- 
permeable membranes  ;  we  now  see  that  mere  arithmetic  often  fails  us  ;  and  so 
we  come  to  the  question  to  which  we  have  been  so  long  leading  up,  viz.,  how 
osmotic  pressure  is  actually  determined. 

Determination  of  Osmotic  Pressure  by  means  of  the  Freezing-point. — 
This  is  the  method  which  is  almost  universally  employed.  A  very  simple  apparatus 
(Beckmann's  differential  tiiermometer)  is  all  that  is  necessary.  The  principle  on 
which  the  method  depends  is  the  following  : — ^The  freezing-point  of  any  substance 
in  solution  in  water  is  lower  than  that  of  water  ;  the  lowering  of  the  freezing-point 
is  proportional  to  the  molecular  concentration  of  the  dissolved  substance,  and  that, 
as  we  have  seen,  is  proportional  to  the  osmotic  pressure. 

When  a  gramme-molecule  of  any  substance  is  dissolved  in  a  litre  of  water,  the 
freezing-point  is  lowered  by  187  C. ,  and  the  osmotic  pressure  is,  as  we  have  seen, 
equal  to  22-4  atmospheres,  that  is,  22*4  x  760  =  17,024  mm.  of  mercury. 

We  can,  therefore,  calculate  the  osmotic  pressure  of  any  solution  if  we  know 
the  lowering  of  its  freezing-point  in  degrees  Centigrade  ;  the  lowering  of  the 
freezing-point  is  usually  expressed  by  the  Greek  letter  A. 

Osmotic  pressure  =  ^.„_  x  17,024. 

1   o/ 

For  example,  a  1  per  cent,  solution  of  sugar  would  freeze  at  -0'052''  C.  ;  its 

.     ,,        „         -0.^.2x17,024     ,_,  ,  •       4.  I 

osmotic  pressure   is   therefore  :.^n^ =  4/:]   mm.,   a   number  approximately 

equal  to  that  we  obtained  by  calculation. 

Mammalian  blood  serum  gives  A  =0-.56"  C.     A  0  9  per  cent,  solution  of  sodium 

chloride  has  the  same  A  ;  hence  serum  and  a  0'9  per  cent,  solution  of  common  salt 

have  the  same  osmotic  pressure,  or  are  viotonir.     The  osmotic  pressure  of  blood 

.    -.".ex  17,024     ^  ...  f  I 

serum  is  r-r7= =  o000  mm.  of  mercury  approximately,  or  a  pressure  or  nearly 

1  'o7 

7  atmospheres. 


326  LYMPH    AND    LYMPHATIC    GLANDS  [CH.  XXII. 

The  osmotic  pressure  of  solutions  may  also  be  compared  by  observing  their 
effect  on  red  blood  corpuscles,  or  on  vegetable  cells  such  as  those  in  Tradescantia. 
If  the  solution  is  h_i/pertonic,  i.e.,  has  a  greater  osmotic  pressure  than  the  cell 
contents,  the  protoplasm  shrinks,  and  loses  water,  or  if  red  corpuscles  are  used, 
they  become  crenated  ;  if  the  solution  is  Iti/potonic,  I.e.,  has  a  less  osmotic  pressure 
than  the  material  within  the  cell-wall,  no  shrinking  of  the  protoplasm  in  the 
vegetable  cell  takes  ])lace ;  and  if  red  corpuscles  are  used  they  swell  and  liberate 
their  pigment.  Isotonic  solutions,  such  as  physiological  salt  solution,  produce  neither 
of  these  effects,  because  they  have  the  same  molecular  concentration  and  osmotic 
pressure  as  the  material  within  the  cell-wall. 

Physiological  Applications. — It  will  at  once  be  seen  how  important  all  these 
considerations  are  from  the  physiological  standpoint.  In  the  body  we  have  aqueous 
solutions  of  various  substances  separated  from  one  another  by  membranes.  Thus 
we  have  the  endothelial  walls  of  the  capillaries  separating  the  blood  from  the  lymph  ; 
we  have  the  epithelial  walls  of  the  kidney  tubules  separating  the  blood  and  lymph 
from  the  urine ;  we  have  similar  epithelium  in  all  secreting  glands  ;  and  we  have 
the  wall  of  the  alimentary  canal  separating  the  digested  food  from  the  blood-vessels 
and  lacteals.  In  such  important  problems,  then,  as  lymph-formation,  the  forma- 
tion of  urine  and  other  excretions  and  secretions,  and  absorption  of  food,  we  have 
to  take  into  account  the  laws  which  regulate  the  movements  both  of  water  and  of 
substances  which  are  held  in  solution  by  the  water.  In  the  body  osmosis  is  not  the 
only  force  at  work,  but  we  have  also  to  consider  filtration,  that  is,  the  forcible 
passage  of  materials  through  membranes,  due  to  differences  of  mechanical  pressure. 
Further  complicating  these  two  processes  we  have  to  take  into  account  another 
force,  namely,  the  secretory  or  selective  activity  of  the  living  cells  of  which  the 
membranes  in  question  are  composed.  This  is  sometimes  called  by  the  name  vital 
action,  which  is  an  unsatisfactory  and  unscientific  expression.  The  laws  which 
regulate  filtration,  inhibition  (or  adsorption),  and  osmosis  are  fairly  well  known  and 
can  be  experimentally  verified.  But  we  have  undoubtedly  some  other  force,  or 
some  other  manifestation  of  force,  in  the  case  of  living  membranes.  It  probably 
is  some  physical  or  chemical  property  of  living  matter  which  has  not  yet  been 
brought  into  line  with  the  known  chemical  and  physical  forces  which  operate  in  the 
inorganic  world.  We  cannot  deny  its  existence,  for  it  sometimes  operates  so  as  to 
neutralise  the  known  forces  of  osmosis  and  filtration. 

The  more  one  studies  the  question  of  lymph-formation,  the  more  convinced  one 
becomes  that  mere  osmosis  and  filtration  will  not  explain  it  entirely.  The  basis  of 
the  action  is  no  doubt  physical,  but  the  living  cells  do  not  behave  like  the  dead 
membranes  of  a  dialyser  ;  they  have  a  selective  action,  picking  out  some  substances 
and  passing  them  through  to  the  lymph,  while  they  reject  others. 

The  question  of  gaseous  interchanges  in  the  lungs  is  another  of  a  similar 
kind.  Some  maintain  that  all  can  be  explained  by  the  laws  of  diffusion  of  gases  ; 
others  assert  that  the  action  is  wholly  vital.  Probably  those  are  most  correct 
who  admit  a  certain  amount  of  truth  in  both  views  ;  the  main  facts  are  explicable 
on  a  physical  basis,  but  there  are  also  some  puzzling  data  that  show  that  the 
pulmonary  epithelium  is  able  to  exercise  some  other  force  as  well  which  inter- 
feres to  some  extent  with  the  known  physical  process.  Take  again  the  case  of 
absorption.  The  object  of  digestion  is  to  render  the  food  soluble  and  diffusible  ;  it 
can  hardly  be  supposed  that  this  is  useless  ;  the  readily  diffusible  substances  will 
pass  more  easily  through  into  the  blood  and  lymph  :  but  still,  as  Waymouth  Reid 
has  shown,  if  the  living  epithelium  of  the  intestine  is  removed,  absorption  comes 
very  nearly  to  a  standstill,  although  from  the  purely  physical  standpoint  removal  of 
the  thick  columnar  epithelium  would  increase  the  facilities  for  osmosis  and  filtration. 

The  osmotic  pressure  exerted  by  crystalloids  is  very  considerable,  but  their 
ready  diffusibility  limits  their  influence  on  the  flow  of  water  in  the  body.  Thus  if  a 
strong  solution  of  salt  is  injected  into  the  blood,  the  first  effect  will  be  the  setting 
up  of  an  osmotic  .stream  from  the  tissues  to  the  blood.  The  salt,  however,  would 
soon  diffuse  out  into  the  tissues,  and  would  now  exert  osmotic  pressure  in  the 
opposite  direction.  Moreover,  both  effects  will  be  but  temporary,  because  excess  of 
salt  is  soon  got  rid  of  by  the  excreting  organs. 

Osmotic  Pressure  of  Proteins.  — It  has  been  generally  assumed  that  proteins. 


en.   XXII.]  OSMOTIC    PRESSUKE    OF    PKOTEINS  ?>27 

tlie  Tuost  abunilant  aiul  important  constituents  of  tlie  blood,  I'xt-rt  little  or  no 
osmotic  pressure.  Starling,  however,  has  claimed  that  they  have  a  small  osmotic 
pressure;  if  this  is  so,  it  is  of  importance,  for  proteins,  unlike  salt,  do  not  diffuse 
readily,  and  their  effect  therefore  remains  as  an  almost  permanent  factor  in  the 
blood.  Starlinii'  jiives  the  osmotic  pressure  of  the  proteins  of  the  blood-plasma  as 
equal  to  ".(»  mm.  of  mercury.  We  should  from  the  theoretical  standpoint  find  it 
ditfieult  to  imagine  that  a  pure  protein  can  exert  more  than  a  minimal  osmotic 
pressure.  It  is  made  up  of  such  huge  molecules  that,  even  when  the  proteins  are 
present  to  the  extent  of  7  or  8  per  cent.,  as  they  are  in  blood-j)lasma,  there  are 
comparatively  few  protein  molecules  j^resent,  and  these  are  in  a  state  of  colloidal 
solution,  not  true  solution.  Still,  by  means  of  this  weak  but  constant  j)ressure  it  is 
possible  to  explain  the  fact  that  an  isotonic  or  even  a  hypertonic  solution  of  a 
diffusible  crystalloid  may  be  completely  absorbed  from  the  peritoneal  cavity  into 
the  blood. 

The  functional  activity  of  the  tissue  elements  is  accompanied  by  the  breaking 
down  of  their  protein  c'onstituents  into  such  simple  materials  as  urea  (and  its 
precursors)  sulphates  and  phosphates.  These  materials  pass  into  the  lymph,  and 
increase  its  molecular  concentration  and  its  osmotic  pressure  ;  thus  water  is 
attracted  (to  use  the  older  way  of  putting  it)  from  the  blood  to  the  lymph,  and  so 
the  volume  of  the  lymph  rises  nnd  its  flow  increases.  On  the  other  hand,  as  these 
substances  accunuilate  in  the  lymph  they  will  in  time  attain  there  a  greater  concen- 
tration than  in  the  blood,  and  so  they  will  diffuse  towards  the  blood,  by  which  they 
are  carried  to  the  organs  of  exi-retion. 

But,  again,  we  have  a  dilfieulty  with  the  proteins  ;  they  are  most  important  for 
the  nutrition  of  the  tissues,  but  they  are  practically  indiffusible.  We  must  pro- 
visionally assume  that  their  presence  in  the  Ij'mph  is  due  to  filtration  from  the  blood. 
The  plasma  in  the  c-apillaries  is  under  a  somewhat  higher  pressure  than  the  lymph 
in  the  tis.sues,  and  this  tends  to  squeeze  the  constituents  of  the  blood,  including 
the  proteins,  through  the  capillary  walls.  I  have,  however,  already  indicated  that 
the  question  of  lymph-formation  is  one  of  the  many  physiological  problems  which 
await  solution  by  the  physiologists  of  the  future. 

Waymouth  Reid  finds  that  absolutely  pure  proteins  exert  no  osmotic  pressure  ; 
the  pressure  observed  is  due  to  saline  and  other  materials  from  which  it  is  difficult  to 
disentangle  the  protein.  '  Haemoglobin  is  an  exception  to  this  rule  ;  it  exerts  a  small 
osmotic  pressure  and  forms  a  true  solution  with  water. 

Dr  C.  J.  Martin  has  suggested  to  me  a  way  of  illustrating  the  so-called  selective 
action  of  living  membranes.  Suppose  a  number  of  fishes  are  swimming  about  in  a 
tank,  like  moving  molecules  or  ions  in  solution ;  across  the  tank  is  a  wall  which 
divides  it  into  two  parts;  the  fi.shes  are  all  in  one  compartment  of  the  tank. 
Suppose,  next,  the  wall  has  in  it  a  number  of  holes  guarded  by  valves,  so  arranged 
that  the  fish  can  pass  through  into  the  second  compartment,  but  cannot  return. 
After  a  time,  as  the  fish  discover  these  holes,  there  will  be  an  equal  number  of  fish 
in  both  compartments  ;  but  this  is  not  the  end,  for  on  waiting  further,  more  fish  will 
find  their  way  through,  and  as  none  are  able  to  return,  they  will  all  in  time  accumu- 
late in  the  second  compartment.  It  is  not  difficult  to  grasp  the  idea  that  the  arrange- 
ment of  molecules  in  a  living  membrane  is  possibly  such  that  the  orifices  through 
which  other  molecides  pass  are  valvular,  and  such  a  conception  is  useful  if  it 
merely  serves  to  rob  the  word  "vital"  of  its  mystery. 

*  Bayliss  has  shown  that  the  saline  constituents  found  in  a  native  protein  are 
not  mechanically  mixed  with  it,  and  are  also  not  in  true  chemical  combination  with 
it,  but  are  in  a  condition  intermediate  between  these  two  extremes,  to  which  the 
term  mhorption  is  applied.  Many  dyes  used  for  staining  fabrics  and  histological 
preparations  are  also  adsorbed. 


CHAPTER  XXIII 

THE   DUCTLESS    GLANDS 

The  ductless  glands  form  a  heterogeneous  group  of  organs,  most  of 
which  are  related  in  function  or  development  with  the  circulatory 
system.  They  include  the  lymphatic  glands,  the  spleen,  the  thymus, 
the  thjToid,  the  suprarenal  capsules,  the  pineal  body,  the  pituitary 
body,  and  the  carotid  and  coccygeal  glands.  The  function  of  a  gland 
that  has  a  duct  is  a  comparatively  simple  physiological  problem,  but 
the  use  of  ductless  glands  has  long  been  a  puzzle  to  investigators. 
Recent  research  has,  however,  shown  that  most  of,  if  not  all,  the 
ductless  glands  do  form  a  secretion,  and  this  internal  secretion,  as  it 
is  termed,  leaves  the  gland  by  the  venous  blood  or  lymph,  and  thus 
is  distributed  and  ministers  to  the  needs  of  parts  of  the  body  else- 
where. Many  of  the  glands  which  possess  ducts  and  form  an  external 
secretion,  form  an  internal  secretion  as  well.  Among  these,  the  liver, 
pancreas,  and  kidney  may  be  mentioned. 

In  many  cases  the  internal  secretion  is  essential  for  life,  and 
removal  of  the  gland  that  forms  it,  leads  to  a  condition  of  disease 
culminating  in  death.  In  other  cases  the  internal  secretion  is  not 
essential,  or  its  place  is  taken  by  that  formed  in  similar  glands  in 
other  parts  of  the  body. 

The  body  is  a  complex  machine ;  each  part  of  the  machine  has 
its  own  work  to  do,  but  must  work  harmoniously  with  other  parts. 
Just  as  a  watch  will  stop  if  any  of  its  numerous  wheels  get  broken, 
so  the  metabolic  cycle  will  become  disarranged  or  cease  altogether  if 
any  of  the  links  in  the  chain  break  down. 

In  unravelling  the  part  which  the  ductless  glands  play  in  this 
cycle,  it  is  at  present  impossible  in  many  cases  to  state  precisely 
what  the  particular  function  of  each  is ;  all  one  can  say  is,  when 
the  gland  is  removed  or  its  function  interfered  with,  that  the  meta- 
bolic round  is  broken  somehow,  and  that  this  upsets  the  whole  of 
the  machinery  of  the  body.  The  difficulty  of  investigating  this 
subject  is  increased  by  the  fact  that  it  is  impossible  to  get  the 
internal  secretion  in  a  state  of  purity  and  examine  it ;  it  is  always 


CH.  XXIII.]  THE   SPLEEN  329 

mixed  with,  and  masked  by,  the  lymph  or  blood  into  which   it  is 
poured. 

In  spite  of  this,  however,  our  knowledge  in  this  branch  of 
physiology  is  increasing,  particularly  in  connection  with  some  of 
these  ductless  glands.  The  methods  of  investigation  which  have 
been  employed  are  the  following : — 

1.  Extirpation. — The  gland  in  question  is  removed,  and  the 
effect  of  the  absence  of  the  internal  secretion  noted. 

2.  Disease. — In  cases  where  the  function  of  the  gland  is  in 
abeyance,  owing  to  its  being  diseased,  the  symptoms  are  closely 
observed. 

3.  Injection  of  Extracts. — The  gland  is  taken  in  a  fresh  condition  ; 
an  extract  is  made  of  it,  and  this  is  injected  into  the  circulation 
of  healthy  animals,  and  into  that  of  those  animals  from  which  the 
gland  has  been  previously  removed,  and  the  effects  watched. 

4  Transplantation. — After  the  gland  is  removed  and  the  usual 
effect  produced,  the  same  gland  from  another  animal  is  transplanted 
into  the  first  animal,  and  restoration  of  function  looked  for. 

The  case  of  the  lymphatic  glands  we  have  already  studied ;  they 
form  an  internal  secretion  which  consists  of  lymph-cells,  and  these 
furnish  the  blood  with  a  supply  of  certain  kinds  of  colourless 
corpuscles.  Removal  of  lymphatic  glands  is  not  fatal,  as  the  other 
lymphatic  glands  and  other  collections  of  lymphoid  tissue  that  remain 
behind  carry  on  the  work  of  those  that  are  removed. 

The  internal  secretion  theory  of  the  ductless  glands  is  that  which  is  most  in 
vogue  at  present.  It  should  be  mentioned,  however,  that  there  is  another  theory, 
which  may  be  called  the  auto-intoxication  theory.  According  to  this  view  the  gland 
is  excretory  {i.e.,  gets  rid  of  waste  and  harmful  materials)  rather  than  secretory  {i.p., 
production  of  something  useful  to  the  organism).  When  the  gland  is  removed, 
the  waste  products  therefore  accumulate  and  produce  harmful  results.  It  is 
possible  that  as  our  knowledge  increases,  it  may  be  found  in  certain  cases  that 
both  these  theories  may  be  in  part  true. 

The  Spleen. 

The  Spleen  is  the  largest  of  the  ductless  glands ;  it  is  situated 
to  the  left  of  the  stomach,  between  it  and  the  diaphragm.  It  is  of 
a  deep  red  colour  and  of  variable  shape.  Vessels  enter  and  leave 
the  gland  at  a  depression  on  the  inner  side  called  the  hilus.  The 
spleen  is  covered  externally  almost  completely  by  a  serous  coat 
derived  from  the  peritoneum,  while  within  this  is  the  proper  fibrous 
coat  or  capsule  of  the  organ.  The  latter  is  composed  of  connective- 
tissue,  with  a  large  preponderance  of  elastic  fibres  and  a  certain  pro- 
portion of  unstriated  muscular  tissue.  Prolonged  from  its  inner 
surface  are  fibrous  processes  or  traheculce,  containing  much  unstriated 
muscle,  which  enter  the  interior  of  the  organ,  and,  dividing  and 
anastomosing   in  all   parts,  form   a   supporting   framework   in    the 


330 


THE   DUCTLESS    GLANDS 


[CH.  xxin. 


interstices  of  which  the  proper  substance  of  the  spleen  {spleen-pulp) 
is  contained. 

At  the  hilus  of  the  spleen,  the  blood-vessels,  nerves,  and  lym- 
phatics enter  or  leave,  and  the  fibrous  coat  is  prolonged  into  the 
spleen  substance  in  the  form  of  investing  sheaths  for  the  arteries 
and  veins,  which  sheaths  again  are  continuous  with  the  trabecule 
before  referred  to. 

The  spleen-pulp,  which  is  of  a  dark  red  or  reddish-brown  colour, 


Fifi.  309.— Section  of  injected  dog's  spleen,  c,  capsule;  tr,  trabeculse ;  m,  two  Malpighian  bodies  witli 
numerous  small  arteries  and  capillaries  ;  a,  artery  ;  I,  lymphoid  tissue,  consisting  of  closely-packed 
lymphoid  cells  supported  by  very  delicate  retiform  tissue  ;  a  light  space  unoccupied  by  cells  is  seen 
all  round  the  trabecular,  which  corresponds  to  the  "lymph-path  "  in  lymphatic  glands.     (Schofield.) 

is  composed  chiefly  of  cells,  imbedded  in  a  network  formed  of  fibres, 
and  the  branchings  of  large  nucleated  cells.  The  network  so  formed 
is  thus  very  like  a  coarse  kind  of  retiform  tissue.  The  spaces  of 
this  network  are  only  partially  occupied  by  cells  and  form  a  freely 
communicating  system.  Of  the  cells  some  are  granular  corpuscles 
resembling  the  lymph-corpuscles,  both  in  general  appearance  and  in 
being  able  to  perform  amoeboid  movements;  others  are  red  blood - 
corpuscles  of  normal  appearance  or  variously  changed ;  while  there 


CII.  XXIIl.]  THE    SPLEEN  331 

are  also  large  cells  containing  either  a  pigment  allied  to  the  colouring 
matter  of  the  blood,  or  rounded  corpuscles  like  red  corpuscles. 

The  splenic  artery,  after  entering  the  spleen  by  its  concave  surface, 
divides  and  subdivides,  with  but  little  anastomosis  between  its 
branches;  at  the  same  time  its  branches  are  sheathed  by  the  pro- 
longations of  the  fdjrous  coat,  which  they,  so  to  speak,  carry  into 
the  spleen  with  them.  The  arteries  soon  leave  the  trabecule,  and 
their  outer  coat  is  then  replaced  by  one  of  lymphoid  tissue;  they 
end  in  an  open  brush-work  of  capillaries,  the  endothelial  cells  of 
which  become  continuous  with  those  of  the  rete  of  the  spleen-pulp. 
The  veins  begin  by  a  similar  open  set  of  capillaries  from  the  large 
blood  spaces  of  the  pulp.  The  veins  soon  pass  into  the  trabecular, 
and  ultimately  unite  to  form  the  splenic  vein.  This  arrangement 
readily  allows  lymphoid  and  other  corpuscles 
to  be  swept  into  the  blood -current. 

On  the  face  of  a  section  of  the  spleen  can 
be  usually  seen  readily  with  the  naked  eye, 
minute,  scattered,  rounded  or  oval  whitish 
spots,  mostly  from  J^j-  to  ^  inch  (f  to  |  mm.) 
in  diameter.  These  are  the  Malpighian  cor- 
puscles of  the  spleen,  and  are  situated  on  the 
sheaths  of  the  minute  splenic  arteries.  They 
are  in  fact   outgrowths    of   the  outer  coat  of     ^     „,„„.., 

.  .  is.  „  1    .        /  j^        o/\n\        F'"'  310.— Reticulum  or  the 

lymphoid  tissue  just  reierred  to  (see  ng.  oUy).  spleen  of  a  cat,  shown  by 

Blood  capillaries  traverse  the  Malpighian  cor-  i^:^fl?"j  "''"  ^'''••^*'"'^- 

puscles  and  form   a   plexus  in    their   interior. 
The  structure  of  a  Malpighian  corpuscle  of  the  spleen  is  practically 
identical  with  that  of  a  lymphoid  nodule. 

The  spleen  has  the  following  functions : — 

(1.)  The  spleen,  like  the  lymphatic  glands,  is  engaged  in  the 
formation  of  colourless  Uood-corpuscles.  For  it  is  quite  certain,  that 
the  blood  of  the  splenic  vein  contains  an  unusually  large  proportion 
of  white  corpuscles ;  and  in  the  disease  termed  leucocythcemia,  in 
which  the  white  corpuscles  of  the  blood  are  remarkably  increased  in 
number,  there  is  found  a  hypertrophied  condition  of  the  spleen, 
especially  of  the  Malpighian  corpuscles.  The  white  corpuscles 
formed  in  the  spleen  also  doubtless  partly  leave  that  organ  by 
lymphatic  vessels. 

By  stimulating  the  spleen  to  contract  in  a  case  of  splenic 
leucocythsemia  by  means  of  an  electric  current  applied  over  it  through 
the  skin,  the  number  of  leucocytes  in  the  blood  is  almost  immediately 
increased. 

Eemoval  of  the  spleen  is  not  fatal ;  but  after  its  removal  there  is 
an  overgrowth  of  the  lymphatic  glands  to  make  up  for  its  absence. 

(2.)  It  forms  coloured  corpuscles,  at  any  rate,  in  some  animals ;  in 


332  THE   DUCTLESS   GLANDS  [CH.  XXHL 

these  animals,  cells  are  found  in  the  spleen  similar  to  those  we  have 
described  in  red  marrow,  and  called  hcematoUasts.  In  these  animals, 
if  the  spleen  is  removed,  the  red  marrow  hypertrophies. 

(3.)  There  is  reason  to  believe  that  in  the  spleen  many  of  the  red 
corpuscles  of  the  blood,  those  probably  which  have  discharged  their 
office  and  are  worn  out,  undergo  disintegration ;  for  in  the  coloured 
portions  of  the  spleen-pulp  an  abundance  of  such  corpuscles,  in  various 
stages  of  degeneration,  are  found,  and  in  those  cases  of  disease  in 
which  the  destruction  of  blood-corpuscles  is  increased  (pernicious 
anasmia)  iron  accumulates  in  the  spleen  as  in  the  liver.  It  was 
formerly  supposed  that  the  spleen  broke  down  the  corpuscles  and 
liljerated  haemoglobin,  which,  passing  in  the  blood  of  the  splenic  vein 
to  the  liver,  was  discharged  by  that  organ  as  bile-pigment.  But  this 
is  not  the  case;  the  disintegration  does  not  proceed  so  far  as  to 
actually  liberate  haemoglobin ;  there  is  no  free  haemoglobin  in  the 
blood-plasma  of  the  splenic  vein. 

(4.)  The  spleen  participates  in  nitrogenous  metabolism,  especially 
in  the  formation  of  uric  acid  fsee  Uric  Acid  formation  in  Chapter 
XXXVII.). 

(5.)  Besides  these  direct  offices,  the  spleen  fulfils  some  purpose 
in  regard  to  the  portal  circulation  with  which  it  is  in  close  connec- 
tion. From  the  readiness  with  which  it  admits  of  being  distended, 
and  from  the  fact  that  it  is  senerallv  small  while  eastric  digestion  is 
going  on,  and  enlarges  when  that  act  is  concluded,  it  is  supposed  to 
act  as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal 
system,  or  more  particularly  to  the  vessels  of  the  stomach.  That  it 
may  serve  such  purpose  is  also  made  probable  by  the  enlargement 
which  it  undergoes  in  certain  affections  of  the  heart  and  Hver, 
attended  with  obstruction  to  the  passage  of  blood  through  the  latter 
organ,  and  by  its  diminution  when  the  congestion  of  the  portal  system 
is  relieved  by  discharges  from  the  bowels,  or  by  the  effusion  of  blood 
into  the  stomach.  This  mechanical  influence  on  the  circulation, 
however,  can  hardly  be  supposed  to  be  more  than  a  very  subordinate 
function. 

Influence  of  the  Nervous  System  upon  the  Spleen. — When  the 
spleen  is  enlarged  after  digestion,  its  enlargement  is  due  to  two 
causes :  (1)  a  relaxation  of  the  muscular  tissue  which  forms  so  large 
a  part  of  its  framework ;  (2)  a  dilatation  of  the  vessels.  Both  these 
phenomena  are  under  control  of  the  nervous  system.  It  has  been 
found  by  experiment  that  when  the  splenic  nerves  are  cut  the  spleen 
enlarges,  and  that  contraction  can  be  brought  about  by  stimulation  of 
the  peripheral  ends  of  the  divided  nerves.  If  the  splenic  nerves  are 
not  cut,  contraction  is  produced  by  (1)  stimulation  of  the  spinal 
cord ;  (2)  reflexly  by  stimulation  of  the  central  stumps  of  certain 
divided  nerves,  e.g.,  vagus  and  sciatic ;  (3)  by  local  stimulation  by  an 


CH.  XXIII.] 


SPLENIC    WAVES 


333 


electric  current ;  (4)  by  the  administration  of  quinine  and  some  other 
drugs. 

It  has  been  sliown  hy  the  oncometer  (see  p.  308)  tliat  the  spleen 
undergoes  rhythmical  contractions  and  dilatations,  due  to  the  con- 
traction and  relaxation  of  the  muscular  tissue  in  its  capsule  and 
trabeculae.  A  tracing  also  shows  waves  due  to  the  rhythmical  alter- 
ations of  the  general  blood-pressure.  Fig.  311  is  a  typical  tracing 
obtained  by  Schafer's  air  oncometer  from  a  dog's  spleen. 

It  shows,  first,  the  large  waves  occurring  about  once  a  minute, 
due  to  the  splenic  systole  and   diastole;  secondly,  smaller  waves  on 


0.  PRESSURE 


SECONDS 


Fio.  311. — The  upper  tracing  is  the  .spleen  record;  the  next  is  carotid  blood-pressure  taken  with  a 
mercurial  kymograph.  The  straight  line  beneath  this  is  the  abscissa  of  the  arterial  pressure  ;  and 
the  lowest  tracinj'  is  the  time  in  seconds. 


this,  due  to  the  effect  of  respiration  on  the  blood-pressure ;  and  on 
these,  smaller  waves  still,  corresponding  with  the  individual  heart- 
beats. The  large  waves  due  to  the  splenic  contractility  still  go  on 
after  the  division  of  all  the  splenic  nerves.  These  nerve-fibres  leave 
the  spinal  cord  in  numerous  thoracic  anterior  roots ;  they  have  cell 
stations  in  the  sympathetic  chain  (Schafer)  or  semi-lunar  ganglia 
(Langley). 

Haemolymph  Glands. 

The  existence  of  glands  which  partake  of  the  nature  both  of  the 
spleen  and  of  lymphatic  glands,  has  long  been  known.  They  have 
been  recently  more  fully  investigated  by  T.  Lewis.  He  finds  them  in 
most  mammals,  and  they  can  be  readily  distinguished  from  ordinary 
lymphatic  glands  by  their  red  colour.     He  divides  them  into  (1)  hcsmal 


334 


THE    DUCTLESS    GLANDS 


[CH.  XXIIL 


glands,  which  are  characterised  by  the  fact  that  the  sinuses  contain 
blood  only;  the  spleen  is  in  fact  a  large  haemal  gland;  and  (2) 
hccmal  lymphatic  glands,  in  which  the  sinuses  are  filled  by  a  mixture 
of  blood  and  lymph. 

The  Thymus. 

This  gland  is  a  temporary  organ ;  it  attains  its  greatest  size  early 
after  birth,  and  after  the  second  year  gradually  diminishes,  until  in 


Fig.  312.— Thymus  of  a  calf,     c,  cortex  of  follicle ;  h,  medulla  ;  r,  interfollicular  tissue. 
Magnilied  about  twelve  times.    (Watney.) 

adult   life  hardly  a  vestige  remains.     At   its  greatest  development 

it  is  a  long  narrow  body,  situated  in  the  front  of  the  chest  behind 

the  sternum  and  partly  in  the  lower  part  of  the  neck.     It  is  of  a 

reddish   or  greyish   colour,   and   is   distinctly 

lobulated. 

The  gland  is  surrounded  by  a  fibrous  cap- 
sule, which  sends  in  processes,  forming  trabe- 
culse,  that  divide  the  gland  into  lobes,  and 
carry  the  blood-  and  lymph-vessels.  The  large 
trabeculas  branch  into  small  ones,  which  divide 
the  lobes  into  lobules.  The  lobules  are  further 
subdivided  into  follicles  l)y  fine  connective- 
tissue.  A  follicle  is  polyhedral  in  shape,  and 
consists  of  cortical  and  medullary  portions, 
both  of  which  are  composed  of  adenoid  or 
lymphoid  tissue,  but  in  the  medullary  portion 
the  matrix  is  coarser,  and  is  not  so  filled  up  with  lymphoid  cor- 
puscles as  in  the  cortex.  Scattered  in  the  lymphoid  tissue  of  the 
medulla  are  the  concentric  corpuscles  of  Hassall  (fig.  313),  which 
consist   of    a   nucleated   granular   centre,   surrounded    by   flattened 


Fig.  313. — The  reticulum  of 
the  thymus,  a,  lymph 
cells  ;  h,  corpuscles  of 
HassaU.    (Cadiat.) 


CH.  XXIII.]  THE   THYMUS    AND    THYROID  335 

nucleated  epithelial  colls.  These  are  islands  of  epithelial  cells  cut  off 
from  the  epithelium  of  the  pharynx  in  process  of  development.  They 
are  not  occluded  blood-vessels,  as  was  at  one  time  supposed.  They 
remind  one  somewhat  of  the  epithelial  nests  seen  in  some  varieties  of 
cancer. 

The  arteries  radiate  from  the  centre  of  the  gland.  Lymph  sinuses 
may  be  seen  occasionally  surrounding  the  periphery  of  the  follicles 
(Klein).     The  nerves  are  very  minute. 

From  the  thymus  various  substances  may  be  extracted,  many  of 
them  similar  to  those  obtained  from  the  spleen,  e.g.,  xanthine,  hypo- 
xanthine,  adenine,  and  leucine. 

The  main  constituent  of  the  cells  is  protein,  and  especially  nucleo- 
protein.  Indeed,  the  thymus  is  usually  employed  as  the  source  of 
nucleo-protein  when  one  wishes  to  inject  that  substance  into  the 
blood-vessels  of  an  animal  to  produce  experimentally  intravascular 
clotting.  It  is,  however,  not  characteristic  of  the  thymus,  but  is 
found  in  all  protoplasm.  The  method  of  preparation  will  be  given 
later  (see  Coagulation  of  Blood). 

The  thymus  takes  part  in  producing  the  colourless  corpuscles  like 
other  varieties  of  lymphoid  tissue.  In  hibernating  animals  it  exists 
throughout  life,  and  as  each  successive  period  of  hibernation  approaches 
it  greatly  enlarges  and  becomes  laden  with  fat.  Hence  it  appears  to 
serve  for  the  storing-up  of  materials  which,  being  reabsorbed  during 
the  inactivity  of  the  hibernating  period,  may  maintain  the  respiration 
and  the  temperature  of  the  body  in  the  reduced  state  to  which  they 
fall  during  that  time.  Some  observers  state  that  it  is  also  a  source 
of  the  red  blood-corpuscles,  at  any  rate  in  early  life. 

Eemoval  of  the  thymus  in  the  frog  (in  which  animal  it  persists 
throughout  life)  produces  muscular  weakness,  paralysis,  and  finally 
death.  Intravenous  injection  of  extracts  of  thymus  lowers  blood- 
pressure,  though  the  heart  may  be  somewhat  accelerated. 

The  Thyroid. 

The  thyroid  gland  is  situated  in  the  neck.  It  consists  of  two 
lobes,  one  on  each  side  of  the  trachea,  extending  upwards  to  the 
thyroid  cartilage,  covering  its  inferior  cornu  and  part  of  its  body; 
these  lobes  are  connected  across  the  middle  line  by  a  middle  lobe 
or  isthmus.  It  is  highly  vascular,  and  varies  in  size  in  different 
individuals. 

The  gland  is  encased  in  a  capsule  of  dense  areolar  tissue.  This 
sends  in  strong  fibrous  trabeculge,  which  enclose  the  thyroid  vesicles — ■ 
which  are  rounded  or  oblong  irregular  sacs,  consisting  of  a  wall  of 
thin  hyaline  membrane  lined  by  a  single  layer  of  short  cylindrical 
or  cubical  cells.     These  vesicles  are  filled  with   transparent  colloid 


336 


THE    DUCTLESS    GLANDS 


[cH.  xxin. 


nucleo-protein  material.  The  colloid  substance  increases  with  age, 
and  the  cavities  appear  to  coalesce.  In  the  interstitial  connective- 
tissue  is  a  round  meshed  capillary  plexus,  and  a  large  number  of 
lymphatics.     The  nerves  adhere  closely  to  the  vessels. 

In  the  vesicles  there  are,  in  addition  to  the  yellowish  glassy  colloid 
material,  epithelium  ceUs,  colourless  blood-corpuscles,  and  also  coloured 
corpuscles  undergoing  disintegration. 

It  is  difficult  to  state  definitely  the  function  of  the  thyroid  body ; 


m 


'^WU 


i'fffe 


Fig.  314. — Part  of  a  section  of  the  human  thyiuia.  ./,  iiuiuus  capsule;  b,  thyroid  vesicles  tilled  with, 
e,  colloid  substance;  c,  supporting  fibrous  tissue;  d,  short  columnar  cells  lining  vesicles;  /, 
arteries;  g,  veins  filled  with  blood;  h,  lymphatic  vessels  filled  with  colloid  substance.  (S.  K. 
Alcock.) 

it  is  one  of  those  organs  of  great  importance  in  the  metabolic  round ; 
and  its  removal  or  disease  is  followed  by  general  disturbances.  It  no 
doubt  forms  an  internal  secretion ;  to  this  the  colloid  material  men- 
tioned contributes,  as  it  is  found  in  the  lymphatic  vessels  of  the 
organ. 

When  the  gland  is  diseased  in  children  and  its  function  obliterated, 
a  species  of  idiocy  is  produced  called  cretinism. 

The  same  condition  in  adults  is  called  myxcedema ;  the  most 
marked  symptoms  of  this  condition  are  slowness,  both  of  body  and 
mind,  usually  associated  with  tremors  and  twitchings.  There  is  also 
a  peculiar  condition  of  the  skin  leading  to  the  overgrowth  of  the 
subcutaneous  tissues,  which  in  time  is  replaced  by  fat ;  the  hair  falls 


CH.  XXIII.]  THE    PARATHYROIDS  337 

off,  the  hands  become  spade-like;  the  whole  body  is  unwieldy  and 
clumsy  like  the  mind. 

A  similar  condition  occurs  after  the  thyroid  is  completely  removed 
surgically;  this  is  called  cachexia  strumipriva ;  this  operation,  which 
was  performed  previous  to  our  knowledge  of  the  importance  of  the 
thyroid,  is  not  regarded  as  justifiable  nowadays. 

Lastly,  in  many  animals  removal  of  the  thyroid  produces  analogous 
symptoms,  in  the  overgrowth  of  the  connective-tissues  especially 
under  the  skin,  and  in  the  nervous  symptoms  (twitchings,  convul- 
sions, etc.). 

The  term  Myxcedema  was  originally  given  under  the  erroneous 
idea  that  the  swelling  of  the  body  is  due  to  mucin.  In  the  early 
stages  of  the  disease  there  is  a  slight  increase  of  mucin,  because 
all  new  connective-tissues  contain  a  relatively  large  amount  of  ground 
substance,  the  most  abundant  constituent  of  which,  next  to  water, 
is  mucin.     But  there  is  nothing  characteristic  about  that. 

The  discovery  of  the  relationships  between  the  thyroid  and  these 
morbid  conditions  is  especially  interesting,  because  important  practical 
results  in  their  treatment  have  foUow^ed  close  on  the  heels  of  experi- 
mental investigation.  The  missing  internal  secretion  of  the  thyroid 
may  be  replaced  in  these  animals  and  patients  by  grafting  the  thyroid 
of  another  animal  into  the  abdomen;  or  more  simply  by  injecting 
thyroid  extract  subcutaneously ;  or  even  by  feeding  on  the  thyroid 
of  other  animals.  This  treatment,  which  has  to  be  kept  up  for  the 
rest  of  the  patient's  life,  is  entirely  successful.  Chemical  physiologists 
have  been  diligently  searching  to  try  and  discover  what  the  active 
material  in  thyroid  extract  is  which  produces  such  marvellous  results ; 
the  view  at  present  held  is  that  the  efficacy  of  thyroid  extract  is  due 
to  a  substance  which  Baumann  separated  from  the  gland,  and  which 
stands  almost  unique  among  physiological  compounds  by  containing 
a  large  percentage  of  iodine  in  its  molecule.  Thyro-iodin  or  lodo- 
thyrin,  as  this  substance  has  been  called,  is  present  in  combination 
with  protein  matter  in  the  colloid  substance. 

Intravenous  injection  of  thyroid  extract  in  a  normal  animal 
lowers  blood-pressure ;  but  in  an  animal  from  which  the  thyroid  has 
been  removed  it  stimulates  the  heart  and  raises  blood-pressure. 

Parathyroids. 

These  are  small  bodies,  usually  four  in  number,  situated  in  the 
neighbourhood  of,  or  embedded  in  the  substance  of,  the  thyroid.  They 
are  made  up  of  elongated  groups  of  polyhedral  cells,  bound  together 
by  connective-tissue  and  well  supplied  with  blood-vessels.  Some 
observers  look  upon  these  as  being  even  more  essential  to  healthy 
life  than  the  thyroid,  but  this  point  is  most  uncertain. 

The  view  has  been  put  forward  that  the  thyroid  supplies  some- 

Y 


338  THE   DUCTLESS    GLANDS  [CH.  XXIIL 

thing  which  is  a  stimulator  of  metabolic  processes,  and  that  the  action 
on  the  nervous  system  is  more  especially  the  work  of  the  para- 
thyroids. According  to  others  the  parathyroid  tissue  is  only  a  stage 
in  the  development  of  thyroid  tissue  proper. 

The  Supra-renal  Capsules. 

These  are  two  triangular  or  cocked-hat-shaped  bodies,  each  resting 
by  its  lower  border  upon  the  upper  border  of  the  kidney. 

The  gland  is  surrounded  by  an  outer  sheath  of  connective-tissue. 


1^ 


iii. 

pi  .^    I 

''\  0  ■  -'    . 

'^e_ 

'^^hmshM-^ 

rlB 

n'ii 


Fig.  315.— Vertical  section  through  part  of  the  cortical  portion  of  supra-renal  of  guinea-pig.  a,  Cap- 
sule; I),  zona  glomerulosa;  c,  zona  faseiculata  ;  d,  connective-tissue  supporting  the  columns  of  the 
cells  of  the  latter,  and  also  indicating  the  position  of  the  blood-vessels.     (S.  K.  Alcock.) 

which  sends  in  fine  prolongations  forming  the  framework  of  the  gland. 
The  gland  tissue  proper  consists  of  an  outside  firmer  cortical  portion 
and  an  inside  soft,  dark  medullary  portion. 

(1.)  The  cortical  portion  is  divided  into  (fig.  315)  columnar  groups 
of  cells  {zona  fasciculata).  Immediately  under  the  capsule,  however, 
the  groups  are  more  rounded  {zona  glomerulosa),  while  next  to  the 
medulla  they  have  a  reticular  arrangement  {zona  reticularis).  The 
cells  themselves  are  polyhedral,  each  with  a  clear  round  nucleus,  and 
often  contain  oil  globules.  The  blood-vessels  run  in  the  fibrous  septa 
between  the  columns,  but  do  not  penetrate  between  the  cells. 

(2.)  The  medullary  substance  consists  of  a  coarse  rounded  or 
irregular  meshwork  of  fibrous  tissue,  in  the  alveoli  of  which  are 
masses   of   multinucleated  protoplasm  (fig.    316);   numerous   blood- 


CH.  XXIII.]  THE   SUPRA-RENAL  BODIES  339 

vessels ;  and  an  abundance  of  nerve-fibres  and  cells.  The  cells  are 
very  irregular  in  shape  and  size,  poor  in  fat,  and  often  branched ;  the 
nerves  run  through  the  cortical  substance,  and  anastomose  over  the 
medullary  portion. 

The  cells  of  the  medulla  are  chai'acterised  by  the  presence  of 
certain  reducing  substances.  One  of  these  takes  a  brown  stain  with 
chromic  acid,  and  gives  other  colour  reactions ;  it  is,  therefore,  called 
a  chromogen.  Another  is  similar  in  many  of  its  characters  to  jecorin,  a 
lecithin -like  substance  also  found  in  the  liver,  spleen,  and  other  organs. 

The  immense  importance  of  the  supra-renal  bodies  was  first  in- 


9^^l^«„^0^ 


Fig.  316. — Section  through  a  portion  of  the  medullary  part  of  the  supra-renal  of  guinea-pig.  The 
vessels  are  very  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the  cortex,  and  is,  more- 
over, reticulated.  The  cells  are  irregular  and  larger,  clpar,  and  free  from  oil  globules.  (8.  K. 
Alcock.) 

dicated  by  Addison,  who,  in  1855,  pointed  out  that  the  disease  now 
known  by  his  name  is  associated  with  pathological  alterations  of  these 
glands.  This  was  tested  experimentally  by  Brown-Sequard,  who 
found  a  few  years  later  that  removal  of  the  supra-renals  in  animals  is 
invariably  and  rapidly  fatal.  The  symptoms  are  practically  the 
same  (although  more  acute)  as  those  of  Addison's  disease,  namely, 
great  muscular  weakness,  loss  of  vascular  tone,  and  nervous  prostra- 
tion. The  pigmentation  (bronzing)  of  the  skin,  however,  which  is  a 
marked  symptom  in  Addison's  disease,  is  not  seen  in  animals.  The 
experiments  of  Brown-Sequard  attracted  much  attention  at  the  time 
they  were  performed,  but  were  almost  forgotten  until  quite  recently, 
when  they  were  confirmed  by  Abelous,  Langlois,  Schafer,  and  others. 
The  effects  on  the  muscular  system  are  the  most  marked  results  both 
after  removal  of  the  capsules  and  after  injection  of  an  extract  of  the 
glands.  The  efifect  of  injecting  such  an  extract  on  the  voluntary 
muscles  is  to  increase  their  tone,  so  that  a  tracing  obtained  from  them 


340  THE   DUCTLESS    GLANDS  [CH.  XXIIL 

resembles  that  produced  by  a  small  dose  of  veratrine,  namely,  a  pro- 
longation of  the  period  of  relaxation.  The  effect  on  involuntary 
muscle  is  equally  marked ;  there  is  an  enormous  rise  of  arterial  blood- 
pressure  due  chiefly  to  a  contraction  of  the  arterioles.  This  is  produced 
by  the  direct  action  of  the  extract  on  the  muscular  tissue  of  the 
arterioles,  not  an  indirect  one  through  the  vaso-motor  centre.*  The 
active  substance  in  the  extract  that  produces  the  effect  is  known  as 
adrenaline;  it  is  the  reducing  substance  alluded  to  above  which  is 
confined  to  the  medulla  of  the  capsules,  and  is  absent  in  cases  of 
Addison's  disease. 

The  capsules,  therefore,  form  something  which  is  distributed  to 
the  muscles  and  is  essential  for  their  normal  tone ;  when  they  are 
removed  or  diseased  the  poisonous  effects  seen  are  the  result  of  the 
absence  of  this  internal  secretion. 

Adrenaline  has  received  various  names  from  the  different  chemists  (Abel,  v. 
Fiirth,  Takamine,  etc.),  who  have  isolated  it.  It  is  very  powerful;  solutions  of  one 
part  in  a  million  will  produce  physiological  effects.  Its  composition  is  shown  by  the 
following  formula: — 

OH 

NOH 


CH.(OH).CHo.NH.CH, 

and  it  is  therefore  a  methyl-amino  derivation  of  catechol  (Pauly,  Jowett).  Recently 
compounds  closely  alHed  to  it  have  been  made  synthetically  (Stolz,  Friedmann, 
Dakin). 

Whether  this  discovery  will  lead  to  the  same  kind  of  results,  as 
in  the  case  of  the  thyroid,  must  be  left  to  the  future  to  decide. 
There  is  already  some  evidence  to  show  that  injection  of  supra-renal 
extract  is  beneficial  in  cases  of  Addison's  disease.  The  discovery  of 
adrenaline  itself  is,  however,  one  of  immense  practical  importance. 
Its  action  on  the  small  blood-vessels  is  so  powerful  that  quite  weak 
solutions  applied  locally  will  arrest  haemorrhage. 

There  are  some  points  of  interest  in  the  development  and  com- 
parative physiology  of  the  supra-renals.  In  mammals  the  medullary 
portion  is  developed  in  connection  with  the  sympathetic,  and  is  at 
first  distinct  and  outside  the  cortical  portion  which  is  developed  in 
connection  with  the  upper  part  of  the  Wolffian  body;  it  gradually 
insinuates  itself  within  the  cortex  (Mitsukiri).  In  Elasmobranch 
fishes  the  supra-renals  consist  throughout  life  of  separate  portions ; 
one,  the  inter-renal  body,  is  median  in  position  and  single;  this  corre- 
sponds to  the  cortex  of  the  mammalian  supra-renal ;  extracts  of  this 
are  inactive,  and  in  the  Teleostean  fishes,  where  it  is  the  sole  repre- 
sentative of  the  supra-renal,  it  may  be  removed  without  any  harm  to 

*  Although  muscular  tissue  is  spoken  of  in  the  above  description,  Brodie's  work 
shows  that  it  is  the  sympathetic  nerve  terminals  which  are  really  affected. 


CH.  XXIII.]        THE    PITUITARY    BODY   AND    THE   PINEAL   GLAND  841 

the  animal.  The  other  portion  of  the  Elasmobranch  supra-renal  is 
paired,  and  derived  from  the  sympathetic  ganglia.  This  corresponds 
to  the  medulla;  it  contains  the  same  chromogen  as  the  medulla  of 
the  mammalian  supra-renal,  and  extracts  of  it  have  the  same  physio- 
logical action  (S.  Vincent). 

The  Pituitary  Body. 

This  body  is  a  small  reddish-grey  mass,  occupying  the  sella 
turcica  of  the  sphenoid  bone.  It  consists  of  two  lobes — a  small 
posterior  one,  and  an  anterior  larger  one,  somewhat  resembling  the 
thyroid  in  structure.  The  anterior  lobe  is  developed  as  a  tubular 
prolongation  from  the  epiblast  of  the  buccal  cavity.  The  growth  of 
intervening  tissue  soon  cuts  off  all  connection  with  the  mouth.  The 
alveoli  are  approximately  spherical ;  they  are  filled  with  nucleated 
cells  of  various  sizes  and  shapes  not  unlike  ganglion  cells,  collected 
together  into  rounded  masses,  filling  the  vesicles,  and  contained  in  a 
colloid  substance.  The  vesicles  are  enclosed  by  connective-tissue, 
rich  in  capillaries.  The  posterior  lobe  is  developed  from  the  floor  of 
the  third  ventricle ;  it  consists  mainly  of  vascular  connective  tissue, 
and  includes  masses  of  epithelial  cells.  In  the  adult  it  contains  no 
distinct  nerve-cells,  but  it  receives  nerve-fibres  which  originate  in 
the  grey  matter  behind  the  optic  chiasma. 

Disease  of  the  pituitary  body  produces  the  condition  called 
acromegaly,  in  which  the  bones  of  limbs  and  face  hypertrophy. 
When  the  gland  is  removed  in  animals,  tremors  and  spasms  occur 
like  those  which  take  place  after  removal  of  the  thyroid.  Death 
usually  occurs  within  fourteen  days.  Some  observers  have  stated 
that  overgrowth  of  the  pituitary  occurs  after  excision  of  the  thyroid. 
But  there  is  no  ground  for  the  assumption  that  the  two  glands  have 
a  similar  function.  Acromegaly  is  a  very  different  disease  from 
myxcedema.  The  injection  of  extracts  of  the  organs  are  also  different, 
Th}Toid  extract  produces  a  fall  of  arterial  pressure.  Extracts  of  the 
anterior  lobe  of  the  pituitary  body  are  inactive ;  but  extracts  of  the 
posterior  lobe  or  infundibular  body  contain  two  active  substances, 
one  of  which  produces  a  rise,  and  the  other  a  fall  of  blood-pressure. 
A  second  dose  of  the  former  of  these  injected  soon  after  the  first  dose 
is  inactive ;  and  so  it  is  not  the  same  thing  as  in  supra-renal  extract. 
The  chemical  nature  of  the  two  substances  is  not  known.  Pituitary 
extracts  when  injected  into  the  blood  also  produce  diuresis  (Schafer), 

The  Pineal  Gland. 

This  gland,  which  is  a  small  reddish  body,  is  placed  beneath  the 
back  part  of  the  corpus  callosum,  and  rests  upon  the  corpora 
quadrigemina.     It  is  composed  of  tubes  and  saccules  lined  and  some- 


342  THE   DUCTLESS    GLANDS  [CH.  XXIIL 

times  filled  with  epithelial  cells,  and  containing  deposits  of  earthy- 
salts  (brain  sand).  These  are  separated  by  vascular  connective  tissue. 
A  few  small  atrophied  nerve-cells  without  axons  are  also  seen. 

In  certain  lizards,  such  as  Hatteria,  the  pineal  gland  is  better 
developed  and  is  connected  by  nerve-fibres  to  a  rudimentary  third 
eye  situated  centrally  on  the  upper  surface  of  the  head,  but  covered 
by  skin. 

The  Coccygeal  and  Carotid  Glands. 

These  so-called  glands  are  situated,  the  one  in  front  of  the  tip  of 
the  coccyx  and  the  other  at  the  point  of  bifurcation  of  the  common 
carotid  artery  on  each  side.  They  are  made  up  of  a  plexus  of  small 
arteries,  and  are  enclosed  and  supported  by  a  capsule  of  fibrous  tissue. 
They  contain  also  polyhedral  cells  collected  into  spheroidal  clumps 
(carotid  gland)  or  irregular  nodules  (coccygeal  gland).  Some  of  the 
cells  of  the  carotid  gland  stain  brown  with  chromic  acid  like  those  of 
the  supra-renal  medulla. 


CHAPTEK   XXIV 

RESPIEATION 

The  respiratory  apparatus  consists  of  the  lungs  and  of  the  air-passages 
which  lead  to  them.  In  marine  animals  the  gills  fulfil  the  same 
functions  as  the  lungs  of  air-breathing  animals.  The  muscles  which 
move  the  thorax  and  the  nerves  that  supply  them  must  also  be  in- 
cluded under  the  general  heading  Eespiratory  System ;  and,  using 
this  expression  in  the  widest  sense,  it  includes  practically  all  the 
tissues  of  the  body,  since  they  are  all  concerned  in  the  using  up  of 
oxygen  and  the  production  of  waste  materials,  like  carbonic  acid. 

Essentially  a  lung  or  gill  is  constructed  of  a  thin  membrane,  one 
surface  of  which  is  exposed  to  the  air  or  water,  as  the  case  may  be, 
while,  on  the  other  is  a  network  of  blood-vessels — the  only  separation 
between  the  blood  and  aerating  medium  being  the  thin  wall  of  the 
blood-vessels,  and  the  fine  membrane  on  one  side  of  which  vessels  are 
distributed.  The  difference  between  the  simplest  and  the  most  com- 
plicated respiratory  membrane  is  one  of  degree  only. 

The  lungs  or  gills  are  only  the  medium  for  the  exchange,  on  the 
part  of  the  blood,  of  carbonic  acid  for  oxygen.  They  are  not  the  seat, 
in  any  special  manner,  of  those  combustion-processes  of  which  the 
production  of  carbonic  acid  is  the  final  result.  These  processes  occur 
in  all  parts  of  the  body  in  the  substance  of  the  tissues. 

The  Respiratory  Apparatus. 

The  lungs  are  contained  in  the  chest  or  thorax,  which  is  a  closed 
cavity  having  no  communication  with  the  outside  except  by  means  of 
the  respiratory  passages.  The  air  enters  these  passages  through  the 
nostrils  or  through  the  mouth,  whence  it  passes  through  the  larynx  into 
the  trachea  or  windpipe,  which  about  the  middle  of  the  chest  divides 
into  two  tubes,  bronchi,  one  to  each  (right  and  left)  lung. 

The  Larynx  is  the  upper  part  of  the  passage,  and  will  be  described 
in  connection  with  the  voice. 

The  Trachea  and  Bronchi. — The  trachea  extends  from  the  cricoid 
cartilage,  which  is  on  a  level  with  the  fifth  cervical  vertebra,  to  a 


344 


KESPIRATION 


[CH.  XXIV. 


point  opposite  the  third  dorsal  vertebra,  where  it  divides  into  the 
two  bronchi,  one  for  each  lung  (fig.  317).     It  measures,  on  an  average, 


Fig.  317. — Outline  showing  the  general  form 
of  the  larynx,  trachea,  and  bronchi,  as 
seen  from  the  front,  h,  The  great  cornu  of 
the  hyoid  bone  :  e,  epiglottis  ;  t,  superior, 
and  t',  inferior  cornu  of  tlie  thyroid  carti- 
lage ;  c,  middle  of  the  cricoid  cartilage ; 
tr,  the  trachea,  showing  sixteen  cartila- 
ginous rings ;  b,  the  right,  and  h',  the  left 
bronchus.    (Allen  Thomson.) 


.  318. — Outline  sliowing  the  general  form  of  the 
larynx,  trachea,  and  bronchi,  as  seen  from 
behind,  h,  Great  cornu  of  the  hyoid  bone; 
t,  superior,  and  t',  the  inferior  cornu  of  the 
thyroid  cartilage ;  c,  epiglottis  ;  ii,  points  to  the 
back  of  both  the  arytenoid  cartilages,  which  are 
surmounted  by  the  cornicula ;  c,  the  middle 
ridge  on  the  back  of  the  cricoid  cartilage ;  tr,  the 
]josterior  membranous  part  of  the  trachea ; 
h,  h',  riglit  and  left  bronchi.    (Allen  Thomson.) 


four  or  four  and  a  half  inches  in  length  and  from  three-quarters  of 
an  inch  to  an  inch  in  diameter,  and  is  essentially  a  tube  of  fibro-elastic 
membrane,  within  the  layers  of  which  are  imbedded  a  series  of  carti- 
laginous rings,  from  sixteen  to  twenty  in  number.     These  rings  ex- 


CH.  XXIV.] 


THE  TRACHEA  AND  BRONCHI 


345 


tend  only  around  tho  front  and  sides  of  the  trachea  (about  two-thirds 
of  its  circumference)  and  are  deficient  behind ;  the  interval  between 
their  posterior  extremities  is  bridged  over  by  a  continuation  of  the 
fibrous  membrane  in  which  they  are  enclosed  (fig.  318).  The  carti- 
lages of  the  trachea  and  bronchial  tubes  are  of  the  hyaline  variety. 
Immediately  within  this  tube, 


at  the  back,  is  a 
striped   muscular 


,tr. 


^-it.\- 


h 


layer  of  un- 
iibres,  which 
extends,  transversely,  between  the 
ends  of  the  cartilaginous  rings 
to  which  they  are  attached,  and 
opposite  the  intervals  between 
them  also ;  their  function  is  to 
diminish,  when  required,  the 
calibre  of  the  trachea  by  ap- 
proximating the  ends  of  the 
cartilages.  Outside  these  are  a 
few  longitudinal  bundles  of  mus- 
cular tissue,  which,  like  the  pre- 
ceding, are  attached  both  to  the 
fibrous  and  cartilaginous  frame- 
work. 

The  mucous  membrane  con- 
sists to  a  great  extent  of  loose 
lymphoid  tissue,  separated  from 
the  ciliated  epithelium  (fig.  322) 
which  lines  it  by  a  homogeneous 
basement  membrane.  In  the 
deeper  part  of  the  corium  of  the 
mucous  membrane  are  many 
elastic  fibres,  between  which  lie 
connective-tissue  corpuscles  and 
capillary  blood-vessels. 

Numerous  mucous  glands  are 
situated  in  the  substance  of  the 
mucous  membrane  of  the  trachea  ; 
their  ducts  perforate  the  various 
structures  which  form  the  wall 
of  the  trachea,  and  open  through  the  mucous  membrane  into  the 
interior  (fig.  319). 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the 
right  is  shorter,  broader,  and  more  horizontal  than  the  left  (fig.  317), 
resemble  the  trachea  in  structure,  with  the  difference  that  in  them 
there  is  a  distinct  layer  of  unstriped  muscle  arranged  circularly 
beneath  the  mucous  membrane,  forming  the  miiscularis  mucosce.     On 


f^ 


9 


ii 


K- 


Fio.  319.— Section  of  the  trachea,  a,  columnar  cili- 
ated epithelium  ;  h  and  c,  corium  of  the  mucous 
membrane,  containing  elastic  fibres  cut  across 
transversely ;  d,  submucous  tissue  containing 
mucous  glands,  e,  separated  from  the  hyaline 
cartilage,  ij,  by  fine  fibrous  tissue,  /;  h,  external 
investment  of  fine  fibrous  tissue.    (S.  K.  Alcock.) 


346 


RESPIRATION 


[CH.  XXIV. 


entering  the  substance  of  the  lungs  the  cartilaginous  rings,  although 
they  still  form  only  larger  or  smaller  segments  of  a  circle,  are  no 
longer  confined  to  the  front  and  sides  of  the  tubes,  but  are  distributed 
impartially  to  all  parts  of  theii-  circumference. 

The  bronchi  divide  and  subdi^dde,  in  the  substance  of  the  lungs, 
into  a  number  of  smaller  and  smaller  branches  (bronchial  tubes), 
which  penetrate  into  every  part  of  the  organ,  until  at  length  they 
end  in  the  smaller  subdivisions  of  the  lungs  called  lobules. 

All  the  larger  branches  have  walls  formed  of  fibrous  tissue,  con- 
taining portions  of  cartilaginous  rings,  by  which  they  are  held  open, 
and  unstriped  muscular  fibres,  as  well  as  longitudinal  bundles  of 
elastic  tissue.  They  are  lined  by  mucous  membrane  the  surface  of 
which,  like  that  of  the  larynx  and  trachea,  is  covered  with  ciliated 


Fig.  320.— Transverse  .section  of  a  bronchial  tube,  about  i  inch  in  diameter,    e,  Epithelium  (ciliated) 
immediately  beneath  it  is  the  corium  of  the  mucous  membrane,  of  varying  thickness  ;  m,  muscular 
layer;  s.m,  submucous  tissue;  /,  fibrous  tissue;  c,  cartilage  enclosed  within  the  layers  of  fibrous 
tissue;  g,  mucous  gland.    (F.  E.  Schulze.) 


epithelium,  but  the  several  layers  become  less  and  less  distinct  until 

the  lining  consists  of  a  single  layer  of  short  columnar  cells  covered 
with  cilia  (fig.  320).  The  mucous  membrane  is  abundantly  provided 
with  mucous  glands. 

As  the  subdivisions  become  smaller  and  smaller,  and  their  walls 
thinner,  the  cartilaginous  rings  become  scarcer  and  more  irregular, 
until,  in  the  smaller  bronchial  tubes,  they  are  represented  only  by 
minute  and  scattered  cartilaginous  flakes.  When  the  bronchial  tubes, 
by  successive  branchings,  are  reduced  to  about  -jV  of  an  inch  ("6  mnx) 
in  diameter  they  lose  their  cartilaginous  element  altogether,  and  their 
walls  are  formed  only  of  a  fibrous  elastic  membrane  with  circular 
muscular  fibres;  they  are  still  lined,  however,  by  a  thin  mucous 
membrane  with  ciliated  epithelium,  the  length  of  the  cells  bearing 
the  cilia  having  become  so  far  diminished  that  the  cells  are  now 
cubical.     In   the   smaller   bronchial   tubes   the   muscular   fibres  are 


CH.  XXIV.] 


THE   LUNGS 


347 


relatively   more   abundant   than    in    the    larger   ones,   and    form    a 
distinct  circular  coat. 

The  Lungs  and  Pleurce. — The  lungs  occupy  the  greater  portion  of 
the  thorax.     Thoy  are  of  a  .spongy  elastic  texture,  and  are  composed 


Fig.  321. — Transverse  section  of  tlje  chest. 


iM00K^S§li^f^^ 


of  numerous  minute  air-sacs,  and  on  section  every  here  and  there  the 
air-tubes  may  be  seen  cut  across.  Any  fragment  of  lung  (unless 
from  a  child  that  has  never  breathed,  or  in  cases  of  disease  in  which 
the  lung  is  consolidated)  floats  in  water ;  no  other  tissue  does  this. 

Each  lung  is  enveloped  by  a  serous  membrane — the  pleura,  one 
layer  of  which  adheres  closely  to 
its  surface,  and  provides  it  with  its 
smooth  and  slippery  covering,  while 
the  other  adheres  to  the  inner  sur- 
face of  the  chest-wall.  The  con- 
tinuity of  the  two  layers,  which 
form  a  closed  sac,  as  in  the  case  of 
other  serous  membranes,  will  be 
best  understood  by  reference  to  fig. 
321.  The  appearance  of  a  space, 
however,  between  the  pleura  which 
covers  the  lung  {visceral  layer)  and 
that  which  lines  the  inner  surface 
of  the  chest  {parietal  layer)  is  in- 
serted in  the  drawing  only  for  the 
sake  of  distinctness.  It  does  not 
really  exist.  The  layers  are,  in  health,  everywhere  in  contact  one 
with  the  other ;  and  between  them  is  only  just  so  much  fluid  as  will 
ensure  the  lungs  gliding  easily,  in  their  expansion  and  contraction, 
on  the  inner  surface  of  the  parietal  layer,  which  lines  the  chest-wall. 


322.— Ciliated  epithelium  of  the  human 
trachea,  a,  Layer  of  longitudinally  arranged 
elastic  fibres;  b,  basement  membrane; 
c,  deepest  cells  circular  in  form  ;  d,  inter- 
mediate elongated  cells ;  e,  outermost  layer 
of  cells  fully  rtevelojied  and  bearing  cilia. 
X   3.:.0.    (Krilliker.) 


348 


RESPIRATION 


[CH.  XXIV. 


If,  however,  an  opening  is  made  so  as  to  permit  air  or  fluid  to 
enter  the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and 
a  considerable  space  is  left  between  it  and  the  chest-wall.  In  other 
words,  the  natural  elasticity  of  the  lungs  would  cause  them  at  all 
times  to  contract  away  from  the  ribs  were  it  not  that  the  contraction 
is  resisted  by  atmospheric  pressure  which  bears  only  on  the  inner 
surface  of  the  air-tubes  and  air-sacs.  On  the  admission  of  air  into 
the  pleural  sac  atmospheric  pressure  bears  alike  on  the  inner  and 
outer  surfaces  of  the  lung,  and  their  elastic  recoil  is  no  longer 
prevented. 

Each  lung  is  partially  subdivided  into  separate  portions  called 
lobes ;  the  right  lung  into  three  lobes,  and  the  left  into  two.     Each 


Fiii.  323. — Terminal  branch  of  a  bronchial 
tube,  with  its  infundibula  and  air-sacs, 
from  the  margin  of  the  lung  of  a  monkey, 
injected  with  quicksilver,  a,  Terminal 
bronchial  twig ;  h  b,  infundibula  and  air- 
sacs.     X  10.    (F.  E.  Schulze.) 


Fio.  324. — Two  small  infundibula  or 
groups  of  air-sacs,  a  a,  with  air-sacs, 
b  b,  and  the  ultimate  bronchial  tubes, 
c  r,  with  which  the  air-sacs  com- 
municate. From  a  new-born  child. 
(K.Uliker.) 


of  these  lobes,  again,  is  composed  of  a  large  number  of  minute  parts, 
called  lobules.  Each  pulmonary  lobule  may  be  considered  to  be  a 
lung  in  miniature,  consisting,  as  it  does,  of  a  branch  of  the  bronchial 
tube,  of  air-sacs,  blood-vessels,  nerves,  and  lymphatics,  witli  a  sparing 
amount  of  areolar  tissue. 

On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of 
which  has  just  been  described  {a,  fig.  323),  divides  and  subdivides; 
its  walls  at  the  same  time  become  thinner  and  thinner,  until  at 
length  they  are  formed  only  of  a  thin  membrane  of  areolar,  muscular, 
and  elastic  tissue,  lined  by  a  layer  of  pavement  epithelium  not  pro- 
vided with  cilia.  At  the  same  time  they  are  altered  in  shape ;  each 
of  the  minute  terminal  branches  widens  out  funnel-wise,  and  its 
walls  are  pouched   out   irregularly  into  small    saccular   dilatations. 


CH.  XXIV.] 


THE   AIR-VESICLKS 


349 


called  air-sacs  (fig.  323,  h).  Such  a  funuel-shaped  terminal  branch 
of  the  bronchial  tube,  with  its  group  of  pouches  or  air-sacs,  is  called 
an  infundihulum  (figs.  323,  324),  and  the  irregular  oblong  space  in 
its  centre,  with  which  the  air-sacs  communicate,  an  intercellular 
passage. 

The  air-sacs,  or  air-vesicles,  may  be  placed  singly,  like  recesses 
from  the  intercellular  passage,  but  more  often  they  are  arranged  in 
groups,  or  even  in  rows,  like  minute  sacculated  tubes ;  so  that  a  short 
series  of  vesicles,  all  communicating  with  one  another,  open  by  a 
common  orifice  into  the  tube.  The  vesicles  are  of  various  forms, 
according  to  the  mutual  pressure  to  wliich  they  are  subject ;  their 


Fio.  325.— Section  of  lung  stained  with  silver  nitrate.  A.  D.,  aheolar  duct  or  intercellular  passage ; 
S,  alveolar  septa;  N,  alveoli  or  air-sacs,  lined  with  large  flat  cells,  with  some  smaller  polyhedral 
cells  ;  M,  plain  muscular  fibres  surrounding  the  alveolar  duct.    (Klein  and  Noble  Smith.) 

walls  are  nearly  in  contact,  and  they  vary  from  -V th  to  ^V^h  of  an 
inch  ("5  to  '3  mm.)  in  diameter.  Their  walls  are  formed  of  fine 
membrane,  like  those  of  the  intercellular  passage ;  this  membrane 
is  folded  on  itself  so  as  to  form  a  sharp-edged  border  at  each  circular 
orifice  of  communication  between  contiguous  air-vesicles,  or  between 
the  vesicles  and  the  bronchial  passages.  Numerous  fibres  of  elastic 
tissue  are  spread  out  between  contiguous  air-sacs,  and  many  of  these 
are  attached  to  the  outer  surface  of  the  fine  membrane  of  which  each 
sac  is  composed,  imparting  to  it  additional  strength  and  the  power  of 
recoil  after  distension.  The  vesicles  are  lined  by  a  layer  of  pavement 
epithelium  (fig.  325)  not  provided  with  cilia.  Outside  the  air-vesicles 
a  network  of  pulmonary  capillaries  is  spread  out  so  densely  (fig.  326) 
that  the  interspaces  or  meshes  are  even  narrower  than  the  vessels 


350 


RESPIRATION 


[CH.  XXIV. 


which  are,  on  an  average,  ynrVoth  of  an  inch  (8^)  in  diameter. 
Between  the  air  in  the  sacs  and  the  blood  in  these  vessels  nothing 
intervenes  but  the  thin  walls  of  the  air-sacs  and  of  the  capillaries ; 
and  the  exposure  of  the  blood  to  the  air  is  the  more  complete, 
because  the  folds  of  membrane  between  contiguous  air-sacs,  and 
often  the  spaces  between  the  walls  of  the  same,  contain  only  a  single 
layer  of  capillaries,  both  sides  of  which  are  thus  at  once  exposed  to 
the  air.  The  arrangement  of  the  capillaries  is  shown  on  a  larger 
scale  in  fig.  233  (p.  222). 

The  vesicles  of  adjacent  lobules  do  not  communicate;  so  that, 
when  any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is 
lost  for  all  the  sacs  opening  into  it  or  its  branches. 


Fig.  326. — Capillary  network  of  the  pulmonary  blood-vessels  in  the  human  lung. 
X  60.    (Kfilliker.) 

Blood-supply. — The  lungs  receive  blood  from  two  sources,  (a)  the 
pulmonary  artery,  (6)  the  bronchial  arteries.  The  former  conveys 
venous  blood  to  the  lungs  to  be  arterialised,  and  this  blood  takes  no 
share  in  the  nutrition  of  the  pulmonary  tissues  through  which  it 
passes.  The  branches  of  the  bronchial  arteries  convey  arterial  blood 
from  the  aorta  for  the  nutrition  of  the  walls  of  the  bronchi,  of  the 
larger  pulmonary  vessels,  of  the  interlobular  connective-tissue,  etc. ; 
the  blood  of  the  bronchial  vessels  is  returned  chiefly  through  the 
bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets: — 1. 
Irregular  lacunae  in  the  walls  of  the  alveoli  or  air-sacs.  The  lym- 
phatic vessels  which  lead  from  these  accompany  the  pulmonary 
vessels  towards  the  root  of  the  lung.  2.  Irregular  anastomosing 
spaces  in  the  walls  of  the  bronchi.  3.  Lymph-spaces  in  the  pul- 
monary  pleura.      The   lymphatic   vessels   from   all   these   irregular 


CH.  XXIV.]  THE    RESPIRATORY    MECHANISM  351 

sinuses  pass  in  towards  the  root  of  the  lung  to  reach  the  bronchial 
lymphatic  glands. 

Nerves. — The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  which  are  formed  by  branches  of 
the  vagus  and  sympathetic.  The  nerves  follow  the  course  of  the 
vessels  and  bronchi,  and  in  the  walls  of  the  latter  many  small  ganglia 
are  situated. 

The  Respiratory  Mechanism. 

Eespiration  consists  of  the  alternate  expansion  and  contraction  of 
the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the 
lungs.     These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that 
is  necessary  is  such  a  movement  of  the  side-walls  or  floor  of  the 
chest,  or  of  both,  that  the  capacity  of  the  interior  shall  be  enlarged. 
By  such  increase  of  capacity  there  will  be  a  diminution  of  the  pressure 
of  the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the 
larynx  and  trachea  to  equalise  the  pressure  on  the  inside  and  outside 
of  the  chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  is  also  evident 
that,  by  an  opposite  movement  which  shall  diminish  the  capacity  of 
the  chest,  the  pressure  in  the  interior  will  be  increased,  and  air  will 
be  expelled,  until  the  pressure  within  and  without  the  chest  are  again 
equal.  In  both  cases  the  air  passes  through  the  trachea  and  larynx, 
whether  in  entering  or  leaving  the  lungs,  there  being  no  other  com- 
munication with  the  exterior  of  the  body ;  and  the  lung,  for  the  same 
reason,  remains,  under  all  the  circumstances  described,  closely  in 
contact  with  the  walls  and  floor  of  the  chest.  To  speak  of  expansion 
of  the  chest,  is  to  speak  also  of  expansion  of  the  lung.  The  move- 
ments of  the  lung  are  therefore  passive,  not  active,  and  depend  on 
the  changes  of  shape  of  the  closed  cavity  in  which  they  are  contained. 
A  perforation  of  the  chest-wall  would  mean  that  the  lung  on  that 
side  would  no  longer  be  of  use ;  a  similar  injury  on  the  other  side 
(double  pneumothorax)  would  cause  death.  If  the  two  layers  of  the 
pleura  were  adherent,  those  portions  of  the  lung  would  be  expanded 
most  where  the  movements  of  the  chest  are  greatest.  The  existence 
of  the  two  layers  prevents  this,  and  thus  the  lung  is  equally  expanded 
throughout. 

Inspiration. — The  enlargement  of  the  chest  in  inspiration  is  a 
muscular  act ;  the  effect  of  the  action  of  the  inspiratory  muscles  is 
an  increase  in  the  size  of  the  chest-cavity  in  the  vertical,  and  in  the 
lateral  and  antero-posterior  diameters.  The  muscles  engaged  in 
ordinary  inspiration  are  the  diaphragm;  the  external  intercostals ; 
parts  of  the  internal  intercostals ;  the  levatores  costarum ;  and  ser- 
ratus  posticus  superior. 


352  RESPIRATION  [CH.  XXIT. 

The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm ;  at  rest,  the  diaphragm  is 
dome-shaped  with  the  convexity  upwards ;  the  central  tendon  forms 
a  slight  depression  in  the  middle  of  this  dome.  On  contraction  the 
muscular  fibres  shorten,  and  so  the  convexity  of  the  double  dome  is 
lessened.  The  central  tendon  is  drawn  down  a  certain  distance,  but 
the  chief  movement  is  at  the  sides.  For  the  effective  action  of  this 
muscle,  its  attachment  to  the  lower  ribs  is  kept  fixed  by  the  con- 
traction of  the  quadratus  lumborum.  The  diaphragm  is  supplied  by 
the  phrenic  nerves. 

The  increase  in  the  lateral  and  antero-posterior  diameters  of  the 
chest  is  effected  by  the  raising  of  the  ribs,  the  upper  ones  being  fixed 
by  the  scaleni.  The  greater  number  of  the  ribs  are  attached  very 
obliquely  to  the  spine  and  sternum. 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the 
sides — the  hinder  ends  being  prevented  from  performing  any  upward 
movement  by  their  attachment  to  the  spine.  The  movement  of  the 
front  extremities  of  the  ribs  is  of  necessity  accompanied  by  an  upward 
and  forward  movement  of  the  sternum  to  which  they  are  attached, 
the  movement  being  greater  at  its  lower  than  at  its  upper  end. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspira- 
tion, are  the  external  intercostals,  and  that  portion  of  the  internal  inter- 
costals  which  is  situated  between  the  costal  cartilages ;  and  these  are 
assisted  by  the  levatores  costarum,  and  the  serratus  posticus  superior. 

In  extraordinary  or  forced  inspiration,  additional  muscles  are 
pressed  into  service,  such  as  the  sternomastoid,  the  serratus  magnus, 
the  pectorales,  and  the  trapezius.  Laryngeal  and  face  muscles  also 
come  into  play. 

The  expansion  of  the  chest  in  inspiration  presents  some  peculi- 
arities in  different  persons.  In  young  children,  it  is  effected  chiefly 
by  the  diaphragm.  The  movement  of  the  abdominal  walls  being  here 
more  manifest  than  that  of  any  other  part,  it  is  usual  to  call  this  the 
abdominal  type  of  respiration.  In  men,  together  with  the  descent  of 
the  diaphragm,  and  the  pushing  forward  of  the  front  wall  of  the 
abdomen,  the  chest  and  the  sternum  are  subject  to  a  wide  movement 
in  inspiration  (inferior  costal  type).  In  women,  the  movement 
appears  less  extensive  in  the  lower,  and  more  so  in  the  upper,  part  of 
the  chest  {superior  costal  type). 

There  are  also  differences  in  different  animals.  In  the  frog,  for 
example,  the  air  is  forced  into  the  lungs  by  the  raising  of  the  floor  of 
the  mouth,  the  mouth  and  nostrils  being  closed. 

Expiration. — From  the  enlargement  produced  in  inspiration,  the 
chest  and  lungs  retui'n,  in  ordinary  tranquil  expiration,  by  their 
elasticity ;  the  force  employed  by  the  inspiratory  muscles  in  distend- 
ing the  chest  and  overcoming  the  elastic  resistance  of  the  lungs  and 


CH.  XXIV.]  STETHOGKAPHS  353 

chost-walls,  is  returned  as  an  expiratory  effort  when  the  muscles  are 
relaxed.  Tliis  elastic  recoil  of  the  chest  and  lungs  is  sufficient,  in 
ordinary  quiet  breathing,  to  expel  air  from  the  lungs  in  the  intervals 
of  inspiration,  and  no  muscular  power  is  required.  In  all  voluntary 
expiratory  efforts,  however,  as  in  speaking,  singing,  blowing,  and  the 
like,  and  in  many  involuntary  actions  also,  as  sneezing,  coughing, 
etc.,  something  more  than  merely  passive  elastic  power  is  necessary, 
and  the  proper  expiratory  muscles  are  brought  into  action.  The 
chief  of  those  are  the  abdominal  muscles,  which,  l)y  pressing  on  the 
viscera  of  the  abdomen,  push  up  the  floor  of  the  chest  formed  by  the 
diaphragm,  and  by  thus  making  pressure  on  the  lungs,  expel  air  froni 
them  through  the  trachea  and  larynx.  All  muscles,  however,  which 
depress  the  ribs,  must  act  also  as  muscles  of  expiration,  and  therefore  we 
must  conclude  that  the  abdominal  muscles  are  assisted  in  their  action  by 
the  interosseous  part  of  the  internal  intcrcostals,  the  triangularis  sterni, 
the  serratus  posticus  inferior,  and  quadratus  lumhorum.  When  by 
the  efforts  of  the  expiratory  muscles,  the  chest  has  been  squeezed  to 
less  than  its  average  size,  it  again,  on  relaxation  of  the  muscles, 
returns  to  the  normal  dimensions  by  virtue  of  its  elasticity.  The 
construction  of  the  chest- walls,  therefore,  admirably  adapts  them  for 
recoiling  against  and  resisting  as  well  undue  contraction  as  undue 
dilatation.  In  the  natural  condition  of  the  parts,  the  lungs  can 
never  contract  to  the  utmost,  but  are  always  more  or  less  "  on  the 
stretch,"  being  kept  closely  in  contact  with  the  inner  surface  of  the 
chest  walls. 

Methods  of  recording  Respiratory  Movements. 

The  movements  of  respiration  may  be  recorded  graphically  in  several  ways. 
One  method  is  to  introduce  a  tube  into  the  trachea  of  an  animal,  and  to  connect 
this  tube  by  some  gutta-percha  tubing  with  a  X-piece  introduced  into  the  cork  of  a 
large  bottle,  the  other  end  of  the  T  having  attached  to  it  a  second  piece  of  tubing, 
which  can  remain  open  or  can  be  partially  or  completely  closed  by  means  of  a  screw 
clamp.  Into  the  cork  is  inserted  a  second  piece  of  glass  tubing  connected  with  a 
Marey's  tambour  by  suitable  tubing.  This  second  tube  communicates  any  altera- 
tion of  the  pressure  in  the  bottle  to  the  tambour,  and  this  may  be  made  to  write  on 
a  recording  surface. 

There  are  various  instruments  for  recording  the  movements  of  the  chest  by 
application  of  apparatus  to  the  exterior.  Such  is  the  stethograph  of  Burdon- 
Sanderson  (fig.  328. )  This  consists  of  a  frame  formed  of  two  parallel  steel  bars 
joined  by  a  third  at  one  end.  At  the  free  end  of  the  bars  is  attached  a  leather  strap, 
by  means  of  which  the  apparatus  may  be  suspended  from  the  neck.  Attached  to 
the  inner  end  of  one  bar  is  a  tambour  and  ivory  button,  to  the  end  of  the  other  an 
ivory  button.  When  in  use,  the  apparatus  is  suspended  with  the  transverse  bar 
posteriorly,  the  button  of  the  tambour  is  placed  on  the  part  of  the  chest  the  move- 
ment of  which  it  is  desired  to  record,  and  the  other  button  is  made  to  press  upon 
the  corresponding  point  on  the  other  side  of  the  chest,  so  that  the  chest  is,  as  it 
were,  held  between  a  pair  of  callipers.  The  tambour  is  connected  by  tubing  and  a 
T-piece  with  a  recording  tambour  and  with  a  ball,  by  means  of  which  air  can  be 
squeezed  into  the  cavity  of  the  tambour.  When  in  work  the  tube  connected  with 
the  air  ball  is  shut  off  by  means  of  a  screw  clamp.  The  movement  of  the  chest  is 
thus  communicated  to  the  recording  tambour. 

Z 


354 


RESPIRATION 


[CH.  XXIV. 


^-•"A  simpler  form  of  this  apparatus  consists  of  a  thick  india-rubber  bag  of  ellipti- 
cal shape  about  three  inches  long,  to  one  end  of  which  a  rigid  gutta-percha  tube  is 


Fig  3-'7  — Stethoi'raph.  /i,  tambour  fixed  at  right  angles  to  plate  of  steel/;  c  and  rf,  arms  by  which 
instioimeut  is^attached  to  chest  by  belt  f.  When  the  chest  expands,  the  arms  are  pulled  asunder, 
which  bends  the  steel  plate,  and  the  tambour  is  aflected  by  the  pressure  of  &,  which  is  attached  to 
it  on  the  one  hand,  and  to  the  upright  in  connection  with  horizontal  screw  g.  (Modified  from 
Marey's  instrument.) 

attached.     This  bag  may  be  fixed  at  any  required  place  on  the  chest  by  means  of  a 
strap  and  buckle.     By  means  of  the  gutta-percha  tube  the  variations  of  the  pres- 


Tambour. 
Ivorj'  button. 


Tube  to  commuui- 
cate  with  record- 
ing tambour. 


Ball  to  fill  apparatus 
with  air. 


Fig.  328.— Stethograph.    (Burdon-Sanderson.) 


CH.  XXIV.] 


KKSPIRATORY   TRACINGS 


356 


sure  of  air  in  the  bap:  produced  by  the  movements  of  the  chest  are  communicated 
to  a  recording  tambour.  This  apjiaratus  is  a  simplified  form  of  Marey's  stetho- 
Krai>h  (Hfr.  327). 

The  variations  of  intrapleural  pressure  may  be  recorded  by  the  introduction  of 
a  cannula  into  the  pleural  cavity,  which  is  connected  with  a  mercurial  manometer. 

Finally,  it  has  been  found  possible  in  various  ways  to  record  the  diaphragmatic 
movements  by  the  insertion  of  an  elastic  bag-  connected  with  a  tambour  into  the 
abdomen  below  it  (phrenograph),  by  the  insertion  of  needles  into  difTerent  parts 
of  its  structure,  or  by  recording-  the  contraction  of  isolated  strijjs  of  the  diaphragm. 
Such  a  striji  attached  in  the  rabbit  to  the  xiphisternal  cartilage  may  be  detached, 
and  attached  by  a  thread  to  a  recording  lever.  This  method  was  largely  used  by 
Head  ;  this  strip  serves  as  a  sample  of  the  diaphragm. 

Fig.  329  shows  a  tracing  obtained  in  this  way  ;  but  in  tracings  taken  with  a 


Fig.  329. — Tracing  of  the  uoniial  diaphragm  respirations  of  rabbit,  a,  with  quick  uio\  ement  of  drum. 
h,  with  slow  movement.  The  upstrokes  represent  inspiration  ;  the  downstrokes,  expiration.  To 
be  read  from  left  to  right.     The  time  tracing  in  each  case  represents  seconds.    (Marckwald.) 

stethograph,  or  any  of  the  numerous  arrangements  of  tambours  which  are  applied  to 
the  chest-walls  of  men  and  animals,  the  large  up-and-down  strokes  due  to  the 
respiratory  movements  have  upon  them  smaller  waves  due  to  heart-beats. 

The  acts  of  expansion  and  contraction  of  the  chest  take  up  a 
nearly  equal  time.  The  act  of  inspiring  air,  however,  especially  in 
women  and  children,  is  a  little  shorter  than  that  of  expelling  it,  and 
there  is  commonly  a  very  slight  pause  between  the  end  of  expiration 
and  the  beginning  of  the  next  inspiration. 

If  the  ear  is  placed  in  contact  with  the  wall  of  the  chest,  or  is 
separated  from  it  only  by  a  good  conductor  of  sound  or  stethoscope, 
a  faint  respiratory  or  vesicular  murmur  is  heard  during  inspiration. 
This  sound  varies  somewhat  in  different  parts — being  loudest  or 
coarsest   in    the   neighbourhood   of   the   trachea  and   large   bronchi 


356  RESPIRATION  [CH.  XXIV. 

(tracheal  and  bronchial  breathing),  and  fading  off  into  a  faint  sighing 
as  the  ear  is  placed  at  a  distance  from  these  (vesicular  breathing).  It 
is  best  heard  in  children,  and  in  them  a  faint  murmur  is  heard  in  ex- 
piration also.  The  cause  of  the  vesicular  murmur  has  received  various 
explanations  ;  but  most  observers  hold  that  the  sound  is  produced  by 
the  air  passing  through  the  glottis  and  larger  tubes,  and  that  this 
sound  is  modified  in  its  conduction  through  the  substance  of  the  lung. 
The  alterations  in  the  normal  breath  sounds,  and  the  various  additions 
to  them  that  occur  in  different  diseased  conditions,  can  only  be 
properly  studied  at  the  bedside. 

During  the  action  of  the  muscles  which  directly  draw  air  into 
the  chest,  those  which  guard  the  opening  through  which  it  enters  are 
not  passive.  In  hurried  breathing  the  instinctive  dilatation  of  the 
nostrils  is  well  seen,  although  under  ordinary  conditions  it  may  not 
be  noticeable.  The  opening  at  the  upper  part  of  the  larjTix  or  rima 
glottidis  is  slightly  dilated  at  each  inspiration  for  the  more  ready 
passage  of  air,  and  becomes  smaller  at  each  expiration  ;  its  condition, 
therefore,  corresponds  during  respu'ation  with  that  of  the  walls  of 
the  chest.  There  is  a  further  likeness  between  the  two  acts  in  that, 
under  ordinary  circumstances,  the  dilatation  of  the  rima  glottidis  is 
a  muscular  act  and  its  narrowing  chiefly  an  elastic  recoil. 

Terms  used  to  express  Quantity  of  Air  breathed. — a.  Tidal 
air  is  the  quantity  of  air  which  is  haljitually  and  almost  uniformly 
changed  in  each  act  of  breathing.  In  a  healthy  adult  man  it  averages 
about  500  c.c,  or  rather  more  than  30  cubic  inches,  according  to  the 
recent  measurements  made  by  Haldane.  This  will  be  expanded  at 
body  temperature  to  600  c.c.  It  will  be  seen  that  this  amount  of  air 
is  not  sufficient  to  iill  the  lungs.  Haldane  gives  the  capacity  of 
the  upper  air  passages  and  bronchial  tubes  as  200  c.c,  and  if  this 
estimate  is  correct,  about  a  third  of  the  tidal  air  is  required  to  fill 
this  dead  space.  At  the  end  of  an  expiration,  however,  the  tubes 
and  alveoli  are  not  empty  of  air,  and  the  sudden  inrush  of  atmos- 
pheric air  during  inspiration  effects  a  complete  mixture  of  this  air 
with  that  left  in  the  air  passages ;  the  air  in  the  axial  stream  of  the 
current  will  penetrate  as  far  as  the  alveoli,  but  what  is  sucked  into 
the  alveoli  is  mainly  some  of  the  mixture  from  the  bronchial  passages, 
and  that  in  turn  is  derived  from  the  mixture  (containing  more  atmos- 
pheric air  in  proportion)  in  the  upper  air  cavities.  During  expiration 
the  air  which  leaves  the  lungs  will  come  in  part  from  the  alveoli,  but 
the  effect  of  the  stream  of  outgoing  air  is  mainly  as  before,  to  effect  a 
thorough  admixture  of  the  air  in  the  intermediate  air  passages  ;  thus 
the  alveolar  air  will  become  mixed  with  that  in  the  bronchial  tubes, 
and  that  in  turn  will  be  mixed  with  that  in  the  upper  air  chambers. 
In  a  succession  of  alternate  inspirations  and  expirations  adequate 
ventilation  is  secured,  but  obviously  the  composition  of  the  expired 


CIT.  XXIV.]  VITAL   CAPACITY  357 

air  is  not  the  same  as  that  of  alveolar  air,  for  the  latter,  though  it 
is  ultimately  breathed  out,  is  diluted  on  its  upward  journey  by 
mixture  with  the  bronchial  air,  and  that  in  its  turn  with  the  air  of 
the  upper  air  chambers ;  in  other  words,  the  expired  air  is  alveolar 
air  (rich  in  carbon  dioxide)  diluted  with  bronchial  air  (richer  in 
oxygen)  and  with  atmospheric  air  (still  richer  in  oxygen).  No  doubt 
diffusion  of  gases  occurs  as  well,  oxygen  diffusing  inwards  and  carbon 
dioxide  outwards,  but  this  molecular  movement  is  too  slow  to  be  of 
any  real  use  in  aerating  the  blood,  for  almost  inmiediately  the 
respiratory  movements  cease,  death  occurs. 

b.  CompUmental  air  is  the  quantity  over  and  above  this  which 
can  be  drawn  into  the  lungs  in  the  deepest  inspiration  ;  its 
amount  averages  100  cubic  inches,  or  about  1600  c.c. 

c.  Reserve  or  su23plemental  air. — After  an  ordinary  expiration,  such 
as  that  which  expels  the  breathing  or  tidal  air,  a  certain  quantity  of 
air,  about  100  cubic  inches  (1600  c.c.)  remains  in  the  lungs,  which 
may  be  expelled  by  a  forcible  and  deeper  expiration.  This  is  termed 
reserve  or  supplemental  air. 

d.  Residual  air  is  the  quantity  which  still  remains  in  the  lungs 
after  the  most  violent  expiratory  effort.  Its  amount  depends  in  great 
measure  on  the  absolute  size  of  the  chest,  but  may  be  estimated  at 
about  100  cubic  inches,  or  about  1600  c.c. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs 
of  an  adult,  at  rest,  in  24  hours,  varies  from  400,000  (Marcet)  to 
680,000  (Hutchinson)  cubic  inches.  This  quantity,  however,  is 
increased,  and  may  be  more  than  doubled  by  exertion. 

e.  Respiratory  or  Vital  Capacity. — The  vital  capacity  of  the  chest 
is  indicated  by  the  quantity  of  air  which  a  person  can  expel  from  his 
lungs  by  a  forcible  expiration  after  the  deepest  inspiration  possible. 
The  average  capacity  of  an  adult,  at  15*4°  C.  (60"  F.),  is  about  225  to 
250  cubic  inches,  or  3500  to  4000  c.c.  It  is  the  sum  of  the  coni- 
plemental,  tidal,  and  supplemental  air. 

The  respiratory  capacity,  or  as  John  Hutchinson  called  it,  ritdl  capacity,  is 
usually  measured  by  a  modified  gasometer  or  splrijinefer,  into  which  the  experi- 
menter breathes, — making  the  most  prolonged  expiration  possible  after  the  deepest 
possible  inspiration.  The  quantity  of  air  which  is  thus  expelled  from  the  lungs  is 
indicated  by  the  height  to  which  the  air-chamber  of  the  spirometer  rises  ;  and  by 
means  of  a  scale  placed  in  connection  with  this,  the  number  of  cubic  inches  is  read 
off.  Haldane  measures  the  volume  of  air  expired  by  the  reduction  which  takes 
place  in  the  volume  of  the  body  when  placed  within  a  plethysmograph  large 
enough  to  take  a  man,  with  the  exception  of  his  head. 

The  number  of  respirations  in  a  healthy  adult  person  usually  ranges 
from  14  to  18  per  minute.  It  is  greater  in  infancy  and  childhood. 
It  varies  also  much  according  to  different  circumstances,  such  as 
exercise  or  rest,  health  or  disease,  etc.  Variations  in  the  number  of 
respirations   correspond   ordinarily  with   similar   variations   in    the 


358  RESPIRATION  [CH.  XXIV. 

pulsations  of  the  heart.  In  health  the  proportion  is  about  1  to  4, 
or  1  to  5,  and  when  the  rapidity  of  the  heart's  action  is  increased, 
that  of  the  chest  movement  is  commonly  increased  also  ;  but  not  in 
every  case  in  equal  proportion.  It  happens  occasionally  in  disease, 
especially  of  the  limgs  or  air  passages,  that  the  number  of  respiratory 
acts  increases  in  quicker  projDortion  than  the  beats  of  the  pulse ;  and, 
in  other  affections,  much  more  commonly,  that  the  number  of  the 
pulse-beats  is  greater  in  proportion  than  that  of  the  respirations. 

The  Force  of  Inspiratory  and  Expiratory  Muscles. — The  force  with 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in 
individuals  of  the  height  of  from  five  feet  seven  inches  to  five  feet 
eight  inches,  and  will  elevate  a  column  of  nearly  three  inches  (about 
60  mm.)  of  mercury.  Above  this  height  the  force  decreases  as  the 
stature  increases ;  so  that  the  average  of  men  of  six  feet  can  elevate 
only  about  two  and  a  half  inches  of  mercury.  The  force  manifested 
in  the  strongest  expiratory  acts  is,  on  the  average,  one-third  greater 
than  that  exercised  in  inspiration.  But  this  difference  is  in  great 
measure  due  to  the  power  exerted  by  the  elastic  reaction  of  the  walls 
of  the  chest ;  and  it  is  also  much  influenced  by  the  disproportionate 
strength  which  the  expiratory  muscles  attain,  from  their  being  called 
into  use  for  other  purposes  than  that  of  simple  expiration.  The  force 
of  the  inspiratory  act  is,  therefore,  better  adapted  than  that  of  the 
expiratory  for  testing  the  muscular  strength  of  the  body.  (John 
Hutchinson.) 

In  ordinary  quiet  breathing,  there  is  a  negative  pressure  of  only 
1  mm.  during  inspiration,  and  a  positive  pressure  of  from  2  to  3  mm. 
mercury  during  expiration. 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  expiratory 
power  was  a  mercurial  manometer,  to  which  was  attached  a  tube  fitting  the  nostrils, 
and  through  which  the  inspiratory  or  expiratory  effort  was  made. 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is 
employed  in  overcoming  the  resistance  offered  by  the  elasticity  of 
the  lungs. 

In  man  the  pressure  exerted  by  the  elasticity  of  the  lungs  alone  is 
about  6  mm.  of  mercury.  This  is  estimated  by  tying  a  manometer 
into  the  trachea  of  a  dead  subject,  and  observing  the  rise  of  mercury 
that  occurs  on  puncture  of  the  chest-walls.  If  the  chest  is  distended 
beforehand  so  as  to  imitate  a  forcible  inspiration,  a  much  larger  rise 
(30  mm.)  of  the  mercury  is  obtained.  In  the  body  this  elastic  force 
is  assisted  by  the  contraction  of  the  plain  muscular  fibres  of  the 
alveoli  and  bronchial  tubes,  the  pressure  of  which  probably  does  not 
exceed  1  or  2  mm.  Hutchinson  calculated  that  the  total  force  to  be 
overcome  by  the  muscles  in  the  act  of  inspiring  200  cubic  inches  of 
air  is  more  than  450  lbs. 

It  is  possible  that  the  contractile  power  which  the  bronchial  tu]ies 


CH.  XXIV.]  THE    KKSPIRATORY   CENTRE  359 

and  air-vesicles  possess,  by  means  of  their  muscular  fibres,  may  assist 
in  expiration ;  but  it  is  more  likely  that  the  chief  purpose  of  this 
muscular  tissue  is  to  regulate  and  adapt,  in  some  measure,  the 
quantity  of  air  admitted  to  the  lungs,  and  to  each  part  of  them, 
according  to  the  supply  of  blood :  the  muscular  tissue  also  contracts 
upon  and  gradually  expels  collections  of  mucus,  which  may  have 
accumulated  within  the  tubes,  and  which  cannot  be  ejected  by  forced 
expiratory  efforts,  owing  to  collapse  or  other  morbid  conditions  of  the 
portion  of  lung  connected  with  the  obstructed  tubes  (Gairdner). 

The  Respiratory  Centre. 

In  the  central  nervous  system  there  is  a  specialised  small  district 
called  the  respiratory  centre.  This  gives  out  impulses  which  travel 
down  the  spinal  cord  to  the  centres  of  the  spinal  nerves  that 
innervate  the  muscles  of  respiration.  It  also  receives  various  afferent 
fibres,  the  most  important  of  which  are  contained  in  the  trunk  of  the 
vagus.  The  vagus  is  chiefly  an  afferent  nerve  in  relation  to  respira- 
tion. It,  however,  also  is  in  a  minor  degree  efferent,  for  it  supplies 
the  muscular  tissue  of  the  lungs  and  bronchial  tubes,  and  exercises  a 
trophic  influence  on  the  lung. 

The  respiratory  centre  was  discovered  by  Flourens ;  it  is  situated 
at  the  tip  of  the  calamus  scriptorius,  and  coincides  in  position 
with  the  sensory  centre  of  the  vagus.  The  existence  of  subsidiary 
respiratory  centres  in  the  spinal  cord  has  been  mooted,  but  the 
balance  of  experimental  evidence  is  against  their  existence.  Flourens 
found  that  when  the  respiratory  centre  is  destroyed,  respiration  at 
once  ceases,  and  the  animal  dies.  He  therefore  called  it  the  "  vital 
knot "  (noeud  vitale). 

The  centre  is  affected  not  only  by  the  afferent  impulses  which 
reach  it  by  such  nerves  as  the  vagus,  but  also  by  those  from  the 
cerebrum ;  so  that  we  have  a  limited  amount  of  voluntary  control 
over  the  respiratory  movements. 

The  question  has  been  much  debated  whether  the  activity  of  the 
respiratory  centre  is  automatic  or  reflex.  The  word  automatic  is  not 
a  very  happy  one,  but  the  meaning  is  that  the  rhythmic  discharges 
proceeding  from  the  centre  depend  on  local  changes  induced  by  the 
condition  of  its  blood  supply.  The  word  reflex  implies  that  the 
rhythm  of  the  centre  is  due  to  the  stimulations  it  receives  from 
afferent  nerves.  In  other  words,  the  question  before  us  is  whether 
we  have  to  deal  with  chemical  stimuli  via  the  blood,  or  with  nervous 
stimuli  via  afferent  nerves.  There  is  no  doubt  that  under  normal 
circumstances  we  have  to  deal  with  both  kinds  of  stimulus,  and  in 
abnormal  conditions  one  or  the  other  may  rise  into  prominence ; 
thus  the  great  increase  of  respiratory  activity  {dyspncea)  which 
occurs  during  asphyxia,  is  undoubtedly  due   to   the  stimulation  of 


360  RESPIRATION  [CH.  XXIV. 

the  centre  by  the  great  increase  of  carbonic  acid  in  the  venous 
blood.  On  the  other  hand,  the  effects  on  respiration  produced  by 
the  artificial  stimulation  of  nerves  are  extremely  pronounced. 

It  will  be  best  to  consider  the  two  kinds  of  stimuli  separately, 
and  we  will  take  the  nervous  stimuli  first. 

The  Nervous  Cause  of  Respiration. 

During  foetal  life,  the  need  of  the  embryo  for  oxygen  is  small, 
and  is  amply  met  by  the  transference  of  oxygen  from  the  maternal 
blood  through  the  thin  walls  of  the  ftetal  capillaries  in  the  placenta. 
But  when  the  child  is  born,  this  source  of  oxygen  is  no  longer  avail- 
able, and  the  increasing  venosity  of  the  blood  stimulates  the  respira- 
tory centre  to  action,  and  is  the  essential  cause  of  the  first  inspiratory 
efforts  the  new-born  child  makes  to  obtain  the  oxygen  it  requires  by 
breathing.  If  the  placental  circulation  is  stopped  while  the  child  is 
still  in  utero,  respiratory  efforts  are  also  made.  But  in  the  new-born 
child,  the  sensory  nerves  of  the  skin  have  also  an  effect,  and  tlie 
action  of  the  air  on  its  body  surface  is  no  doubt  an  accessory  cause 
of  the  first  respirations,  and  these  may  in  feeble  children  be  increased 
by  stimulating  the  skin  for  instance  by  the  application  of  cold  water 
to  it.    This  in  fact  always  causes  deep  inspirations,  even  in  the  adult. 

There  are  many  other  nerves,  stimulation  of  which  influences  the 
respiratory  act ;  for  instance,  stimulation  of  the  central  end  of  the 
splanchnics  causes  expiration.  Stimulation  of  the  central  end  of  the 
glosso-pharyngeal  causes  an  inhibition  of  the  respiratory  movements 
for  a  short  period ;  this  accounts  for  the  very  necessary  cessation  of 
breathing  during  swallowing.  Stimulation  of  the  central  end  of  the 
cut  superior  laryngeal  nerve,  or  of  its  terminations  in  the  mucous  mem- 
brane of  the  larynx,  as  when  a  crumb  is  "  swallowed  the  wrong  way," 
produces  an  increase  of  expiratory  efforts,  culminating  in  coughing. 

These  nerves,  however,  are  none  of  them  of  such  importance  or 
are  in  such  constant  action  as  the  vagi.  Still,  respiration  continues 
after  the  vagi  are  cut.  The  character  of  the  respiration  becomes 
altered,  especially  if  both  nerves  are  severed ;  it  is  slower  and  deeper. 
This  is  due  to  the  cessation  of  the  impulses  that  normally  run  up  the 
vagi  to  the  respiratory  centre.  The  animal,  however,  lives  a  con- 
siderable time;  a  warm-blooded  animal  usually  dies  after  about  a 
week  or  ten  days  from  vagus  pneumonia,  due  to  the  removal  of 
trophic  influences  from  the  lungs.  Cold-blooded  animals  live  longer ; 
they  exhibit  fatty  degeneration  of  the  heart-muscle  also. 

We  may,  however,  best  describe  the  action  of  the  vagi  by  giving 
an  account  of  the  very  systematic  investigation  of  their  functions, 
which  was  carried  out  by  Dr  Head. 

His  method  of  recording  the  movements  was  by  means  of  that  con- 
venient slip  of  the  diaphragm  which  is  foimd  in  rabbits  (see  p.  355). 


CH.  XXIV.] 


THE   VArrTTS    AND   TIRSPIHATION 


361 


His  method  of  divicling  the  vagus  was  Ly  freezing  it;  lie  laid  it 
across  a  copper  wire,  the  end  of  which  was  placed  in  a  freezing 
mixture.  This  method  is  free  from  the  disadvantage  which  a  cut 
with  a  knife  or  scissors  possesses,  namely,  a  stimulation  at  the 
moment  of  section.  On  dividing  one  vagus,  respiration  became 
slightly  slower  and  deeper  ;  on  dividing  the  second  nerve,  this  effect 
was  much  more  marked. 

On  exciting  the  central  end  of  the  divided  nerve,  inspiratory 
efforts  increased  until  at  last  the  diaphragm  came  to  a  standstill  in 
the  inspiratory  position.  But  if  a  weak  stimulus  was  employed,  the 
reverse  was  the  case ;  the  expiratory  efforts  increased,  inspiration 
becoming  weaker  and  weaker,  until  at  last  the  diaphragm  stopped  in 
the  position  of  expiration. 

Most  of  these  facts  were  known  previously,  but  the  interpretation 
of  them,  in  the  light  of  further  experiments  immediately  to  be 
described,  is  the  following : — 

That  there  are  in  the  vagus  two  sets  of  fibres,  one  of  which  pro- 
duces an  increased  activity  of  the  inspiratory  part  of  the  respiratory 
centre,  and  the  other  an  increased  activity  of  the  expiratory  part  of 
that  centre.  Stimulation  of  the  first  stops  expiration  and  produces 
inspiration ;  stimulation  of  the  second  does  the  reverse. 

The  question  now  is.  What  is  it  that  normally  produces  this 
alternate  stimulation  of  the  two  sets  of  fibres  ?  If  we  discover  this 
we  shall  discover  the  prime  moving  cause  in  the  alternation  of  the 
inspiratory  and  expiratory  acts. 
It  was  sought  and  found  in  the 
alternate  distension  and  con- 
traction of  the  air-vesicles  of 
the  lungs  where  the  ^'agus 
terminations  are  situated. 

In  one  series  of  experiments 
positive  ventilation  was  per- 
formed ;  that  is,  air  was  pumped 
repeatedly  into  the  lungs,  and  so 
increased  their  normal  disten- 
sion ;  this  was  found  to  decrease 
the  inspiratory  contractions  of 
the  diaphragm,  until  at  last 
they  ceased  altogether,  and  the 
diaphragm  stood  still  in  the 
expiratory  position  (fig.  330,  A). 

In  a  second  series  of  ex- 
periments, negative  ventilation  was  performed ;  that  is,  the  air  was 
pumped  repeatedly  out  of  the  lungs,  and  a  condition  of  collapse  of  the 
air-vesicles  produced.    This  was  found  to  increase  the  inspiratory  con- 


330. — Tracings  of 'liapliragm.  The  upward  move- 
ments of  the  tracings  represent  inspiration  ;  the 
downward  movements,  expiration.  A,  result  of 
positive,  B,  of  negative  ventilation.    (After  Head.) 


362  KESPIRATIOX  [CH.  XXIV. 

tractions  of  the  diaphragm,  expiration  became  less  and  less,  and  at  last 
the  diaphragm  assumed  the  position  of  inspiratory  standstill  (fig.  330, B). 

Distension  of  the  air-vesicles,  therefore,  stimulates  the  fibres  of  the 
vagus  which  excite  the  expiratory  phase  of  respiration;  collapse 
stimulates  those  which  excite  the  inspiratory  phase. 

Ordinary  respiration  is  an  alternate  positive  and  negative 
\'entilation,  though  not  so  excessive  as  in  the  experiments  just 
described.  Inspiration  is  positive  ventilation,  and  so  provides  the 
nervous  mechanism  of  respiration  with  a  stimulus  that  leads  to 
expiration.  Expiration  is  a  negative  ventilation,  and  so  provides  the 
stimulus  that  leads  to  inspiration. 

It  is  probable  that  of  the  two  sets  of  impulses,  those  which  are 
started  by  the  inspiratory  movement  play  a  more  active  part  in  the 
regulation  of  respiration  than  those  started  by  the  expiratory  move- 
ment. Gad  explains  the  latter  by  supposing  they  are  simply  due  to 
a  cessation  of  the  former,  or,  in  other  words,  that  there  only  exists 
one  class  of  afferent  fibres  in  the  vagus  concerned  in  respiration. 
This  view  has  not,  however,  met  with  general  acceptance. 

Apnoea. — If  positive  and  negative  ventilation  are  used  together 
rapidly  and  alternately  at  a  rate  quicker  than  the  respiratory  rhythm, 
both  inspiratory  and  expiratory  processes  are  inhibited,  and  the  respira- 
tion ceases  for  a  short  time.  This  follows  naturally  from  the  experi- 
ments previously  described.  This  can  be  done  on  an  animal  with  a 
pair  of  bellows  fixed  to  a  tube  in  the  trachea ;  or  voluntarily  by  one- 
self taking  a  number  of  deep  breaths  rapidly.  This  condition,  called 
apnma,  is  not  due,  as  at  one  time  supposed,  to  over-oxygenation  of  the 
blood,  but  is  produced  refiexly.  Under  normal  circumstances  arterial 
blood  is  always  fully  oxygenated.  It  is  observed  if  inert  gases,  like 
nitrogen  or  hydrogen,  are  used  instead  of  air.  The  pause,  however, 
is  then  shorter,  as  the  blood  becomes  venous,  and  in  a  short  time 
stimulates  the  respiratory  centre  to  activity. 

Under  abnormal  circumstances,  namely,  after  division  of  the  vagi, 
apnoea  cannot  obviously  be  due  to  such  reflex  action.  Fredericq 
holds  that  even  ordinary  apnoea  has  a  chemical  rather  than  a  nervous 
origin.  He  attributes  it,  however,  not  to  over-oxygenation,  but  to  a 
lessening  of  the  carbonic  acid  in  the  blood. 

The  Chemical  Cause  of  Respiration. 

A  consideration  of  apnoea  thus  leads  us  back  to  the  study  of  the 
chemical  stimuli  that  play  their  part  in  the  respiratory  process. 
Their  importance  has  been  recently  demonstrated  by  Haldane  and 
Priestley.  In  the  first  place,  they  introduced  a  new  and  simple 
method  of  obtaining  the  composition  of  the  air  in  the  alveoli.  It 
consists  in  collecting  a  sample  of  air  expired  at  the  end  of  a  deep 


Cir.  XXIV.]  ACTION    OF   CAKBON    DIOXIDE  363 

expiration  following  an  ordinary  quiet  inspiration,  and  another 
similar  sample  following  a  quiet  expiration ;  the  mean  of  the  two 
gives  the  composition  of  alveolar  air.  This  is  much  simpler  than 
the  methotl  formerly  employed  by  Pfliiger,  which  consisted  in 
pumping  off  the  air  from  an  occluded  portion  of  a  dog's  lung  ])y 
means  of  a  fine  elastic  catheter  introduced  via  the  trachea  and 
bronchus.  It  has  the  further  advantage  that  it  can  be  applied  to 
the  human  subject. 

They  found  that,  under  constant  atmospheric  pressure,  in  man  the 
alveolar  air  contains  a  nearly  constant  percentage  of  carbon  dioxide 
in  the  same  person.  In  different  individuals  this  percentage  varies 
somewhat,  but  averages  5'1  per  cent,  of  an  atmosphere  in  men, 
and  4"7  in  women  and  children. 

With  varying  atmospheric  pressures,  the  percentage  varies 
inversely  as  the  atmospheric  pressure,  so  that  the  pressure  or  tension 
of  the  carbon  dioxide  remains  constant.  The  oxygen  pressure, 
however,  varies  widely  under  the  same  conditions. 

These  observations  and  the  next  to  be  immediately  described 
furnish  the  chemical  key  to  the  cause  of  the  amount  of  pulmonary 
ventilation,  and  play  an  important  part  in  conjunction  with  the 
respiratory  nervous  system  in  the  regulation  of  breathing.  For  the 
respiratory  centre  is  not  only  affected  by  the  impulses  reaching  it  by 
the  vagi  and  other  afferent  nerves,  but  it  is  also  very  sensitive  to 
any  rise  in  the  tension  of  carbon  dioxide  in  the  blood  that  supplies 
it.  The  changes  in  the  tension  of  this  gas  in  the  arterial  blood  are 
normally  proportional  to  the  changes  in  the  carbon  dioxide  pressure 
in  the  alveoli,  and  the  changes  in  the  lung  alveoli  are  transmitted  to 
the  respiratory  centre  by  the  blood.  They  found  that  a  rise  0'2  per 
cent,  in  the  alveolar  carbon  dioxide  pressure  is  sufficient  to  double 
the  amount  of  alveolar  ventilation  during  rest.  During  work  the 
alveolar  carbon  dioxide  pressure  increases  slightly,  and  the  pulmonary 
ventilation  is  consequently  increased. 

Changes  in  the  oxygen  pressure  within  wide  limits  have  no  such 
influence ;  the  normal  chemical  stimulus  to  respiration  is,  therefore, 
presence  of  an  increase  of  carbon  dioxide,  and  not  diminution  of 
oxygen.  If  these  limits  are  exceeded,  as  when  the  oxygen  pressure 
falls  below  13  per  cent,  of  an  atmosphere,  the  respiratory  centre 
begins  to  be  excited  by  want  of  oxygen,  for  the  alveolar  carbon 
dioxide  pressure  is  lower  than  normal  under  such  circumstances. 

We  have  seen  that  apnoea  is  the  name  given  to  the  cessation  of 
breathing  which  temporarily  follows  excessive  ventilation  of  the 
lungs,  as  when  one  takes  a  number  of  deep  breaths  in  rapid  succes- 
sion. The  deep  and  rapid  breathing  clears  out  the  carbon  dioxide  in 
the  alveoli  until  it  is  so  small  in  quantity  that  it  is  insufficient  to 
excite  the  respiratory  centre  vid   the  l^lood  to  action,  the   oxygen 


364  RESPIRATION  [CH.  XXIV. 

pressure  at  the  same  time  remaining  sufficiently  high  not  to  excite 
the  centre  either.  Hence  breathing  ceases.  As  already  stated,  the 
old  idea  that  apncea  is  due  to  over-oxygenation  of  the  blood  has  been 
abundantly  disproved ;  but  Head  and  others  have  gone  to  an  extreme 
in  assuming  that  apnosa  is  purely  nervous  in  origin.  Haldane,  like 
Fredericq,  considers  it  is  unnecessary  to  assume  the  existence  of  a 
vagus  apnoea  in  man  at  all  under  normal  circumstances.  In  normal 
breathing  both  nervous  and  chemical  factors  are  at  play;  it  is  prob- 
ably the  rhythm  of  respiration  which  is  mainly  under  nervous  control, 
while  the  amount  of  ventilation  (dependent  chiefly  on  the  deptli.  of 
each  respiratory  act)  is  especially  regulated  l)y  the  chemical  stimulus. 

Special  Respiratory  Acts. 

Coughing. — In  the  act  of  coughing  tliere  is  first  of  all  a  deep  in- 
spiration, followed  by  an  expiration ;  but  the  latter,  instead  of  being 
easy  and  uninterrupted,  as  in  normal  breathing,  is  obstructed,  the 
glottis  being  momentarily  closed  by  the  approximation  of  the  vocal 
cords.  The  abdominal  muscles,  then  strongly  acting,  push  up  the 
viscera  against  the  diaphragm,  and  thus  make  pressure  on  the  air  in 
the  lungs  until  its  tension  is  sufficient  to  noisily  open  the  vocal  cords 
which  oppose  its  outward  passage.  In  this  way  considerable  force  is 
exercised,  and  mucus  or  any  other  matter  that  may  need  expulsion 
from  the  air  passages  is  quickly  and  sharply  expelled  by  the  out- 
streaming  current  of  air.  The  act  is  a  reflex  one,  the  sensory  surface 
which  is  excited  being  the  mucous  membrane  of  the  larynx,  and  the 
superior  laryngeal  nerve  is  the  afferent  nerve;  stimulation  of  other 
parts  of  the  respiratory  mucous  membrane  will  also  produce  cough, 
and  the  point  of  bifurcation  of  the  trachea  is  specially  sensitive. 
Other  sensory  surfaces  may  also  act  as  the  "signal  surface"  for  a 
cough.  Thus,  a  cold  draught  on  the  skin,  or  tickling  the  external 
auditory  meatus,  in  some  people  will  set  up  a  cough. 

The  question  has  been  discussed  whether  such  a  thing  as  a  stomach 
cough  exists ;  it  has  not  been  produced  experimentally,  but  there  is  no 
reason  why  irritation  of  the  gastric  mucous  membrane,  supj)lied  as  it 
is  by  the  vagus,  should  not  cause  the  reflex  act  of  coughing. 

Sneezing. — The  same  remarks  that  apply  to  coughing  are  almost 
exactly  applicable  to  the  act  of  sneezing;  but,  in  this  instance,  the 
blast  of  air,  on  escaping  from  the  lungs,  is  directed,  by  an  instinctive 
contraction  of  the  pillars  of  the  fauces  and  descent  of  the  soft 
palate,  chiefly  through  the  nose,  and  any  offending  matter  is  thence 
expelled. 

The  "  signal  surface  "  is  usually  the  nasal  mucous  membrane,  but 
here,  as  in  coughing,  other  causes  (such  as  a  bright  light)  will  some- 
times set  the  reflex  goins. 


CH.  XXIV.] 


CHEYNE-STOKES    RESPIRATION 


365 


Hiccough  is  au  involuntary  sudden  contraction  of  tlie  diaphragm, 
causing  au  inspiration  which  is  suddenly  arrested  by  the  closure  of  the 
glottis,  causing  a  characteristic  sound.    It  arises  from  gastric  irritation. 

Snoring  is  due  to  vibration  of  the  soft  palate. 

Sobbing  consists  of  a  series  of  convulsive  inspirations  at  the  moment 
of  which  the  glottis  is  partially  closed. 

Sighing  and  Yawning  are  emotional  forms  of  inspiration,  the  latter 
associated  with  stretching  movements  of  jaws  and  limbs.  They  appear 
to  be  efforts  of  nature  to  correct,  by  an  extra  deep  inspiration,  the 
venosity  of  the  blood  due  to  inactiNdty  produced  by  ennui  or  grief. 
Their  contagious  character  is  due  to  sympathy. 

Among  abnormal  disturbances  of  the  nervous  mechanism  of 
respiration,  the  following  diseases  must  be  mentioned:  laryngismus 
stridulus,  asthma,  and  whooping-cough. 

Chcyne- Stokes  respiration  is  due  to  rhythmical  activity  of  the 
respiratory  centre.     It  reminds  one  somewhat  of  the  Traube-Hering 


Fig.  331.— Cheyne-Stokes  respiration.    (After  Waller.) 

waves  due  to  a  similar  rhythmical  activity  of  the  vaso-motor  centre. 
It  is  seen  in  many  nervous  diseases  and  in  fatty  degeneration  of  the 
heart.  A  typical  tracing  of  the  condition  is  given  above  (fig.  331). 
It  is  seen  to  a  slight  extent  during  ordinary  sleep,  and  is  very  marked 
in  hibernating  animals. 

Pembrey  and  Pitts  have  recently  taken  graphic  records  of  this 
condition  in  the  hibernating  dormouse,  hedgehog,  marmot  and   bat. 


Fig.  332. — Cheyne-Stokes  respiration  in  hibernating  dormouse.  Tlie  liue  marked  T  gives  time  in  seconds. 
Line  1  gives  the  tracing  of  a  respiratory-  group  which  occurred  once  everj'  SO  seconds,  the  tempera- 
ture of  the  animal  being  11  C.  On  warming  the  animal  to  13'  C.  the  respiratory  groups  became 
more  frequent  (line  2).  On  warming  the  animal  still  further  it  awakened,  and  breathing,  at  first 
accompanied  by  shivering,  became  continuous.    (Pembrey  and  Pitts.) 

In  some  cases  the  respiration  has  the  typical  Cheyne-Stokes  character, 
with  a  gradual  waxing  and  waning  (fig.  332).     In  other  cases  periods 


366  RESPIRATION  [CH.  XXIV, 

of  respiratory  activity  alternate  ^with  periods  of  apnoea,  but  all  the 
respiratory  efforts  are  about  equal  in  force.     (Biot's  respiration.) 

The  Effect  of  Respiration  onfthe  Circulation. 

The  main  effect  of  respiration  on  the  circulation  is  shown  in  the 
accompanying  figure.     It  will  be  noticed  that  the  arterial  pressure 


Fio.  333. — Comparison  of  blood -pressure  curve  with  curve  of  iutra-tlioracic  pressure.  (To  be  read  fruiu 
left  to  right.)  a  is  the  curve  of  blood-pressure  with  its  respiratory  undulations,  the  slower  beats 
on  the  descent  being  very  marked  ;  '/  is  the  curve  of  intra-thoracic  pressure  obtained  by  connecting 
one  limb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i  and  expiration  at  e. 
The  intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  tlie  inspiratorj'  ettbrt,  and  then 
slowly  falls  as  the  air  issues  from  the  chest ;  at  the  beginning  of  the  inspiratory  eflbrt  the  fall 
becomes  more  rapid.     (M.  Foster.) 

rises  with  inspiration  and  falls  with  exph-ation,  but  that  the  two 
events  are  not  quite  synchronous,  the  rise  of  pressure  beginning  a 
little  later  than  the  inspiratory  act,  and  the  fall  a  little  later  than 
the  expiratory  act. 

It  will  also  be  seen  that  the  heart  beats  more  rapidly  during  the 
rise  of  blood-pressure  than  during  the  fall.  This  difference  disappears 
when  the  vagi  are  cut.  Eespu^atory  undulations,  however,  are  still 
present,  though  not  so  marked  as  before ;  hence  the  cardiac  variations 
are  not  their  sole  cause.  They  are  chiefly  the  result  of  the  mechanical 
conditions  dependent  on  the  lungs  and  heart  with  its  large  vessels 
being  contained  within  the  air-tight  thorax.  When  the  capacity  of 
the  chest  is  increased  in  inspiration,  the  tension  of  the  lung  tissue 
due  to  its  greater  expansion  is  increased ;  hence  the  difference  between 
the  intra-pleural  pressure,  and  that  in  the  lungs  (which  is  atmos- 
pheric) becomes  more  marked,  for  the  difference  of  pressure  is  to  be 
measured  by  the  elastic  force  of  the  lung  tending  to  produce  its 
collapse.  If  the  intra-thoracic  pressure  is  measm-ed,  it  is  found  that 
it  varies  from  —  5  to  —  7  mm.  of  mercury  at  the  end  of  expiration  to 
—  30  at  the  end  of  a  deep  inspiration ;  that  is  to  say,  from  5  to  7  to 


CH.  XXIV.]  EFFECTS    ON    CIRCULATION  367 

30  mm.  less  than  the  atmospheric  pressure  (760  mm.  of  mercury). 
The  pressure  outside  the  heart  and  large  vessels  is  correspondingly 
diminished  during  inspiration  to  the  same  extent,  and  produces  its 
main  effect  (distension)  upon  the  veins  because  they  are  never  fully 
distended,  and  because  the  pressure  within  them  is  low.  This 
increase  in  the  "  pressure  gradient "  {i.e.,  the  rate  of  fall  of  pressure) 
between  the  intra  and  extra  thoracic  great  veins  results  in  a  pro- 
portionately more  rapid  flow  of  blood  into  the  thorax,  and  therefore 
into  the  right  side  of  the  heart ;  for  within  certain  limits  the  right 
heart  can  be  easily  expanded  more  fully  if  a  greater  supply  of  blood 
is  provided.  Consequently,  the  output  from  the  right  side  increases, 
and  thus  vid  the  pulmonary  circuit  the  inflow  into  the  left  heart  is 
increased ;  in  its  turn,  therefore,  the  output  from  the  left  ventricle 
rises,  and  so  the  aortic  pressure  is  raised.  If  the  aorta  and  its 
branches  within  the  thorax  were  as  undistended  as  the  veins  and 
right  auricle,  this  effect  would  be  counteracted,  but  inasmuch  as  the 
aorta  and  arteries  are  thick-walled  and  already  fully  distended,  an 
increased  inflow  into  them  must  lead  to  a  further  rise  of  pressure. 
For  we  may  altogether  neglect  the  change  in  rate  of  flow  along  these 
vessels  due  to  the  change  in  pressure  gradient,  not  because  it  is 
insufficient  in  itself  to  produce  a  distinct  change  in  the  flow,  if  the 
blood  were  free  to  move  easily,  but  because  the  outflow  from  the 
arteries  has  to  take  place  through  a  high  peripheral  resistance,  and 
this  small  pressure  change  is  not  able  to  exert  any  appreciable  effect 
in  accelerating  the  flow  through  such  a  high  peripheral  resistance. 
We  must  note,  too,  that  the  change  in  pressure  gradient  would  tend 
to  decrease  the  outflow,  not  to  increase  it.  All  these  conditions  are 
reversed  when,  with  the  expiratory  act,  the  thorax  returns  to  its 
former  size,  and  the  arterial  blood-pressure  falls  in  consequence. 

The  effect  of  inspiration  on  arterial  blood-pressure  is  at  first 
assisted  by  the  pressure  of  the  diaphragm  as  it  descends  on  the 
abdominal  veins,  and  blood  is  thus  sent  upwards  into  the  chest  by 
the  vena  cava  inferior.  On  the  other  hand,  this  is  to  some  extent 
counterbalanced  by  the  obstruction  in  the  passage  of  the  blood 
downwards  in  the  abdominal  aorta,  and  upwards  from  the  veins  of 
the  lower  extremities,  but  again  the  veins  are  the  vessels  more  easily 
influenced  by  moderate  changes  in  external  pressure. 

We  now  come  to  the  cause  of  the  delay  we  have  noted  in  the 
blood-pressure  tracing  in  following  the  respiratory  movements.  One 
effect  of  the  diminished  intra-thoracic  pressure  which  occurs  during 
inspiration  is  an  increase  in  the  capacity  of  the  pulmonary  capillaries, 
and  thus,  though  more  blood  is  sent  into  the  pulmonary  circulation, 
the  resulting  increase  in  outflow  is  for  a  time  delayed  because  the 
capacity  of  the  pulmonary  vessels  has  simultaneously  become  greater. 
As  soon  as  this  increase  in  capacity  is  satisfied,  the  accelerated  flow 


368  RESPIRATION  [CH.  XXIV. 

from  the  right  heart  makes  itself  felt  on  the  left  side  with  the  results 
already  explained.  In  some  animals,  such  as  the  rabbit,  the  rise  of 
blood-pressure  occurs  during  expiration,  and  the  fall  accompanies 
inspiration.  This  is  simply  because  the  rabbit  is  an  animal  which 
breathes  very  quickly  ;  wo  have  seen  there  is  a  delay  in  the  inspiratory 
rise  of  pressure ;  if  the  animal  breathes  quickly  enough,  inspiration 
is  over  and  expiration  has  begun  before  the  rise  of  pressure  occurs. 
By  making  the  rabbit  breathe  slowly  (Fredericq  accomplished  this  by 
cooling  the  medulla  oblongata),  the  tracing  obtained  is  similar  to  that 
which  is  got  from  an  animal  like  a  dog,  which  normally  breathes 
slowly. 

When  the  chest  of  an  animal  is  freely  opened,  and  artificial 
respiration  performed  in  order  to  keep  it  alive,  respiratory  undulations 
on  the  arterial  pressure  curve  are  still  seen,  but  they  are  in  the 
reverse  direction.  These  obviously  cannot  be  produced  in  the 
mechanical  way  just  described.  The  forcible  inflation  with  air  at 
first  squeezes  more  blood  out  of  the  alveolar  capillaries,  that  is,  the 
capacity  of  these  vessels  is  diminished,  and  this  temporarily  increases 
the  quantity  of  blood  thrown  into  the  left  ventricle,  and  so  causes  a 
rise  of  arterial  pressure.  But  the  increased  intra-alveolar  pressure 
has  also  been  shown  to  lead  to  an  increased  resistance  to  the  pulmonary 
circulation,  and  the  rate  of  flow  into  the  left  side  consequently  falls ; 
the  aortic  pressure  therefore  falls,  while  the  pressure  in  the  pulmonary 
artery  rises.  If  the  high  positive  intra-pulmonary  air-pressure 
persisted,  a  condition  would  soon  be  reached,  in  which  the  increased 
blood-pressure  in  the  pulmonary  artery  would  lead  to  a  greater  flow, 
and  the  aortic  blood-pressure  would  remain  constant ;  this,  however, 
has  been  shown  to  take  a  much  longer  time  than  an  ordinary  respira- 
tion period.  Hence  the  main  effect  of  inflations  of  the  lungs  at  the 
ordinary  respiration  rate  is  to  diminish  the  aortic  blood-pressure ; 
this  rises  again,  for  the  opposite  reasons,  in  the  intervals  of  deflation 
which  correspond  to  expiration. 

If  artificial  respiration  is  performed  while  the  thorax  is  not  opened, 
a  further  complication  arises  from  the  fact  that  the  increased  intra- 
pleural pressure  decreases  the  rate  of  flow  of  blood  into  the  thorax, 
and  under  these  conditions  the  blood-pressure  in  the  pulmonary 
artery  falls,  and  in  consequence  the  fall  in  the  aortic  blood-pressure 
l)ecomes  more  marked  with  each  inflation  than  it  does  when  the 
thorax  is  open. 

The  last  point  of  detail  we  have  to  consider  is  the  cause  of  the 
greater  frequency  of  the  heart  during  the  inspiratory  phase,  a 
phenomenon  which  is  evidently  due  to  lessening  of  vagus  action, 
since  the  inequality  of  the  heart  rate  disappears  when  the  vagi  are 
cut.  The  question  before  us  is.  What  is  the  cause  of  the  rhythm  in 
the  activity  of  the  vagus  centre  ?     There  appear  to  be  two  factors 


CH.  XXIV.]  EFFECT   OF   RESPIRATION    ON    HEART  369 

couceriiod  in  its  causation:  uno  is  a  re  Hex  acti(jn,  tho  other  is  what 
may  be  termed  a  central  overtlow.     We  will  consider  these  separately. 

1.  The  rejicx.  Stimulation  of  the  pulmonary  Ijranches  of  the  vagus 
by  electrical  stimuli,  or  of  their  terminations  in  the  alveoli  ]jy  certain 
irritating  vapours  like  bromine,  causes  a  reflex  inhibition  of  the  heart ; 
great  distension  of  the  alveoli  has  a  similar  effect,  but  moderate 
distension,  such  as  occurs  in  an  ordinary  inspiration,  has  the  opposite 
reflex  effect,  causing  the  heart  to  beat  more  rapidly.  The  afferent 
fibres  from  the  pulmonary  alveoli  enter  the  bulb  by  the  upper  set  of 
the  rootlets  of  the  comliined  glossopharyngeal-vagus-spinal  accessory 
nucleus  (the  a  group,  p.  247).  Sometimes  the  rootlets  of  this  group  are 
three  in  number,  sometimes  two.  When  there  are  two,  the  lower 
rootlet,  when  there  are  three,  the  lower  two  rootlets,  contain  the  fibres 
in  question  (Cadman). 

2.  The  overfioiv.  The  respiratory  centre  exhibits  alternate  phases 
of  activity,  or  what  is  termed  a  rhythmical  action.  It  is  in  close 
anatomical  connection  with  two  other  important  centres  in  the  bulb, 
namely,  the  cardio-inhibitory  and  the  vaso-motor  centres.  Consider- 
ing how  closely  these  three  centres  are  connected  by  association 
fibres,  it  is  not  surprising  that  the  cells  of  the  two  latter  centres 
should  be  affected  by  the  rhythm  of  the  cells  of  the  respiratory 
centre,  and  the  term  overflow  is  an  expression  that  roughly  indicates 
what  occurs.  This  overflow  from  the  respiratory  centre  affects  its 
two  neighbours  in  the  same  way.  During  inspiration  the  activity 
of  both  the  cardio-inhibitory  centre  and  of  the  vaso-motor  centre  is 
diminished,  hence  the  heart  beats  faster.  The  factor  which  we  have 
termed  the  overflow  is  more  important  than  that  which  we  have 
described  as  the  reflex. 

These  facts  show  us  that  the  parallelism  of  the  respiratory  and 
arterial  pressure  curves  is  not  merely  the  result  of  the  mechanical 
conditions  already  described,  though  these  are  the  most  important. 
But  in  the  normal  condition  with  the  thorax  closed,  and  the  vagi 
uncut,  certain  nervous  factors  come  also  into  play.  During  inspira- 
tion these  are : — 

1.  A  reflex  from  the  terminations  of  the  vagi  in  the  pulmonary 
alveoli,  which  produces  a  lessening  of  vagus  action,  and  so  quickening 
of  the  heart. 

2.  An  overflow  from  the  respiratory  to  the  cardio-inhibitory 
centre,  which  is  still  more  powerful  in  producing  the  same  effect. 

3.  An  overflow  from  the  respiratory  to  the  vaso-motor  centre, 
which  produces  decreased  constriction  of  the  systemic  arterioles. 
By  itself  the  third  nervous  factor  would  lessen  arterial  pressure,  but 
in  conjunction  with  the  other  two,  and  in  conjunction  also  with  the 
mechanical  conditions  described,  the  main  result  is  a  rise  of  arterial 
pressure  during  inspiration, 

2  A 


370  RESPIRATION  [CH.  XXIY. 

Valsalva's  Experiment. — In  speaking  of  the  effects  of  expiration, 
we  have  considered  only  ordinary  quiet  expiration.  With  forced 
expiration,  there  is  considerable  impediment  to  the  circulation ;  this 
is  markedly  seen  in  what  is  called  Valsalva's  experiment.  This  con- 
sists in  making  a  forced  expiratory  effort  with  the  mouth  and  nose 
shut ;  the  effects  are  most  marked  in  people  with  an  easily  compres- 
sible thorax.  By  such  an  act  the  intrathoracic  and  abdominal 
pressures  rise  so  greatly  that  the  outlets  of  the  veins  of  the  limbs, 
head,  and  neck  into  the  thorax  are  blocked.  At  first,  the  blood  in 
the  abdominal  veins  is  drawn  on  into  the  right  heart ;  this  produces 
a  slight  rise  of  arterial  pressure;  but  soon,  if  the  effort  is  continued, 
the  lungs  are  emptied  of  blood,  the  filling  of  the  right  heart  is 
opposed,  and  the  blood  is  dammed  back  in  the  peripheral  veins,  where 
the  pressure  rises  to  mean  arterial  pressure.  The  arterial  pressure 
begins  then  to  fall ;  but  before  any  considerable  fall  occurs,  the 
expiratory  effort  ceases  from  exhaustion  of  the  subject  of  the  experi- 
ment, and  a  deep  inspiration  is  taken.  During  this  inspiration,  the 
blood  delivered  by  the  right  heart  is  all  used  in  the  filling  of  the 
dilated  and  comparatively  empty  pulmonary  vessels ;  thus  several 
beats  of  the  left  ventricle  become  abortive,  and  produce  no  effect  on 
the  radial  artery ;  the  face  blanches,  and  the  subject  becomes  faint  from 
cerebral  anaemia. 

Asphyxia. 

Asphyxia  may  be  produced  in  various  ways :  for  example,  by 
the  prevention  of  the  due  entry  of  oxygen  into  the  blood,  either  by 
direct  obstruction  of  the  trachea  or  other  part  of  the  respiratory 
passages,  or  by  introducing  instead  of  ordinary  air  a  gas  devoid  of 
oxygen,  or  by  interference  with  the  due  interchange  of  gases  between 
the  air  and  the  blood. 

The  symptoms  of  asphyxia  may  be  roughly  divided  into  three 
stages:  (1)  the  stage  of  exaggerated  breathing;  (2)  the  stage  of  con- 
vulsions ;  (3)  the  stage  of  exhaustion. 

In  the  first  stage  the  breathing  becomes  more  rapid,  and  at  the 
same  time  deeper  than  usual,  inspiration  at  first  being  especially 
exaggerated  and  prolonged.  The  muscles  of  extraordinary  inspiration 
are  called  into  action,  and  the  effort  to  respire  is  laboured  and  painful. 
This  is  soon  followed  by  a  similar  increase  in  the  expiratory  efforts, 
which  become  excessively  prolonged,  being  aided  by  all  the  muscles 
of  extraordinary  expiration.  During  this  stage,  which  lasts  a  vary- 
ing time  from  a  minute  upwards,  according  as  the  deprivation  of 
oxygen  is  sudden  or  gradual,  the  lips  become  blue,  the  eyes  are 
prominent,  and  the  expression  intensely  anxious.  The  prolonged 
respirations  are  accompanied  by  a  distinctly  audible  sound ;  the 
muscles  attached  to  the  chest  stand  out  as  distinct  cords.     This  stage 


CH.  XXIY.]  ASPHYXIA  371 

includes  tlio  two  conditions  hyperpno&a  (excessive  breathing)  and 
dyspnosa  (difficult  breathing),  which  follows  later.  It  is  due  to  the 
increasingly  powerful  stimulation  of  the  respiratory  centre  by  the 
increasingly  venous  blood. 

In  the  second  stage,  which  is  not  marked  by  any  distinct  line  of 
demarcation  from  the  first,  the  violent  expiratory  efforts  become 
convulsive,  and  then  give  way,  in  men  and  other  warm-blooded 
animals,  to  general  convulsions,  which  arise  from  the  further  stimula- 
tion of  the  centres  in  brain  and  cord  by  venous  blood.  Spasms  of 
the  muscles  of  the  body  in  general  occur,  and  not  of  the  respiratory 
muscles  onl3^  The  convulsive  stage  is  a  short  one,  and  lasts  less 
than  a  minute. 

The  third  stage,  or  stage  of  exhaustion.  In  it  the  res^jirations  all 
but  cease,  the  spasms  give  way  to  flaccidity  of  the  muscles,  there  is 
insensibility,  the  conjunctivae  are  insensitive  and  the  pupils  are 
widely  dilated.  Every  now  and  then  a  prolonged  sighing  inspiration 
takes  place,  at  longer  and  longer  intervals,  until  breathing  ceases 
altogether,  and  death  ensues.  During  this  stage  the  pulse  is  scarcely 
to  be  felt,  but  the  heart  may  beat  for  some  seconds  after  the  respira- 
tion has  stoppetl.  The  condition  is  due  to  the  gradual  paralysis  of 
the  centres  by  the  prolonged  action  of  the  venous  blood.  This  stage 
may  last  three  minutes  and  upwards. 

After  death  from  asphyxia  it  is  found  in  the  great  majority  of 
cases  that  the  right  side  of  the  heart,  the  pulmonary  arteries,  and 
the  systemic  veins  are  gorged  with  dark,  almost  black,  blood,  and 
the  left  side  of  the  heart,  the  pulmonary  veins,  and  the  arteries  are 
empty.  The  explanation  of  these  appearances  may  be  thus  summar- 
ised :  when  oxygenation  ceases,  venous  blood  at  first  passes  freely 
through  the  lungs  to  the  left  heart,  and  so  to  the  great  arteries. 
Owing  to  the  stimulation  of  the  vaso-motor  centres  by  the  venous 
blood,  the  arterioles,  particularly  those  of  the  splanchnic  area, 
are  constricted ;  the  arterial  blood -pressure  therefore  rises,  and  the 
left  side  of  the  heart  becomes  distended.  The  highly  venous  blood 
passes  through  the  arterioles,  and,  favoured  by  the  laboured  respira- 
tory movements,  arrives  at  the  right  side  of  the  heart,  which  it 
fills  and  distends ;  the  right  side  of  the  heart  is  becoming  feebler  at 
the  same  time,  and  therefore  unable  to  effectively  discharge  its  blood 
through  the  pulmonary  circuit.  Simultaneously  the  left  ventricle  is 
also  becoming  weakened,  and  therefore  its  suction  action  diminishes. 
In  this  way  the  blood  is  dammed  back  in  the  right  heart  and 
veins,  and  the  left  side  of  the  heart  therefore  gets  into  the  empty 
condition  in  which  it  is  found  after  death.  Some  consider  that  the 
early  onset  of  rigor  mortis  in  the  left  ventricle  may  be  in  part  a 
cause  of  its  contracted  and  empty  condition. 

In  the  first  and  second  stages  of  asphyxia,  the  arterial  pressure 


372 


RESPIRATION 


[CH.  XXIY. 


rises  above  the  normal ;  this  is  due  to  the  constriction  of  the  arterioles. 
The  fall  of  pressure  in  the  last  stage  is  mainly  due  to  heart  failure. 
If  the  vagi  are  not  divided  previously,  the  rise  of  pressure  is  much 


t'"  2 
.5  2  3 


S  °  3 
.5  <c  o 


■-Co 

3  I  > 

1^^ 


^  u2 

O  .5   =n 


less,  and  the  heart  beats  very  slowly :  this  enables  the  heart  to  last 
longer,  and  is  due  to  excitation  of  the  cardio-inhibitory  centre  by 
venous  blood.  The  accompanying  photograph  of  a  tracing,  which  I 
owe  to  Dr  C.  J.  Martin,  shows  these  effects ;  it  has  been  somewhat 


CH.  XXIV.]  EFFECT   OF   FOREIGN   GASES  373 

reduced  in  size  for  purposes  of  reproduction.  The  lower  tracing  is 
that  of  venous  pressure  taken  with  a  salt  solution  manometer  from 
the  jugular  vein.  It  will  be  noticed  that  the  fall  of  arterial  pressure 
is  accompanied  with  a  great  rise  of  venous  pressure  due  to  the  venous 
congestion  just  described. 

Effects  of  Breathing  Gases  other  than  the  Atmosphere. 

The  diminution  of  oxygen  has  a  less  direct  influence  in  the  production  of 
asphyxia  than  the  increased  amount  of  carbonic  acid.  Nevertheless,  tlie  fatal  effect 
of  carbonic  acid  in  the  blood  when  a  due  supply  of  oxygen  is  maintained,  resembles 
rather  the  action  of  a  narcotic  poison  than  it  does  asphyxia. 

Then,  again,  we  must  carefully  distinguish  the  asphyxiating  effect  of  an 
insufficient  supply  of  oxygen  from  the  directly  poisonous  action  of  such  a  gas  as 
carbonic  oxide,  which  is  contained  to  a  considerable  amount  in  common  coal-gas. 
The  fatal  effects  often  produced  by  this  gas  (as  in  accidents  from  burning  charcoal 
stoves  in  small,  close  rooms)  are  due  to  its  entering  into  combination  with  the 
haemoglobin  of  the  blood-corpuscles,  and  thus  expelling  the  oxygen.  Haldane  has 
shown  that  animals  c-an  live  in  a  pressure  of  two  atmospheres  of  oxygen  after  all 
the  haemoglobin  is  taken  up  by  carbonic  oxide,  for  then  sufficient  oxygen  is 
dissolved  in  the  blood  plasma.  Hydrogen  may  take  the  place  of  nitrogen  if  the 
oxygen  is  in  the  usual  proportion,  with  no  marked  ill  effect.  Sulphuretted 
hydrogen  interferes  with  the  oxygenation  of  blood.  Nitrous  oxide  acts  directly 
on  the  nervous  system  as  a  narcotic.  Certain  gases,  such  as  carbon  dioxide  in 
more  than  a  certain  proportion  ;  sulphurous  and  other  acid  gases,  ammonia, 
and  chlorine  produce  spasmodic  closure  of  the  glottis,  and  are  irrespirable. 

Alterations  in  the  Atmospheric  Pressure. 

The  normal  condition  of  breathing  is  that  the  oxygen  of  the  air  breathed  should 
be  at  the  pressure  of  4,  of  the  atmosphere,  viz. ,  i  of  760  mm.  of  mercury,  or  1.52  mm. , 
but  considerable  variations  liiay  occur  without  producing  ill  effects.  This  is  due  to 
the  fact  that  the  blood  gases  are  mostly  in  a  state  of  chemical  combination,  not  of 
simple  solution.  Variations  beyond  certain  limits  are,  however,  fatal.  When  the 
tension  of  oxygen  exceeds  3i  atmospheres  {i.e.,  in  air  at  a  pressure  of  17  atmos- 
pheres), slow  but  powerful  poisonous  (narcotic)  effects  are  produced  on  all  living 
matter.  (Bert.)  'I'he  excised  sartorius  is  paralysed  by  about  half  an  hour's  exposure 
to  80  atmospheres  of  oxygen  ;  and  the  excised  frog's  heart  ceases  to  beat  in  about 
two  hours  under  the  same  conditions.  It  is  dangerous  for  men  to  work  in  caissons 
where  the  atmospheric  pressure  is  greater  than  4  atmospheres.  Even  lower 
pressures  may  be  followed  on  "  decompression  "  {I.e.,  on  coming  out  of  the  increased 
pressure),  by  what  are  called  "bends,"  that  is,  pains  in  the  joints  and  muscles,  by 
paralysis,  and  auditory  symptoms  such  as  deafness  and  vertigo.  The  cause  of 
such  symptoms  is  the  setting  free  of  bubbles  of  nitrogen  in  the  lymph  spaces 
and  capillaries  ;  any  oxygen  set  free  is  rapidly  re-absorbed  by  the  blood.  Capillary 
embolism  from  gas  bubbles  in  the  central  nervous  system  is  the  main  L-ause  of 
the  paralysis.  (Bert.)  Prolonged  exposure  to  even  two  atmospheres  of  oxygen  is 
followed  by  pneumonia  (Lorrain  Smith),  and  so  oxygen  poisoning  may  be  a 
secondary  cause  of  the  symptoms.  Short  shifts  are  essential  for  caisson  workers, 
for  then  the  body  has  not  time  to  become  saturated  with  gas  at  the  caisson 
pressure.     Decompression  must  also  be  gradual  and  slow. 

A  toad  was  but  slightly  effected  by  5  minutes'  exposure  to  20  atmospheres  of 
oxygen,  but  after  40  minutes  on  "  decompression  "  it  went  into  tetanic  convulsions 
and  died  ;  the  heart  was  distended  with  frothed  blood  ;  bubbles  of  gas  were  in  all 
the  lymph  spaces,  in  the  anterior  chamber  of  the  eye,  and  other  parts.  A  mouse 
in  a  similar  high  pressure  is  narcotised,  and  on  "  decompression  "  convulsions  and 
death  ensue.  (L.  Hill.)  Mechanical  pressure  by  itself  has  little  or  no  influence  ; 
thus  frog's  muscle  is  not  injured  by  exposure  to  fluid  pressure  in  salt  solution  equal 


374 


RESPIRATION 


[CH.  XXIV. 


to  400  atmospheres.     Crustacea  are  found  alive  on  marine  telegraph  cables  at  a 
depth  where  the  pressure  is  as  great. 

Turning  now  to  diminution  of  pressure,  we  find  that  "  mountain  sickness  "  occurs 
at  the  height  of  4800  metres,  the  summit  of  Mt.  Blanc.  Here  the  pressure  of  oxygen 
is  only  1 1  '5'j  per  cent,  of  an  atmosi)here.  The  inalady  is  increased  by  muscular  effort, 
and  is  due  to  want  of  oxygen.  In  those  who  habitually  live  in  high  altitudes, 
the  number  of  red  blood-corpuscles  is  increased.  Croce-SpineUi,  the  balloonist, 
perished  at  an  altitude  of  8600  metres,  where  the  tension  of  oxygen  would  be  7 
percent,  of  an  atraosjjhere.  His  companion  Tissandier  recovered.  In  such  cases 
muscular  paralysis  occurs  before  loss  of  consciousness.  Higher  asc-ents  could  be 
made  by  aeronauts  if  they  breathed  oxygen  from  a  gas  cylinder.     (Bert.) 


Chemistry  of  Eespikation. 

The  intake  of  oxygen  is  the  commencement,  and  the  output  of 
carbonic  acid  is  the  end  of  the  series  of  changes  known  as  respiration. 
The  gaseous  interchange  in  the  lungs  is  called  external  respiration. 
The  actual  combustion  processes  take  place  all  over  the  body,  and 
constitute  what  is  known  as  internal  or  tissue-resjnration.  The 
oxygen  which  goes  into  the  blood  is  held  there  in  loose  combination 
as  oxyhpemoglobin.  In  the  tissues  this  substance  parts  with  its 
respiratory  oxygen.  The  oxygen  does  not  necessarily  undergo 
immediate  union  with  carbon  to  form  carbonic  acid,  and  with 
hydrogen  to  form  water,  but,  as  in  muscle  (see  p.  149),  is  held  in 
reserve  by  the  tissue  itself.  Of  the  ultimate  products,  the  carbonic 
acid  and  a  portion  of  the  water  find  an  outlet  by  the  lungs. 

Inspired  and  Expired  Air. — The  composition  of  the  inspired  or 
atmospheric  air  and  the  expired  air  may  be  compared  in  the  following 
table : — 


Inspired  air. 


Expired  air. 


Oxygen  . 

Nitrogen 
Carbonic  acid 
Watery  vapour 
Temperature  . 


20-96  vols,  per  cent.     16 'OS  vols,  per  cent. 
79  „  „  79 

0-04      „  „  4-4 

variable  saturated 

thatof  body  (37-C.) 


The  nitrogen  remains  unchanged.  The  recently  discovered  gases 
argon,  crypton,  etc.,  are  in  the  above  table  reckoned  in  with  the 
nitrogen.  They  are,  however,  only  present  in  minute  quantities.  The 
chief  change  is  in  the  proportion  of  oxygen  and  carbonic  acid.  The 
loss  of  oxygen  is  about  5,  the  gain  in  carbonic  acid  about  4'5.  If  the 
inspired  and  expired  airs  are  carefully  measured  at  the  same  tempera- 
ture and  barometric  pressure,  the  volume  of  expired  air  is  thus  found 
to  be  rather  less  than  that  of  the  inspired.*  The  conversion  of 
oxygen  into  carbonic  acid  would  not  cause  any  change  in  the  volume 

*  This  diminution  of  volume  will  cause  a  slight  rise  in  the  proportionate  volume 
of  nitrogen  per  cent. 


C».  XXIV.] 


COMPOSITION    OF   THE    AIR 


375 


of  the  gas  ;  for  a  molecule  of  oxygen  (0.,)  would  give  rise  to  a  molecule 
of  carbonic  acid  (CO.,)  which  would  occupy  the  same  volume  (Avo- 
gadro's  law).  It  must,  however,  be  remembered  that  carbon  is  not 
the  only  element  which  is  oxidised.  Fat  and  proteid  contain  a 
number  of  atoms  of  hydrogen,  which,  during  metabolism,  are  oxidised 
to  form  water  ;  a  small  amount  of  oxygen  is  also  used  in  the  formation 
of  urea.  Carbohydrates  contain  sufficient  oxygen  in  their  own  mole- 
cules to  oxidise  their  hydrogen ;  hence  the  apparent  loss  of  oxygen  is 
least  when  a  vegetable  diet  (that  is,  one  consisting  largely  of  starch 
and  other  carbohydrates)  is  taken,  and  greatest  when  much  fat  and 

proteid  are  eaten.     The  quotient   ^  "  ^     ,    ,    is  called  the  respiratory 

4-5 
quotient.     Normally  it  is  ^  =  09,  but  it  varies  considerably  with  diet 

o 

as  just  stated. 

The  amount  of  respiratory  interchange  of  gases  is  estimated  by 
enclosing  an  animal  in  an  air-tight  chamber,  except  that  there  is  a 
tube  entering  and  another  leaving  it ;  by  one  tube  oxygen  or  air  can 
enter,  and  is  measured  by  a  gas-meter  as  it  passes  in.  The  air  is 
drawn  through  the  chamber,  and  leaves  it  by  the  other  tube ;  this  air 
has  been  altered  by  the  respiration  of  the  animal,  and  in  it  the  car- 
bonic acid  and  water  are  estimated  ;  it  is  drawn  into  bottles  containing 
a  known  amount  of  an  alkali ;  this  combines  with  the  carbonic  acid 
and  is  increased  in  weight :  the  increase  in  weight  gives  the  amount 
of  carbonic  acid ;  the  alkali  used  in  Eegnault  and  Eeiset's  apparatus 
was  potash;  Pettenkofer  used  baryta  water;  Haldane  recommends 
soda-lime.  The  water  is  estimated  in  bottles  containing  pumice 
moistened  with  sulphuric  acid. 

The  accompanying  drawing  (fig.  335)  shows  the  essential  part  of 


Fig.  335.— Haldane's  apparatus  for  estimating  the  carbonic  acid  and  aqueous  vapour  given  ofl  by  an 

animal. 

the  simple  but  effective  apparatus  used  by  Haldane.  The  animal  is 
placed  in  the  vessel  a  ;  air  is  sucked  through  the  apparatus  (which 
must  be  perfectly  air-tight)  by  a  water  pump  at  a  suitable  rate.  The 
arrows  indicate  the  direction  in  which  the  air  passes.  It  goes  first 
through  two  Woulff s  bottles,  1  and  2.  No.  1  contains  soda-lime, 
which  frees  the  air  from  carbonic  acid ;  No.  2  contains  pumice-stone 


376  KESPIRATION  [CH.  XXIV. 

moistened  with  sulphuric  acid,  which  frees  the  air  from  aqueous 
vapour.  The  air  next  reaches  the  animal  chamber,  and  the  animal 
gives  off  to  it  carbonic  acid  and  aqueous  vapour.  It  passes  then 
through  the  three  bottles,  3,  4,  and  5.  No.  3  contains  pumice  and 
sulphuric  acid,  which  removes  the  water ;  No.  4  contains  soda-lime, 
which  absorbs  the  carbonic  acid ;  and  No.  5  contains  pumice  and  sul- 
phuric acid,  which  absorbs  any  water  carried  over  from  bottle  4.  The 
increase  of  weight  in  bottle  3  at  the  end  of  a  given  time  (e.g.,  an  hour) 
is  the  weight  of  water  given  off  by  the  animal  in  that  time ;  the  in- 
crease of  weight  in  bottles  4  and  5  weighed  together  gives  the  amount 
of  carbonic  acid  produced  by  the  animal  in  the  same  time. 

Eanke  gives  the  following  numbers  from  experiments  made  on  a 
man,  who  was  taking  a  mixed  diet  consisting  of  100  grammes  of 
protein,  100  of  fat,  and  250  of  carbohydrate  in  the  twenty-four  hours. 
The  amount  of  oxygen  absorbed  in  the  same  time  was  666  grammes; 
of  which  560  passed  off  as  carbonic  acid,  9  in  urea,  19  as  water 
formed  from  the  hydrogen  of  the  protein,  and  78  from  that  of  the  fat. 

Vierordt  from  a  number  of  experiments  on  human  beings  gives  the 
following  average  numbers :  the  amount  of  oxygen  absorbed  in  the 
twenty-four  hours,  744  grammes ;  this  leads  to  the  formation  of  900 
grammes  of  carbonic  acid  (this  contains  about  half  a  pound  of  carbon) 
and  360  grammes  of  water. 

The  respiratory  interchange  is  lessened  during  sleep.  It  is  especi- 
ally small  in  the  winter  sleep  of  hibernating  animals.  During  hiber- 
nation the  respiratory  quotient  sinks  to  0'5,  so  that  the  animals 
actually  gain  weight  from  retention  of  oxygen. 

Circumstances  affecting  the  amount  of  carbonic  acid  e.vcreted.  (a)  Affe  and  se.r. 
In  males  the  quantity  increases  with  growth  till  the  age  of  30  ;  at  50  it  begins  to 
diminish  again.  In  females  the  decrease  begins  when  menstruation  ceases.  In 
females  the  quantity  exhaled  is  always  less  than  in  males  of  the  same  age. 

(b)  Respirator//  movemt^iifs. — The  quic-ker  the  respiration  the  smaller  is  the  pro- 
portionate quantity  of  carbonic  acid  in  each  volume  of  expired  air.  The  total 
quantity  is,  however,  increased,  not  because  more  is  formed  in  the  tissues,  but 
more  is  got  rid  of.  The  last  portion  of  the  expired  air  which  comes  from  the  more 
remote  parts  of  the  lungs  is  the  richest  in  carbonic  acid. 

(c)  E.i'tern(d  temperature. — In  cold-blooded  animals,  a  rise  in  the  external 
temperature  causes  a  rise  in  their  body  temperature,  accompanied  with  increased 
chemical  changes,  including  the  formation  of  a  larger  amount  of  carbonic  acid.  In 
warm-blooded  animals,  it  is  just  the  reverse  ;  in  cold  weather  the  body  temperature 
has  to  be  kept  at  the  normal  level,  and  so  increased  combustion  is  necessary. 

(d)  Food. — This  produces  an  increase  which  usually  comes  on  about  an  hour 
after  a  meal. 

(e)  E.cercise. — Moderate  exercise  causes  an  increase  of  about  30  to  40  per  cent, 
in  the  amount  excreted.     With  excessive  work,  the  increase  is  still  greater. 

Diffusion  of  Gases  within  the  Lungs. — If  two  chambers  con- 
taining a  mixture  of  gases  in  unequal  amount  are  connected  together, 
a  slow  movement  called  diffusion  takes  place  until  the  percentage 
amount  of  each  gas  in  each  chamber  is  the  same.     Let  us  suppose 


CH.  XXIV.]  GASES    OF   THE    BLOOD  377 

that  one  chamber  contains  a  large  quantity  of  oxygen  and  a  small 
quantity  of  carbonic  acid ;  and  the  other  a  small  quantity  of  oxygen 
and  a  large  quantity  of  carbonic  acid ;  the  oxygen  moves  from  the 
first  to  the  second,  and  the  carbonic  acid  from  the  second  to  the  first 
chamber.  The  pressure  of  a  gas  is  proportional  to  the  percentage 
amount  in  which  it  is  present  in  a  mixture.  This  is  true  for  each  gas 
in  a  mixture,  the  presence  of  the  others  making  no  difference. 

In  the  atmosphere,  for  instance,  the  total  barometric  pressure  is 
760  mm.  of  mercury ;  the  amount  of  oxygen  in  the  air  is  roughly  one- 
fifth,  and  the  pressure  it  exercises  is  also  one-fifth  of  760 ;  the  nitro- 
gen accounts  for  the  other  four-fifths.  The  carbonic  acid  is  present 
in  such  small  quantities  that  the  pressure  it  exercises  is  only  a  frac- 
tion of  a  millimetre. 

In  the  alveolar  air  the  carbonic  acid  is  present  in  larger  and  the 
oxygen  in  smaller  amount ;  and  in  the  intermediate  air  passages  there 
is  an  intermediate  condition :  hence,  as  in  the  two  chambers  we  first 
considered,  oxygen  diffuses  down  to  the  air  vesicles,  and  carbonic  acid 
from  them  (see  p.  363  for  Haldane's  method  of  obtaining  the  composi- 
tion of  alveolar  air).  These  movements  are,  however,  by  themselves 
too  slow  to  be  efficient,  and  are  assisted  by  the  large  draughts  which 
are  created  in  the  respiratory  tract  by  the  respiratory  movements  of 
the  chest. 

Gases  of  the  Blood. — From  100  volumes  of  blood,  about  60 
volumes  of  gas  can  be  removed  by  the  mercurial  air-pump.  The 
average  composition  of  this  gas  in  dog's  blood  is : — 

Venous  blood. 

8  to  12 

1  to  2 

46 

The  nitrogen  in  the  blood  is  simply  dissolved  from  the  air  just  as 
water  would  dissolve  it ;  it  has  no  physiological  importance.  The 
other  two  gases  are  present  in  much  greater  amount  than  can  be 
explained  by  simple  solution ;  they  are,  in  fact,  chiefly  present  in 
loose  chemical  combinations.  Less  than  one  volume  of  the  oxygen  and 
about  two  of  carbonic  acid  are  present  in  simple  solution  in  the  plasma. 

Oxygen  in  the  Blood. — The  weight  of  gas  dissolved  in  a  liquid 
varies  with  the  pressure  of  the  gas;  double  the  pressure  and  the 
weight  of  gas  dissolved  is  doubled.  The  oxygen  of  the  blood 
does  not  vary  directly  with  oxygen  pressure,  for  the  amount  of 
that  gas  in  simple  solution  forms  only  a  small  fraction  of  the  total 
present.  This  small  amount  is  of  course  doubled  by  doubling  the 
pressure,  but  such  an  increase  is  insignificant,  the  bulk  of  the 
oxygen  being  in  chemical  union  with  hfemoglobin.  The  oxygen  of 
oxyhsemoglobin  can  be  replaced  by  equivalent  quantities  of  other 
gases    like    carbonic    oxide       The    tension   or   partial    pressure   of 


Arterial  blood. 

Oxygen . 

20 

Nitrogen 

1  to  2 

Carbonic  acid 

40 

378  KESPIEATION  [CH.  XXIV. 

oxygen  in  the  air  of  the  alveoli  is  less  than  that  in  the  atmosphere, 
but  greater  than  that  in  venous  blood ;  hence  oxygen  passes  from  the 
alveolar  air  into  the  blood  plasma ;  the  oxygen  immediately  combines 
with  the  hsemoglobin,  and  thus  leaves  the  plasma  free  to  absorb  more 
oxygen ;  and  this  goes  on  until  the  haemoglobin  is  entirely,  or  almost 
entirely,  saturated  with  oxygen.  The  reverse  change  occurs  in  the 
tissues  when  the  partial  pressure  of  oxygen  is  lower  than  in  the 
plasma,  or  in  the  lymph  that  bathes  the  tissue  elements ;  the  plasma 
parts  with  its  oxygen  to  the  lymph,  the  lymph  to  the  tissues ;  the 
oxyhsemoglobin  then  undergoes  dissociation  to  supply  more  oxygen  to 
the  plasma  and  lymph,  and  thus  in  turn  to  the  tissues  once  more. 
This  goes  on  until  the  oxyhsemoglobin  loses  a  great  portion  of  its 
store  of  oxygen,  but  even  in  asphyxia  it  does  not  lose  all. 

The  following  values  give  the  tension  of  oxygen  in  percentages 
of  an  atmosphere : — 

External  air 20 '96  >^ 

Alveolar  air 13  to  16  ^ 

"Arterial  blood 14  } 

Tissues 0  ^ 

The  arrow  shows  the  direction  in  which  the  gas  passes. 

When  the  gases  are  being  pumped  off  from  the  blood,  very  little 
oxygen  comes  off  till  the  pressure  has  been  greatly  reduced,  and  then, 
at  a  certain  point,  it  is  disengaged  at  a  burst.  This  shows  that  it 
is  not  in  simple  solution,  but  is  united  chemically  to  some  constituent 
of  the  blood,  which  is  suddenly  dissociated  at  the  redviced  pressure. 
This  constituent  of  the  blood  is  haemoglobin. 

The  ability  of  the  tissues  to  form  reduction  products  is  shown  by 
Ehrlich's  experiments  with  methylene  blue  and  similar  pigments. 
Methylene  blue  is  more  stable  than  oxyhsemoglobin ;  but  if  it  is 
injected  into  the  circulation  of  a  living  animal,  and  the  animal  killed 
a  few  minutes  later,  the  blood  is  found  to  be  dark  blue,  but  the  organs 
(especially  those  which  like  glandular  organs  are  in  a  state  of  activity) 
are  colourless.  On  exposure  to  oxygen  the  organs  become  blue.  In 
other  words,  the  tissues  have  formed  a  colourless  reduction  product 
from  the  methylene  blue,  and  on  exposure  to  air  or  oxygen  this  is 
oxidised  and  the  blue  pigment  is  thus  regenerated. 

Carbonic  Acid  in  the  Blood — What  has  been  said  for  oxygen 
holds  good  in  the  reverse  direction  for  carbonic  acid.  Compounds  are 
formed  in  the  tissues  where  the  tension  of  the  gas  is  high :  these  pass 
into  the  lymph,  then  into  the  blood,  and  in  the  lungs  they  undergo 
dissociation,  carbonic  acid  passing  into  the  alveolar  air,  where  the 
tension  of  the  gas  is  comparati\'ely  low,  though  it  is  greater 
here  than   in   the  expired   air.      If   blood   is   divided   into   plasma 

*  For  more  recent  estimations  of  oxygen  tension  in  arterial  blood,  see  p.  384. 


CH.  XXIV.]  CARBONIC    ACID    IN    THE    BLOOD  379 

and  corpuscles,  it  will  bo  found  that  both  yield  carbonic  acid,  but  the 
yield  from  the  plasma  is  the  greater.  If  we  place  blood  in  a  vacuum 
it  l)ubbles,  and  gives  out  all  its  gases;  addition  of  a  weak  acid  causes 
no  further  liberation  of  carbonic  acid.  When  plasma  or  serum  is 
similarly  treated  the  gas  also  comes  off,  but  about  5  per  cent,  of  the 
carbonic  acid  is  fixed — that  is,  it  requires  the  addition  of  some  stronger 
acid,  like  phosphoric  acid,  to  displace  it.  Fresh  red  corpuscles  will, 
however,  take  the  place  of  the  phosphoric  acid,  and  thus  it  has  been 
surmised  that  oxyhaemoglobin  has  the  properties  of  an  acid. 

One  hundred  volumes  of  venous  blood  contain  forty-six  volumes 
of  carbonic  acid.  Whether  this  is  in  solution  or  in  chemical  combina- 
tion is  determined  by  ascertaining  the  tension  of  the  gas  in  the  blood. 
One  hundred  volumes  of  blood  plasma  would  dissolve  more  than  an 
equal  volume  of  the  gas  from  an  atmosphere  of  carbonic  acid,  if  its  solu- 
bility in  plasma  were  equal  to  that  in  water.  If,  then,  the  carbonic  acid 
were  in  a  state  of  solution,  its  tension  would  be  very  high,  but  it  proves 
to  be  only  equal  to  about  5  per  cent,  of  an  atmosphere.  This  means 
that  when  venous  blood  is  brought  into  an  atmosphere  containing  5  per 
cent,  of  carbonic  acid,  the  blood  neither  gives  off  any  carbonic  acid 
nor  takes  up  any  from  that  atmosphere.  Hence  the  remainder  of  the 
gas,  95  per  cent.,  is  in  a  condition  of  chemical  combination.  The 
chief  compound  appears  to  be  sodium  bicarbonate. 

The  carbonic  acid  and  phosphoric  acid  of  the  blood  are  in  a  state 
of  constant  struggle  for  the  possession  of  the  sodium.  The  salts 
formed  by  these  two  acids  depend  on  their  relative  masses.  If 
carbonic  acid  is  in  excess,  we  get  sodium  carbonate  (ISra.jCOg),  and 
mono-sodium  phosphate  (NaH.,P04);  but  if  the  carbonic  acid  is 
diminished,  the  phosphoric  acid"  obtains  the  greater  share  of  sodium 
to  form  disodium  phosphate  (Na2HP04).  In  this  way,  as  soon  as  the 
amount  of  free  carbonic  acid  diminishes,  as  in  the  lungs,  the  amount 
of  carbonic  acid  in  combination  also  decreases ;  whereas  in  the  tissues, 
where  the  tension  of  the  gas  is  highest,  a  large  amount  is  taken  up 
into  the  blood,  where  it  forms  carbonates. 

The  tension  of  the  carbonic  acid  in  the  tissues  is  high,  but  one 
cannot  give  exact  figures ;  we  can  measure  the  tension  of  the  gas  in 
certain  secretions :  in  the  urine  it  is  9,  in  the  bile  7  per  cent.  The 
tension  in  the  cells  themselves  must  be  higher  still. 

The  following  figures  (from  Fredericq)  give  the  tension  of  carbonic 
dioxide  in  percentages  of  an  atmosphere : — 

Tissues 5  to  9     "I 

Venous  blood 3 '8  to  5*4  V  in  dog. 

Alveolar  air 2  -8       j 

External  air       .......  0  '04 

The  arrow  indicates  the  direction  in  which  the  gas  passes,  namely, 
in  the  direction  of  pressure  from  the  tissues  to  the  atmosphere. 


380  RESPIRATION  [CH.  XXIV. 

In  some  other  experiments,  also  on  dogs,  the  following  are  the 
figures  given : — 

Arterial  blood 2*8     ^ 

Venous  blood 5*4    y 

Alveolar  air S'5Q   ] 

Expired  air 2'8     » 

It  will  be  seen  from  these  figures  that  the  tension  of  carbonic  acid 
in  the  venous  blood  (5-4)  is  higher  than  in  the  alveolar  air  (3-56) ;  its 
passage  into  the  alveolar  air  is  therefore  intelligible  by  the  laws  of 
diffusion.  Diffusion,  however,  should  cease  when  the  tension  of  the 
gas  in  the  blood  and  alveolar  air  are  equal.  But  the  transference  goes 
beyond  the  establishment  of  such  an  equililjrium,  for  the  tension  of 
the  gas  in  the  blood  continues  to  sink  until  it  is  ultimately  less  (2-8) 
than  in  the  alveolar  air. 

The  whole  question  is  beset  with  great  difficulties  and  contradic- 
tions. Analyses  by  different  observers  have  given  very  different 
results,  but  if  such  figures  as  those  just  quoted  are  ultimately  found 
to  be  correct,  we  can  only  explain  this  apparent  reversal  of  a  law  of 
nature  by  supposing  with  Bohr  that  the  alveolar  epithehum  possesses 
the  power  of  excreting  carbonic  acid,  just  as  the  cells  of  secreting 
glands  are  able  to  select  certain  materials  from  the  blood  and  reject 
others.  Eecent  work  by  Bohr  and  Haldane  has  also  shown  that  in 
all  probability  the  same  explanation — epithelial  activity — must  be 
called  in  to  account  for  the  absorption  of  oxygen.  In  the  swim- 
bladder  of  fishes  (which  is  analogous  to  the  lungs  of  mammals)  the 
oxygen  is  certainly  far  in  excess  of  anything  that  can  be  explained  by 
mere  diffusion.  The  storage  of  oxygen,  moreover,  ceases  when  the 
vagus  nerves  which  supply  the  swim-bladder  are  divided. 

Tension  of  Gases  in  Fluids. — This  expression  so  frequently  used 
in  the  foregoing  paragraphs  demands  further  explanation. 

The  first  questions  which  arise  are,  "  Under  what  circumstances 
will  a  gas  dissolved  in  a  fluid  diffuse  out  of  the  fluid  into  the  air  in 
contact  with  it  ? "  and,  "  Under  what  circumstances  will  a  gas  diffuse 
out  of  the  air  into  the  fluid,  and  at  what  rate  will  it  do  so  ? " 

These  are  questions  which  depend  upon  the  physical  constants  of 
the  fluid  and  of  the  atmosphere;  these  constants  must  be  deter- 
mined experimentally. 

The  following  instance  may  be  taken — 100  c.c.  of  water  charged 
with  80  c.c.  of  carbonic  acid  may  be  shaken  with  pure  air  in  a 
closed  bottle  of  500  c.c.  capacity  at  room  temperature  (say  14"  C). 
The  carbonic  acid  will  come  out  of  the  water  at  first,  but  as  the 
shaking  continues,  the  carbonic  acid  will  come  out  more  and  more 
slowly  until  at  last  it  ceases  to  do  so.  Analysis  of  the  air  and  of 
the  water  in  the  bottle  would  show  that  the  water  had  not  parted 
with   aU   its   carbonic   acid.     It   would   be   found   that   the   water 


CH.  XXIV.] 


TENSION   OF   GASES    IN    FLUIDS 


381 


contained  16  c.c.  of  carbonic  acid  dissolved  in  it  whilst  64  c.e.  had 
diffused  out  into  the  air. 

At  the  end  of  this  experiment,  then,  there  will  bo  in  the 
air  in  the  bottle  64  c.c.  of  carbonic  acid  in  a  space  of  400  c.c.  If 
the  whole  space  (400  c.c.)  were  filled  with  carbonic  acid,  its  pres- 
sure would  bo  760  mm.  of  mercury.     The  partial  pressure  of  car- 

64 
bonic  acid  in  the  air  of  the  bottle  is  therefore  760  X  ^tttt.  =  122  mm. 

400 

of  mercury.     Water,  therefore,  containing  16  volumes  per  cent,  of 

carbonic  acid  is  in  equilibrium  with  an  atmosphere  in  which  the 

carbonic  acid  exerts  a  pressure  of    122  mm.      This  fact  is  stated 

shortly  by  the  phrase,  "When  water  has  a  carbonic  acid  tension  of 

122  mm.  it  contains  16  per  cent,  of  carbonic  acid." 

The  amount  of  carbonic  acid  which  would  be  contained  in  any 
other  fluid  when  it  was  in  equilibrium  with  an  atmosphere  having  a 
carbonic  acid  pressure  of  122  mm.  would  be  different  from  that 
contained  in  water;  for  instance,  alcohol  would  contain  50  per  cent, 
of  the  gas. 

In  both  fluids  the  tension  of  carbonic  acid  is  the  same,  but  the 
quantities  of  carbonic  acid  would  be  as  stated  and  therefore  different. 

The  tension  of  a  gas  in  a  liquid,  therefore,  is  the  pressure  of  that 
gas  in  an  atmosphere  of  such  a  composition  that  the  liquid  would 
neither  acquire  that  gas  from  the  atmosphere  nor  impart  that  gas  to 
it,  if  the  liquid  and  the  atmosphere  were  brought  into  intimate 
contact,  as  by  shaking. 

Measurement  of  tension  in  Jluids — aerotonometer. — The  measure- 
ment of  the  tension  of  gases  in  fluids  is  conducted  upon  the 
principles  of  the  example  just  given.  The 
instrument  for  the  purpose  is  called  an 
aerotonometer.  The  form  used  by  Loewy 
consists  simply  of  a  closed  bottle  (fig.  336) 
into  which  the  blood  and  the  air  can  be 
put  and  from  which  they  can  be  withdrawn 
by  suitable  means.  Through  the  stopper  of 
the  bottle  three  tubes  pass,  A,  B,  and  C, 
each  of  which  is  provided  with  a  piece  of 
rubber  tubing  and  a  clip.  The  tube  A 
is  used  for  introducing  or  expelling  the 
blood  E ;  C  is  used  for  introducing  or 
expelling  the  air;  B  is  connected  with  a 
flexible  rubber  bag  D  containing  water  inside 
the  bottle,  whilst  outside  a  connection  can 
be  made  with  a  syringe.     A  little  mercury 

should  be  put  into  the  bottle  to  defibrinate  the  blood.     To  determine 
the  carbonic  acid  tension  in  blood,  several  bottles  should  be  filled 


Fio.  336. — Diagram  of  Loewy's 
aerotonometer. 


382  irESPiRATioN  [en.  xxrv. 

with  gases  nf  known  composition  from  gasometers  before  the  experi- 
ment. Into  each  bottle  some  blood  is  drawn  from  the  animal.  This 
is  done  by  attaching  A  to  a  cannula  in  one  of  the  animal's  blood- 
vessels, and  then  when  water  is  withdrawn  from  the  bag  D  by  the 
syringe,  a  corresponding  amount  of  blood  enters  the  aerotonometer. 
Each  bottle  is  so  treated,  and  the  bottle  is  shaken  vigorously  for  some 
time.  When  equilibrium  has  been  established,  the  au-  can  be  taken 
from  the  air  space  F  by  attaching  C  to  an  air-analysis  apparatus  and 
forcing  water  into  the  bag  D  from  the  syringe  attached  to  B.  An 
example  may  illustrate  the  results  which  might  be  obtained. 

Determination  of  carbonic  acid  tension  of  blood. 

Bottle  I.  II.  III.  IV.  V. 

Initial  percentage  of  1        ,,  ^  ,  _  ,  „  ,  _  . 

the  gas  present.      |       ^'^  ^  "  "^  ^'^  ^ 


Final  percentage  of  )^       ,.„  ^,.  .., 

gas  present.  J 


4-7  4-3 


From  the  above  figures  it  will  be  seen  that  the  blood  has  acquired 
carbonic  acid  from  the  air  in  bottles  I.  and  II.,  whilst  the  reverse  has 
taken  place  in  bottles  III.,  IV.,  and  V.  The  carbonic  acid  tension  of 
the  blood  is  therefore  between  5*4  and  5'1  per  cent. 

Relation  of  tension  to  cojnposition.-^^The  aerotonometer  may  be 
used  to  determine  the  relation  of  the  tension  of  a  gas  in  the  blood 
(oxygen  or  carbonic  acid)  to  the  quantity  contained  in  that  fluid. 
The  example  given  above  might  be  extended  for  this  purpose  in  the 
following  way.  After  the  air  has  been  withdrawn  for  analysis,  it  is 
only  necessary  to  attach  A  to  the  blood-bulb  on  a  mercurial  blood-gas 
pump  and,  by  forcing  more  water  into  B,  expel  a  sufficient  quantity 
of  blood  for  analysis.  If  an  analysis  was  made  for  each  of  the  bottles, 
the  quantity  of  carbonic  acid  would  be  determined  corresponding  to 
the  tensions  5"8,  5'4,  5"1,  4"7,  and  4'3  per  cent,  respectively. 

The  comparison  of  the  quantity  of  carbonic  acid  in  the  blood  with 
its  tension  is  not  of  importance,  but  the  corresponding  measurements 
for  oxygen  have  been  carried  out  with  great  care  by  a  number  of 
observers,  both  for  blood  and  for  solutions  of  haemoglobin. 

It  is  found  that  the  two  sets  of  observations  agree  very  closely, 
and  this  fact  forms  the  most  substantial  evidence  for  our  belief  that 
the  oxygen  in  the  blood  is  almost  entirely  associated  with  the  haemo- 
globin. 

The  relation  of  the  quantity  of  oxygen  in  the  blood  to  the  tension 
which  it  exerts  may  be  conveniently  set  forth  in  a  curve  which  is 
called  the  dissociation  curve  of  oxyhaemoglobin,  as  in  the  following 
figure  (fig.  337). 

An  example  may  illustrate  the  use  to  which  the  information, 
given   in   this   curve,  may   be   put.     Suppose   that   one   wishes    to 


en.  xxTV.] 


TENSION   OF   GASES    IN    BLOOD 


383 


determine  the  tension  of  oxygen  in  the  blood  leaving  the  pancreas. 
The  amount  of  blood  which  comes  from  that  organ  is  too  small  to 
allow  of  a  direct  determination  being  made.  We  can,  however, 
calculate  it  from  the  following  data:  (1)  the  amount  of  oxygen 
which  the  blood  would  contain  if  saturated  (this  can  be  arrived  at  by 


100 
90 
80 

B^ 

r" 

— ' 

^ 

-— 

^^^ 

/ 

H^ 

l^ 

70 

/■ 

/ 

L^ 

/ 

/ 

sn 

1/ 

/ 

49 
40 

30 
20 
10 

// 

'. 

7 

k 

r     ' 

■ 

10  '    20    30    40     50    60    70 
14 


80     90     100    no    120    130    140    150 


Fio.  337. — Dissociation  curves  of  blood  (B)  and  of  a  solution  of  hiemoglobln  (H).  The  numbers  along 
the  base  line  represent  pressure  in  millimetres  of  mercury;  those  along  the  ordinate  represent 
percentages  of  oxygen.    (Atter  Bohr.) 

saturating  arterial  blood  and  analysing  it)  ;  (2)  the  amount  of  oxygen 

in  the  venous  blood.     In  an  actual  experiment  (1)  was  22'0  c.c,  (2) 

10-7 
was  10"7  c.c.     The  percentage  saturation  then  was  100x^^  =  49 

per  cent.  By  referring  to  the  dissociation  curve  (fig.  337)  we  see 
that  49  per  cent,  saturation  corresponds  to  an  oxygen  tension  of 
about  14  mm.  of  mercury  or  1"8  per  cent,  of  an  atmosphere. 

The  Carbonic  Oxide  Method  of  Estimating  the  Oxygen  Tension  of 
Arterial  Blood. — This  method  was  devised  by  Haldane,  and  is  considered  by  him 
and  Lorrain  Smith  to  give  more  trustworthy  results  than  those  obtained  by  the 
aerotonometer.  If  blood  is  exposed  to  a  mixture  of  carbonic  oxide  and  oxygen,  the 
haemoglobin  will  become  saturated  by  these  gases  according  to  their  relative 
tensions.  If  a  number  of  experiments  are  performed  using  different  percentages  of 
carbonic  oxide,  the  results  may  be  expressed  graphically  as  the  curve  of  dissociation 
of  carboxyhaemoglobin  in  air.  When  in  place  of  such  experiments  in  vitro,  an 
animal  is  made  to  breathe  air  containing  a  known  percentage  of  carbonic  oxide, 
the  comparison  of  the  saturation  of  its  blood  with  the  saturation  of  its  blood  in 
I'itro  exposed  to  the  same  percentage  of  carbonic  oxide  in  air  (which  has  an  oxygen 
tension  of  20*9  per  cent.)  gives  us  the  means  of  discovering  the  oxygen  tension  in 
the  arterial  blood  of  the  lung  capillaries  ;  this  wiU  be  higher  or  lower  than  that  of 
the  air  according  as  the  saturation  by  carbonic  oxide  is  correspondingly  lower  or 
higher.  A  small  animal  like  a  mouse  is  made  to  breathe  air  containing  a  known 
percentage  of  carbonic  oxide.  After  a  sufficient  time  the  animal  is  killed  and  the 
amount  of  carboxyhaemoglobin  is  determined  colorimetrically  in  a  drop  of  its  blood. 


384  RESPIEATION  [CH.  XXIV. 

The  (lata  thus  obtained  are  compared  with  the  data  previously  expressed  in  the 
curve  of  dissociation  of  carboxyhaemoglobin  in  air ;  it  is  then  easy  to  calculate 
whether  the  oxygen  tension  in  the  blood  is  higher  or  lower  than  that  of  air.  The 
results  of  the  method  show  generally  that  the  tension  of  oxygen  in  the  arterial 
blood  as  it  leaves  the  lungs  is  higher  than  could  result  from  simple  diifusion  of  the 
oxygen  through  the  alveolar  epithelium  ;  in  other  words,  the  epithelial  cells  are 
capable  of  secreting  oxygen  into  the  blood  until  an  oxygen-pressure  is  reached 
considerably  above  that  in  the  alveolar  air. 

The  results  expressed  in  percentages  of  an  atmosphere  are  as  follows  : — 
Oxygen  tension  of  arterial  blood  in  man,  3S'5  ;  in  mouse,  22'6  ;  in  dog,  21  ;  in 
cat,  -jd'o  ;  in  rabbit,  27 '6,  and  in  birds,  30  to  '>0  per  cent.  The  results  in  the  case 
of  man  and  larger  animals  probably  require  revision,  as  it  is  not  certain  that  the 
time  allowed  for  the  establishment  of  the  balance  of  carbonic  oxide  and  oxygen 
has  been  sufficient  in  any  of  the  experiments. 

Tissue  Respiration. — As  has  been  already  stated,  respiration 
may  be  divided  into  internal  or  tissue  respiration  and  external  or 
pulmonary  respiration.  External  respiration  is  much  the  less 
obscure,  and  we  have  treated  of  it  at  considerable  length,  not  only 
on  this  account,  but  also  on  account  of  the  very  frequent  impair- 
ments of  the  pulmonary  mechanism  which  are  met  with  in  disease. 
It  must  be  borne  in  mind,  however,  that  pulmonary  respiration  is 
but  the  means,  and  tissue  respiration  is  the  end.  Our  knowledge  of 
tissue  respiration  is  so  scanty  that  we  can  say  little  about  its 
pathological  bearing,  but  as  a  general  rule,  the  proneness  to  patho- 
logical change  as  well  as  the  vascularity  (p.  221)  is  connected  with 
the  degree  of  metabolism  of  the  tissue. 

The  following  are  the  amounts  of  oxygen  used  per  minute  by 
one  gramme  of  certain  epithelial  and  muscular  organs  respectively. 

Submaxillary  gland  0"0-i  c.c,  pancreas  O'Oo  c.c,  kidney  0"03  c.c, 
heart  (contracting  very  feebly  and  slowly)  0'007  c.c,  muscles  of  leg 
(with  spinal  cord  destroyed)  0"003  c.c. 

Methods  of  studying  tissue  respiration. — In  order  to  obtain  data, 
such  as  the  above,  it  is  necessary  (1)  to  analyse  the  blood  going  to 
the  organ ;  (2)  to  analyse  the  blood  emerging  from  the  organ ;  (3)  to 
determine  the  amount  of  blood  passing  through  the  organ  in  a  given 
time,  say  one  minute. 

The  analysis  of  blood  may  be  performed  by  either  of  two  methods  : 
(1)  the  mercurial  air-pump,  or  (2)  the  chemical  method  of  expelling 
the  oxygen  and  carbonic  acid  from  the  blood  by  means  of  potassium 
ferricyanide  and  phosphoric  acid  respectively. 

The  mercurial  air-pum}^. — The  extraction  of  the  gases  from  the 
blood  by  means  of  the  mercurial  air-pump  depends  upon  the  fact 
that  blood  yields  all  the  oxygen  and  carbonic  acid  which  are  dissolved 
in  it  when  it  is  boiled  for  a  sufficient  length  of  time  in  a  vacuum. 
The  instrument  consists  essentially  of  the  following  parts  (fig.  338): 
(1)  a  small  bulb  or  tube  for  measuring  accurately  the  amount  of 
blood  analysed ;  (2)  a  vacuous  chamber  or  froth  chamber.  When 
the  part  of  the  apparatus  from  2  to  4  is  rendered  a  vacuum,  the 


CM.  XXIV.] 


THE   MERCURIAL   Allt-PUMP 


385 


blood  is  emptied  from  1  into  2,  and  is  then  kept  continuously  boiling 
by  means  of  a  water-bath  (C) 


around  its  lower  portion ;  a 
condenser   (D)   packed  with 
ice   and    salt   surrounds    the 
upper  part.     There  is  always 
a  stream  of  aqueous  vapour 
carrying  the  boiled  out  gases 
to   the  top  of  the  chamber ; 
the  vapour  is  condensed  and 
returns  to  the  blood  as  drops 
of  water  running  down  the 
side    of  the   chamber,  while 
the  gases  are  free  to  go  into 
the  vacuous  pump.     In  doing 
so  they  pass  through  (3)  the 
drying    chamber    containing 
sulphuric  acid.     So  much  of 
the   gases   as   has   expanded 
into  the  pump  (4)  can  then 
be   expelled    by    lifting   the 
mercury  bottle  (A)  which  is 
connected   by  strong  rubber 
tubing  to  the  glass  tube  F. 
In  the  figure  only  the  attach- 
ments of  this  rubber  tube  are 
shown.     The  mercury  is  pre- 
vented by  a  valve  (V)  from 
going  backwards  to  the  dry- 
ing chamber;   it   expels  the 
gases  down  the  tube  B  into  a 
eudiometer  tube  E  in  which 
they  are  collected  for  measure- 
ment  and    analysis.      After 
boiling    for    a     considerable 
time,  a  few  exhaustions  with 
the   pump   are    sufficient   to 
deliver  all   the  gases  which 
have  been  boiled  off  from  the 
blood. 

The  total  gas  obtained  is 
first  measured  ;  then  the  car- 
bonic acid  is  removed  by 
caustic  potash,  and  the  gas 
that  remains  then  consists  of 


Fig.  338.— Mercurial  air-pump  for  obtaining  the  gases 
of  the  blood  (diagrammatic). 

2  B 


386 


RESPIKATION 


[CH.  XXIV. 


oxygen  and   nitrogen ;   the  oxygen  is  then  removed  hy  pyrogallic 
acid,  and  the  residual  gas  is  nitrogen. 

Chemical   metJiod   of  hlood  gas    analysis. — When   a   solution   of 
hemoglobin  is  treated  with  potassium  ferricyanide,  it  yields  all  its 

oxygen  to  the  air  on  shaking,  just  as 
urea  yields  its   nitrogen  when  treated 
with  sodium  hypobromite.     The  appa- 
ratus used  for  determining  the  oxygen 
in  blood  is  very  similar  to  a  Duprc's 
urea  apparatus  (see  Chapter  XXXVIL). 
The  blood  (5  c.c.)  is  placed  in  the  large 
bottle  (fig.  339,  A)  underneath  a  layer 
of   dilute  ammonia  solution  (B).     The 
blood   is   thus   protected   from  the  air 
whilst  the  apparatus  becomes  equal  in 
temperature  to  the  bath  in  which  it  is 
placed.     The  blood  is  shaken  with  the 
ammonia     solution     which     lakes     it 
thoroughly;    the   ferricyanide   solution 
is  then  spilt  into  the  laked  blood  from 
the  tube  C,  and  the  oxygen  is  shaken 
out  of  the  solution.     When  the  oxygen 
has    been    determined     the    bottle    is 
opened  and  phosphoric  acid  is  placed 
in   the   small   tube   C;    this   is  subse- 
quently spilt  into  the  mixture  of  blood, 
ammonia  and  ferricyanide ;  it  liberates 
the  carbonic  acid  which  is  also  shaken 
out   of   the   fluid.     The   carbonic   acid 
does  not  come  completely  out,  however, 
and  a  correction  has  to  be  introduced 
for  the  quantity  which  remains  in  solu- 
tion.     The    gas    (oxygen   or    carbonic 
acid,  as  the  case  may  be)  passes  over 
into  the  tube  D,  which  was  previously 
filled  up  to  the  zero  mark  with  water, 
and  connected   to  a  reservoir  F ;    this 
would  drive  water  out  of  F  into  the 
open  tube  E,  and  the  water  will  there- 
fore rise  in  E;   but  in  practice  it  is   convenient  to  keep    the  gas 
always   at   the   same   volume;   this   may   be   done   by   raising   the 
pressure  in  the  open  limb  (E)  of  the  pressure  gauge  by  squeezing 
some  of  the  water,  with  which  the  gauge  is  filled,  out  of  a  rubber 
reservoir  G  which  forms  the  base  of  the  gauge,  thus  the  level  of 
the  water  in  D  is  maintained  at  the  zero  mark,  while  that  in  E  rises 


-Apparatus  for  blood  gas 
analysis. 


CIl.  XXIV. J 


TISSUE    RESPIRATION 


887 


from  H  to  I.  The  ucLual  incasuioment  then  is  the  increase  of 
pressure  {i.e.,  the  height  of  the  column  of  water  HI)  which  is 
necessary  to  keep  the  gas  at  the  same  volume  after  the  oxygen  or 
carbonic  acid  has  been  shaken  off  as  it  previously  occupied.  From 
this  the  quantity  coming  off  can  be  calculated. 

The  chemical  method  is  not  quite  so  accurate  as  the  vacuum 
pump,  but  it  is  much  more  convenient  for  the  study  of  many 
problems,  as  it  requires  less  blood,  and,  owing  to  its  simplicity, 
a  great  number  of  observations  can  be  made  upon  a  single  animal. 

Changes  in  tissue  respiration  caused  hy  activity. — In  all  organs, 
so  far  as  is  known,  increased  activity  is  associated  with  increased 
tissue  respiration.  The  increase  is  commonly  three  to  six  fold.  It 
is  often  more  easy  to  demonstrate  the  augmented  oxygen  consump- 
tion than  the  augmented  output  of  carbonic  acid.  This  is  due  to 
several  causes : — {!)  carbonic  acid  is  soluble  in  the  tissues  in  which 
it  is  produced,  and  (2)  any  change  in  the  chemical  reaction  of  the 
tissues  alters  the  amount  of  carbonic  acid  which  they  give  out  to 
the  blood ;  if,  for  instance,  it  becomes  more  alkaline,  it  retains  a 
greater  portion  of  its  carbonic  acid. 

The  following  table  shows  the  variations  which  take  place  in  the 
oxygen  in-take  of  several  organs  of  chloroformed  animals  as  the 
result  of  activity,  produced  by  widely  different  forms  of  stimulus 
(Barcroft). 


Organ. 

Condition  of  Rest. 

Oxygen  used 
per  minute. 

j 
Condition  of          '    Oxygen  used 
Activity.            i     per  minute. 

! 

Mu.scle. 

Nerves  cut. 

0-003  C.C. 

Tonic       (nerves 
uncut). 

0-006  c.c. 
0-020  c.c. 

Heart. 

Very  slow  and 
feeble      con- 
tractions. 

0-007  C.C, 

Normal  contrac-       0-014 

tions. 
Very  active.               0-054 

Sub-maxillary 
gland. 

Nerves  cut. 

0-04  C.C. 

Chorda  stimula- 
tion. 

0-12  C.C. 

Pancreas. 
Kidney. 

Not  secreting. 

0-05  C.C. 

Secretion     after 
injection       of 
secretin. 

0-20 

Scanty  secretion. 

i 

0-03  C.C. 

After     injection 
of  diuretic. 

0-07  c.c. 

The  relation  of  the  oxygen  taken  in  to  the  carbonic  acid  given 


388 


EESPIEATION 


[CH.  XXIV. 


out  is  well  shown  in  the  following  experiment  performed  l:)y  Zuntz 
on  the  leg  of  a  dog. 


Blood-vessel. 

Gases  in  Blood 
per  cent. 

Remarks. 

Oxygen. 

Carbon- 
dioxide. 

Femoral  vein 
Carotid  artery 

1-2 
14-4 

36-32 
21-92 

Muscles  tonic  (nerves  uncut). 

Exchange      .... 

13-20 

14-4 

P'emoral  vein 
Carotid  artery 

Exchange      .... 

2-85       33-16 
13-30       23-06 

After    section    of   sciatic    and 
crural  nerves. 

10-45       10-1 

Two  points  must  be  noted  in  considering  the  above  table : — 

(1)  That  the  exchange  of  gases  was  decreased  on  cutting  the 

nerves.  The  decrease  in  metabolism  was  greater  even 
than  the  figures  show,  for  the  blood-flow  through  the 
leg  was  decreased. 

(2)  That  the  oxygen  exchange  and  the  carbonic  acid  exchange 

alter  in  about  the  same  proportions.     The  ratio  of  the 

carbonic   acid  given   out   to  the  oxygen  taken   in  was 

14-4     .  ,   ,,  •  .    .      J    101      ..,  ,, 

-r-r-^  with  the  nerves  intact  and  ^ .  ._  with  the  nerves  cut. 

lo-2  10-45 

Effect  of  redwcd  oxygen  tension  on  tissue  respiration. — Even  when 

the  oxygen  tension  in  the  blood  is  considerably  reduced,  the  tissues  still 

take  up  the  same  quantity  of  oxygen  as  before  and  give  out  as  much, 

or  slightly  more,  carbonic  acid ;  thus,  in  the  case  of  a  dog,  when  the 

oxygen  tension  in  the  blood  was  approximately  18  mm.  of  mercury  or 

one-fortieth  of  an  atmosphere,  163  c.c.  of  oxygen  per  minute  were 

used  up  by  the  animal,  and  172  c.c.  of  carbonic  acid  were  given  out; 

normally  by  the  same  animal  the  oxygen  consumption  was  157  c.c. 

and  the  carbonic  acid  output  158  c.c.     The  reason  why  the  tissues 

extract  oxygen  with  such  readiness  from  the  blood,  even  when  the 

oxygen  exists  in  the  blood  at  a  low  tension,  is  that  there  is  no  free 

oxygen  in  the  tissues  themselves  (and  they  always  thirst  for  it). 

This  fact  can  be  demonstrated  in  more  than  one  way. 

(1)  No  oxygen  can  he  extracted  from  the  tissues  by  exposing 

them  to  the  vacuum  of  an  air-pump. 

(2)  The  tissues  possess  the  power  of  reducing  such  substances 

as  methylene  blue,  as  explained  on  p.  378. 


CH.  XXIV.]  VENTILATION  389 

Ventilation. — It  is  necessary  to  allude  in  conclusion  to  this  very  important 
practical  outcome  of  our  consideration  of  respiration. 

Some  Continental  observers  have  stated  that  certain  noxious  substances  are 
ordinarily  conbiined  in  expired  air  which  are  much  more  poisonous  than  carbonic 
acid,  but  researches  in  this  country  have  failed  to  substantiate  this.  If  precautions 
be  taken  by  absolute  cleanliness  to  prevent  admixture  of  the  air  with  exhalations 
from  skin,  teeth,  and  clothes,  the  expired  air  only  contains  one  noxious  substance, 
and  that  is  carbonic  acid. 

Absolute  cleanliness  is,  however,  not  the  rule ;  and  the  air  of  rooms  becomes 
stuffy  when  the  amount  of  expired  air  in  them  is  just  so  much  as  to  raise  the 
percentage  of  carbonic  acid  to  0*1  per  cent.  An  adult  gives  otf  about  0 '6  cubic 
feet  of  carbonic  acid  per  hour,  and  if  he  is  supplied  with  1000  cubic  feet  of  fresh 
air  per  hour  he  will  add  O'G  to  the  0*4  cubic  feet  of  carbonic  acid  it  already 
contains;  in  other  words,  the  percentage  of  that  gas  will  be  raised  to  O'l.  An 
hourly  supply  of  2000  cubic  feet  of  fresh  air  will  lower  the  percentage  of  carbonic 
acid  to  0*07,  and  of  3000  cubic  feet  to  0-06,  and  this  is  the  supply  which  is  usually 
recommended.  In  order  that  the  air  may  be  renewed  without  giving  rise  to 
draughts,  each  adult  should  be  allotted  sufficient  space  in  a  room,  at  least  1000 
cubic  feet. 


CHAPTEE  XXV 

THE  CHEMICAL  COMPOSITION  OF  THE  BODY 

The  body  is  built  up  of  a  large  number  of  chemical  elements,  which 
are  in  most  instances  united  together  into  compounds. 

The  elements  found  in  the  body  are  carbon,  nitrogen,  hydrogen, 
oxygen,  sulphur,  phosphorus,  fluorine,  chlorine,  iodine,  silicon,  sodium, 
potassium,  calcium,  magnesium,  lithium,  iron,  and  occasionally  traces 
of  manganese,  copper,  and  lead. 

Of  these  very  few  occur  in  the  free  state.  Oxygen  (to  a  small 
extent)  and  nitrogen  are  found  dissolved  in  the  blood ;  hydrogen  is 
formed  by  putrefaction  in  the  ahmentary  canal.  With  some  few 
exceptions  such  as  these,  the  elements  enumerated  above  are  found 
combined  with  one  another  to  form  what  are  called  compounds. 

The  compounds,  or,  as  they  are  frequently  termed  in  physiology, 
the  proximate  principles,  found  in  the  body  are  divided  into — 

(1)  Mineral  or  inorganic  compounds. 

(2)  Organic  compounds,  or  compounds  of  carbon. 

The  inorganic  compounds  present  are  water,  various  acids  (such 
as  hydrochloric  acid  in  the  gastric  juice),  ammonia  (as  in  the  urine), 
and  numerous  salts,  such  as  calcium  phosphate  in  bone,  sodium  chloride 
in  blood  and  urine,  and  many  others. 

The  organic  compounds  are  more  numerous ;  they  may  be  sub- 
divided into — 

(Proteins — e.g.,  albumin,  myosin,  casein,  gelatin,  etc. 
Nitrogenous.         -  Simpler  nitrogenous  bodies — e.g.,  lecithin,  urea, 
I      creatine. 

fFats — e.g.,  butter,  fats  of  adipose  tissue, 
^T         ■^  \  Carhohmlrates—e.c/.,  sugar,  starch. 

^on-n^trogenous.-  simple  organic  hodies-e.g.,  cholesterin,  lactic 
[     acids. 

The  subdivision  of  the  organic  proximate  principles  into  proteins, 
fats,  and  carbohydrates  forms  the  starting-point  of  chemical  physiology. 

Carbohydrates. 

The  Carbohydrates  are  found  chiefly  in  vegetable  tissues,  and 
many  of  them  form  important  foods.     Some  carbohydrates  are,  how- 

390 


CH.  XXV.]  CARBOHYDRATES  391 

ever,  found  in  or  formed  by  the  animal  organism.  The  most  important 
of  these  are  glycogen,  or  animal  starch ;  dextrose ;  and  lactose,  or  milk 
sugar. 

The  carbohydrates  may  be  conveniently  defined  as  compounds  of 
carbon,  hydrogen,  and  oxygen,  the  two  last  named  elements  being  in 
the  proportion  in  which  they  occur  in  water.  But  this  definition  is 
only  a  rough  one,  and  if  pushed  too  far  would  include  many  substances 
such  as  acetic  acid,  lactic  acid,  and  inosite,  which  are  not  carbohydrates. 
Research  has  shown  that  the  chemical  constitution  of  the  simplest 
carbohydrates  is  that  of  an  aldehyde,  or  a  ketone,  and  that  the  more 
complex  carbohydrates  are  condensation  products  of  the  simple  ones. 
In  order,  therefore,  that  we  may  understand  the  constitution  of  these 
substances,  it  is  first  necessary  that  we  should  understand  what  is 
meant  by  the  terms  aldehyde  and  ketone. 

A  primary  alcohol  is  one  in  which  the  hydroxyl  (OH)  is  attached 
to  the  last  carbon  atom  of  the  chain ;  its  end  group  is  CHoOH.  Thus 
the  formula  for  common  alcohol  (primary  ethyl  alcohol)  is 

CHg.CH.OH. 

The  formula  for  the  next  alcohol  of  the  same  series  (primary 
propyl  alcohol)  is 

CH3.CH2.CH0OH. 

If  a  primary  alcohol  is  oxidised,  the  first  oxidation  product  is 
called  an  aldehyde  ;  thus  ethyl  alcohol  yields  acetic  aldehyde : — 
CHg.CHoOH    +    O    =    CH3.CHO    +    HoO. 

[Ethyl  alcohol.]  [Acetic  aldehyde.] 

The  typical  end-group  CHO  of  the  aldehyde  is  not  stable,  but  is 
easily  oxidisable  to  form  the  group  COOH,  and  the  compound  so  formed 
is  called  an  acid ;  in  this  way  acetic  aldehyde  forms  acetic  acid  : — 
CH3.CHO   +   O   =   CH3.COOH. 

[Acetic  aldehyde.]  [Acetic  acid.] 

The  majority  of  the  simple  sugars  are  aldehydes  of  more  complex 
alcohols  than  this ;  they  are  spoken  of  as  aldoses.  The  readiness  with 
which  aldehydes  are  oxidisable  renders  them  powerful  reducing  agents, 
and  this  furnishes  us  with  some  of  the  tests  for  the  sugars. 

Let  us  now  turn  to  the  case  of  the  ketones.  A  secondary  alcohol 
is  one  in  which  the  OH  group  is  attached  to  a  central  carbon  atom ; 
thus  secondary  propyl  alcohol  has  the  formula 

CH3.CHOH.CH3. 

Its  typical  group  is  therefore  CHOH.  When  this  is  oxidised,  the 
first  oxidation  product  is  called  a  ketone,  thus : — 

CH3.CHOH.CH3  +  o  =  CH3.CO.CH3  +  up. 

[Secondary  propyl  alcohol.]  [Propyl  ketone.] 

It   therefore  contains   the  group  CO  in  the  middle  of   the  chain. 


392         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

Some  of  the  sugars  are  ketones  of  more  complex  alcohols ;  these  are 
called  ketoses.  The  only  one  of  these  which  is  of  physiological  interest 
is  levulose. 

The  alcohols  of  which  we  have  already  spoken  are  called  monatomic, 
because  they  contain  only  one  OH  group.  Those  which  contain  two 
OH  groups  (like  glycol)  are  called  diatomic ;  those  which  contain 
three  OH  groups  (like  glycerin)  are  called  triatomic ;  and  so  on.  The 
hexatomic  alcohols  are  those  which  contain  six  OH  groups.  Three 
of  these  hexatomic  alcohols  with  the  formula  CgHg  (OH)g  are  of 
physiological  interest ;  they  are  isomerides,  and  their  names  are  sorbite, 
mannite,  and  dulcite.  By  careful  oxidation  their  aldehydes  and 
ketones  can  be  obtained ;  these  are  the  simple  sugars ;  thus,  dextrose 
is  the  aldehyde  of  sorbite;  mannose  is  the  aldehyde  of  mannite; 
levulose  is  the  ketone  of  mannite ;  and  galactose  is  the  aldehyde  of 
dulcite.  These  sugars  all  have  the  empirical  formula  CqH^oOq.  The 
constitutional  formula  for  dextrose  is : — 

H        H        H        H        H        H 

i           I           I           I           I  I 

H C C C C C C 

OH     OH     OH     OH     OH       O 

By  further  oxidation,  the  sugars  yield  acids  with  various  names. 
If  we  take  such  a  sugar  as  a  typical  specimen,  we  see  that  their  general 
formula  is 

and  as  a  general  rule  n  =  m;  that  is,  the  number  of  oxygen  and  carbon 
atoms  are  equal.  This  number  in  the  case  of  the  sugars  already 
mentioned  is  six.     Hence  they  are  called  hexoses. 

Sugars  are  known  to  chemists,  in  which  this  number  is  3,  4,  .5,  7,  etc,  and 
these  are  called  trioses,  tetroses,  pentoses,  heptoses,  etc.  The  majority  of  these 
have  no  physiological  interest.  It  should,  however,  be  mentioned  that  a  pentose 
has  been  obtained  from  the  nucleoprotein  of  the  pancreas,  of  the  liver,  and  of  yeast. 
If  the  pentoses  that  are  found  in  various  plants  are  given  to  an  animal,  they  are 
excreted  in  great  measure  unchanged  in  the  urine. 

The  hexoses  are  of  great  physiological  importance.  The  principal 
ones  are  dextrose,  levulose,  and  galactose.  These  are  called  mono- 
saccharides. 

Another  important  group  of  sugars  are  called  disaccharides  ; 
these  are  formed  by  what  is  called  condensation ;  that  is,  two  mole- 
cules of  monosaccharide  combine,  together  with  the  loss  of  a  molecule 
of  water,  thus : — 

C,U,.p,   +    C,H,Pe    =    C,^,Pn    +    H^O. 

The  principal  members  of  the  disaccharide  group  are  cane-sugar, 
lactose,  and  maltose. 


CH.  XXV.]  SUGARS  393 

If  more  than  two  molecules  of  the  monosaccharide  group  undergo 
a  corresponding  condensation,  we  get  what  are  called  polysaccharides. 

«C,,H,p,   =   (C,H,,0,)„    +    "H,0. 

The  principal  polysaccharides  are  starch,  glycogen,  various  dextrins, 
and  cellulose.  We  may,  therefore,  arrange  the  important  carbo- 
hydrates of  the  hexose  family  in  a  tabular  form  as  follows : — 


1.  Monosaccharides  or         2.  Disaccharides  Sucroses,  I  3   p^i  saccharides  or  Amy- 
Glucoses,  C^H.^O,.  or  Saccharoses.  loses  (CeH,„0,)„. 


+  Dextrose.  +  Cane  sugar.  +  Starch. 

-  Levulose.  +  Lactose.  +  Glycogen. 

+  Galactose.  4  Maltose.  +  Dextrin. 

Cellulose. 


The  +  and  —  signs  in  the  above  list  indicate  that  the  substances 
to  which  they  are  prefixed  are  dextro-  and  levo-rotatory  respectively 
as  regards  polarised  light.  The  formulae  given  in  the  table  are  merely 
empirical ;  the  quantity  n  in  the  starch  group  is  variable  and  often 
large.  The  following  are  the  chief  facts  in  relation  to  each  of  the 
principal  carbohydrates. 

Dextrose  or  Grape  Sugar. — This  carbohydrate  is  found  in  many 
fruits,  honey,  and  in  minute  quantities  in  the  blood  and  numerous 
tissues,  organs,  and  fluids  of  the  body.  It  is  the  form  of  sugar  found 
in  large  quantities  in  the  blood  and  urine  in  the  disease  known  as 
diabetes. 

Dextrose  is  soluble  in  hot  and  cold  water  and  in  alcohol.  It  is 
crystalline,  but  not  so  sweet  as  cane  sugar.  When  heated  with  strong 
potash  certain  complex  acids  are  formed  which  have  a  yellow  or 
brown  colour.  This  constitutes  Moore's  test  for  sugar.  In  alkaline  solu- 
tions dextrose  reduces  salts  of  silver,  bismuth,  mercury,  and  copper. 
The  reduction  of  cupric  to  cuprous  salts  constitutes  Trommer's  test, 
which  is  performed  as  follows :  put  a  few  drops  of  copper  sulphate 
into  a  test-tube,  then  solution  of  dextrose,  and  then  strong  caustic 
potash.  On  adding  the  potash  a  precipitate  is  first  formed  which 
dissolves,  forming  a  blue  solution.  On  boiling  this  a  yellow  or  red 
precipitate  (cuprous  hydrate  or  oxide)  forms. 

On  boiling  a  solution  of  dextrose  with  an  alkaline  solution  of 
picric  acid,  a  dark  red  opaque  solution  due  to  reduction  to  picramic 
acid  is  produced. 

Another  important  property  of  grape  sugar  is  that  under  the 
influence  of  yeast  it  is  converted  into  alcohol  and  carbonic  acid 
(CoHiA  =  2C,H,0  +  2CO,). 

Dextrose  may  be  estimated  by  the  fermentation  test,  by  the  polari- 


394         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

meter,  and  by  the  use  of  Fehling's  solution.  The  last  method  is  the 
most  important :  it  rests  on  the  same  principles  as  Trommer's  test, 
and  we  shall  study  it  in  connection  with  diabetic  urine. 

Levulose. — When  cane  sugar  is  treated  with  dilute  mineral  acids 
it  undergoes  a  process  known  as  inversion — i.e.,  it  takes  up  water  and 
is  converted  into  equal  parts  of  dextrose  and  levulose.  The  previously 
dextro-rotatory  solution  of  cane  sugar  then  becomes  levo-rotatory,  the 
levo-rotatory  power  of  the  levulose  being  greater  than  the  dextro- 
rotatory power  of  the  dextrose  formed.  Hence  the  term  inversion. 
The  same  hydrolytic  change  is  produced  by  certain  ferments,  such  as 
the  invert  ferment  of  the  intestinal  juice. 

Pure  levulose  can  be  crystallised,  but  so  great  is  the  difficulty  of 
obtaining  crystals  of  it  that  one  of  its  names  was  uncrystallisable 
sugar.  Small  quantities  of  levulose  have  been  found  in  blood,  urine, 
and  muscle.  It  has  been  recommended  as  an  article  of  diet  in  diabetes 
in  place  of  ordinary  sugar ;  but  there  are  no  substantial  grounds  for 
believing  that  levulose  is  less  harmful  than  other  sugars  in  this  disease. 
Levulose  gives  the  same  general  reactions  as  dextrose. 

Galactose  is  formed  by  the  action  of  dilute  mineral  acids  or  of 
inverting  ferments  on  lactose.  It  resembles  dextrose  in  its  action  on 
polarised  light,  in  reducing  cupric  salts  in  Trommer's  test,  and  in  being 
directly  fermentable  with  yeast.  When  oxidised  by  means  of  nitric 
acid  it  yields  an  acid  called  mucic  acid  (CyHj^Og),  which  is  only  slightly 
soluble  in  water.  Dextrose  when  treated  in  this  way  yields  an  iso- 
meric acid — i.e.,  an  acid  with  the  same  empirical  formula,  called  sac- 
charic acid,  which  is  very  soluble  in  water. 

Cane  Sugar  is  generally  distributed  in  the  vegetable  kingdom, 
but  especially  in  the  juices  of  the  sugar  cane,  beetroot,  mallow,  and 
sugar  maple.  It  is  a  substance  of  great  importance  as  a  food.  It 
undergoes  inversion  in  the  alimentary  canal.  It  is  crystalline,  and 
dextro-rotatory.  With  Trommer's  test  it  gives  a  blue  solution,  but 
no  reduction  occurs  in  boiling.  After  inversion  it  is,  of  course, 
strongly  reducing. 

Inversion  may  be  accomplished  by  boiling  with  dilute  mineral 
acids,  or  by  means  of  inverting  ferments  such  as  that  occurring  in  the 
intestinal  juice.  It  then  takes  up  water,  and  is  split  into  equal  parts 
of  dextrose  and  levulose. 

C12H22OU    +    H,0   =    C,U,.p,   +   C,Hi,0,. 

[Cane  sugar.]  [Dextrose.]  [Levulose.] 

With  yeast,  cane  sugar  is  first  inverted  by  means  of  a  special  soluble 
ferment  secreted  by  the  yeast  cells,  and  then  there  is  an  alcoholic 
fermentation  of  the  glucoses  so  formed. 

Lactose,  or  Milk  Sugar,  occurs  in  milk.  It  is  occasionally 
found  in  the  urine  of  women  in  the  early  days  of  lactation,  or  after 


CH.  XXV.]  SUGARS  •  395 

weaning.  It  is  crystallisable,  tlextro-rotatory,  much  less  soluljle  in 
water  than  other  sugars,  and  has  only  a  slightly  sweet  taste.  It 
gives  Tromnier's  test,  but  when  the  reducing  power  is  tested  quanti- 
tatively by  Fehling's  solution  it  is  found  to  be  a  less  powerful  reduc- 
ing agent  than  dextrose,  in  the  proportion  of  7  to  10. 

When  hydrolysed  by  similar  agencies  as  those  mentioned  in  con- 
nection with  cane  sugar,  it  takes  up  water  and  splits  into  dextrose 
and  galactose. 

Ci..H.,,Oii    +    H,0    =    C,Hi,0,,    +    C,Hj,Og. 

[Lacloso.]  [Dextrose.]  [Galactose.] 

With  yeast  it  is  first  inverted,  and  then  alcohol  is  formed.  This,  how- 
ever, occurs  slowly. 

The  lactic  acid  fermentation  which  occurs  when  milk  turns  sour 
is  brought  about  by  micro-organisms,  which  are  somewhat  similar  to 
yeast  cells.  Putrefactive  bacteria  in  the  intestine  bring  about  the 
same  result.  The  two  stages  of  the  lactic  acid  fermentation  are 
represented  in  the  following  equations : — 

(1.)  C,2ii,.Pn   +   H^O   =    4C3H,03. 

[Lactose.]  [Lactic  acid.] 

(2.)  iC.,Up,   =    2C,HgO,   +    4C0,,   +    4H,. 

[Lactic  acid.]  [Butyric  acid.] 

Maltose  is  the  chief  end  product  of  the  action  of  malt  diastase  on 
starch,  and  is  also  formed  as  an  intermediate  product  in  the  action  of 
dilute  sulphuric  acid  on  the  same  substance.  It  is  the  chief  sugar 
formed  from  starch  by  the  diastatic  ferments  contained  in  the  saliva 
and  pancreatic  juice.  It  can  be  obtained  in  the  form  of  acicular 
crystals,  and  is  strongly  dextro-rotatory.  It  gives  Trommer's  test ; 
but  its  reducing  power,  as  measured  by  Fehling's  solution,  is  one-third 
less  than  that  of  dextrose.      With  yeast  it  yields  alcohol. 

By  prolonged  boiling  with  water,  or,  more  readily,  by  boiling  with 
a  dilute  mineral  acid,  or  by  means  of  an  inverting  ferment,  such  as 
occurs  in  the  intestinal  juice,  it  is  converted  into  dextrose. 

Ci,H.„0,,    +    H,0    =    2CeH,,0,. 

[Maltose.]  [Dextrose.] 

Phenyl  Hydrazine  Test. — The  three  important  reducing  sugars 
with  which  we  have  to  deal  in  physiology  are  dextrose,  lactose,  and 
maltose.  They  may  be  distinguished  by  their  relative  reducing 
powers  on  Fehling's  solution,  or  by  the  characters  of  their  osazones. 
The  osazone  is  formed  in  each  case  by  adding  phenyl  hydrazine  hydro- 
chloride, and  sodium  acetate,  and  boiling  the  mixture  for  about  half  an 
hour.  In  each  case  the  osazone  is  deposited  in  the  form  of  bright 
canary-coloured,  needle-like  crystals,  usually  in  bunches,  which  differ 
in  their  crystalline  form,  melting-point,  and  solubilities.  Cane  sugar 
does  not  yield  an  osazone. 


396         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

Starch  is  widely  diffused  through  the  vegetable  kingdom.  It 
occurs  in  nature  in  the  form  of  microscopic  grains,  varying  in  size  and 
appearance,  according  to  their  source.  Each  consists  of  a  central  spot, 
round  which  more  or  less  concentric  envelopes  of  starch  proper  or 
granulose  alternate  with  layers  of  cellulose.  Cellulose  has  very  little 
digestive  value,  but  starch  is  a  most  important  food. 

Starch  is  insoluble  in  cold  water :  it  forms  an  opalescent  solution 
in  boiling  water,  which  if  concentrated  gelatinises  on  cooling.  Its 
most  characteristic  reaction  is  the  blue  colour  it  gives  with  iodine. 

On  heating  starch  with  mineral  acids,  dextrose  is  formed.  By  the 
action  of  diastatic  ferments,  maltose  is  the  chief  end  product.  In 
both  cases  dextrin  is  an  intermediate  stage  in  the  process. 

Before  the  formation  of  dextrin  the  starch  solution  loses  its  opal- 
escence, a  substance  called  soluble  starch  being  formed.  This,  like 
native  starch,  gives  a  blue  colour  with  iodine.  Although  the  mole- 
cular weight  of  starch  is  unknown,  the  formula  for  soluble  starch  is 
probably  5(Ci2H2oOio).,o.  E(|uations  that  represent  the  formation  of 
sugars  and  dextrins  from  this  are  very  complex, 
and  are  at  present  only  hypothetica]. 

Dextrin  is  the  name  given  to  the  inter- 
mediate products  in  the  hydrolysis  of  starch  or 
glycogen,  and  two  chief  varieties  are  distin- 
guished : — erythro-dextrin,  which  gives  a  reddish- 
brown  colour  with  iodine;   and  achroo- dextrin, 

Fig.  340.  -Grains  of  potato        which  doCS  UOt. 

It  is  readily  soluble  in  water,  but  insoluble 
in  alcohol  and  ether.  It  is  gummy  and  amorphous,  ft  does  not 
give  Trommer's  test,  nor  does  it  ferment  with  yeast.  It  is  dextro- 
rotatory.    By  hydrolysing  agencies  it  is  converted  into  glucose. 

Glycogen,  or  animal  starch,  is  found  in  liver,  muscle,  and  white 
blood  corpuscles.     It  is  also  abundant  in  all  embryonic  tissues. 

Glycogen  is  a  white  tasteless  powder,  soluble  in  water,  but  it 
forms,  like  starch,  an  opalescent  solution.  It  is  insoluble  in  alcohol 
and  ether.  It  is  dextro-rotatory.  With  Trommer's  test  it  gives  a 
blue  solution,  but  no  reduction  occurs  on  boiling. 

With  iodine  it  gives  a  reddish  or  port-wine  colour,  very  similar  to 
that  given  by  erythro-dextrin.  Dextrin  may  be  distinguished  from 
glycogen  by  (1)  the  fact  that  it  gives  a  clear,  not  an  opalescent,  solu- 
tion with  water ;  and  (2)  it  is  not  precipitated  by  basic  lead  acetate 
as  glycogen  is.  It  is,  however,  precipitated  by  basic  lead  acetate  and 
ammonia.  (3)  Glycogen  is  precipitated  by  55  per  cent,  of  alcohol ; 
the  dextrins  require  85  per  cent,  or  more. 

Cellulose. — This  is  the  colourless  material  of  which  the  cell-walls 
and  woody  fibres  of  plants  are  composed.  By  treatment  with  strong 
mineral  acids  it  is,  like  starch,  converted  into  glucose,  but  with  much 


CH.  XXV.]  THE   FATS  397 

greater  difficulty.  The  various  digestive  ferments  have  little  or  no 
action  on  cellulose ;  hence  the  necessity  of  boiling  starch  before  it  is 
taken  as  food.  Boiling  bursts  the  cellulose  envelopes  of  the  starch 
grains,  and  so  allows  the  digestive  juices  to  get  at  the  starch 
proper. 

Cellulose  is  found  in  a  few  animals,  as  in  the  test  or  outer  invest- 
ment of  the  Tunicates. 

[Inosite,  formerly  called  muscle  sugar  (C,;Hi.,0,;),  is  found  in  muscle,  kidney, 
liver,  and  other  parts  of  the  body  in  small  quantities.  It  is  also  largely  found  in 
the  vegetable  kingdom.  It  is  crystallisable,  and  has  the  same  empirical  formula  as 
the  glucoses.  It  is,  however,  not  a  sugar,  and  careful  analysis  has  shown  that  it 
really  belongs  to  the  aromatic  series.] 

The  Pats. 

Pat  is  found  in  small  quantities  in  many  animal  tissues.  It  is, 
however,  found  in  large  quantities  in  three  situations,  viz.,  marrow, 
adipose  tissue,  and  milk. 

The  contents  of  the  fat  cells  of  adipose  tissue  are  fluid  during  life, 
the  normal  temperature  of  the  body  (37°  C,  or  99°  F.)  being  con- 
siderably above  the  melting-point  (25°  C.)  of  the  mixture  of  the  fats 
found  there.  These  fats  are  three  in  number,  and  are  called  palmitin, 
stearin,  and  olein.  They  differ  from  one  another  in  chemical  com- 
position and  in  certain  physical  characters,  such  as  melting-point  and 
solubilities.  Olein  melts  at  —  5°  C,  palmitin  at  45°  C,  and  stearin 
at  53-66°  C.  It  is  thus  olein  which  holds  the  other  two  dissolved  at 
the  body  temperature.  Fats  are  all  soluble  in  hot  alcohol,  ether,  and 
chloroform,  but  insoluble  in  water. 

Chemical  Constitution  of  the  Pats. — The  fats  are  compounds  of 
fatty  acids  with  glycerin,  and  may  be  termed  glycerides  or  glyceric 
ethers. 

The  fatty  acids  form  a  series  of  acids  derived  from  the  monatomic 
alcohols  by  oxidation.  Thus,  to  take  ordinary  ethyl  alcohol,  CoHyO, 
the  first  stage  in  oxidation  is  the  removal  of  two  atoms  of  hydrogen 
to  form  aldehyde,  CH^O ;  on  further  oxidation  an  atom  of  oxygen  is 
added  to  form  acetic  acid,  C.^H^O^. 

A  similar  acid  can  be  obtained  from  all  the  other  alcohols, 
thus : — 


From  methyl 

alcohol 

CH.HO, 

formic      acid      H.COOH  is  obtained. 

„     ethyl 

c.,h;ho. 

acetic         „     CH.,.COOH 

,,     propyl 

c:h1.ho, 

propionic  „   C.,H,XOOH 

„     butyl 

C4H,.H0, 

butyric      „   C.:H..C00H 

,,     amyl 

C-^Hii.HO, 

valeric       „   C^HyCOOH 

„     hexyl 

CeH,3.H0, 

caproic      „  CgHu.COOH 

and  so  on. 

Or  in  general  terms : — 

From    the    alcohol    with    formula   C^Hon+i-HO,    the   acid   with 


398         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

formula  C,i-iH2,i,_i.C00H  is  obtained.  The  sixteenth  term  of  this 
series  has  the  formula  C10H31.COOH,  and  is  called  palmitic  acid; 
the  eighteenth  has  the  formula  C17H35.COOH,  and  is  called  stearic 
acid.  Each  acid,  as  will  be  seen,  consists  of  a  radical,  C^iHor-iCO, 
united  to  hydroxyl  (OH).  Oleic  acid,  however,  is  not  a  member  of 
this  series,  but  belongs  to  a  somewhat  similar  series  known  as  the 
acrylic  series,  of  which  the  general  formula  is  Cto_iHo,i_3.COOH.  It 
is  the  eighteenth  term  of  the  series,  and  its  formula  is  C17H33.COOH. 

The  first  member  of  the  group  of  alcoliols  from  which  this  acryhc  series  of 
acids  is  obtained  is  called  (tlbil  alrolml  (CH.,:  CH.CHoOH) ;  the  aldehyde  of 
this  is  acrolfin  (CHo :  CH.CHO),  and  the  formula  for  tlie  acid  (acrylic  acid)  is 
CHo:CH.COOH.  It  will  be  noticed  that  two  of  the  carbon  atoms  are  united  by 
two  valencies,  and  tiiese  bodies  are  therefore  unsaturated  ;  they  are  unstable  and 
are  prone  to  undergo  by  uniting  with  another  element  a  conversion  into  bodies  in 
which  the  carbon  atoms  are  united  by  only  one  bond.  This  accounts  for  their 
reducing  action,  and  it  is  owing  to  this  that  the  colour  reactions  with  osmic  acid 
and  Sudan  III.  are  due.  Fat  which  contains  any  memlier  of  the  acrylic  series  such 
as  oleic  acid  blackens  osmic  acid,  by  reducing  it  to  a  lower  (black)  oxide.  The 
fats  palmitin  and  stearin  do  not  give  this  reaction. 

Glycerin  or  Glycerol  is  a  triatomic  alcohol,  03115(110)3 — i.e.,  three 
atoms  of  hydroxyl  united  to  a  radical  glyceryl  (C3H5).  The  hydrogen 
in  the  hydroxyl  atoms  is  replaceable  by  other  organic  radicals.  As 
an  example,  take  the  radical  of  acetic  acid  called  acetT/l  (CH3.CO). 
The  following  formulae  represent  the  derivatives  that  can  be  obtained 
by  replacing  one,  two,  or  all  three  hydroxyl  hydrogen  atoms  in  this 
way: — 

[OH  rOH  fOH  rO.CH.CO 

C.Hg   OH    C.,H,    OH  CH,    O.CH..CO     CH,    O.CHJ.CO 

iOH  t0.CH,C0  Io.CH;;.CO       "       I  O.CH,.CO 

[Glycerin.]  [Monoacetiii.]  [Diacetin.]  [Triacetin.] 

Triacetin  is  a  type  of  a  neutral  fat;  stearin,  palmitin,  and  olein 
ought  more  properly  to  be  called  tristearin,  tripalmitin,  and  triolein 
respectively.  Each  consists  of  glycerin  in  which  the  three  atoms  of 
hydrogen  in  the  hydroxyls  are  replaced  by  radicals  of  the  fatty  acid. 
This  is  represented  in  the  following  formulae : — 

Acid.  Radical.  Fid. 

Palmitic  acid  Ci,H.,,.COOH  Palmityl  C,,H.,,.CO  Palmitin  C.,H,(OC„H..,.CO)., 

Stearic  acid    CivH.,s.COOH  Stearyl    CnH.,,.CO  Stearin    C.'H-,(OCi7H'',.CO). 

Oleic  acid       0^^11^,^.00011  Oleyl       Ci-H;;;,.CO  Olein       C:H,(OCnH.i;,.CO);, 

Decomposition  Products  of  the  Fats — The  fats  split  up  into 
the  substances  out  of  which  they  are  built  up. 

Under  the  influence  of  superheated  steam,  mineral  acids,  and  in 
the  body  by  means  of  certain  ferments  (for  instance,  the  fat-splitting 
ferment,  steapsin,  of  the  pancreatic  juice),  a  fat  combines  with  water 
and  splits  into  glycerin  and  the   fatty  acid.     The  following  equa- 


en.  XXV.]  THE  proteins  399 

tion    represents    what    occurs    in    a    fat,    taking    tripalmitin    as   an 
example : — 

C3H,(O.Ci.H.„CC)).,    +    DH.p    =    CaH.XOH).,  3C,,^H,jCO.OH. 

[Tiipahnitiii — a  tat.]  "  [Glycerin.]  ll'alniilic  aciii  — a 

fatty  add.) 

In  the  process  of  saponification  much  the  same  sort  of  reaction 
occurs,  the  final  products  being  glycerin  and  a  compound  of  the  base 
with  the  fatty  acid  which  is  called  a  soap.  Suppose,  for  instance,  that 
potassium  hydrate  is  used  ;  we  get — 

C3H,(O.C,,H3iCO)3    +    3KH0    =    C3H,(()H)3  +    SCj.Hg^CO.OK. 

[Triiialmitin— a  fat.]  [Glycerin.]  [Totassium  palmltate  - 

a  soap.] 

Emulsification. — Another  change  that  fats  undergo  in  the  body 
is  very  different  from  saponification.  It  is  a  physical  rather  than  a 
chemical  change ;  the  fat  is  broken  up  into  very  small  globules,  such 
as  are  seen  in  the  natural  emulsion — milk. 

Lecithin  (C4.2HS4NPO9). — This  is  a  very  complex  fat,  which  yields 
on  decomposition  not  only  glycerin  and  fatty  acids  (stearic  and  oleic), 
but  phosphoric  acid,  and  an  alkaloid  [N.(CH3)3C.,HyOo]  called  choline  in 
addition.  This  substance  is  found  to  a  great  extent  in  the  nervous 
system  (see  p.  176),  and  to  a  small  extent  in  bile.  Together  with 
cholesterin,  a  crystallisable,  monatomic  alcohol  (C27H45.HO),  which 
we  shall  consider  more  at  length  in  connection  with  the  bile,  it  is 
found  in  small  quantities  in  the  protoplasm  of  all  cells. 

The  Proteins. 

The  proteins  are  the  most  important  substances  that  occur  in 
animal  and  vegetable  organisms,  and  proteiii  metaholism  is,  as  already 
noted  (p.  7),  the  most  characteristic  sign  of  life. 

They  are  highly  complex  compounds  of  carbon,  hydrogen,  oxygen, 
nitrogen,  and  sulphur,  occurring  in  a  solid  viscous  condition  or  in 
solution  in  nearly  all  parts  of  the  body.  The  different  members  of 
the  group  present,  however,  great  differences  in  their  chemical  and 
physical  properties. 

The  proteins  in  the  food  form  the  source  of  the  proteins  in  the 
body  tissues,  but  the  latter  are  usually  different  in  composition  from 
the  former.  The  food  proteins  are  in  the  process  of  digestion  broken 
up  into  simpler  substances,  usually  called  cleavage  j)roducts,  and  it  is 
from  these  that  the  body  cells  reconstruct  the  proteins  peculiar  to 
themselves.  As  a  result  of  katabolic  processes  in  the  body,  the 
proteins  are  finally  again  broken  down,  carbonic  acid,  water, 
sulphuric  acid  (combined  as  sulphates),  urea,  and  creatinine  being 
the  principal  final  products  which  are  discharged  in  the  urine  and 
other  excretions.  The  substances  intermediate  between  the  proteins 
and  these  final  katabolites  will  be  discussed  under  urine. 


400         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

The  following  figures  will  convince  the  student  how  different  the 
proteins  are  in  elementary  composition.  Hoppe-Seyler  many  years 
ago  gave  the  variations  in  percentage  composition  as  follows : — 

C  H  N  S  O 

From 51-5        6-9        15-2        0-3        20-9 

To 54-5        7-3        17-0        2-0        23-5 

Eecent  research  has  since  shown  that  the  variations  are  even  greater 
than  those  just  stated. 

The  same  fact  is  brought  home  more  vividly  when  the  cleavage 
products  are  separated  and  estimated.  These  differ  both  in  kind 
and  in  amount,  but  nearly  all  of  them  are  substances  which  are 
termed  amino- acids.  Emil  Fischer,  to  whom  we  owe  so  much  of  our 
knowledge  in  this  direction,  considers  that  the  proteins  are  linkages 
of  a  greater  or  lesser  number  of  these  amino-acids,  and  there  is  little 
doubt  that  in  the  future  his  work  will  result  in  an  actual  synthesis 
of  the  protein  molecule,  and  with  that  will  come  an  accurate 
knowledge  of  its  constitution. 

AVhen  the  protein  molecule  is  broken  down  in  laboratory 
processes,  or  by  the  digestive  ferments  wdiich  occur  in  the  alimen- 
tary canal,  the  essential  change  is  due  to  what  is  called  hydrolysis ; 
that  is,  the  molecule  unites  with  water  and  then  breaks  up  into 
smaller  molecules.  The  first  cleavage  products,  which  are  called 
proteoses,  retain  many  of  the  characters  of  the  original  protein,  and 
the  same  is  true,  though  to  a  less  degree,  of  the  peptones,  which  come 
next  in  order  of  formation.  The  peptones,  in  their  turn,  are 
decomposed  into  short  linkages  of  amino-acids,  which  are  called 
polypeptides,  and  finally  the  individual  amino-acids  are  obtained 
separated  from  each  other. 

"Whit  we  have  already  learnt  about  the  fatty  acids  will  help  us 
in  understanding  what  is  meant  by  an  amino-acid. 

If  we  take  acetic  acid,  which  is  one  of  the  simplest  of  the  fatty 
acids,  we  see  that  its  formula  is 

CHg .  COOH. 

If  one  of  the  three  hydrogen  atoms  in  the  CHg  group  is  replaced 
by  NH^,  we  get  a  substance  which  has  the  formula 

CH, .  NH. .  COOH. 

The  combination  NH.„  which  has  stepped  in,  is  called  the  amino- 
group,  and  the  new  substance  now  formed  is  called  amino-acetic 
acid ;  it  is  also  termed  glycine  or  glycocoll. 

We  may  take  another  example  from  another  fatty  acid.  Pro- 
pionic acid  is  C0H5 .  COOH  ;  if  we  replace  an  atom  of  hydrogen  by 
the  amino-group  as  before,  we  obtain  C2H^ .  NH^ .  COOH,  which  is 
amino-propionic  acid  or  alanine. 

Groing   a    little   higher   in    the   scale,   and    taking   caproic    acid 


CH.  XXV.]  PROTEIN  CLEAVAGE  TRODUCTS  401 

C5H11 .  COOH,    we    obtain    from    it    in   an   exactly    similar    way, 
C5H10 .  NHo .  COOH,  which  is  amino-caproic  acid  or  leucine. 

AH  the  three  amino-acids  mentioned  (glycine,  alanine,  and  leucine) 
are  found  among  the  final  cleavage  products  of  most  proteins;  but 
there  are  a  good  many  more  in  addition,  for  instance : — 

Amino-valeric  acid, 

Amino-succinamic  acid  (asparagine), 

Amino-succinic  acid  (aspartic  acid), 

Amino-pyrotartaric  acid  (glutamic  acid), 

Amino-hydroxy-propionic  acid  (serine), 
some  of  which  are  derived  from  fatty  acids  of  a  different  series  from 
those  just  enumerated. 

But  in  all  these  cases  there  is  only  one  replacement  of  an  atom 
of  hydrogen  by  NH^ ;  hence  they  are  called  mono-amino-acids. 

Passing  to  the  next  stage  in  complexity,  we  come  to  another  group 
of  amino-acids  which  are  called  diamino -Sioid.^ ;  that  is,  fatty  acids  in 
which  two  hydrogen  atoms  are  replaced  by  NHo  groups.  Of  these  we 
may  particularly  mention  lysine,  ornithine,  arginine,  and  histidine. 

Lysine  is  diamino-caproic  acid.  Caproic  acid  is  CjH^j .  COOH. 
Mono-amino-caproic  acid  or  leucine,  we  have  already  learnt,  is 
CjH^jo .  NH., .  COOH.  Lysine  or  diamino-caproic  acid  is  C-Hg . 
(NH,), .  CO'OH. 

Ornithine  is  diamino-valeric   acid,  and    the   following   formulae 
will  show  its  relationship  to  its  parent  fatty  acid. 
C4H9COOH  is  valeric  acid. 
C^H;(NHo).>COOH  is  diamino-valeric  acid  or  ornithine. 

Arginine  is  a  somewhat  more  complex  substance,  which  contains 
the  ornithine  radical.  It  belongs  to  the  same  group  of  substances  as 
creatine,  another  important  cleavage  product  of  the  protein  molecule. 
Creatine  is  methyl-guanidine  acetic  acid,  and  has  the  formula 

HN       ; 

\;C    — N(CH3)CH, .  COOH 

On  boiling  it  with  baryta  water,  it  takes  up  water  (H^O)  and  splits  at 
the  dotted  line  into  urea  (CO  (]SrH2)2)  and  sarcosine,  as  shown  below. 


>C— O 

H„N/ 


NH.CH„.  CH,  .COOH 


(Urea)  (Sarcosine  or  Methyl-glycine.) 

Arginine  splits  in  a  similar  way,  urea  being  split  off  on  the  left, 

2  C 


402         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

and  ornithine  instead  of  sarcosine  on  the  right.  Arginine  is,  there- 
fore, a  compound  of  ornithine  with  a  urea  group. 

Histidine,  the  last  member  of  this  class,  has  the  formula 
CgHgN.^Oo,  and  is  probably  also  a  diamino-acid,  but  its  exact  consti- 
tution has  not  yet  been  made  out  with  certainty. 

These  substances  we  have  hitherto  described  as  acids,  but  they 
may  also  play  the  part  of  bases,  for  the  introduction  of  a  second 
amino-group  into  the  fatty  acid  molecules  confers  upon  them  basic 
properties.     The  three  substances : — 

Lysine  .         .         C.H^.N.O, 

Arginine  .  .  CgHj^N^O., 

Histidine         .         .         CgHgNgO, 

are  in  fact  often  called  the  hexone  bases,  because  each  of  them 
contains  6  atoms  of  carbon,  as  the  above  empirical  formulae  show. 

But  there  is  still  an  important  group  of  amino-acids  to  be 
considered,  and  these  are  termed  the  aromatic  amino-acids  ;  that  is, 
amino-acids  united  to  the  benzene  ring,  and  of  these  we  will  mention 
three,  namely,  phenyl- alanine,  tyrosine,  and  a  nearly  related 
substance  called  tryptophane. 

Phenyl-alanine  is  alanine  or  amino-propionic  acid  in  which  an 
atom  of  hydrogen  is  replaced  by  phenyl  (Cj-Hg). 

Propionic  acid  has  the  formula  CgHg .  COOH. 

Alanine  (amino-propionic  acid)  is  C.,H4NHo .  COOH. 

Phenyl-alanine  is  CoH, .  CgHs .  NH^^  COOH. 

The  formula  of  phenyl-alanine  may  also  be  written  another  way. 
The  grapliic  formula  of  benzene  (C,;H^.)  is : — 

H 

n—cf    \c— H 

I  i        II 

H  — C.\        /C  — H 

I 
H 

If  the  H  placed  lowermost  in  the  above  formula  is  replaced  by 
CH,CH  .  NH., .  COOH,  we  obtain  the  formula  of  phenyl-alanine  :— 


CHg .  CHNH^COOH 

the  remainder  of  the  benzene  ring,  which  is  unaltered,  being  repre- 
sented as  usual  by  a  simple  hexagon. 


CH.  XXV.]  PROTEIN  CLEAVAGE  PRODUCTS  403 

Tyrosine  is  a  little  more  complicated;  it  is  oxyphcnyl-alanine; 
that  is,  instead  of  phenyl  (C^Hg)  in  the  formula  of  phenyl-alanine, 
we  have  now  oxyphcnyl  (C,;H, .  OH) ;  this  gives  us 
C.Hy .   (C,;H^ .  OH)  Nil, .  COOH 
as  the  formula  for  tyrosine  written  one  way,  or 

HO 


CH, .  CHNH,, .  COOH 

when  written  in  the  other  way. 

Tryptophane  is  more  complex  still ;  it  is  indole  amino-propionic 
acid :  that  is,  amino-propionic  acid  united  to  another  ringed  deriva- 
tive called  indole.  Tryptophane  is  the  portion  of  the  protein 
molecule  which  is  the  parent  substance  of  two  evil-smelling  products 
of  protein  decomposition  called  indole 

/CH  .  CH 


C.H. 


NH 


and  scatole  or  methyl  indole.  Tryptophane  is  also  the  radical  in 
the  protein  molecule  which  is  responsible  for  the  colour  test  called 
the  Adamkiewicz  reaction. 

We  may  summarise  what  we  have  learnt  up  to  this  point  by 
enumerating  the  principal  members  of  these  three  groups  of  amino- 
acids  :■ — 

|1.  The  mono-amino-acids :  glycine,  alanine,  leucine,  amino-valeric 
acid,  asparagine,  aspartic  acid,  glutamic  acid,  serine. 

2.  The  di-amino-acids :  lysine,  ornithine,  arginine,  and  histidine. 

3.  The  ringed  amino-acids :  phenyl-alanine,  tyrosine,  and  trypto- 

phane. 

But  this  does  not  bring  us  to  the  end  of  the  list  of  the  cleavage 
products  of  proteins,  for  we  have  still  left  several  other  groups,  most 
of  which  are  still  more  complex,  and  which  we  will,  therefore,  be 
content  with  merely  mentioning,  namely : — 

4  Pyrimidine  bases,  such  as  thymine  and  cytosine. 

5.  Pyrrolidine  derivatives. 

6.  Cystine,  a  complex  amino-acid  in  which  sulphur  is  present, 

and  in  which  the  greater  part  of  the  sulphur  of  the  protein 
molecule  is  combined, 

7.  Ammonia, 

Our  list  now  represents  the  principal  groups  of  chemical  nuclei 
united  together  in  the  protein  molecule,  and  its  length  makes  one 


404 


THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXY. 


realise  the  complicated  nature  of  that  molecule  and  the  difficulties 
which  beset  its  investigation. 

The  workers  in  Fischer's  laboratory  are  steadily  working  through 
the  various  known  proteins,  taking  them  to  pieces  and  identifying 
and  estimating  the  fragments.  I  do  not  intend  to  burden  the 
readers  of  this  book  with  anything  more  than  a  sample  of  their 
results,  and  will,  therefore,  only  give  in  a  brief  table  the  results 
obtained  with  some  of  the  cleavage  products  of  a  few  proteins.  The 
numbers  given  are  percentages. 


c 

a 

a 

^ 

"S-d 

(C 

c 

1 

0 

"3 

o 

J-- 

O    M 

MO. 

E 

i 

< 

to 

60 

S 

3 

o 
c 

a: 

o 

45 
"3 

O 

Is 

is 

E 
P 

c" 

.2 

s 

H 

5 

tS"" 

S  o 

'5 

3 

M 

m 

N3 

Glycine     . 

0 

0 

3-5 

0 

16-.5 

0-3 

3-8 

+ 

0-9 

Leucine 

20-0 

6-1 

18-7 

10-5 

2-1 

7-1 

lo'o 

11-2 

6-0 

Glutamic  acid   . 

7-7 

8-0 

8-5 

11-0 

0-8 

3-7 

17-2 

n-8 

36-5 

Tyrosine    . 

2-1- 

1-1 

2-5 

4-5 

0 

3-2 

2-1 

10-1 

2-4 

Arginine    . 

4-8 

7-6 

11-7 

TS 

2-75 

Tryptophane     . 

+ 

+ 

+ 

1-5 

0 

31  ore 
than  10 

+ 

0 

Cystine 

2-3 

0-2 

0-7 

0-06 

0-2 

Such  numbers,  of  course,  are  not  to  be  committed  to  memory,  but 
they  are  sufficient  to  convey  to  the  reader  the  differences  between 
the  proteins.  There  are  several  blanks  left,  on  account  of  no  accurate 
estimations  having  yet  been  made.  Where  the  sign  +  occurs,  the 
substance  in  question  has  been  proved  to  be  present,  but  not  yet 
determined  quantitively.  Among  the  more  striking  points  brought 
out  are : — 

1.  The  absence  of  glycine  from  albumins. 

2.  The  high  percentage  of  glycine  in  gelatin. 

3.  The  absence  of  tyrosine  and  tryptophane  in  gelatin. 

4.  The  high  percentage  of  the  sulphur  containing  substance 
(cystin)  in  keratin. 

5.  The  high  percentage  of  glutamic  acid  in  vegetable  proteins. 
Emil  Fischer  in  his  work  has  sought  to  make  such  a  list  complete, 

and  month  by  month  the  details  are  being  filled  in.  He  has  next 
tried  to  discover  the  way  in  which  the  amino-acids  are  linked 
together  into  groups ;  and  the  culmination  of  his  work  will  be  the 
discovery  of  the  way  in  which  such  groups  are  linked  together  to 
form  the  protein  molecule.  The  last  stage  he  has  not  yet  reached, 
but  it  will  be  interesting  to  see  what  progress  he  has  made  in  ascer- 
taining how.  the  amino-acids  are  linked  together  into  groups. 


CH.  XXV. ]  POLYPEPTIDES  405 

The  groups  he  ternia p^tides  ov  polypeptides ;  many  of  these  have 
l)een  made  synthetically  in  his  laboratory,  and  so  the  synthesis  of  the 
protein  molecule  is  foreshadowed. 

We  may  take  as  our  examples  of  the  peptides  some  of  the 
simplest,  and  may  write  the  formulae  of  a  few  amino-acids  as 
follows : — 

NH,  .CHg.COOH  Glycine 
NH.; .  CH^  .  COOH  Alanine 
NH;,  .  C^Hjo  .  COOH       Leucine 


or  in  general  terms 


HNH  .  K  .  COOH. 


Two  amino-acids  are  linked  together  as  shown  in  the  following 
formula : — 


HNH  .  R  .  CO    OH  .  H    NH  .  R  .  COOH 


What  happens  is  that  thehydroxyl  (OH)  of  the  carboxyl  (COOH) 
group  of  one  acid  unites  with  one  atom  of  the  hydrogen  of  the  next 
amino  (HXH)  group,  and  water  is  thus  formed,  as  shown  within  the 
dotted  lines :  this  is  eliminated  and  the  rest  of  the  chain  closes  up . 
In  this  way  we  get  a  dipeptide.  The  names  glycyl,  alanyl,  leucyl, 
etc.,  are  given  by  Fischtr  to  the  NH.^ .  E .  CO  groups  which  replace 
the  hydrogen  of  the  next  NH.,  group.  Thus  glycyl-glycine,  glycyl- 
leucine,  leucyl-alanine,  alanyl-leucine,  and  numerous  other  combina- 
tions and  permutations  are  obtained.  If  the  same  operation  is 
repeated  we  obtain  tripeptides  (leucyl-glycyl-alanine,  alanyl-leucyl- 
tyrosine,  etc.) ;  then  come  the  tetrapeptides  and  so  on.  In  the  end, 
by  coupling  the  chains  sufficiently  often  and  in  appropriate  order, 
Fischer  has  already  obtained  substances  which  give  some  of  the 
reactions  of  peptone. 

Solubilities. — The  proteins  are  insoluble  in  alcohol  and  ether. 
Some  are  soluble  in  water,*  others  insoluble.  Many  of  the  latter  are 
soluble  in  weak  saline  solutions.  Some  are  insoluble,  others  soluble 
in  concentrated  saline  solutions. 

All  proteins  are  soluble  with  the  aid  of  heat  in  concentrated 
mineral  acids  and  alkalies.  Such  treatment,  however,  decomposes  as 
well  as  dissolves  the  protein.  Proteins  are  also  soluble  in  gastric  and 
pancreatic  juices ;  but  here,  again,  they  undergo  a  change,  as  we  have 
already  seen  (p.  400). 

Heat  Coagulation. — Most  native  proteins.  Like  white  of  egg,  are 

*  The  proteins  are  not  truly  .soluble  in  water ;  they  are  in  a  state  of  rolloUlul 
solution,  a  condition  intermediate  between  true  solution  and  suspension.  Many  of 
their  properties  are  due  to  this  fact. 


406 


THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 


rendered  insoluble  when  their  solutions  are  heated.  The  temperature 
of  heat  coagulation  differs  in  different  proteins ;  thus  myosinogen  and 
fibrinogen  coagulate  at  56'  C,  serum  albumin  and  serum  globulin  at 
about  TS""  C. 

The  proteins  ^Yhich  are  coagulated  by  heat  come  mainly  under  two 
classes :  the  albumins  and  the  glohulins.  These  differ  in  solubility ; 
the  albumins  are  soluble  in  distilled  water,  the  true  globidins  require 
salts  to  hold  them  in  solution. 

Indiffusibility. — The  proteins  (peptones  excepted)  belong  to  the 
class  of  substances  called  colloids  by  Thomas  Graham ;  that  is,  they 

pass  with  difficulty,  or  not  at  all,  through 
anunal  membranes.  In  the  construction  of 
dialysers,  vegetable  parchment  is  largely 
used. 

Proteins  may  thus  be  separated  from 
diffusible  {crystalloid)  substances  like  salts, 
but  the  process  is  a  tedious  one.  If  some 
serum  or  white  of  egg  is  placed  in  a 
dialyser  (fig.  341)  and  distilled  water  out- 
side, the  greater  amount  of  the  salts  passes 
into  the  water  through  the  membrane  and 
is  replaced  by  water;  the  two  proteins 
albumin  and  globulin  remain  inside;  the 
globulin  is,  however,  precipitated,  as  the 
salts  which  previously  kept  it  in  solution 
are  removed. 

Crystallisation. — Haemoglobin,  the  red 
pigment  of  the  blood,  is  a  protein  substance 
and  is  crvstallisable  (for  further  details,  see 
The  Blood,  Chapter  XXVI.).  Like  other 
proteins  it  has  an  enormously  large  mole- 
cule ;  though  crystalline,  it  is  not,  however, 
crystalloid  in  Graham's  sense  of  that  term.  Blood  pigment,  however, 
is  not  the  only  crystallisable  protein.  Long  ago  crystals  of  protein 
(globulin  or  vitellin)  were  observed  in  the  aleurone  grains  of  many 
seeds,  and  in  the  somewhat  similar  granules  occurring  in  the  egg-yolk 
of  some  fishes  and  amphibians.  By  appropriate  methods  these  have 
been  separated  and  re-crystallised.  Further,  egg  albumin  itself  has 
been  crystaUised.  If  a  solution  of  white  of  egg  is  diluted  with  an 
equal  volume  of  saturated  solution  of  ammonium  sulphate,  the  globulin 
present  is  precipitated  and  is  removed  by  filtration.  The  filtrate  is 
now  allowed  to  remain  some  days  at  the  temperature  of  the  air,  and 
as  it  becomes  more  concentrated  from  evaporation,  minute  spheroidal 
globules  and  finally  minute  needles,  either  aggregated  or  separate, 
make  their  appearance  (Hofmeister).     Crystallisation  is  more  rapid 


Fig.  341. — Dialyser  made  of  a  tube 
of  parchment  paper,  suspended 
in  a  vessel  through  which  water 
is  kept  flowing. 


CH.  XXV.]  REACTIONS    OF   PKOTEIKS  407 

if  a  little  acetic  or  sulphuric  acid  is  added  (Hopkins).  Serum 
albumin  (from  some  animals)  has  also  been  similarly  crystallised 
(Giirbor). 

Action  on  Polarised  Light. — All  proteins  are  lovo-rotatory,  the 
amount  of  rotation  varying  with  individual  proteins.  Several  of 
the  compound  proteins,  e.g.,  haemoglobin,  and  nucleo-proteins  are 
dextro-rotatory,  though  their  protein  components  are  levo-rotatory 
(Gamgee). 

Colour  Reactions. — The  principal  colour  reactions  by  which 
proteins  are  recognised  are  the  following: — 

(1)  The  xantho-proteic  reaction  ;  if  a  few  drops  of  nitric  acid  are 
added  to  a  solution  of  a  protein  such  as  white  of  egg,  the  result  is  a  white 
precipitate ;  this  and  the  surrounding  liquid  become  yellow  on  boiling 
and  are  turned  orange  by  ammonia.  The  preliminary  white  pre- 
cipitate is  not  given  by  certain  proteins  such  as  peptones ;  but  the 
colours  are  the  same.  The  colour  is  due  to  the  formation  of  nitro- 
derivatives  from  the  aromatic  portion  of  the  protein  molecule. 

(2)  Millon's  reaction.  Millon's  reagent  is  a  mixture  of  mercuric 
and  mercurous  nitrate  with  excess  of  nitric  acid.  This  gives  a  white 
precipitate  with  proteins  which  is  turned  brick -red  on  boiling.  This 
reaction  depends  on  the  presence  in  proteins  of  the  tyrosine  radical. 

(3)  Copper  sulphate  {Base's  or  Piotrowski's)  test.  A  trace  of  copper 
sulphate  and  excess  of  strong  caustic  potash  give  with  most  proteins 
a  violet  solution.  Proteoses  and  peptones,  however,  give  a  rose-red 
colour  instead;  this  same  colour  is  given  by  the  substance  called 
biuret;  hence  the  test  is  generally  called  the  biuret  reaction.  This 
name  does  not  imply  that  biuret  is  present  in  protein;  but  both 
protein  and  biuret  give  the  reaction  because  they  possess  a  common 
radical,  probably  two  CONH  groups  linked  to  a  carbon  or  nitrogen 
atom,  or  to  one  another. 

Biuret  is  formed  by  heating  solid  urea  ;  ammonia  passes  off  and  leaves  biuret 
thus : — 

2CON,H4    =    C2O2N3H5    +    NHg. 

[Urea.]  [Biuret.]  [Ammonia.] 

(4)  Adamkiewicz  reaction.*  When  a  solution  of  protein  is  added 
to  a  dilute  solution  of  formaldehyde,  and  then  excess  of  commercial 
sulphuric  acid  is  added,  an  intense  violet  colour  is  obtained.  This 
is  due  to  the  tryptophane  radical. 

Precipitants  of  Proteins. — Solutions  of  most  proteins  are  pre- 
cipitated by : — 

Strong  acids  such  as  nitric  acid ;    picric  acid ;    acetic  acid  and 

*  In  the  original  test,  glacial  acetic  acid  was  used,  but  it  is  really  an  impurity 
in  this  acid  that  gives  the  reaction.  According  to  Hopkins,  this  impurity  is 
glyoxylic  acid  ;  according  to  Rosenheim,  it  is  formaldehyde.  The  presence  of 
impurities  (oxidising  agents)  in  the  sulphuric  acid  is  also  necessary. 


408         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

potassium  ferrocyaiiide ;  acetic  acid  and  excess  of  a  neutral  salt  such 
as  sodium  sulphate,  when  these  are  boiled  with  the  protein  solution ; 
salts  of  the  heavy  metals  such  as  copper  sulphate,  mercuric  chloride, 
lead  acetate,  silver  nitrate,  etc. ;  tannin ;  alcohol ;  saturation  with 
certain  neutral  salts  such  as  ammonium  sulphate. 

It  is  necessary  that  the  words  coagulation  and  precipitation  should 
in  connection  with  proteins  be  carefully  distinguished.  The  term 
coagulation  is  used  when  an  insoluble  protein  (coagulated  protein)  is 
formed  from  a  soluble  one.     This  may  occur : 

1.  When  a  protein  is  heated — heat  coagulation  ; 

2.  Under  the  influence  of  a  ferment ;  for  instance,  when  a  curd  is 
formed  in  milk  by  rennet  or  a  clot  in  shed  blood  by  the  fibrin  ferment 
— -ferment  coagulation  ; 

3.  When  an  insoluble  precipitate  is  produced  by  the  addition  of 
certain  reagents  (nitric  acid,  picric  acid,  tannin,  etc.). 

There  are,  however,  other  precipitants  of  proteins  in  which  the 
precipitate  formed  is  readily  soluble  in  suitable  reagents  such  as  saline 
solutions,  and  the  protein  continues  to  show  its  typical  reactions. 
Such  precipitation  is  not  coagulation.  Such  a  precipitate  is  produced 
by  saturation  with  ammonium  sulphate.  Certain  proteins,  called 
globulins,  are  more  readily  precipitated  by  such  means  than  others. 
Thus,  serum  globulin  is  precipitated  by  half -saturation  with  ammonium 
sulphate.  Full  saturation  with  ammonium  sulphate  precipitates  all 
proteins  but  peptone.  The  globulins  are  precipitated  by  certain  salts 
such  as  sodium  chloride  and  magnesium  sulphate,  which  do  not  precipi- 
tate the  albumins.  This  method  of  precipitation  is  called  "salting 
out." 

The  precipitation  produced  by  alcohol  is  peculiar  in  that  after  a 
time  it  becomes  a  coagulation.  Protein  freshly  precipitated  by 
alcohol  is  readily  soluble  in  water  or  saline  media ;  but  after  it  has 
been  allowed  to  stand  some  weeks  under  alcohol  it  becomes  more  and 
more  insoluble.  Albumins  and  globulins  are  most  readily  rendered 
insoluble  by  this  method ;  proteoses  and  peptones  are  never  rendered 
insoluble  by  the  action  of  alcohol.  This  fact  is  of  value  in  the 
separation  of  these  proteins  from  others. 

Classification  of  Peoteins. 

The  knowledge  of  the  chemistry  of  the  proteins,  which  is  slowly 
progressing  under  Emil  Fischer's  leadership,  will,  no  doubt,  in  time 
enable  us  to  give  a  classification  of  these  substances  on  a  strictly 
chemical  basis.  But  until  that  time  arrives,  we  must  be  content 
very  largely  with  the  artificial  classification  (on  the  basis  of  solubility 
and  so  forth)  which  has  hitherto  prevailed.  The  following  classifica- 
tion must  therefore  be  regarded  as  a  provisional  one,  which  while  it 


CH.  XXV.]  PROTAMINKS   AND   HISTONES  409 

retains  the  old  familiar  names  as  far  as  possible,  yet  attempts  also  to 
incorporate  some  of  the  new  ideas. 

The  classes  of  proteins  then,  beginning  with  the  simplest,  are  as 
follows : — 

1.  Protamines.  6.  Phospho-proteins. 

2.  Histones.  7.  Conjugated  proteins. 

3.  Albumins.  i.  Chromo-proteins. 

4.  Globulins.  ii.  Gluco-proteins. 

5.  Sclero-proteins.  iii.  ISTucleo-proteins. 

We  will  take  these  classes  one  by  one. 

1.  The  Protamines. 

These  substances  are  obtainable  from  the  heads  of  the  spermatozoa 
of  certain  fishes,  where  they  occur  in  combination  with  nuclein. 
Kossel's  view  that  they  are  the  simplest  proteins  in  nature  has  met 
with  general  acceptance,  and  they  give  such  typical  protein  reactions 
as  the  copper  sulphate  test  (Eose's  or  Piotrowski's  reaction).  On 
hydrolytic  decomposition  they  first  yield  substances  of  smaller 
molecular  weight  analogous  to  the  peptones  which  are  eaXled  protones, 
and  then  they  split  up  into  amino-acids.  The  number  of  resulting 
amino-acids  is  small  as  compared  with  other  proteins,  hence  the 
hypothesis  that  they  are  simple  proteins  is  confirmed.  Notable 
among  their  decomposition  products  are  the  diamino-acids  or  hexone 
bases  (see  p.  402). 

The  protamines  differ  in   their  composition  according  to    their 

source,  and  yield  these  products  in  different  proportions. 

Salmine  (from  the  salmon  roe)  and  clupeine  (from  the  herring  roe)  appear  to  be 
identical,  and  have  the  empirical  formula  CjnHj-Ni-O,; ;  its  principal  decomposi- 
tion product  isarginine,  but  amino- valeric  acid  and  a  small  quantity  of  an  unknown 
residue  are  also  found.  Stiirine  (from  the  sturgeon)  yields  the  same  products  with 
lysine  and  histidine  in  addition.  With  one  exception,  the  protamines  yield  no 
aromatic  amino-acids.  The  exception  is  rj/clopterine  (from  Ci/clopterus  liimpiis); 
this  substance  is  thus  an  important  chemical  link  between  the  other  protamines 
and  the  more  complex  members  of  the  protein  family. 

2.  The  Histones. 

These  are  substances  which  have  been  separated  from  blood 
corpuscles ;  globin,  the  protein  constituent  of  haemoglobin,  is  a  well- 
marked  instance.  They  yield  a  larger  number  of  amino-compounds 
than  do  the  protamines.  They  are  coagulable  by  heat,  soluble  in 
dilute  acids,  and  precipitable  from  such  solutions  by  ammonia.  The 
precipitability  by  ammonia  is  a  property  possessed  by  no  other 
protein  group. 

3.  The  Albumins. 

These  are  typical  proteins,  and  yield  the  majority  of  the  cleavage 
products  enumerated  on  pp.  400-403. 


410 


THE  CHEMICAL  COMPOSITION  OF  THE  BODY    [CH.  XXV. 


They  enter  into  colloidal  solution  in  water,  in  dilute  saline  solu- 
tions, and  in  saturated  solutions  of  sodium  chloride  and  magnesium 
sulphate.  They  are,  however,  precipitated  by  saturating  their 
solutions  with  ammonium  sulphate.  Their  solutions  are  coagulated 
by  heat  usually  at  70-73°  C.  Serum  albumin,  egg  albumin,  and 
lact -albumin  are  instances. 

4.  The  Globulins. 

The  globulins  give  the  same  general  tests  as  the  albumins;  they 
are  coagulated  by  heat,  but  differ  from  the  albumins  mainly  in  their 
solubilities.  This  difference  in  solubility  may  be  stated  in  tabular 
form  as  follows : — 


Keagent. 

Albumin. 

Globulin. 

Water 

Dilute  saline  solution     .... 

Saturated  solution  of  magnesium  sul- 
phate or  sodium  chloride  . 

Half-saturated  solution  of  ammonium 
sulphate 

Saturated  solution  of  ammonium  sul- 
phate          

soluble 
soluble 

soluble 

soluble 

insoluble 

insoluble 
soluble 

insoluble 

insoluble 

insoluble 

In  general  terms  globulins  are  more  readily  salted  out  than 
albumins ;  they  may  therefore  be  precipitated,  and  thus  separated 
from  the  albumins  by  saturation  with  such  salts  as  sodium  chloride, 
or  better  magnesium  sulphate,  or  by  half  saturation  with  ammonium 
sulphate. 

The  typical  globulins  are  also  insoluble  in  water,  and  so  may  be 
precipitated  by  removing  the  salt  which  keeps  them  in  solution. 
This  may  be  accomplished  by  dialysis  (see  p.  406).  Their  temperature 
of  heat-coagulation  varies  considerably.  The  following  are  the 
commoner  globulins : — fibrinogen  and  serum  globulin  in  blood,  egg 
globulin  in  white  of  egg,  paramyosinogen  in  muscle,  and  crystallin  in 
the  crystalline  lens.  We  must  also  include  under  the  same  heading 
certain  proteins  which  are  the  result  of  ferment  coagulation  on 
globulins,  such  as  fibrin  (see  blood)  and  myosin  (see  muscle). 

The  most  striking  and  real  distinction  between  globulins  and 
albumins  is  that  the  former  on  hydrolysis  yield  glycine,  whereas  the 
albumins  do  not. 

5.  The  Sclero-proteins. 

These  substances  form  a  heterogeneous  group  of  substances, 
which  are  frequently  termed  albuminoids.    The  prefix  sclero  indicates 


CH.  XXV.]  CLASSES   OF   PROTEINS  411 

the  skeletal  origin  and  often  insoluble  nature  of  the  members  of  the 
group.     The  princijial  proteins  under  this  head  are : — 

Collagen,  the  substance  of  which  the  white  fibres  of  connective 
tissue  are  composed.  Some  observers  regard  it  as  the  anhydride  of 
gelatin.     In  bone  it  is  often  called  ossein. 

Gelatin — This  substance  is  produced  by  boiling  collagen  with 
water.  It  possesses  the  peculiar  property  of  setting  into  a  jelly  when 
a  solution  made  with  hot  water  cools.  On  digestion  it  is  like  ordinary 
proteins  converted  into  peptone-like  substances,  and  is  readily 
absorbed.  Though  it  will  replace  in  diet  a  certain  quantity  of  such 
proteins,  acting  as  what  is  called  a  "  protein-sparing  "  food,  it  cannot 
altogether  take  their  place  as  a  food.  Animals  whose  sole  nitrogenous 
food  is  gelatin  waste  rapidly.  The  reason  for  this  is  that  gelatin 
contains  neither  the  tyrosine  or  the  tryptophane  groups,  and  so  it 
gives  neither  Millon's  nor  the  Adamkiewicz  reactions.  Animals  who 
receive  a  mixture  of  gelatin,  tyrosine,  and  tryptophane  in  their  diet 
thrive  better. 

Chondrin  is  the  name  given  to  the  mixture  of  gelatin  and  mucoid 
which  is  obtained  by  boiling  cartilage. 

Elastin. — This  is  the  substance  of  which  the  yellow  or  elastic 
fibres  of  connective  tissue  are  composed.  It  is  a  very  insoluble 
material.  The  sarcolemma  of  muscular  fibres  and  certain  basement 
membranes  are  very  similar. 

Keratin,  or  horny  material,  is  the  substance  found  in  the  surface 
layers  of  the  epidermis,  in  hairs,  nails,  hoofs,  and  horns.  It  is  very 
insoluble,  and  chiefly  differs  from  most  other  proteins  in  its  high 
percentage  of  sulphur.  A  similar  substance,  called  neurokeratin,  is 
found  in  neuroglia  and  nerve-fibres.  In  this  connection  it  is  interest- 
ing to  note  that  the  epidermis  and  the  nervous  system  are  both 
formed  from  the  same  layer  of  the  embryo — the  epiblast. 

6.  The  Phospho-proteins. 

Vitellin  (from  egg-yolk),  caseinogen,  the  principal  protein  of 
milk,  and  casein,  the  result  of  the  action  of  the  rennet-ferment 
on  caseiuogen  (see  milk),  are  the  chief  members  of  this  group. 
Among  their  decomposition  products  is  a  considerable  quantity  of 
phosphoric  acid.  They  have  been  frequently  confused  with  the 
nucleo-proteins  we  shall  be  studying  immediately,  and  the  prefix 
nucleo — so  often  applied  to  them — is  entirely  misleading,  since  they 
do  not  yield  the  products  (purine  bases,  etc.)  which  are  characteristic 
of  nucleo-compounds. 

7.  The  Conjugated  Proteins. 

These  are  compounds  in  which  the  protein  molecule  is  united  to 
other  organic  materials,  which  are  as  a  rule  also  of  complex  nature. 


412  THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

This  second  constituent  of  the  compound  is  usually  termed  a  pros- 
thetic group.      They  may  be  divided  into  the  following  sub-classes : — 

i.  Chromo-proteins. — These  are  compounds  of  protein  with  a 
pigment,  which  usually  contains  iron.  They  are  typified  by  hfemo- 
globin  and  its  allies,  which  will  be  fully  considered  under  blood. 

ii.  Gluco-proteins. — These  are  compounds  of  protein  with  a 
carbohydrate  group.     This  class  includes  the  mucins  and  the  mucoids. 

The  mucins  are  widely  distributed  and  may  occur  in  epitheHal 
cells,  or  be  shed  out  by  these  cells  (mucus,  mucous  glands,  goblet 
cells).  The  mucin  obtained  from  different  sources  varies  in  composi- 
tion and  reactions,  but  they  all  agree  in  being  viscid  and  tenacious, 
soluble  in  dilute  alkalis  such  as  lime  water,  and  precipitable  from 
solution  by  acetic  acid. 

The  mucoids  differ  from  the  mucins  in  minor  details.  The  term 
is  applied  to  the  mucin-like  substances  which  form  the  chief  con- 
stituent of  the  ground  substance  of  connective  tissues  (tendo-mucoid, 
chondro-mucoid,  etc.).  Another  (ovo-mucoid)  is  found  in  white  of 
egg,  and  others  (pseudo-mucin  and  para-mucin)  are  occasionally  found 
in  dropsical  effusions,  and  in  the  fluid  of  ovarian  cysts. 

It  is  probable  that  the  differences  between  the  mucins  and 
mucoids  are  due  either  to  the  nature  of  the  carbohydrate  group,  or 
more  probably  to  the  nature  of  the  protein  to  which  it  is  united. 
The  carbohydrate  substance  in  the  majority  of  cases  is  not  sugar,  but 
a  nitrogenous  substance  which  has  a  similar  reducing  power  to  sugar, 
and  which  is  called  glucosa.mine  (CgHj^O.XHo),  that  is,  glucose  in 
which  HO  is  replaced  by  XH.,. 

Pavy  and  others  have  shown  that  a  small  quantity  of  the  same 
carbohydrate  derivative  can  be  split  off  from  various  other  proteins 
which  we  have  already  placed  among  the  albumins  and  globulins. 
It  is,  however,  probable  that  this  must  not  be  considered  a  prosthetic 
group,  but  is  more  intimately  united  within  the  protein  molecule. 

iii.  Nucleo-proteins. — These  are  compounds  of  protein  with  a 
complex  organic  acid  called  nucleic  acid  which  contains  phosphorus. 
They  are  found  both  in  the  nuclei  and  cell-protoplasm  of  cells.  In 
physical  character  they  often  simulate  mucin. 

NvAcin  is  the  name  given  to  the  chief  constituent  of  cell-nuclei. 
It  is  identical  with  the  chromatin  of  histologists  (see  p.  11). 

On  decomposition  it  yields  an  organic  acid  called  nucleic  acid, 
together  with  a  variable  Ijut  usually  small  amount  of  protein.  It 
contains  a  high  percentage  (10-11)  of  phosphorus. 

The  nuclein  obtained  from  the  nuclei  or  heads  of  the  spermatozoa 
consists  of  nucleic  acid  without  any  protein  admixture.  In  fishes' 
spermatozoa,  however,  there  is  an  exception  to  this  rule,  for  there  it 
is,  as  we  have  already  seen,  united  to  protamine. 

The  inpslco-proteins  of  cell  protoplasm  are  compounds  of   nucleic 


CH.  XXV.]  NUCLF.O-PIIOTEINS  413 

acid  with  a  much  larger  quantity  of  protein,  so  that  they  usually 
contain  only  1  per  cent,  or  less  of  phosphorus.  Some  also  contain 
iron,  and  the  normal  supply  of  iron  to  the  body  is  contained  in  the 
nucleo -proteins  or  hcemator/ens  (Bunge)  of  plant  or  animal  cells. 

Nuclco-proteins  may  be  prepared  from  cellular  structures  like  thymus,  testis, 
kidney,  etc. ,  by  two  principal  methods  : — 

1.  ]Vool(lrii/t/i;\i  method.— The  organ  is  minced,  and  soaked  in  water  for  twenty- 
four  hours.  Dilute  acetic  acid  added  to  the  aqueous  extract  precipitates  the  nucleo- 
protein. 

2.  Sodium  chloride  method.— The  minced  organ  is  ground  up  in  a  mortar  with 
solid  sodium  chloride ;  the  rcsultinf,'  viscous  mass  is  poured  into  excess  of  water, 
and  the  nucleo-protein  rises  in  strings  to  tlie  top  of  the  water. 

The  solvent  usually  employed  for  a  nucleo-protein,  whichever  method  it  is 
prepared  by,  is  a  1  per  cent,  solution  of  sodium  carbonate.  The  relationship  of 
nucleo-proteins  to  the  coagulation  of  the  blood  is  described  under  tiiat  heading. 

Nurleic  acid  yields,  among  its  decomposition  products,  phosphoric 
acid,  various  bases  of  the  xanthine  group,  and  bases  also  of  the 
pyrimidine  group  (cytosine,  thymine,  uracil).  In  some  cases  a  carbo- 
hydrate radical  is  also  obtained ;  thus  a  pentose  is  obtained  from  the 
nucleic  acid  of  the  pancreas,  the  liver,  and  yeast  cells.  There  appear 
to  be  several  nucleic  acids,  which  vary  in  the  relative  amount  they 
yield  of  their  decomposition  products,  especially  of  the  members  of 
the  xanthine  family  which  are  sometimes  called  alloxuric  or  more 
usually  purine  bases.  The  purine  bases  are  closely  allied  chemically 
to  uric  acid,  and  we  shall  have  to  study  them  again  in  relation  to 
that  substance.  The  following  diagrammatic  way  of  representing 
the  decomposition  of  nucleo-protein  will  assist  the  student  in 
remembering  the  relationships  of  these  substances : — - 

XuCLEO-PltOTEIN 

subjected  to  gastric  digestion  yields 


Protein  converted  into  peptone,  Nuclein,  which  remains  as  an  insoluble 

which  goes  into  solution.  residue.     If  this  is  dissolved  in  alkali 

and  hydrochloric  acid  added,  it  yields 


Protein— converted  into  acid  A    precipitate    consisting    of    nucleic 

albumin  in  solution.  acid.     If  this  is  heated  in  a  sealed 

tube  with  hydrochloric  acid,  it  yields 
a  number  of  substances.      But  the 
best  known  and  most  constant  pro- 
ducts of  its  decomposition  are 
I 

I  \  i 

Phosphoric  acid.                    Purine  bases,  viz.  : —  Pyriniidine  bases. 

Adenine.  viz.  : — 

Hypoxanthine.  Uracil. 

Guanine.  Thymine. 

Xanthine.  Cytosine. 


414         THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 

Protein-hydrolysis. 

When  protein  material  is  subjected  to  hydrolysis,  as  it  is  when 
heated  with  mineral  acid,  or  superheated  steam,  or  to  the  action  of 
such  ferments  as  pepsin  or  trypsin  in  the  alimentary  canal,  it  is 
finally  resolved  into  the  numerous  amino -acids  of  which  it  is  built. 
But  before  this  ultimate  stage  is  reached,  it  is  split  into  substances  of 
progressively  diminishing  molecular  size,  which  still  retain  many  of 
the  protein  characters.  The  products  may  be  classified  in  order  of 
formation  as  follows: — 

1.  Meta-proteins. 

2.  Proteoses. 

3.  Peptones. 

4.  Polypeptides. 

5.  Amino-acids. 

The  polypeptides  are  linkages  of  two  or  more  amino-acids,  as 
already  explained.  They  do  not  give  the  biuret  reaction.  Although 
most  of  the  polypeptides  at  present  known  are  products  of  laboratory 
synthesis,  some  have  been  definitely  sejDarated  from  the  digestion  of 
proteins,  and  so  they  must  appear  in  our  classification.  The  pro- 
teoses and  peptones  give  the  biuret  reaction  ;  the  peptones,  however, 
cannot  be  salted  out  of  solution  like  the  proteoses :  their  molecules 
are  smaller  than  those  of  the  proteoses.  We  shall  study  them  more 
fully  under  digestion. 

It  is,  however,  convenient  to  add  here  a  brief  description  of  the 
meta-proteins.  They  are  obtained  as  the  first  stage  of  hydrolysis,  and 
also  by  the  action  of  dilute  acids  or  alkalis  on  either  albumins  or 
globulins.  The  general  properties  of  the  acid-alhumin  or  syntonin 
and  the  alkali-alhumin,  which  are  thereby  respectively  formed,  are  as 
follows : — They  are  insoluble  in  pure  water,  but  are  soluble  in  either 
acid  or  alkali,  and  are  precipitated  by  neutralisation  unless  certain 
disturbing  influences  like  sodium  phosphate  are  present.  They  are 
precipitated  as  globulins  are  by  saturation  with  such  neutral  salts  as 
sodium  chloride  or  magnesium  sulphate.  They  are  not  coagulated  by 
heat  if  in  solution. 

The  name  albuminate  used  to  be  applied  to  these  substances  ;  but  this  is  an 
objectionable  term,  for  these  first  degradation  products  of  protein  hydrolysis  are 
not  salts,  as  the  termination  (tfe  would  imply.  Moreover,  they  are  obtainable  from 
both  albumins  and  globulins.  The  prefix  "meta"  (or  possibly  "infra,"  which 
some  prefer)  may  be  taken  as  an  indication  of  comparatively  slight  chemical 
alteration. 

A  variety  of  alkali-  albumin  (probably  a  compound  containing  a  large  quantity 
of  alkali)  may  be  formed  by  adding  strong  potash  to  undiluted  white  of  egg.  The 
resulting  jelly  is  called  Lieberkiihns  jelli/.  A  similar  jelly  is  obtainable  by  adding 
strong  acetic  acid  to  undiluted  egg  white. 

The  word  albuminate  is  also  iised  for  compounds  of  protein  with  mineral 
substances.  Thus  if  a  solution  of  copper  sulphate  is  added  to  a  solution  of 
albumin,  a  precipitate  of  copper  albuminate  is  formed.     Similarly,  by  the  addition 


CH.  XXV.]  TTTE    I'OLARIMETER  415 

of  other  salts  of  the  heavy  metals,  other  inetalhc  allnuuinates  are  obtainable.  The 
halogens  (chlorine,  broiuinc,  iodine)  also  form  albuminates  in  this  sense,  and  may 
be  used  for  the  jirecipitation  of  proteins. 

It  should  be  noted  in  conclusion  that  the  forep^oinf:;  classification  of  proteins  is 
mainly  applical)le  to  those  of  animal  origin.  The  vegetable  proteins  may  roughly 
be  arranged  under  the  same  main  headings,  although  it  is  doubtful  if  a  real  and 
complete  analogy  exists  in  all  cases.  The  cleavage  products  of  the  vegetable 
proteins  are  in  the  rhain  the  same  as  those  of  the  animal  proteins,  but  the  quantity 
of  each  yielded  is  usually  different.  Vegetable  proteins,  for  instance,  as  a  rule 
give  a  very  much  higher  yield  of  glutamic  acid  than  do  those  of  animal  origin. 

Further,  there  are  certain  vi'getable  proteins  which  have  hitherto  been  regarded 
as  peptones,  but  which  do  not  give  the  biuret  reaction.  It  seems  impossible  at 
present  to  bring  exceptional  substances  of  this  kind  into  any  general  classification, 
and  the  same  is  true  for  those  curious  vegetable  proteins,  such  as  gliadin  from  the 
gluten  of  wheat,  and  zein  from  maize,  which  stand  apart  from  all  other  members  of 
the  group  in  being  soluble  in  alcohol. 

The  Polarimeter. 

This  instrument  is  one  by  means  of  which  the  action  of  various  substances  on 
the  plane  of  polarised  light  can  be  observed  and  measured. 

Most  of  the  carbohydrates  are  dextro-rotatory. 

All  the  proteins  are  levo-rotatory. 

There  are  many  varieties  of  the  instrument ;  these  can  only  be  properly  studied 
in  a  practical  class,  and  all  one  can  do  here  is  to  state  briefly  the  principles  on 
which  they  are  constructed. 

Sui)pose  one  is  shooting  arrows  at  a  fence  made  up  of  narrow  vertical  palings  ; 
suppose  also  that  the  arrows  are  flat  like  the  laths  of  a  Venetian  Wind.  If  the 
arrows  are  shot  vertically  they  will  pass  easily  through  the  gaps  between  the 
palings,  but  if  they  are  shot  horizontally  they  will  be  unable  to  pass  through  at 
all.  This  rough  illustration  will  help  us  in  understanding  what  is  meant  by  polarised 
light.  Ordinary  light  is  produced  by  the  undulations  of  ether  occurring  in  all 
directions  at  right  angles  to  the  path  of  propagation  of  the  wave.  Polarised  light 
is  produced  by  undulations  in  one  plane  only;  we"  may  compare  it  to  our  flat 
arrows. 

In  a  polarimeter,  there  is  at  one  end  of  the  instrument  a  Nicol's  prism,  which 
is  made  of  Iceland  spar.  This  polarises  the  light  which  passes  through  it ;  it  is 
called  the  polariser.  At  the  other  end  of  the  instrument  is  another  called  the 
analyser.  Between  the  two  is  a  tube  which  can  be  filled  with  fluid.  If  the  analyser 
is  parallel  to  the  polariser  the  light  will  pass  through  to  the  eye  of  the  observer. 
But  if  the  analyser  is  at  right  angles  to  the  polariser  it  is  like  the  flat  arrows  hitting 
horizontally  the  vertical  palings  of  the  fence,  and  there  is  darkness.  At  inter- 
mediate angles  there  will  be  intermediate  degrees  of  illumination. 

If  the  analyser  and  polariser  are  parallel  and  the  intermediate  tube  filled  with 
water,  the  light  will  pass  as  usual,  because  water  has  no  action  on  the  plane  of 
polarised  light.  But  if  the  water  contains  sugar  or  some  "  optically  active  "  substance 
in  solution  the  plane  is  twisted  in  one  direction  or  the  other  according  as  the  sub- 
stance is  dextro-  or  levo-rotatory.  The  amount  of  rotation  is  measured  by  the 
number  of  angles  through  which  the  analyser  has  to  be  turned  in  order  to  obtain 
the  full  illumination.  This  will  vary  with  the  length  of  the  tube  and  the  strength 
of  the  solution. 

Ferments. 

The  word  fermentation  was  first  applied  to  the  change  of  sugar 
into  alcohol  and  carbonic  acid  by  means  of  yeast.  The  evolution  of 
carbonic  acid  causes  frothing  and  bubbUng ;  hence  the  term  "  fermen- 
tation." The  agent,  yeast,  which  produces  this,  is  called  the  ferment. 
Microscopic  investigation  shows  that   yeast  is  composed  of  minute 


416 


THE  CHEMICAL  COMPOSITION  OF  THE  BODY     [CH.  XXV. 


rapidly-growing    unicellular    organisms   (torulae)    belonging    to    the 
fungus  group  of  plants. 

The  souring  of  milk,  the  transformation  of  urea  into  ammonium 
carbonate  in  decomposing  urine,  and  the  formation  of  vinegar  (acetic 
acid)  from  alcohol  are  brought  about  by  very 
similar  organisms.  The  complex«6eries  of  changes 
known  as  putrefaction,  which  are  accompanied  by 
the  formation  of  malodorous  gases,  and  which  are 
produced  by  the  various  forms  of  bacteria,  also 
come  into  the  same  category. 

That  the  change  or  fermentation  is  produced 
by  these  organisms  is  shown  by  the  fact  that  it 
occurs  only  when  the  organisms  are  present,  and 
stops  when  they  are  removed  or  killed  by  a  high 
temperature  or  by  certain  substances  (carbolic 
acid,  mercuric  chloride,  etc.)  called  antiseptics. 
The  "germ  theory"  of  disease  explains  the  infectious  diseases  by 
considering  that  the  change  in  the  system  is  of  the  nature  of  fermen- 
tation, and,  like  the  others  we  have  mentioned,  produced  by  microbes ; 
the  transference  of  the  bacteria  or  their  spores  from  one  person  to 
another  constitutes  infection.  The  poisons  produced  by  the  growing 
bacteria  appear  to  be  either  alkaloidal  (ptomaines)  or  protein  in  nature. 
The  existence  of  poisonous  proteins  is  a  very  remarkable  thing,  as  no 
marked  chemical  differences  can  be  shown  to  exist  between  them  and 
those  which  are  not  poisonous,  but  which  are  useful  as  foods.     The 


Fig.  342.— Cells  of  the 
yeast  plant  in  process 
of  budding. 


o      0 

°  6> 


■^.^ 


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C^ 


<^ 


Oo 


^ 


Fig.  343. — Types  of  micro-organisms:  a,  micrococci  arranged  singly;  in  twos,  diplococci — if  all  the 
micrococci  at  a  were  grouped  together  they  would  be  called  staphylococci — and  in  fours,  sarcinse  ; 
6,  micrococci  in  chains,  streptococci;  c  and  d,  bacilli  of  various  kinds  (one  is  represented  with 
a  flageUum);  e,  various  forms  of  spirilla ;  /,  spores,  either  free  or  in  bacilli. 


most  virulent  poison  in  existence,  namely,  snake  poison,  is  a  protein 
of  the  proteose  class. 

There  is  another  class  of  chemical  transformations  which  at  first 
sight  differ  very  considerably  from  all  of  these.  They,  however, 
resemble   these   fermentations   in   the   fact   that   they   occur  inde- 


en.  XXV.]  FERMENTS  417 

pendenfcly  of  any  apparent  change  in  tlio  agents  that  produce 
them.  The  agents  that  produce  them  are  not  living  organisms, 
but  chemical  substances,  the  result  of  the  activity  of  living  cells. 
The  change  of  starch  into  sugar  by  the  ptyalin  of  the  saliva  is  an 
instance. 

Ferments  may  therefore  be  divided  into  two  classes : — 

1.  The  organised  ferments — torulae,  bacteria,  etc. 

2.  The  unorganised  ferments,  or  enzymes — such  as  ptyalin. 

The  distinction  between  organised  ferments  and  enzymes  is,  how- 
ever, more  apparent  than  real;  for  the  micro-organisms  exert  their 
action  by  enzymes  which  they  secrete.  This  has  long  been  known 
in  connection  with  the  invertin  of  yeast,  and  for  the  enzyme 
secreted  by  the  micrococcus  urese,  which  converts  urea  into  ammonium 
carbonate.  In  recent  years  Buchner,  by  crushing  yeast  cells,  succeeded 
in  obtaining  from  them  an  enzyme  which  produces  the  alcoholic  fer- 
mentation, and  there  is  no  doubt  that  what  is  true  for  yeast  is  equally 
true  for  all  the  organised  ferments,  and  in  many  cases  this  has  been 
already  proved  experimentally. 

The  unorganised  ferments  may  be  classified  as  follows : — 

{a)  Amylolytic — those  which  change  amyloses  (starch,  glycogen) 
into  sugars.     Examples :  ptyalin,  diastase,  amylopsin. 

(6)  Proteolytic — those  which  change  proteins  into  proteoses  and 
peptones.     Examples:  pepsin,  trypsin. 

(c)  Steatolytic — those  which  split  fats  into  fatty  acids  and 
glycerin.     An  example,  steapsin,  is  found  in  pancreatic  juice. 

{d)  Inversive  —  those  which  convert  saccharoses  (cane  sugar, 
maltose,  lactose)  into  glucose.  Examples :  invertin  of  intestinal 
juice  and  of  yeast  cells. 

(e)  Coagulative — those  which  convert  soluble  into  insoluble 
proteins.     Examples :  rennet,  fibrin  ferment. 

Most  ferment  actions  are  hydrolytic — i.e.,  water  is  added  to  the 
material  acted  on,  which  then  splits  into  new  materials.  This  is 
seen  by  the  following  examples : — 

1.  Conversion  of  cellulose  into  carbonic  acid  and  marsh  gas 
(methane)  by  putrefactive  organisms — 

(C,Hi,pj«    +    «H,.0    =    3«COo    +    3/jCH^. 

[Cellulose.]  [Water.]  [Carbonic  [Methane.] 

acid.] 

2.  Inversion  of  cane  sugar  by  the  unorganised  ferment  invertin — 

q,H,,Pii    +    H,0    =    C,Hi,0,   +    C,Hi,0,, 

[Cane  sugar.]  [Water.]  [Dextrose.]  [Levulose.] 

Some  enzymes,  called  oxidases,  are  oxygen  carriers,  and  produce 
oxidation.     They  occur  in  living  tissues. 

A  remarkable  fact  concerning  the  ferments  is  that  the  substances 

2  D 


418  THE    CHEMICAL   COMPOSITION    OF   THE   BODY  [CH.  XXV. 

they  produce  in  time  put  a  stop  to  their  activity ;  thus,  in  the  case  of 
the  organised  ferments,  the  alcohol  produced  by  yeast,  the  phenol, 
cresol,  etc.,  produced  by  putrefactive  organisms  from  proteins,  first 
stop  the  growth  of  and  ultimately  kill  the  organisms  which  produce 
them.  In  the  case  of  the  enzjTnes  also  the  products  of  their  activity 
hinder  and  finally  stop  their  action,  but  on  the  removal  of  these  pro- 
ducts the  ferments  resume  work. 

This  fact  suggested  to  Croft  Hill  the  question  whether  ferments 
will  act  in  the  reverse  manner  to  their  usual  action ;  and  in  the  case 
of  one  ferment,  at  any  rate,  he  found  this  to  be  the  case.  Inverting 
ferments,  as  we  have  just  seen,  usually  convert  a  disaccharide  into 
monosaccharides.  One  of  these  inverting  ferments,  called  maltasc, 
converts  maltose  into  dextrose.  If  the  ferment  is  allowed  to  act  on 
strong  solutions  of  dextrose,  it  converts  a  small  proportion  of  that 
sugar  back  into  maltose  again.  This  discovery  of  Croft  Hill's  has 
since  been  confirmed  by  others  in  relation  to  other  enzymes. 

Ferments  act  best  at  a  temperature  of  about  40  C.  Their  activity 
is  stopped,  but  the  ferments  are  not  destroyed,  by  cold ;  it  is  stopped 
and  the  ferments  kiUed  by  too  great  heat.  A  certain  amount  of 
moisture  and  oxygen  is  also  necessary ;  there  are,  however,  certain 
micro-organisms  that  act  without  free  oxygen,  and  are  called  anae- 
robic in  contradistinction  to  those  which  require  oxygen,  and  are 
called  aerobic. 

The  enzymes  act  as  catalysts,  that  is  to  say,  they  are  able  to 
increase  the  velocity  of  chemical  changes,  which  occur  in  their 
absence  so  slowly,  that  for  all  practical  purposes  they  may  be  con- 
sidered not  to  occur  at  all.  The  organism  is  thus  enabled  to  bring 
about,  at  body  temperature,  many  chemical  reactions  which  would 
otherwise  necessitate  a  high  temperature  or  powerful  reagents.  The 
enzymes,  however,  differ  from  most  inorganic  catalysts  in  some  of 
their  properties:  one  such  property  is  that  they  are  destroyed  by 
heat;  the  explanation  of  this  and  other  differences  is  that  the 
enzymes,  like  the  proteins,  are  in  a  colloidal  condition. 

It  is  necessary  to  correct  a  notion  which  I  find  widespread  among  students, 
that  in  the  chemical  changes  brought  about  by  ferments  there  is  a  conversion  of 
potential  into  actual  energy  (heat  and  kinetic  energy).  This  is  not  the  case  in  the 
majority  of  ferment  actions,  namely,  those  which  are  hydrolytic  ;  the  total  potential 
energy  of  the  products  is  there  equal  to  that  of  the  substance  acted  upon.  This  has 
been  proved  by  actual  experiment.  Moreover,  if  a  transformation  of  energj'  did 
occur,  it  would  be  incompatible  with  the  fact  that  ferment  action  is  reversible. 


CHAPTEK  XXVI 

THE   BLOOD 

The  blood  is  the  fluid  medium  by  means  of  which  all  the  tissues  of 
the  body  are  directly  or  indirectly  nourished ;  by  means  of  it  also 
such  of  the  materials  resulting  from  the  metabolism  of  the  tissues 
which  are  of  no  further  use  in  the  economy  are  carried  to  the  excre- 
tory organs.  It  is  a  somewhat  viscid  fluid,  and  in  man  and  in  all 
other  vertebrate  animals,  with  the  exception  of  two,*  is  red  in  colour. 
It  consists  of  a  yellowish  fluid,  called  plasma  or  liquor  sanguinis, 
in  which  are  suspended  numerous  blood  corpuscles,  the  majority  of 
which  are  coloured,  and  it  is  to  their  presence  that  the  red  colour  of 
the  blood  is  due.  In  addition  to  the  red  corpuscles,  there  are  a 
smaller  number  of  colo^irless  coijouscles,  and  some  extremely  small 
particles  called  blood-platelets. 

Even  when  examined  in  very  thin  layers,  blood  is  opaque,  on 
account  of  the  different  refractive  powers  possessed  by  its  two  con- 
stituents, viz.,  the  plasma  and  the  corpuscles.  On  treatment  with 
ether,  water,  and  other  reagents,  however,  it  becomes  transparent  and 
assumes  a  lake  colour,  in  consequence  of  the  colouring  matter  of  the 
corpuscles  having  been  discharged  into  the  plasma.  The  average 
specific  gravity  of  blood  at  15"  C.  (60'  F.)  varies  from  1055  to  1062. 
A  rapid  and  useful  method  of  estimating  the  specific  gravity  of  blood 
was  invented  by  Eoy.  Drops  of  blood  are  taken  and  allowed  to  fall 
into  fluids  of  known  specific  gravity.  When  the  drop  neither  rises 
nor  sinks  in  the  fluid  it  is  taken  to  be  of  the  same  specific  gravity  as 
that  of  the  standard  fluid.  The  reaction  of  blood  is  faintly  alkaline 
and  the  taste  saltish.  Its  temperature  varies  slightly,  the  average 
being  37'8'  C.  (100  R).  The  blood-stream  is  warmed  by  passing 
through  the  muscles,  nerve  centres,  and  glands,  but  is  somewhat 
cooled  on  traversing  the  capillaries  of  the  skin.  Eecently  drawn 
blood  has  a  distinct  odour,  which  in  many  cases  is  characteristic  of 
the  animal  from  which  it  has  been  taken ;  it  may  be  further 
developed  by  adding  to  blood  a  mixture  of  equal  parts  of  sulphuric 
acid  and  water. 

*  The  amiihioTus  and  the  leptoc^n>halns. 
419 


420  THE   BLOOD  [CH.  XXVI. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  an  animal 
is  usually  estimated  in  the  following  manner : — A  small  quantity 
of  blood  is  taken  from  an  animal  by  venesection ;  it  is  defibrinated 
and  measured,  and  used  to  make  standard  solutions  of  blood.  The 
animal  is  then  rapidly  bled  to  death,  and  the  blood  which  escapes  is 
collected.  The  blood-vessels  are  next  washed  out  with  saline  solu- 
tion until  the  washings  are  no  longer  coloured,  and  these  are  added 
to  the  previously  withdrawn  blood  ;  lastly,  the  whole  animal  is  finely 
minced  with  saline  solution.  The  fluid  obtained  from  the  mincings 
is  carefully  filtered  and  added  to  the  diluted  blood  previously  obtained, 
and  the  whole  is  measured.  The  next  step  in  the  process  is  the  com- 
parison of  the  colour  of  the  diluted  blood  with  that  of  standard  solu- 
tions of  blood  and  water  of  a  known  strength,  until  it  is  discovered 
to  what  standard  solution  the  diluted  blood  corresponds.  As  the 
amount  of  blood  in  the  corresponding  standard  solution  is  known,  as 
well  as  the  total  quantity  of  diluted  blood  obtained  from  the  animal, 
it  is  easy  to  calculate  the  absolute  amount  of  blood  which  the  latter 
contained,  and  to  this  is  added  the  small  amount  which  was  with- 
drawn to  make  the  standard  solutions.  This  gives  the  total  amount 
of  blood  which  the  animal  contained.  It  is  contrasted  with  the 
weight  of  the  animal,  previously  known.  The  result  of  experiments 
performed  in  this  way  showed  that  the  quantity  of  blood  in  various 
animals  differs  a  good  deal,  but  in  the  dog  averages  yV  to  ^  of  the 
total  body-weight. 

Haldane  and  Lorrain  Smith  have  invented  another  method  which 
has  the  advantage  of  being  applicable  to  man.  The  data  required 
are  (1)  the  percentage  of  haemoglobin  in  the  blood,  and  (2)  the  extent 
to  which  the  haemoglobin  is  saturated  by  a  measured  amount  of 
carbonic  oxide  absorbed  into  the  blood. 

The  percentage  of  haemoglobin  is  determined  colorimetrically  by 
the  Gowers'  or  Gowers'-Haldane  haemoglobinometer  (see  p.  449).  In 
the  latter  instrument  the  standard  100  per  cent,  of  colour  corresponds 
to  a  capacity  of  18"5  c.c.  of  oxygen  or  carbonic  oxide  per  100  c.c.  of 
blood.  The  subject  whose  blood  is  to  be  measured  breathes  a  known 
volume  of  carbonic  oxide,  and  a  few  drops  of  the  blood  are  taken  and 
the  saturation  of  his  haemoglobin  is  determined  colorimetrically. 
From  this  result  the  total  capacity  of  the  blood  for  carbonic  oxide  is 
calculated.  The  "  carbonic  oxide  capacity "  is  the  same  as  the 
"  oxygen  capacity."  The  volume  of  the  blood  is  then  calculated  from 
the  total  "  oxygen  capacity,"  and  the  percentage  capacity  as  deter- 
mined by  the  haemoglobinometer.  The  following  is  an  example : — The 
subject's  blood  in  a  given  case  has,  let  us  say,  the  colour  of  the  100 
per  cent,  standard,  and  therefore  has  a  capacity  of  18'5  c.c.  per  100 
c.c.  blood.  He  is  then  allowed  to  breathe  75  c.c.  of  carbonic  oxide, 
and  it  is  then  found  that  his  blood  is  15  per  cent,  saturated.     The 


CH,  XXVI.] 


COAGULATION   OF   THE    BLOOD 


421 


amount  required  to  completely  saturate  his  blood,  or  in  other  words 

his  total  capacity,  must  be  75  x        =  500  c.c.     Since  185  c.c.  of  this 

total  is  carried  by  100  c.c.  of  his  blood,  the  total  volume  required  to 

contain  500  c.c.  is  500x^^^  =  2700  c.c.     The  subject  has  therefore 

27  litres  of  blood.     The  total  weight  is  obtained  by  multiplying  the 
volume  by  the  specific  gravity  (about  1"055). 

Some  of  the  results  of  this  method  are  as  follows : — The  mass  of 

the  blood  in  man  is  about  4-9  per  cent.  ( srp )    of  the  body-weight. 

The  corresponding  ratio  of  the  blood  volume  is  4'62  c.c.  per  100 


grammes,  or    ^j^      In   pathological   conditions    the 


numbers    are 


different;  thus  in  anaemia  from  haemorrhage,  the  volume  ratio  is  6 "5, 
in  pernicious  anaemia  8"6,  in  chlorosis  10"8.  In  other  words,  in 
various  forms  of  anaemia  the  actual  volume  of  the  blood  is  increased, 
but  of  course  the  corpuscular  and  solid  constituents  are  correspond- 
ingly diminished. 

Coagulation  of  the  Blood. 

After  the  blood  is  shed  it  rapidly  becomes  more  viscous  and  then 
sets  into  a  firm  red  jelly.     The  jelly  soon  contracts  and  squeezes  out 


Fig.  344. — Reticulum  of  fibrin,  from  a  drop  of  human  blood,  after  treatment  with  rosanilin.    The 
entangled  corpuscles  are  not  seen.    (Ranvier.) 

a  Straw-coloured  fluid  called  the  serum.  With  the  microscope, 
filaments  or  fine  threads  are  seen  forming  a  network  throughout  the 
fluid  (fig.  344),  many  radiating  from  small  clumps  of  blood-platelets. 
These  threads  entangle  the  corpuscles,  and  so  the  clot  is  formed. 


422  THE   BLOOD  [CH.  XXVI. 

The  threads  are  composed  of  a  protein  substance  called  Jibrin,  and 
the  formation  of  fibrin  is  the  essential  act  of  coagulation.  Fibrin  is 
formed  from  the  plasma,  and  may  be  obtained  free  from  corpuscles 
when  plasma  is  allowed  to  clot,  the  corpuscles  having  previously- 
been  removed  by  methods  we  shall  immediately  study.  It  may  also 
be  obtained  from  blood  by  whipping  it  with  a  bunch  of  twigs ;  the 
fibrin  adheres  to  the  twigs  and  entangles  but  few  corpuscles ;  these 
may  be  removed  by  subsequent  washing  with  water. 

Serum  is  plasma  minus  the  fibrin,  which  it  forms.  The  relation 
of  plasma,  serum,  and  clot  can  be  seen  at  a  glance  in  the  following 
scheme  of  the  constituents  of  the  blood : — 


Blood 


^r),  Serum 

l^ribrm^ 

'  Clot 


Corpuscles 


It  may  be  roughly  stated  that  in  100  parts  by  weight  of  blood  60-65 
parts  consist  of  plasma  and  35-40  of  corpuscles. 

The  huffy  coat  is  seen  when  blood  coagulates  slowly,  as  in  horse's 
blood.  The  red  corpuscles  sink  more  rapidly  than  the  white,  and 
the  upper  stratum  of  the  clot  (buffy  coat)  consists  mainly  of  fibrin 
and  white  corpuscles. 

Coagulation  is  hastened  by — 

1.  A  temperature  a  little  over  that  of  the  body. 

2.  Contact  with  foreign  matter. 

3.  Injury  to  the  vessel  walls. 

4.  Agitation. 

5.  Addition  of  calcium  salts. 

6.  Injection  of  nucleo -protein  into  the  circulation  causes  intra- 

vascular clotting. 

Coagulation  is  hindered  or  prevented  by — 

1.  A  low  temperature.     In  a  vessel  cooled  by  ice,  coagulation 

may  be  prevented  for  an  hour  or  more. 

2.  The  addition  of  a  large  quantity  of  neutral  salts  such  as  sodium 

sulphate  or  magnesium  sulphate. 

3.  Addition  of  a  soluble  oxalate,  fluoride,  or  citrate, 

4.  Injection  of  commercial  peptone   (which  consists  chiefly  of 

proteoses)  into  the  circulation  of  the  living  animal. 

5.  Addition  of  leech  extract  to  the  blood,  or  injection  of  leech 

extract  into  the  circulation  while  the  animal  is  alive. 

6.  Contact  with  the  living  vascular  walls. 

7.  Contact  with  oil. 


CII.  XXVI.]  ORIGIN   UF    FIBRIN    FERMENT  423 

The  causo  of  the  coagulation  of  the  blood  may  Ije  briefly  stated 
as  follows : — 

"When  blood  is  within  the  vessels,  one  of  the  constituents  of  the 

plasma,  a  protein  of  the  globulin  class,  called  Jihrinogen,  exists  in  a 

soluble  form.     When  the  blood  is  shed,  the  fibrinogen  molecule  is 

altered  in  such  a  way  that  it  gives  rise  to  the  comparatively  insoluble 

material  fibrin. 

The  statement  has  been  made  that  the  fibrinogen  molecule  is  split  into  two 
parts  ;  one  part  is  a  globulin  (fibrino-globuHn),  wliich  remains  in  solution,;  the 
other  and  larger  part  is  the  insoluble  substance  fibrin.  It  is,  however,  doubtful  if 
this  really  represents  what  occurs,  for  recent  work  seems  to  show  that  the  fibrino- 
globulin  is  not  a  product  of  fibrinogen,  but  exists  in  the  blood-plasma  beforehand. 
At  any  rate,  whether  this  is  so  or  not,  the  fact  remains  that  fibrin  is  the  important 
product  and  the  only  one  which  need  concern  us. 

The  next  question  is,  What  causes  the  transformation  of  fibrinogen 
into  fibrin  ?  and  the  answer  to  that  is,  that  the  change  is  due  to  the 
activity  of  an  enzyme  which  is  called  fibrin-ferment  or  thrombin. 

This  ferment  does  not  exist  in  healthy  blood  contained  in  healthy 
blood-vessels,  but  is  formed  by  the  disintegration  of  the  blood- 
platelets  and  colourless  corpuscles  which  occurs  when  the  blood 
leaves  the  blood-vessels  or  comes  into  contact  with  foreign  matter. 
Hence  the  blood  does  not  coagulate  during  life.  But  it  will  be  said, 
disintegration  of  the  blood- corpuscles  occurs  during  life,  why,  then, 
does  the  blood  not  coagulate  ?  The  reason  is,  that  although  the 
formed  elements  do  disintegrate  in  the  living  blood,  such  a 
phenomenon  takes  place  very  slowly  and  gradually,  so  that  there 
can  never,  under  normal  circumstances,  be  any  massive  liberation 
of  fibrin-ferment,  and  further,  that  there  are  agencies  at  work  to 
neutralise  the  fibrin-ferment  as  it  is  formed.  The  most  noteworthy 
of  these  neutralising  agencies  is  the  presence  in  the  blood  of  an 
antiferment  called  antithrombin,  analogous  to  the  antipepsin  and 
antitrypsin  which  we  shall  see  are  efficacious  in  preventing  the 
stomach  and  intestines  from  undergoing  self-digestion. 

Thrombin  or  fibrin-ferment  belongs  to  the  class  of  nucleo- 
proteins,  and  other  nucleo-proteins  obtained  from  most  of  the 
cellular  organs  of  the  body  produce  intravascular  clotting  when 
injected  into  the  circulation  of  a  living  animal.  In  certain  diseased 
conditions,  intravascular  clotting  or  thrombosis  sometimes  occurs. 
This  must  be  due  either  to  the  entrance  of  nucleo-protein  into  the 
circulation  from  diseased  tissues,  or  to  a  failure  of  the  body  to 
produce  sufficient  antithrombin  to  neutralise  its  effect,  or  to  both 
of  these  conditions  together. 

Thrombin  is  believed  to  originate  chiefly  from  the  blood-platelets 
and  in  part  from  the  leucocytes.  Birds'  blood  clots  very  slowly, 
and  the  absence  of  blood-platelets  in  this  variety  of  blood  will,  in 
part,  account  for  this.     Lymph,  which  contains  colourless  corpuscles, 


424  THE   BLOOD  [CH.  XXVI. 

but  no  platelets,  also  clots  in  time,  so  in  tliis  case  the  colourless 
corpuscles  must  be  the  source  of  the  ferment.  One  should,  however, 
be  careful  in  speaking  of  the  disintegration  of  leucocytes  to 
remember  that  the  word  disintegration  does  not  mean  complete 
breakdown  leading  to  disappearance;  the  colourless  corpuscles  do 
not  appreciably  diminish  in  number  when  the  blood  clots,  but  what 
occurs  is  a  shedding  out  from  the  surviving  leucocytes  of  certain 
products,  among  which  fibrin-ferment  is  one. 

We  have  now  traced  fibrin  formation,  the  essential  cause  of 
blood-clotting,  to  the  activity  of  thrombin ;  it  is  next  necessary  to 
allude  to  what  has  been  discovered  in  relation  to  the  origin  of 
thrombin.  Like  other  ferments,  it  is  preceded  by  a  mother-substance 
or  zymogen.  This  zymogen  is  called  protln'ombin  or  throvibogen, 
and  there  appear  to  be  two  necessary  agents  concerned  in  the 
conversion  of  thrombogen  into  tlu'ombin  ;  one  of  these  is  the  action 
of  calcium  salts,  the  other  is  the  j)resence  of  an  activating  agent 
(analogous  to  the  enterokinase,  which  activates  pancreatic  juice) 
called  thromhokinasc.  The  exact  role  played  by  each  is  still  a 
matter  of  speculation,  but  we  may  learn  a  good  deal  by  studying  a 
little  more  in  detail  some  of  the  methods  already  enumerated  for 
preventing  the  blood  from  coagulating. 

The  part  played  by  calcium  salts  is  well  illustrated  by  the  fact 
that  coagulation  is  prevented  by  the  decalcification  of  the  blood. 
This  can  be  accomplished  by  the  addition  of  a  small  amount  of  a 
soluble  oxalate  or  fluoride  to  the  blood  immediately  it  is  shed.  The 
calcium  of  the  blood  plasma  is  then  immediately  precipitated  as 
insoluble  calcium  oxalate  or  fluoride,  and  is  thus  not  available  for 
the  transformation  of  thrombogen  into  thrombin.  The  addition  of  the 
oxalate  or  fluoride  must  be  rapidly  performed,  otherwise  time  will  be 
given  for  the  conversion  of  thrombogen  into  thrombin,  and  thrombin, 
when  formed,  will  act  upon  fibrinogen  whether  the  calcium  has  been 
removed  or  not.  In  other  words,  calcium  is  only  necessary  for  the 
formation  of  fibrin-ferment,  and  not  for  the  action  of  fibrin-ferment  on 
fibrinogen.     Fibrin  is  thus  not  a  compound  of  calcium  and  fibrinogen. 

The  action  of  a  soluble  citrate  is  also,  in  a  certain  sense,  a 
decalcifying  action,  for  although  calcium  citrate  is  a  soluble  salt,  it 
does  not  ionise  in  solution  so  as  to  liberate  the  free  calcium  ions 
which  are  essential  for  thrombin  formation. 

Oxalated  blood  (or  oxalated  plasma)  will  clot  when  the  calcium 
is  once  more  restored  by  the  addition  of  a  small  amount  of  calcium 
chloride,  but  such  addition  to  fluoride  plasma  will  not  induce 
clotting ;  in  this  case,  thrombin  itself  must  be  added.  In  some  way 
sodium  fluoride  interferes  with  the  formation  of  thrombin,  probably 
by  preventing  the  liberation  of  thrombokinase  from  the  corpuscular 
elements  of  the  blood.     The  latter  are  certainly  very  well  preserved. 


CH.  XXVI.]  PEPTONE   AND    ANTI-THROMBIN  425 

The  second  activating  agent,  however,  thrombokinase,  is  not  only 
liberated  from  the  blood-corpuscles,  but  it  is  also  obtained  from  many 
other  tissues.  If  a  htemorrhage  takes  place  under  ordinary  circum- 
stances the  blood  as  it  flows  from  the  wound  passes  over  the  muscles 
and  skin  that  have  been  cut,  and  rapidly  clots  owing  to  the  throm- 
bokinase supplied  by  those  tissues.  If  blood  is  obtained  by  drawing 
it  off  through  a  perfectly  clean  cannula  into  a  clean  vessel  without 
allowing  it  to  touch  the  tissues,  it  remains  unclotted  for  a  long 
time ;  in  the  case  of  birds'  blood  this  time  may  extend  to  many  days ; 
but  the  addition  of  a  small  piece  of  a  tissue  such  as  muscle,  or  of  an 
extract  of  such  a  tissue,  produces  almost  immediate  clotting.  If  a 
solution  of  fibrinogen  is  prepared  and  calcium  added  it  will  not  clot ; 
if  thrombin  or  a  fluid  such  as  serum  which  contains  thrombin  is  added 
it  will  clot.  It  will  not  clot  if  birds'  plasma  obtained  as  above  is  added 
to  it ;  nor  if  tissue  extract  is  added  to  it ;  but  if  both  are  added  it  will. 
In  other  words,  the  thrombogen  of  the  birds'  plasma  plus  the  throm- 
bokinase of  the  tissue  extract  have  the  same  effect  as  thrombin. 

The  next  point  to  consider  is  why  blood  obtained  after  the 
previous  injection  of  proteoses  (or  commercial  peptone)  into  the 
circulation  does  not  clot.  It  certainly  contams  calcium  salts,  and 
probably  both  thrombogen  and  thrombokinase,  for  it  can  be  made  to 
clot  without  the  addition  of  either,  for  instance  by  dilution,  or  the 
passage  of  a  stream  of  carbon  dioxide  through  it.  There  must  be 
sometliing  in  peptone  blood  which  antagonises  the  action  of  thrombin. 
This  something  is  an  .  excess  of  antithrombin.  Peptone  will  not 
hinder  blood-coagulation,  or  only  very  slightly  if  it  is  added  to  the 
blood  after  it  is  shed.  The  antithrombin  must  therefore  have  been 
added  to  the  blood  while  it  was  circulating  in  the  body.  We  can 
even  go  further  than  this,  and  say  what  part  of  the  body  it  is  which 
is  concerned  in  the  production  of  antithrombin.  It  is  the  liver ;  for 
if  the  liver  is  shut  off  from  the  circulation,  peptone  is  ineffective  in 
its  action.  The  converse  experiment  confirms  this  conclusion,  for  if 
a  solution  of  peptone  is  artificially  perfused  through  an  excised 
surviving  liver,  a  substance  is  formed  which  has  the  power  of  hinder- 
ing or  preventing  the  coagulation  of  shed  blood.  Peptone  blood  is 
very  poor  in  leucocytes;  the  cause  of  their  disappearance  is  not 
clear. 

"We  are  thus  justified  in  two  conclusions: — 

(1)  That  the  antithrombin  (normally  present  in  healthy  blood  in 
sufficient  quantities  to  prevent  intravascular  clotting)  is  formed  in 
the  liver. 

(2)  That  commercial  peptone,  in  virtue  of  the  proteoses  it 
contains,  stimulates  this  action  to  such  an  extraordinary  degree 
that  the  accumulation  of  antithrombin  in  the  blood  becomes  so 
great  that  the  blood  does  not  clot  even  after  it  is  shed. 


426  THE   BLOOD  [CH.  XXVI. 

We  will  conclude  by  considering  only  one  more  of  the  hindrances 
to  coagulation,  and  that  by  no  means  the  least  interesting.  The 
leech  lives  by  sucking  the  blood  of  other  animals ;  from  the  leech's 
point  of  view  it  is  therefore  necessary  that  the  blood  should  flow 
freely  and  not  clot.  The  glands  at  the  head  end  of  the  leech,  often 
spoken  of  roughly  as  its  salivary  glands,  secrete  something  which 
hinders  the  blood  from  coagulating,  and  everyone  knows  by  experi- 
ence, who  has  been  treated  by  leeches,  how  difficult  it  is  to  prevent 
a  leech-bite  from  bleeding  after  the  leech  has  been  removed ;  com- 
plete cleansing  is  necessary  to  wash  away  the  leech's  secretion  from 
the  wound.  Now  if  an  extract  of  leeches'  heads  is  made  with  salt 
solution  and  filtered,  that  fluid  will  prevent  coagulation  whether  it  is 
injected  into  the  blood  stream  or  added  to  shed  blood.  The  sub- 
stance in  question  is  believed  to  be  antithrombin  itself.  Blood  so 
obtained  can  be  made  to  clot  by  the  addition  of  thrombin  or  such  a 
fluid  as  serum  that  contains  thrombin  in  sufficient  amount. 

We  may  summarise  our  present  knowledge  of  the  causes  of 
coagulation  in  the  following  tabular  way : — 

%    From  the  platelets,  and  From  the  formed  ele- 

to  a  lesser  degree  from  the  ments  of  the  blood,  but 

leucocytes,    a    nucleo-pro-  also  from  the  tissues  over 

tein  is  shed  out,  called —  which  the  escaping  blood 

I  flows,  is  shed  out  an  acti- 

I  vating  agent,  called — 

Thrombogen.  Thrombokinase. 

I I 

In  the  blood  plas-  In  the  presence   of  calciuji   salts,   thrombokinase 

ma    a    protein    sub-       activates   thrombogen  in  such  a  way  that  an  active 
stance  exists, called—       ferment  is  produced,  which  is  called — 

Fibrinogen,  Thrombin. 

I  I 


Thrombin  or  fibrin-ferment  acts  on  fibrinogen  in  such  a  way  that  it  is  trans- 
formed into  the  insoluble  stringy  material  which  is  called — 

Fibrin. 
The  Plasma  and  Serum. 

The  liquid  in  which  the  corpuscles  float  may  be  obtained  by 
employing  one  or  other  of  the  methods  already  described  for  pre- 
venting the  blood  from  coagulating.  The  corpuscles,  being  heavy, 
sink,  and  the  supernatant  plasma  can  then  be  removed  by  a  pipette 
or  siphon,  or  more  thoroughly  by  the  use  of  a  centrifugal  machine 
(see  fig.  345). 

On  counteracting  the  influence  which  has  prevented  the  blood 
from  coagulating,  the  plasma  then  itself  coagulates.  Thus  plasma 
obtained  by  the  use  of  cold  clots  on  warming  gently ;  plasma  which 


CIl.  XXVI.] 


BLOOD    PLASMA 


427 


has  been  decalcified  by  the  action  of  a  soluble  oxalate  clots  on  the 
addition  of  a  calcium  salt ;  plasma  obtained  by  the  use  of  a  strong 
solution  of  neutral  salt  coagulates  when  this  is  diluted  by  the  addition 
of  water,  the  addition  of  fibrin-ferment  being  necessary  in  most  cases ; 
where  coagulation  occurs  without  the  addition  of  fibrin-ferment  no 
doubt  some  is  present  from  the  partial  disintegration  of  the  corpuscles 


Fig.  345.— Plan  and  section  of  centrifugal  machine,  a,  an  iron  socket  secured  to  top  of  table  b  ;  c,  a 
steel  spindle  carrying  the  turntable  d,  and  turning  freely  in  a  ;  e,  a  flange  round  turntable  d  ; 
F  F,  shallow  grooves  on  face  of  d  in  which  the  test-tubes  are  fixed  by  clamps  o  o  ;  h,  a  pulley  fixed 
to  end  of  spindle  c,  and  turned  by  the  cord  k  ;  1 1  are  two  guide  pulleys  for  cord  k.  The  upper  part 
of  the  figure  is  a  surface  view  of  the  rotating  turntable.    (Gamgee.) 

which  has  already  occurred.  Pericardial  and  hydrocele  fluids 
resemble  pure  plasma  very  closely  in  composition.  As  a  rule, 
however,  they  contain  few  or  no  white  corpuscles,  and  do  not  clot 
spontaneously,  but  after  the  addition  of  fibrin-ferment,  or  liquids  such 
as  serum  that  contain  fibrin-ferment,  they  always  yield  fibrin. 

Pure  plasma  may  be  obtained  from  horse's  veins  by  what  is  known 
as  the  "  living  test-tube  "  experiment.     If  the  jugular  vein  is  ligatured 


428  THE   BLOOD  [CH.  XXVI. 

in  two  places  so  as  to  include  a  quantity  of  blood  within  it,  then 
removed  from  the  animal  and  hung  in  a  cool  place,  the  blood  will  not 
clot  for  many  hours.  The  corpuscles  settle,  and  the  supernatant 
plasma  can  be  removed  with  a  pipette. 

The  plasma  is  alkahne,  yellowish  in  tint,  and  its  specific  gravity 
is  about  1026  to  1029.     1000  parts  of  plasma  contain  : — 

Water 902-90 

Solids 97-10 

Proteins:  1.  yield  of  fibrin 4'05 

2.  other  proteins 78*84 

Extractives  (including  fat) 5-66 

Inorganic  salts 8  "So 

In  round  numbers,  plasma  contains  10  per  cent,  of  solids,  of  which 
8  are  protein  in  nature.  Fibrinogen,  as  judged  from  the  yield  of 
fibrin,  is  the  least  abundant  of  the  proteins  present. 

Serum  contains  the  same  three  classes  of  constituents — proteins, 
extractives,  and  salts.  The  extractives  and  salts  are  the  same  in 
both  liquids.  The  proteins  are  different,  as  is  shown  in  the  following 
table : — 

Proteins  of  Plasma.  Proteins  of  Serum. 

Fibrinogen.  Serum  globulin. 

Serum  globulin.  Serum  albumin. 

Serum  albumin.  Fibrin-ferment  (nucleo-protein). 

The  gases  of  plasma  and  serum  are  small  quantities  of  oxygen, 
nitrogen,  and  carbonic  acid.  The  greater  part  of  the  oxygen  of  the 
blood  is  combined  in  the  red  corpuscles  with  haemoglobin;  the 
carbonic  acid  is  chiefly  combined  as  carbonates.  The  gases  of  the 
blood  have  already  been  considered  under  Eespiration  (see  p.  377). 

We  may  now  study  one  by  one  the  various  constituents  of  the 
plasma  and  serum. 

A.  Proteins. — Fibrinogen,  the  mother-substance  of  fibrin,  is  a 
globulin.  It  differs  from  serum  globulin,  and  may  be  separated  from 
it  by  making  use  of  the  fact  that  half-saturation  with  sodium 
chloride  precipitates  it.  It  coagulates  by  heat  at  the  low  tempera- 
ture of  56    C. 

Serum  globulin  and  serum  albumin. — These  substances  exhibit  the 
usual  differences  already  described  between  albumins  and  globulins 
(p.  410).  Both  are  coagulated  by  heat  at  a  little  over  70'  C.  They 
may  be  separated  by  dialysis  or  the  use  of  neutral  salts.*  The 
readiest  way  to  separate  them  is  to  add  to  the  serum  an  equal  volume 
of  saturated  solution  of  ammonium  sulphate.  This  is  equivalent  to 
semi-saturation,   and   it   precipitates   the   globulin.     If   magnesium 

*  The  globulin  of  the  serum  precipitated  by  "  salting  out"  really  consists  of 
two  proteins,  one  of  which  is  precipitated  by  dialysis  (euglobulin),  and  the  other  is 
not  (pseudo-globulin). 


CH.  XXVI.]  THE  RED  CORPUSCLES  429 

sulphate  is  used  as  a  precipitant  of  the  globulin  it  must  be  added  in 
the  form  of  crystals,  and  the  mixture  well  shaken  to  ensure  complete 
saturation. 

Fibrin-ferment. — Schmidt's  method  of  preparing  it  is  to  take 
serum  and  add  excess  of  alcohol.  This  precipitates  all  the  proteins, 
fibrin-ferment  included.  After  some  weeks  the  alcohol  is  poured  off; 
the  sermn  globulin  and  serum  albumin  have  been  by  this  means 
rendered  insoluble  in  water ;  an  aqueous  extract  is,  however,  found 
to  contain  fibrin-ferment,  which  is  not  so  easily  coagulated  by  alcohol 
as  the  other  proteins  are.  Prepared  in  this  way,  however,  it  differs 
in  some  of  its  properties  from  the  thrombin  that  is  formed  in  shed 
blood,  and  to  which  no  chemical  reagents  have  been  added. 

B.  Extractives. — These  are  non-nitrogenous  and  nitrogenous. 
The  non-nitrogenous  are  fats,  soaps,  cholesterin,  and  sugar;  the 
nitrogenous  are  urea  (002  to  0*04  per  cent.),  and  still  smaller 
quantities  of  uric  acid,  creatine,  creatinine,  xanthine,  and  hypo- 
xanthine  and  amino-acids. 

C.  Salts. — The  most  abundant  salt  is  sodium  chloride;  it  con- 
stitutes between  60  and  90  per  cent,  of  the  total  mineral  matter. 
Potassium  chloride  is  present  in  much  smaller  amount.  It  consti- 
tutes about  4  per  cent,  of  the  total  ash.  The  other  salts  are 
phosphates  and  sulphates. 

Schmidt  gives  the  following  table  : — 

1000  parts  of  plasma  yield — 

Mineral  matter 8*550 

Chlorine 3'640 

SO, 0-115 

PoOg 0-191 

Potassium 0-323 

Sodium 3-341 

Calcium  phosphate 0  311 

Magnesium  phosphate 0-222 

The  Blood-Corpuscles. 

Red  or  Coloured  Corpuscles. — Human  red  blood-corpuscles  are 
circular  biconcave  discs  with  rounded  edges,  -auVo  i^ich  in  diameter 
(7/x  to  8/x)  and  ^..l^y^J  inch,  or  about  2^,  in  thickness.  When  viewed 
singly  they  appear  of  a  pale  yellowish  tinge ;  the  deep  red  colour 
which  they  give  to  the  blood  is  observable  in  them  only  when  they 
are  seen  en  masse. 

According  to  Rollett  they  are  composed  of  a  transparent  filmy  framework 
infiltrated  in  all  parts  by  the  red  pigment  hcemoglohin.  This  stroma  is  elastic,  so 
that  as  the  corpuscles  circulate,  they  admit  of  change  in  form,  and  recover  their 
natural  shape  as  soon  as  they  escape  from  compression.  According  to  this  theory, 
the  consistency  of  the  peripheral  part  of  the  stroma  is  greater  than  that  of  the 
central  portions  ;  the  outer  layer  thus  plays  the  part  of  a  membrane  in  the  processes 
of  osmosis  that  occur  when  water  or  salt  solutions  are  added  to  the  corpuscles. 
This  view  of  Rollett  has  been  questioned,  particularly  by  Schafer,  who  regards  the 


430 


THE  BLOOD 


[CH.  XXVI. 


red  corpuscles  as  composed  of  a  colourless  envelope  enclosing  a  solution  of  haemo- 
globin. The  presence  of  a  membrane  on  the  exterior  of  the  corpuscle  is  undoubted, 
and  can  be  clearly  distinguished  by  a  good  microscope  in  the  larger  corpuscles  of 
amphibia.  It  is,  however,  difficult  to  explain  the  elasticity  of  the  corpuscles,  and 
the  central  position  of  the  nucleus  in  nucleated  red  corpuscles,  unless  we  also  assume 
that  delicate  fibres  pass  across  the  interior  of  the  corpuscles. 

Mammalian  red  corpuscles  have  no  nuclei ;  the  unequal  refraction 
of  transmitted  light  gives  the  appearance  of  a  central  spot,  darker  or 
brighter  than  the  border,  according  as  it  is  viewed  in  or  out  of  focus. 
Their  specific  gravity  is  about  1088. 

The  corpuscles  of  all  mammals,  with  the  exception  of  the  camel 
tribe,  are  circular  and  biconcave.     They  are  generally  very  nearly 


® 


mm] 


Fig.  346. — Red  corpuscles  in  rouleaux.    The 
white  corpuscles  are  uncoloured. 


Fig.  347.— Corpuscles  of  the  frog.  The 
central  mass  consists  of  nucleated 
coloured  corpuscles.  The  other  cor- 
puscles are  two  varieties  of  the 
colourless  form. 


the  size  of  human  red  corpuscles.  They  are  smallest  in  the  deer 
tribe  and  largest  in  the  elephant.  In  the  camelidse  they  are 
biconvex.  In  all  mammals  the  corpuscles  are  non-nucleated,  and 
in  all  other  vertebrates  (birds,  reptiles,  amphibia,  and  fishes)  the 
corpuscles  are  oval,  biconvex,  and  nucleated  (fig.  348)  and  larger 
than  in  mammals.  They  are  largest  of  all  in  certain  amphibians 
(amphiuma,  proteus). 

The  red  corpuscles  are  not  all  alike,  for  in  almost  every  specimen 
of  blood  may  be  also  observed  a  certain  number  of  corpuscles  smaller 
than  the  rest.  They  are  termed  microcytes,  or  hcematoblasts,  and  are 
probably  immature  corpuscles. 

A  property  of  the  red  corpuscles,  which  is  exaggerated  in  inflam- 
matory blood,  is  a  tendency  to  adhere  together  in  rolls  or  columns 
(rouleaux),  like  piles  of  coins.     These  rolls  quickly  fasten  together 


en.  XXVI.] 


TIIF,    KRD    CORPUSCLES 


431 


by  their  ends,  and  cluster;  so  that,  when  the  blood  is  spread  out  tliiuly 
on  a  glass  they  form  an  irregular  network  (fig.  346). 


MAMMALS. 


ELEPHANT         MOUSE  HORSE         MUSK  DEER  CAMEL 


■3200        I     1-3099       I      1-2745       I     l--*26a       1      l.+eOO.'-    1-12325".         1-3123 


Fio.  348.— The  above  illustration  is  .somewhat  altered  from  a  drawing  by  Gulliver,  in  the  Proceed. 
Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in  the  main  divisions  of  the 
Vertebrata.  The  fractions  are  these  of  an  inch,  and  represent  the  average  diameter.  In  the  case 
of  the  oval  cells,  only  the  long  diameter  is  here  given.  It  is  remarkable,  that  although  the  size  of 
the  red  blood-cells  varies  so  much  in  the  diflerent  classes  of  the  vertebrate  kingdom,  that  of  the 
white  corpuscles  remains  comparatively  uniform,  and  thus  they  are,  in  some  animals,  larger,  in 
others  smaller,  than  the  red  corpuscles. 

Action  of  Reagents. — Considerable  light  has  been  thrown  on  the  physical  and 
chemical  constitution  of  red  blood-cells  by  studying  the  effects  produced  by 
mechanical  means  and  by  various  reagents  ;  the  following  is  a  brief  summary  of 
these  reactions  : —  b«£'\ 

Water. — When  water  is  added  gradually  to  frog's  blood,  the  oval  disc-shaped 
corpuscles  become  spherical,  and  gradually  discharge  their  haemoglobin,  a  pale, 
transparent  stroma  or  envelope  being  left  behind  :  human  red  blood-cells  swell, 
change  from  a  discoidal  to  a  spheroidal  form,  and  discharge  their  pigment, 
becoming  quite  transparent  and  all  but  invisible.     This  effect  is  due  to  osmosis. 

Phi/sioioc/ical  xaline  solution  causes  no  effect  on  the  red  corpuscles  beyond  pre- 
venting them  rimning  into  rouleaux.  If  a  stronger  salt  solution  is  used,  the  cor- 
puscles shrink  and  become  crenated  (fig.  349)  owing  to  osmosis  of  water  outwards. 


f 


432  THE   BLOOD  [CH.  XXVI. 

Dilute  acetic  acid  causes  the  nucleus  of  the  red  blood-cells  in  the  frog  to  become 
more  clearly  defined;   if  the  action  is  prolonged,  the  nucleus  becomes  strongly 

granulated,  and  all  the  colouring  matter  seems  to 

«g^  _^  .([ijiS||i  be   concentrated  in   it,  the   surrounding  cell-sub- 

^^*  <jij*ai  stance  and   outline   of  the  cell   becoming  almost 

^  )^8jr!)  invisible ;   after  a  time  the  cells  lose  their  colour 

^^«C  altogether.     The    cells    in    the    figure    (fig.    350) 

^'of  saline^so^u-  ^I^P^  represent    the  successive  stages   of   the   change. 

tion      (crena-       Fig.  350.— Effect     ^  similar   loss    of  colour   occurs   in  the  red   cor- 

tion).  of  acetic  acid.       puscles  of   human   blood,    which,   however,   from 

the  absence  of  nuclei,  seem  to  disappear  entirely. 
Dilute  alkalis  cause  the  red   blood-cells   to   dissolve   slowly,  and   finally  to 
disappear. 

Chloroform,  ether,  and   other  reagents   that  dissolve  fats   dissolve  the  fatty 
substance  (lecithin,  etc.)  of  the  membrane  that  surrounds  the 
corpuscles,  and  so  produce  laking  of  the  blood.  ^        f\  ^^ 

Tannic  acid. — When  a  2  per  cent,  fresh  solution  of  tannic  /-%    >  ® )  lO  j 

acid  is  applied  to  frog's  blood  it  causes  the  appearance  of  a        J*^    ^^     \ 
sharply-defined   little   knob,  projecting  from  the  free  surface  jf^ 

{Roberts'  macula) :  the  colouring  matter  becomes  at  the  same  v^-^ 

time  concentrated  in  the  nucleus,  which   grows  more  distinct      Fm.  351.— Effect  of 
(fig.  351).    A  somewhat  similar  effect  is  produced  on  the  human  tannin. 

red   blood-corpuscle,   the  colouring   matter    being   discharged 
and  coagulated  as  a  little  knob  of  hsematin  on  the  surface  of  the  corpuscle. 

Boric  acid. — A  2  per  cent,  solution  applied  to  nucleated  red  blood-cells  will 

cause  the  concentration   of  all  the  colouring 
matter  in  the  nucleus  ;  the  coloured  body  thus 
»         «      formed  gradually  quits  its  central  position,  and 
<|§?   @i^        comes  to  be  partly,  sometimes   entirely,  pro- 
Pio.  352.-Effect  pj^  353  _Effect     ^'^^^^^  ^^^^  ^^e  surface  of  the  now  colourless 

of  boric  acid.  of  heat.  ^^^^    (^S'    353).       When    applied   to  the   non- 

nucleated  mammalian  corpuscle  its  effect  merely 
resembles  that  of  other  dilute  acids. 

Heat.— The  effect  of  heat  up  to  50°— 60"  C.  (120°— 140°  F.)  is  to  cause  the  forma- 
tion of  a  number  of  bud-like  processes. 

The  Colourless  Corpuscles. — In  human  blood  the  white  or 
colourless  corpuscles  or  leucocytes  are  nearly  spherical  masses  of 
granular  protoplasm  when  they  are  at  rest.  In  all  cases  one  or 
more  nuclei  exist  in  each  corpuscle.  The  size  of  the  corpuscles 
varies  considerably,  but  averages  -0-5V0  of  an  inch  (10//)  in  diameter. 

In  health,  the  proportion  of  white  to  red  corpuscles,  which,  taking 
an  average,  is  about  1  to  500  or  600,  varies  considerably  even  in  the 
course  of  the  same  day.  The  variations  appear  to  depend  chiefly  on 
the  amount  and  probably  also  on  the  kind  of  food  taken  ;  the  number 
of  leucocytes  is  generally  increased  by  a  meal,  and  diminished  by 
fasting.  Also  in  young  persons,  during  pregnancy,  and  after  great 
loss  of  blood,  there  is  a  larger  proportion  of  colourless  blood-cor- 
puscles.    In  old  age,  on  the  other  hand,  their  proportion  is  diminished. 

There  are  four  principal  varieties  of  colourless  corpuscles  found 
in  human  blood : — 

1.  Poly-morpho-nuclear  cells. — These  contain  several  nuclei  united 
by  fine  threads  of  chromatin.  Their  protoplasm  is  filled  with  fine 
granules,  which  are  termed  oxyphile  on  account  of  their  aJSinity  for 


CH.  XXVI.] 


COLOURLESS  BLOOD  CORPUSCLES 


433 


acid  dyes  like  eosiii.     These  are  the  most  important  leucocytes,  con- 
stituting from  60  to  70  per  cent,  of  the  total. 

2.  Eosinophile  cells. — These  are  not  so  actively  amoeboid  as  the 
first  variety.  Their  nucleus  is  simple  or  lobed.  Their  protoplasmic 
granules  are  large,  and  are  much  more  deeply  stained  by  eosin  than 
the  fine  granules  of  the  first  variety.  They  comprise  about  5  per 
cent,  of  the  total  leucocytes. 

3.  Lympliocytes. — These  have  a  large  spherical  nucleus  and  a 
limited  amount  of  clear  protoplasm  around  it.  Transitional  forms 
between  them  and  the  next  variety  are  also  found.  They  constitute 
from  15  to  30  per  cent,  of  the  total. 

4.  Hyaline  cells. — These  differ  from  the  last  by  having  more  proto- 
plasm around  the  nucleus.  The  protoplasm  is  amoeboid,  and  is  clear. 
It,  however,  stains  slightly  with  methylene  blue,  and  this  is  perhaps 
due  to  the  presence  of  fine  basophile  granules. 

The  nuclei  of  all  these  varieties  are  basophile,  i.e.,  they  have  a 
strong  affinity  for  basic  aniline  dyes  like  methylene  blue.  Cells,  with 
large  basophile  granules,  are  very  rare  in  healthy  human  blood. 

Amoeboid  Movement. — The  remarkable  property  of  the  colour- 


Healthy  bacillus 

Healthy  bacillus 


—.-.Healthy  bacillus. 

Partially  digested  bacillus. 


Partially  digested  leucocyte.. 
Nuclei  vacuolated -- 


Nucleus. 

/S^-^fcTS^i-'X--  Bacillus  in  leucocyte. 

-'-,:  .  Partially  digested  leucocyte. 

"^  ; 

'    .Foreign  matter. 


Foreign  matter  „ /^./|l#y -Particles  of  foreign  matter. 

'5  Particles  of  foreign  matter. 

.  .      ("„ V-Ta  ^i Particles  of  foreign  matter. 

Leucocytes -^  ___ ^"^i^^ 

Fig.  354. — Macrophages  containing  bacilli  and  other  structures  undergoing  digestion.    (Ruffer.) 


less  corpuscles  of  spontaneously  changing  their  shape  was  first  demon- 
strated by  Wharton  Jones  in  the  blood  of  the  skate. 

The  full  consideration  of  amoeboid  movement  is  given  on  p.  12. 

2  E 


'434  THE   BLOOD  [CH.  XXVI. 

An  interesting  variety  of  amoeboid  movement  is  that  which  leads  to 
the  ingestion  of  foreign  particles.  This  gives  to  the  leucocytes  their 
power  of  taking  in  and  digesting  bacilli  {phagocytosis).  The  multi- 
nucleated, finely  granular  corpuscles  are  the  most  vigorous  phagocytes. 
Fig.  354  illustrates  this ;  the  cells  represented,  however,  are  not 
leucocytes,  but  the  large  amoeboid  cells  found  in  connective  tissues, 
especially  in  inflamed  parts. 

The  process  of  emigration  of  the  leucocytes  is  described  on 
p.  294. 

Action  of  Reagents  on  the  colourless  cojpuscles. —  Water  causes  the 
corpuscles  to  swell  and  their  nuclei  to  become  apparent.  Acetic  acid 
(1  per  cent.)  has  a  similar  action  ;  it  also  causes  the  granules  to  aggre- 
gate round  the  nucleus.  Dilute  alkalis  produce  swelling  and  bursting 
of  the  corpuscles. 

The  Blood-Platelets. 

Besides  the  two  principal  varieties  of  blood-corpuscles,  a  third 
kind  has  been  described  under  the  name  blood-platelets  {Blut-pldtchen). 
These  are  colourless  disc-shaped  or  irregular  bodies,  much  smaller  than 
red  corpuscles.  Different  views  are  held  as  to  their  origin.  At  first 
they  were  regarded  as  immature  red  corpuscles ;  but  this  view  has  been 
discarded.  Some  state  that  they  are  merely  a  precipitate  of  nucleo- 
protein  which  occurs  when  the  plasma  dies  or  is  cooled.  There  is, 
however,  no  doubt  that  they  do  occur  in  living  blood,  and  have  been 
seen  to  undergo  amoeboid  movement ;  some  observers  state  that  they 
are  nucleated. 

Enumeration  of  the  Blood-Corpuscles. 

Several  methods  are  employed  for  counting  the  blood-corpuscles  ;  most  of  them 
depend  upon  the  same  principle,  /.  c. ,  the  dilution  of  a  minute  volume  of  blood  with 
a  given  volume  of  a  colourless  saline  solution  similar  in  specific  gravity  to  blood 
plasma,  so  that  the  size  and  shape  of  the  corpuscles  is  altered  as  little  as  possible. 
A  minute  quantity  of  the  well-mixed  solution  is  then  taken,  examined  under  the 
microscope,  either  in  a  flattened  capillary  tube  (Malassez)  or  in  a  cell  (Hayem  & 
Nachet,  Gowers)  of  known  capacity,  and  the  number  of  corpuscles  in  a  measured 
length  of  the  tube,  or  in  a  given  area  of  the  cell,  is  counted.  The  length  of  the  tube 
and  the  area  of  the  cell  are  ascertained  by  means  of  a  micrometer  scale  in  the  micro- 
scope ocular ;  or  in  the  case  of  Gowers'  modification,  by  the  division  of  the  cell 
area  into  squares  of  known  size.  Having  ascertained  the  number  of  corpuscles  in 
the  diluted  blood,  it  is  easy  to  calculate  the  number  in  a  given  volume  of  normal 
blood. 

Gowers'  Ilamaci/tomcter  consists  of  a  small  pipette  (a),  which,  when  filled  up 
to  a  mark  on  its  stem,  holds  995  cubic  millimetres.  It  is  furnished  with  an  india- 
rubber  tube  and  glass  mouth-piece  to  facilitate  filling  and  emptying ;  a  capillary 
tube  (b)  marked  to  hold  5  cubic  millimetres,  and  also  furnished  with  an  indiarubber 
tube  and  mouth-piece  ;  a  small  glass  jar  (n)  in  which  the  dilution  of  the  blood  is 
performed ;  a  glass  stirrer  (e)  for  mixing  the  blood  and  salt  solution  thoroughly  ; 
(f)  a  needle,  the  length  of  which  can  be  regulated  by  a  screw  ;  a  brass  stage  plate 
(c)  carrying  a  glass  slide,  on  which  is  a  cell  one-fifth  of  a  millimetre  deep,  and  the 
bottom  of  which  is  divided  into  one-tenth  millimetre  squares.  On  the  top  of  the 
cell  a  cover-shp  rests.     A  standard  saline  solution  of  sodium  sulphate,  or  similar 


CH.  XXVI.] 


ENUMERATION    OF   CORPUSCLES 


435 


salt,  of  specific  gravity  1025,  is  made,  and  995  cubic  millimetres  are  measured  by 
means  of  the  pipette  into  the  glass  jar,  and  with  this  5  cubic  millimetres  of  blood, 
obtained  by  prickinji;  the  finger  with  the  needle,  and  measured  in  the  capillary 
pipette  (it)  are  tlioroughly  mixed  by  tlie  glass  stirring-rod.  A  drop  of  this  diluted 
blood  is  then  j)la(ed  in  the  cell  and  covered  with  a  cover-slip,  whic-h  is  fixed  in 
position  by  means  of  the  two  lateral  springs.  The  layer  of  diluted  blood  between 
the  slide  and  cover-glass  is  one-fifth  of  a  millimetre  thick.  The  preparation  is 
then  examined  under  a  microscope  with  a  power  of  about  400  diameters,  and 
focussed  until  the  lines  dividing  the  cell  into  S(}uares  are  visible. 

After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom  of  the 
cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares,  and  the  number 
of  white  corpuscles  noted.  By  adding  together  the  numbers  coimted  in  ten  (one- 
tenth  millimetre)  squares,  and,  as  the  blood  has  been  diluted,  multiplying  by  ten 
thousand,  the  number  of  corpuscles  in  one  cubic  millimetre  of  blood  is  obtained. 


Pig.  355. — Hsemacytometer.    (Gowers.) 


The  average  number  of  corpuscles  per  cubic  millimetre  of  healthy  blood,  according 
to  Vierordt  and  Welcker,  is  5,000,000  in  adult  men,  and  4,500,000  in  women  ; 
this  corresponds  to  an  average  of  50  and  45  corpuscles  respectively  per  square  of 
Gowers'  instrument. 

A  haemacytometer  of  another  form,  and  one  that  is  much  used  at  the  present 
time,  is  known  as  the  Thoma-Zeiss  haemacytometer.  It  consists  of  a  carefully 
graduated  pipette,  in  which  the  dilution  of  the  blood  is  done ;  this  is  so  formed 
that  the  capillary  stem  has  a  capacity  equalling  one-hundredth  of  the  bulb  above 
it.  If  the  blood  is  drawn  up  in  the  capillary  tube  to  the  line  marked  1  (fig.  357) 
the  saline  solution  may  afterwards  be  drawn  up  the  stem  to  the  line  101  ;  in  this 
way  we  have  101  parts,  of  which  the  blood  forms  1.  As  the  contents  of  the  stem 
can  be  displaced  unmixed  we  shall  have  in  the  mixture  the  proper  dilution.  The 
blood  and  the  saline  solution  are  well  mixed  by  shaking  the  pipette,  in  the  bulb 
of  which  is  contained  a  small  glass  bead  for  the  purpose  of  aiding  the  mixing. 
The  other  part  of  the  instrument  consists  of  a  glass  slide  (fig.  356)  upon  which  is 
mounted  a  covered  disc,  m,  accurately  ruled  so  as  to  present  one  square  milhmetre 


436 


THE   BLOOD 


[CH.  XXVI. 


divided  into  400  squares  of  one-twentieth  of  a  millimetre  each.  The  micrometer 
thus  made  is  surrounded  by  another  annular  cell,  r,  which  has  such  a  height  as  to 
make  the  cell  project  exactly  one-tenth  millimetre  beyond  m.     If  a  drop  of  the 


IM-C 


^mmmmmmm^^^ 


m\ 


^-///,  v//'//////y//,. 


diluted  blood  is  placed  upon  m,  and  c  is  covered  with  a  perfectly  flat  cover-glass, 

the  volume  of  the  diluted  blood  above  each  of  the  squares  of  the  micrometer,  i.e., 

above  each  j^f.n,  will  be  jr.V.j  of  a  cubic  millimetre.     An  aver- 

Fiii.  307.  age  of  ten  or  more  squares  is  then  taken,  and  this  number 

multiplied  by  4000    x  100  gives  the  number  of  corpuscles  in  a 

cubic  millimetre  of  undiluted  blood. 

Dr  George  Oliver's  Hsemacytometer  is  a  much  easier 
instrument  to  use,  and  the  results  obtained  are  accurate ;  it 
does  not  enable  one,  however,  to  ascertain  the  proportion  of 
red  and  white  corpuscles.  A  small  measured  quantity  of 
blood  is  taken  up  into  a  pipette  and  washed  out  into  a 
graduated  flattened  test-tube  with  Hayem's  fluid  (sodium 
chloride  0"5  gramme,  sodium  sulphate  0'25  gr. ,  corrosive 
sublimate  0'25  gr.,  distilled  water  100  c.c).  The  graduations 
of  the  tube  are  so  adjusted  that  with  normal  blood  (/.«.,  blood 
containing  .5,000,000  red  corpuscles  per  cubic  millimetre)  the 
light  of  a  small  wax  candle  placed  three  yards  from  the  eye  in 
a  dark  room,  is  just  visible  as  a  thin  bright  line  when  looked 
at  through  the  tube  held  edgeways  between  the  fingers,  and 
filled  up  to  the  100  mark  with  Hayem's  fluid.  If  the  number 
of  corpuscles  is  less  than  normal,  less  of  the  diluting  solution 
is  required  before  the  light  is  transmitted ;  if  more  than 
normal,  more  of  the  solution  is  necessary.  The  graduations 
of  the  tube  correspond  to  percentages  of  the  normal  standard 
which  is  taken  as  100. 

Development  of  the  Blood-Corpuscles. 

The  first  formed  blood-corpuscles  of  the  human 
embryo  differ  much  in  their  general  characters  from 
those  which  belong  to  the  later  periods  of  intra- 
uterine, and  to  all  periods  of  extra-uterine,  life. 
Their  manner  of  origin  is  at  first  very  simple. 

Surromiding  the  early  embryo  is  a  circular  area, 
called  the  vascular  area,  in  which  the  first  rudi- 
ments of  the  l)lood-vessels  and  blood-corpuscles  are  developed.  Here 
the  nucleated  embryonic  cells  of  the  mesoblast,  from  which  the  blood- 
vessels and  corpuscles  are  to  be  formed,  send  out  processes  in  various 
directions,  and  these,  joining  together,  form  an  irregular  mesh  work. 
The  nuclei  increase  in  number,  and  collect  chiefly  in  the  larger  masses 
of  protoplasm,  but  partly  also  in  the  processes.  These  nuclei  gather 
around  them  a  certain  amount  of  the  protoplasm,  and,  becoming 
coloured,  form  the  red  blood-corpuscles.  The  protoplasm  of  the 
cells  and  their  branched  network  in  which  these  corpuscles  lie  then 
become  hollowed  out  into  a  system  of  canals  enclosing  fluid,  in  which 


Figs.  356  and  357.- 

Thoma-Zeiss 

Hemacytometer. 


CH.  XXVI.] 


DEVELOPMENT   OF   BLOOD-OOlirUSCLES 


437 


the  red  nucleated  corpuscles  float.  The  corpuscles  at  first  are  from 
about  .-\y^  to  1  .^iy  of  an  inch  (10/x  to  16/x)  in  diameter,  nu)stly 
spherical,  and  with  granular  contents,  and  a  well-marked  nucleus. 
Their  nuclei,  which  are  about  >-oW  of  an  inch  (5/x)  in  diameter,  are 
central  and  circular. 


.^;\  'til. 


^•^ 


^'^ 


M 


Fig.  358.— Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig.  U, 
blood-corpuscles  becoming  free  iu  an  enlarged  and  hollowed-out  part  of  the  network;  a,  process  of 
protoplasm.    (E.  A.  Schiifer.) 

The  corpuscles  then  strongly  resemble  the  colourless  corpuscles 
of  the  fully  developed  blood,  but  are  coloured.  They  are  capable  of 
amoeboid  movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver  begins 
to  be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of 


Kio.  359.— Development  of  red  corpuscles  in  connective  tissue  cells.  From  the  subcutaneous  tissue  of 
a  new-bom  rat.  h,  a  cell  containing  hemoglobin  in  a  diffused  form  in  the  protoplasm  ;  h',  one 
containing  coloured  globules  of  varying  size  and  vacuoles  ;  h",  a  cell  tilled  with  coloured  globules  of 
nearly  uniform  size  ;  /,  /,  developing  fat  cells.    (B.  A.  Schiifer.) 

blood  ceases,  and  new  blood-cells  are  produced  by  this  organ,  and 
also  by  the  lymphatic  glands,  thymus  and  spleen.  These  are  at  first 
colourless  and  nucleated,  but  afterwards  acquire  the  ordinary  blood- 
tinge,  and  resemble  very  much  those  of  the  first  set.  They  also 
multiply  by  division.  In  whichever  way  produced,  however,  whether 
from  the  original  formative  cells  of  the  embryo,  or  by  the  liver  and  the 


438 


THE   BLOOD 


[CH.  XXVI. 


other  organs  mentioned  above,  these  coloured  nucleated  cells  begin 
very  early  in  foetal  life  to  be  mingled  with  coloured  wo?i-nucleated 
corpuscles  resembling  those  of  the  adult,  and  at  about  the  fourth  or 
fifth  month  of  embryonic  existence  are  completely  replaced  by  them. 

During  fcetal  life,  and  possibly 
in  some  animals,  e.g.  the  rat,  which 
are  born  in  an  immature  condition, 
for  some  little  time  after  birth,  the 
blood  discs  have  been  stated  by 
Schafer  to  arise  in  the  connective 
tissue  cells  in  the  following  way. 
Small  globules,  of  varying  size,  of 
colouring  matter  arise  in  the  pro- 
toplasm of  the  cells  (fig.  359) ;  the 
cells  themselves  become  branched, 
and  their  branches  join  the 
branches  of  similar  cells.  The  cells 
next  become  vacuolated,  and  the  red 
globules  are  free  in  a  cavity  filled 
with  fluid  (fig.  360) ;  by  the  exten- 
sion of  the  cavity  of  the  cells  into 
their  processes  anastomosing  vessels 
are  produced,  which  ultimately 
join  with  the  previously  existing 
vessels,  and  the  globules,  now 
having  the  size  and  appearance  of 
the  ordinary  red  corpuscles,  are 
passed  into  the  general  circulation. 
This  method  of  formation  is  called 
intracellular. 

Without  doubt,  the  red  cor- 
puscles have,  like  all  other  parts 
of  the  organism,  a  tolerably  definite  term  of  existence,  and  in  a  like 
manner  die  and  waste  away  when  the  portion  of  work  allotted  to 
them  has  been  performed.  Neither  the  length  of  their  life,  however,- 
nor  the  fashion  of  their  decay,  has  been  yet  wholly  made  out.     A 


Fio.  360. — Further  development  of  blood-cor- 
puscles in  connective  tissue  cells  and  trans- 
formation of  the  latter  into  capillary 
blood-vessels,  o,  an  elongated  cell  with  a 
cavity  in  the  protoplasm  occupied  by  fluid 
and  by  blood-corpuscles  which  are  still 
globular;  h,  a  hollow  cell,  the  nucleus  of 
which  has  multiplied.  The  new  nuclei  are 
arranged  around  the  wall  of  the  cavity,  the 
corpuscles  in  which  have  now  become  dis- 
coid ;  c,  shows  the  mode  of  union  of  a 
"  hjemapoietic  "  cell,  which,  in  this  instance, 
contains  only  one  corpuscle,  with  the  pro- 
longation {111)  of  a  previously  existing  vessel ; 
a  and  c,  from  the  new-born  rat :  h,  from  the 
fretal  sheep.    (E.  A.  Schiifer.) 


Fio.  361. — Coloured  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig. 
(E.  A.  Schafer.) 

certain  number  of  the  coloured  corpuscles  undergo  disintegration  in 
the  liver  and  spleen ;  corpuscles  in  various  degrees  of  degeneration 
have  been  observed  in  both  these  organs. 


en.  XXVI.]  ORIGIN   OF   WHITE   CORrUSCLES  439 

This  being  so,  it  is  necessary  that  the  red  corpuscles  slioukl  bo 
constantly  replenished  throughout  life.  But  after  the  early  foetal 
stage  is  passed,  they  originate,  not  from  connective  tissues  in  general, 
but  in  one  special  form  of  connective  tissue,  namely,  the  red  marrow 
of  bones.  It  is  possible  that  in  some  animals  the  spleen,  which 
contains  cells  very  similar  to  those  of  the  marrow,  may  participate 
in  their  formation.  In  the  red  marrow,  they  arise  from  immature 
nucleated  cells  {normohlasts  or  erythrohlasts) ;  the  nucleus  is  not 
discharged,  but  is  absorbed  within  the  cell,  and  this  is  the  explana- 
tion that  some  observers  give  of  the  biconcave  form  of  the  red  disc. 
Sometimes  immature  nucleated  red  cells  may  make  their  way  from 
the  marrow  into  the  circulation ;  and  the  free  nuclei  of  these  cells 
are  sometimes  found  in  the  blood ;  they  never,  when  once  they  have 
entered  the  blood,  develop  into  discs,  and  are  filtered  out  of  the 
blood  by  the  spleen. 

Origin  of  the  White  Corpuscles. — The  lymphocytes  are  formed 
in  the  lymphoid  tissue  of  the  lymphatic  glands,  tonsils,  and  other 
parts  where  this  tissue  is  present.  They  enter  the  blood  stream  by 
the  thoracic  duct,  and  grow  larger,  the  proportion  of  protoplasm  to 
nucleus  increasing  as  they  become  mature. 

The  hyaline  leucocyte  is,  according  to  some,  a  variety  of  mature 
lymphocyte ;  according  to  others,  it,  like  all  the  rest  of  the  leucocytes, 
originates  from  immature  forms  in  the  red  marrow,  which  are  called 
myelocytes.  The  leucocytes  proper,  as  distinguished  from  the 
lymphocytes,  do  not  grow  larger  in  the  blood  stream,  but  rather 
have  a  tendency  to  shrink  in  size  with  age. 

If  immature  myelocytes  escape  from  the  marrow  into  the  circu- 
lating blood,  they  undergo  no  furl,her  development  there,  and  like 
the  immature  nucleated  red  corpuscles,  are  filtered  off  by  the  spleen. 
This,  of  course,  is  a  pathological  condition,  and  leads  to  the  swelling 
of  the  spleen,  which  is  such  a  marked  feature  in  the  disease  known 
as  splenic  leukaemia. 

Chemistry  of  the  Blood-Corpuscles. 

The  -white  blood-corpuscles. — Our  chemical  knowledge  of  the 
white  corpuscles  is  small.  Their  nucleus  consists  of  nuclein,  their 
cell  protoplasm  yields  proteins  belonging  to  the  globulin  and  nucleo- 
protein  groups.  The  nucleo-protein  is  the  zymogen  of  thrombin 
(see  p.  426).  The  protoplasm  of  these  cells  often  contains  small 
quantities  of  fat  and  glycogen. 

The  red  blood-corpuscles. — 1000  parts  of  red  corpuscles  con- 
tain : — 

Water 688       parts. 

Solids  'Organic 303-88      „ 

^°"^^  (_  Inorganic 8-12      „ 


440 


THE   BLOOD 


[CII.  XXVI. 


One  hundred  parts  of  the  dry  organic  matter  contain — 

Protein 5  to  12  parts. 

Haemoglobin          .         .         .         .         .         .         .         .  86  to  94     „ 

Lecithin 1*8    „ 

Cholesterin .  0*1    „ 

The  protein  present  appears  to  be  identical  with  the  nucleo-protein 
of  white  corpuscles.  The  mineral  matter  consists  chiefly  of  chlorides 
of  potassium  and  sodium,  and  phosphates  of  calcium  and  magnesium. 
In  man  potassium  chloride  is  more  abundant  than  sodium  chloride ; 
this,  however,  does  not  hold  good  for  all  animals. 

Haemoglobin  and  Oxy haemoglobin. — The  pigment  is  by  far 
the  most  abundant  and  important  of  the  constituents  of  the  red 
corpuscles.  It  is  a  conjugated  protem,  a  compound  of  protein  with 
the  iron-containing  pigment  called  haematin. 

It  exists  in  the  blood  in  two  conditions :  in  arterial  blood  it  is 
combined  loosely  with  oxygen,  is  of  a  bright  red  colour,  and  is  called 

oxyhsemoglobin ;   the  other  con- 

'"'^^  ""  dition  is  the  deoxygenated  or  re- 

-^  duced  haemoglobin  (better  called 

.  simply    haemoglobin).      This    is 

/  found  in  the  blood  after  asphyxia. 

It  also  occurs  in  all  venous  blood 

t       _  — that  is,  blood  which  is  return - 

i>*x ""  ing  to  the  heart  after  it  has  sup- 

^^^'    ^«^  plied    the    tissues  with   oxygen. 

^    n  ^^  Venous   blood,  however,  always 

\}'.  contains  a  considerable  quantity 

V  ^  of  oxyhaemoglobin  also.     Haemo- 

^^^•^k^"  globin  is  the   oxygen-carrier  of 

"xV  w  ^^^kr''-^  ^^®  ^5ody,  and  it  may  be  called  a 

^'^~-^L___j^ --^*^  respiratory  pigment.* 

Crystals  of  oxyhaemoglobin + 

Fig.  362. — Crystals  of  oxylioemoglobin— prismatic.  .-^        ,.         t-.i  t 

from  human  blood.  may  DC  obtamed  with  readiness 

from  the  blood  of  such  animals 
as  the  rat,  guinea-pig,  or  dog;  with  difficulty  from  other  animals, 
such  as  man,  ape,  and  most  of  the  common  mammals.  The  follow- 
ing methods  are  the  best : — 

1.  Mix  a  drop  of  defibrinated  blood  of  the  rat  on  a  slide  with  a 
drop  of  water ;  put  on  a  cover-glass ;  in  a  few  minutes  the  corpuscles 

*  In  the  blood  of  invertebrate  animals  haemoglobin  is  sometimes  found,  but 
usually  in  the  plasma,  not  in  special  corpuscles.  Sometimes  it  is  replaced  by  other 
respiratory  pigments,  such  as  the  green  one,  chlorocruorin,  found  in  certain  worms, 
and  the  blue  one,  haemocyanin,  found  in  many  molluscs  and  Crustacea.  Chloro- 
cruorin contains  iron  ;  hsemocyanin  contains  copper. 

+  Crystals  of  haemoglobin  can  also  be  obtained  by  carrying  out  the  crystal- 
lisation in  an  atmosphere  free  from  oxygen. 


CH.  XXVI.] 


H.I^MnOLOBTN 


441 


are  rendered  colourless,  and  then  the  oxyhoemoglobin  crystallises  out 
from  the  solution  so  formed. 

2.  Microscopical  specimens  may  also  bo  made  ])y  Stein's  method, 
which  consists  in  using  Canada  balsam  instead  of  water  in  the  fore- 
going experiment. 

3.  On  a  larger  scale,  crystals  may  be  obtained  by  mixing  the 
blood  with  one-sixteenth  of  its  volume  of  ether ;  the  corpuscles  dis- 
solve, and  the  blood  assumes  a  laky  appearance.  After  a  period  vary- 
ing from  a  few  minutes  to  days,  abundant  crystals  are  deposited. 

In  nearly  all  animals  the  crystals  are  rhombic  prisms  (fig.  362) ; 
but  in  the  guinea-pig  they  are  rhombic  tetrahedra,  or  four-sided 
pyramids  (fig.  363);  in  the  squirrel  and  hamster,  hexagonal  plates 
(fig.  364). 

The  crystals  contain  a  varying  amount  of  water  of  crystallisation  ; 


Fig.  3C3.— Oxyhsemoglobin  crystals— tetraliedral , 
from  blood  of  the  guinea-pig. 


Fig.  364. — Hexagonal  oxyhjemoglobin  crystals, 
from  blood  of  squirrel.    (After  Funke.) 


this  probably  explains  their  different  crystalline  form  and  solubilities. 
Several  observers  have  analysed  hsemoglobin.  They  find  carbon, 
hydrogen,  nitrogen,  oxygen,  sulphur,  and  iron.  The  percentage  of 
iron  is  0'4.  On  adding  an  acid  or  alkali  to  haemoglobin,  it  is  broken 
up  into  two  parts — a  brown  pigment  called  hcematin,  which  contains 
all  the  iron  of  the  original  substance,  and  a  protein  called  globin. 

Hsematin  is  not  crystallisable ;  it  has  the  formula  C32H3oN4Fe03 
(Nencki  and  Sieber) ;  its  constitutional  formula  is,  however,  not 
known.  Haematin  presents  different  spectroscopic  appearances  in 
acid  and  alkaline  solutions  (see  accompanying  plate).  On  decomposi- 
tion it  yields  pyrrol  derivatives. 

Globin  is  coagulable  by  heat,  soluble  in  dilute  acids,  and  pre- 
cipitable  from  such  solutions  by  ammonia.  It  belongs  to  the  class  of 
proteins  called  histones  (see  p.  409). 


442  THE   BLOOD  [CH.  XXVI. 

Haemochromogen  is  sometimes  called  reduced  hasmatin  ;  it  may 
be  formed  by  adding  a  reducing  agent  such  as  ammonium  sulphide  to 
an  alkaline  solution  of  hrematin.  Its  absorption  spectrum,  shown  on 
the  accompanying  plate  (No.  8),  forms  the  best  spectroscopic  test  for 
blood  pigment ;  the  suspected  pigment  is  dissolved  in  potash,  and 
ammonium  sulphide  added.  Very  dilute  specimens  show  the  absorp- 
tion bands,  especially  the  one  midway  between  D  and  E. 

Hsemin  is  of  great  importance,  as  the  obtaining  of  this  substance 
forms  the  best  chemical  test  for  blood.  Haemin  crystals  may  be  pre- 
pared for  microscopical  examination  by  boiling  a  fragment  of  dried 
blood  with  a  drop  of  glacial  acetic  acid  on  -a  slide ;  on  cooling,  triclinic 
plates  and  prisms  of  a  dark  brown  colour,  often  in  star-shaped 
clusters  and  with  rounded  angles  (fig.  365),  separate  out.  In  the 
case  of  an  old  blood  stain  it  is  necessary  to  add  a  crystal  of  sodium 
chloride.     Fresh  blood  contains  sufficient  sodium  chloride  in  itself. 


Fig.  365. — Haemin  crystals.     (Frey.)  Fig.  366.— Hsematoidin  crystals. 

(Frey.) 

The  action  of  the  acetic  acid  is  (1)  to  split  the  haemoglobin  into 
haematin  and  globin;  and  (2)  to  evolve  hydrochloric  acid  from  the 
sodium  cliloride.  Hsemin  is  usually  stated  to  be  a  combination  of 
haematin  with  hydrochloric  acid.  Haemin  may  be  prepared  in  other 
ways,  but  if  prepared  with  the  use  of  acetic  acid,  ISTencki  and  Zaleski 
have  shown  that  it  also  contains  an  acetyl  group,  and  ascribe  to  it  the 
empirical  formula,  Cg^HggO^N^ClFe.  The  chlorine  and  acetyl  are  both 
attached  to  the  iron  atom. 

Hsematoporphyrin  is  iron-free  haematin ;  it  may  be  prepared  by 
mixing  blood  with  strong  sulphuric  acid  •,  the  iron  is  taken  out  as 
ferrous  sulphate.  It  is  also  found  sometimes  in  nature ;  it  occurs  in 
certain  invertebrate  pigments,  and  may  also  be  found  in  certain  forms 
of  pathological  urine.  Even  normal  urine  contains  traces  of  it.  It 
presents  different  spectroscopic  appearances  according  as  it  is  dis- 
solved in  acid  or  alkaline  media.  The  absorption  spectrum  figured 
(Ko.  9)  is  that  of  acid  haematoporphyrin. 

If  oxyhaemoglobin  is  treated  with  dilute  acids  the  result  is  a  formation  of 
haematin  and  globin,  but  if  strong  sulphuric  acid  is  employed  the  iron  is  removed 
from  the  haematin  and  so  haematoporphyrin  is  obtained.     The  stability  of  the  iron 


CII.  XXVI.]  HEMOGLOBIN  443 

in  the  molecule  is  due  to  the  presence  of  oxygen,  for  with  the  reduced  pigment, 
hiPmatoporphyrin  is  obtained  even  when  dilute  acids  are  employed.     Pure  haemato- 

Eorphyrin  can  once  more  be  converted  into  haematin  (that  is,  the  iron  can  be  replaced) 
y  wanning  a  solution  in  dilute  ammonia  and  adding  a  little  Stokes'  fluid,  and  a  few 
drops  of  a  reducing  agent  like  hydrazine  hydrate.  If  cuprammonium  solution  is 
used  instead  of  Stokes'  fluid  in  this  experiment,  a  copper  compound  of  haemato- 
porphyrin  is  obtained,  which  is  identical  with  turacbi,  the  bright  red  copper  containing 
pigment  found  in  the  plumage  of  the  plantain-eating  birds.     (Laidlaw.) 

Hcemopi/rrol  is  a  substance  obtained  by  reduction  from  ha2matoporphyrin.      It 
is  methyl-propyl  pyrrol,  and  its  formula  is  : — 

HC C.CH,.C,H 

HC        C .  CH3 

\/ 

N 

There  is  a  near  relationship  between  haemoglobin  and  chlorophyll,  for  the  same 
substance  is  obtained  from  phylloporphyrin,  a  derivative  of  chlorophyll. 

Haematoidin. — This  substance  is  found  in  the  form  of  yellowish- 
red  crystals  (fig.  366)  in  old  blood  extravasations,  and  is  derived  from 
the  hsemoglobin.  Its  crystalline  form  and  the  reaction  it  gives  with 
fuming  nitric  acid  shows  it  to  be  closely  allied  to  hiliruhin,  the  chief 
colouring  matter  of  the  bile,  and  on  analysis  it  is  found  to  be  identical 
with  it. 

Like  haematoporphyrin,  haematoidin  is  free  from  iron.  These  two 
substances  are  not  identical  {e.g.,  haematoidin  shows  no  spectroscopic 
bands) ;  they  are  probably  isomeric. 

Compounds  of  Haemoglobin. 

Haemoglobin  forms  at  least  four  compounds  with  gases : — 

With  oxvppn  ^^-  Oxyhaemoglobin. 

With  oxygen      .         .         .         .         .  ^2.  Methaemoglobin. 

With  carbonic  oxide  .         .         .         .3.  Carbonic  oxide  haemoglobin. 
With  nitric  oxide        .         .         .         .4.  Nitric  oxide  haemoglobin. 

These  compounds  have  similar  crystalline  forms ;  they  each 
probably  consist  of  a  molecule  of  haemoglobin  combined  with  one  of 
the  gas  in  question.  They  part  with  the  combined  gas  somewhat 
readily ;  they  are  arranged  in  order  of  stability  in  the  above  list,  the 
least  stable  first. 

Oxyhaemoglobin  is  the  compound  that  exists  in  arterial  blood. 
Many  of  its  properties  have  been  already  mentioned.  The  oxygen 
linked  to  the  hsemoglobin,  which  is  removed  by  the  tissues  through 
which  the  blood  circulates,  may  be  called  the  respiratory  oxygen  of 
haemoglobin.  The  processes  that  occur  in  the  lungs  and  tissues, 
resulting  in  the  oxygenation  and  de-oxygenation  respectively  of  the 
haemoglobin,  may  be  imitated  outside  the  body,  using  either  blood  or 
pure  solutions  of  haemoglobin.  The  respiratory  oxygen  can  be 
removed,  for  example,  in  the  Torricellian  vacuum  of  a  mercurial  air- 


444  THE  BLOOD  [CH.  XXVL 

pump,  or  by  passing  a  neutral  gas  such  as  hydrogen  through  the  blood, 
or  by  the  use  of  reducing  agents  such  as  ammonium  sulphide  and 
Stokes'  reagent.*  One  gramme  of  hsemoglobin  will  combine  with 
1"34  c.c.  of  oxygen. 

If  any  of  these  methods  for  reducing  oxyhaemoglobin  is  used,  the 
bright  red  (arterial)  colour  of  oxyhsemoglobin  changes  to  the  purplish 
(venous)  tint  of  haemoglobin.  On  once  more  allowing  oxygen  to 
come  into  contact  with  the  haemoglobin,  as  by  shaking  the  solution 
with  the  air,  the  bright  arterial  colour  returns. 

These  colour-changes  may  be  more  accurately  studied  with  the 
spectroscope,  and  the  constant  position  of  the  absorption  bands  seen 
constitutes  an  important  test  for  blood  pigment.  It  will  be  first 
necessary  to  describe  briefly  the  instrument  used. 

The  Spectroscope. — When  a  ray  of  white  Light  is  passed  through 
a  prism,  it  is  refracted  or  bent  at  each  surface  of  the  prism ;  the 
whole  ray  is,  however,  not  equally  bent,  but  it  is  split  into  its 
constituent  colours,  which  may  be  allowed  to  fall  on  a  screen.  The 
band  of  colours  beginning  with  the  red,  passing  through  orange, 
yellow,  green,  blue,  and  ending  with  -violet,  is  called  a  spectrum :  this 
is  seen  in  nature  in  the  rainbow.  It  may  be  obtained  artificially  by 
the  glass  prism  or  prisms  of  a  spectroscope. 

The  spectrum  of  sunlight  is  interrupted  by  numerous  dark  lines 
crossing  it  vertically,  called  Frauenhofer's  lines.  These  are  perfectly 
constant  in  position  and  serve  as  landmarks  in  the  spectrum.  The 
more  prominent  are  A,  B,  and  C,  in  the  red ;  D,  in  the  yellow ;  E,  h, 
and  F,  in  the  green ;  G  and  H,  in  the  ^dolet.  These  lines  are  due  to 
certain  volatile  substances  in  the  solar  atmosphere.  If  the  light 
from  burning  sodium  or  its  compounds  is  examined  spectroscopically, 
it  will  be  found  to  give  a  bright  yellow  line,  or,  rather,  two  bright 
yellow  lines  very  close  together.  Potassium  gives  two  bright  red 
lines  and  one  %'iolet  line ;  and  the  other  elements,  when  incandescent, 
give  characteristic  lines,  but  none  so  simple  as  sodium.  If  now  the 
flame  of  a  lamp  is  examined,  it  will  be  found  to  give  a  continuous 
spectrum  like  that  of  sunlight  in  the  arrangement  of  its  colours,  but 
unlike  it  in  the  absence  of  dark  lines ;  but  if  the  light  from  the  lamp 
is  made  to  pass  through  sodium  vapour  before  it  reaches  the  spectro- 
scope, the  bright  yellow  light  will  be  found  absent,  and  in  its  place  a 
dark  line,  or,  rather,  two  dark  lines  very  close  together,  occupying 
the  same  position  as  the  two  bright  lines  of  the  sodium  spectrimi. 
The  sodium  vapour  thus  absorbs  the  same  rays  as  those  which  it  itself 
produces  at  a  higher  temperature.  Thus  the  D  line,  as  we  term  it  in 
the  solar  spectrum,  is  due  to  the  presence  of  sodium  vapour  in  the 

*  Stokes'  reagent  must  always  be  freshly  prepared  ;  it  is  a  solution  of  ferrous 
sulphate  to  which  a  little  tartaric  acid  has  been  added,  and  then  ammonia  till  the 
reaction  is  alkaline. 


CH.  XXVI.]  THE   SPECTROSCOPE  445 

solar  atmusphoio.  Tlio  other  dark  linos  aro  similarly  accounted  lor 
by  other  elements. 

The  large  form  of  spectroscope  (fig.  367)  consists  of  a  tul)e  A, 
called  the  collimator,  with  a  slit  at  the  end  S,  and  a  convex  lens  at 
the  end  L.  The  latter  makes  the  rays  of  light  passing  through  tho 
slit  from  the  source  of  light,  parallel :  they  fall  on  the  prism  1*,  and 
then  the  spectrum  so  formed  is  focussed  by  the  telescope  T. 

A  third  tube,  not  shown  in  the  figure,  carries  a  small  transparent 
scale  of  wave-lengths,  as  in  accurate  observations  the  position  of  any 
point  in  the  spectrum  is  given  in  tho  terms  of  the  corresponding 
wave-lengths. 

If  we  now  interpose  between  the  source  of  light  and  the  slit  S  a 
piece  of  coloured  glass  (H  in  fig.  367),  or  a  solution  of  a  coloured 
substance  contained  in  a  vessel  with  parallel  sides  (the  haematoscope 


Fig.  367. — Diagram  of  Spectroscope. 


of  Herrmann),  the  spectrum  is  found  to  be  no  longer  continuous,  but 
is  interrupted  by  a  number  of  dark  shadows,  or  absorption  hands 
corresponding  to  the  light  absorbed  by  the  coloured  medium.  Thus  a 
solution  of  oxyhcemoglobin  of  a  certain  strength  gives  two  bands 
between  the  D  and  E  lines ;  haemoglobin  gives  only  one ;  and  other 
red  solutions,  though  to  the  naked  eye  similar  to  oxyhsemoglobin,  will 
give  characteristic  bands  in  other  positions. 

A  convenient  form  of  small  spectroscope  is  the  direct  visio7i 
spectroscope,  in  which,  by  an  arrangement  of  alternating  prisms  of 
crown  and  flint  glass,  the  spectrum  is  observed  by  the  eye  in  the 
same  line  as  the  tube  furnished  with  the  slit — indeed,  slit  and  prisms 
are  both  contained  in  the  same  tube. 

In  the  examination  of  the  spectrimi  of  small  coloured  objects  a 
combination  of  the  microscope  and  direct  vision  spectroscope,  called  the 
micro-spectroscope,  is  used. 

The  next  figure  illustrates  a  method  of  representing  absorption 
spectra  diagrammatically.     The  solution  was  examined  in  a  layer  1 


446 


THE   BLOOD 


[CH.  XXVI. 


centimetre  thick.  The  base  line  has  on  it  at  the  proper  distances 
the  chief  Frauenhofer  lines,  and  along  the  right-hand  edges  are 
percentages  of  the  amount  of  oxyhsemoglobin  present  in  I,  of 
haemoglobin  in  II.  The  width  of  the  shadings  at  each  level  repre- 
sents the  position  and  amount  of  absorption  corresponding  to  the 
percentages. 

The  characteristic  spectrum  of  oxyhsemoglobin,  as  it  actually 
appears  through  the  spectroscope,  is  seen  in  the  accompanying 
coloured  plate  (spectrum  2).  There  are  two  distinct  absorption 
bands  between  the  D  and  E  lines ;  the  one  nearest  to  D  (the  a 
band)  is  narrower,  darker,  and  has  better-defined  edges  than  the 
other  (the  /3  band).     As  will  be  seen  on  looking  at  fig.  368,  a  solution 


ABC 


F^G.  368.— Graphic  representations  of  the  amount  of  absorption  of  light  by  solution  of  (I)  oxyhsemo- 
globin, (11)  of  haemoglobin,  of  different  strengths.  The  shading  indicates  the  amount  of  absorption 
of  the  spectrum  ;  the  figures  on  the  right  border  express  percentages.    (RoUett.) 

of  oxyhaemoglobin  of  concentration  greater  than  0"65  per  cent,  and 
less  than  0"85  per  cent,  (examined  in  a  cell  of  the  usual  thickness  of 
1  centimetre)  gives  one  thick  band  overlapping  both  D  and  E,  and  a 
stronger  solution  only  lets  the  red  light  through  between  C  and  D. 
A  solution  which  gives  the  two  characteristic  bands  must  therefore  be 
a  dilute  one.  The  one  band  (y  band)  of  haemoglobin  (spectrum  3)  is 
not  so  well  defined  as  the  a  or  /3  bands.  On  dilution  it  fades  rapidly  ; 
so  that  in  a  solution  of  such  strength  that  both  bands  of  oxyhaemoglobin 
would  be  quite  distinct,  the  single  band  of  haemoglobin  has  disappeared 
from  view.  The  oxyhaemoglobin  bands  can  be  distinguished  in  a 
solution  which  contains  only  one  part  of  the  pigment  to  10,000  of 
water,  and  even  in  more  dilute  solutions  which  seem  to  be  colourless 
the  a  band  is  still  visible. 

Haemoglobin  and  its  compounds  also  show  absorption  bands  in 
the  ultra-violet  portion  of  the  spectrum.     This  portion  of  the  spectrum 


CM.  XXVI.] 


THK    rilOTOGlIAlMIIC    SPKCTItUM 


447 


is  not  visible  tu  the  eye,  but  can  be  rendered  visible  l)y  allowing  the 
spectrum  to  fall  on  a  fluorescent  screen,  or  on  a  sensitive  photographic 

G        ^     HK  L    M       N 


Fig.  369. — The  photographic  spectrum  of  hemoglobin  and  oxyhemoglobin.     (Gamgee.) 

plate.     In  order  to  show  absorption  bands  in  this  part  of  the  spectrum 
very  dilute  solutions  of  the  pigment  must  be  used. 

Oxyhsemoglobin  shows  a  band  (Soret's  band)  between  the  lines  G 
and  H.     In  haemoglobin,  carbonic  oxide  haemoglobin,  and  nitric  oxide 


Fig.  370.— The  photographic  spectrum  of  oxyhemoglobin  and  methemoglobin.    (Gamgee.) 

haemoglobin,  this  band   is  rather  nearer   G.     Methaemoglobin   and 
haematoporpli}Tin  show  similar  bands. 

We  owe  most  of  our  knowledge  of  the  "  photographic  spectrum  " 


448  THE   BLOOD  [CH.  XXVI. 

to  Prof.  Gaingee,  thruu^fli  whose  kindness  I  am  enabled  to  pre- 
sent reproductions  of  two  of  his  numerous  photographs  (tigs.  369 
and  370). 

Methaemoglotain. — This  may  be  produced  artificially  in  various 
ways,  as  by  adding  potassium  ferricyanide  or  amyl  nitrite  to  blood, 
and  as  it  also  may  occur  in  certain  diseased  conditions  in  the  urine, 
it  is  of  considerable  practical  importance.  It  can  be  crystallised,  and 
is  found  to  contain  the  same  amount  of  oxygen  as  oxyhfemoglobin, 
only  combined  in  a  different  way.  The  oxygen  is  not  removable  by 
the  air-jjump,  nor  by  a  stream  of  neutral  gas  like  hydrogen.  It  can, 
however,  by  reducing  agents  like  ammonium  sulphide,  be  made  to 
yield  luemoglobin.  Metha3moglobin  is  of  a  brownish-red  colour,  and 
gives  a  characteristic  absorption  band  in  the  red  between  the  C  and 
D  linos  (spectrum  7  in  coloured  plate).  In  dilute  solutions  other 
bands  can  be  seen. 

Potassium  ferricyanide  is  the  most  convenient  reagent  for  makinf>-  metha>mo- 
globiii.  It  is,  however,  necessary  to  mention  tiiat  it  produces  anotiier  effect  as 
well,  namely,  it  causes  an  evolution  of  gas,  if  the  blood  lias  been  previously  lakcd. 
This  gas  is  oxygen  ;  in  fact,  all  the  oxygen  combined  as  oxyhaeraoglobin  is  dis- 
charged, and  this  may  be  collected  and  measured  as  in  the  method  described  on 
p.  38t).  This  discharge  of  oxygen  from  oxyhaemoglobin  is  at  first  sight  puzzling, 
because,  as  just  stated,  mcthaenioglobin  contains  the  same  amount  of  oxygen  that 
is  present  in  oxyhajmoglobin.  What  occurs  is  that  after  the  oxygen  is  discharged 
from  oxyhaemoglobin,  an  eijual  quantity  of  oxygen,  due  to  the  oxidising  action  of 
the  reagents  added,  takes  its  place ;  this  new  oxygen,  however,  is  combined  in 
some  way  different  from  that  which  was  previously  united  to  the  haemoglobin. 
(Haldane.) 

Carbonic  oxide  hsemoglobin  may  be  readily  prepared  by  passing 
a  stream  of  carbonic  oxide  or  coal  gas  through  blood  or  through  a 
S(jlution  of  oxyhsemoglobin.  It  has  a  peculiar  cherry-red  colour.  Its 
absorption  spectrum  is  very  like  that  of  oxyhsemoglobin,  but  the  two 
bands  are  slightly  nearer  the  violet  end  of  the  spectrum  (spectrum  4 
in  coloured  plate).  Eeducing  agents,  such  as  ammonium  sulphide,  do 
not  change  it ;  the  gas  is  more  firmly  combined  than  the  oxygen  in 
hcemoglobin.  CO-hoemoglobin  forms  crystals  like  those  of  oxyhsemo- 
globin.    It  resists  putrefaction  for  a  very  long  time. 

Carbonic  oxide  is  given  off  during  the  imperfect  combustion  of 
carbon  such  as  occurs  in  charcoal  stoves  or  during  the  explosions  that 
occur  in  coal-mines ;  it  acts  as  a  powerful  poison,  by  combining  with 
the  hcemoglobin  of  the  blood,  and  thus  interferes  with  normal  respira- 
tory processes.  The  bright  colour  of  the  blood  in  both  arteries  and 
veins,  and  its  resistance  to  reducing-agents,  are  in  such  cases 
characteristic. 

Nitric  Oxide  Haemoglobin. — When  ammonia  is  added  to  blood, 
and  then  a  stream  of  nitric  oxide  passed  through  it,  this  compound 
is  formed.  It  may  be  obtained  in  crystals  isomorphous  with  oxy- 
and  CO-hoemoglobin.     It  also  has  a  similar  spectrum.     It   is   even 


BLOOD-SPECTRA  COMPARED  WITH  SOl.AR  SPECTRUM. 


B      C 


E     "b 


m 


E      b 


1.  Solar  spectrum. 

2.  Spectrum  of  dilute  solution  of  oxyhcemoglobin. 

3.  ,,  ,.    haemoglobin. 

4.  ),  „    carbonic  oxide  haemoglobin. 

5-  >'           II    acid  htematin  in  ethereal  solution. 

6.  ,,           ,,   alkaline  hsematin. 

7-  „           „    methcemoglobin. 

8.  „           ,,    hoemochromogen. 

9*  11           .,    acid  hoemaioporphyrin. 


[To  face  page  44S. 


HiEMOGLOBINOMETERS 


449 


CH.  XXVI.] 

more  stable  than  CO-haemoglobin  ;  it  has  no  practical  interest,  but  is 
of  theoretical  importance  as  completing  ihe  series. 

Estimation  of  Haemoglobin. — Tht-  most  exact  method  is  by  the  estimation  of 
the  amount  of  iron  (dry  haemoglobin  containing  '42  per  cent,  of  iron)  in  the  ash  of  a 
given  specimen  of  blood,  but  as  this  is  a  somewhat  complicated  process,  various 
colorimetric  methods  have  been  proposed  which,  though  not  so  exact,  have  the 
advantage  of  simplicity. 

Gowers'  Haemoglobinometer.— The  apparatus  (fig.  371')  consists  of  two  glass 
tubes  of  the  same  size.  One  contains  glycerin  jelly  tintecl  with  carmine  to  a 
standard  colour — viz.,  that  of  normal  blood  diluted  100  times  with  distilled  water. 
The  finger  is  pricked  and  20  cubic  millimetres  of  blood  are  measured  out  by  the 
capillary  pipette,  B.  This  is  blown  out  into  the  other  tube  and  diluted  with  distilled 
water,  added  drop  by  drop  from  the  pipette  stopper  of  the  bottle,  A,  until  the  tint 
of  the  diluted  blood  reaches  the  standard  colour.  This  tube  is  graduated  into  100 
parts.     If  the  tint  of  the  diluted  blood  is  the  same  as  the  standard  when  the  tube  is 


Fig.  371. — Hsemoglobinometer  of  Dr  Gowers. 


filled  up  to  the  graduation  100,  the  quantity  of  oxyhaemoglobin  in  the  blood  is 
normal.  If  it  has  to  be  diluted  more  largely,  the  oxyhaemoglobin  is  in  excess  ;  if  to 
a  smaller  extent,  it  is  less  than  normal.  If  the  blood  has,  for  instance,  to  be  diluted 
up  to  the  graduation  50,  the  amount  of  haemoglobin  is  only  half  what  it  ought  to 
be — 50  per  cent,  of  the  normal — and  so  for  other  percentages. 

Haldane's  Modification  of  GoAvers'  Instrument  is  the  one  most  frequently 
used  now,  and  gives  very  accurate  results.  Instead  of  tinted  gelatin,  the  standard 
of  comparison  is  a  sealed  tube  filled  with  a  solution  of  carbonic  oxide  haemoglobin. 
This  keeps  unchanged  for  years.  A  stream  of  coal  gas  is  passed  through  the  blood 
to  be  examined.  This  converts  all  the  haemoglobin  present  into  carbonic  oxide 
haemoglobin  ;  this  is  then  diluted  with  water  to  match  the  standard. 

Von  Pleischl's  Haemometer. — The  apparatus  (fig.  372)  consists  of  a  stand 
bearing  a  white  reflecting  surface  (S)  and  a  platform.  Under  the  platform  is  a  slot 
carrying  a  glass  wedge  stained  red  (K)  and  moved  by  a  wheel  (R).  On  the  platform 
is  a  small  cylindrical  vessel  divided  verticalh'  into  two  compartments,  a  and  «'. 

Fill  with  a  pipette  the  compartment  a'  over  the  wedge  with  distilled  water. 
Fill  about  a  quarter  of  the  other  compartment  (a)  with  distilled  water. 

Prick  the  finger  and  fill  the  short  capillary  pipette  provided  with  the  instru- 

2  F 


450 


THE    BLOOD 


[CH.  XXVI. 


ment  with  blood.     Dissolve  this  in  the  water  in  compartment  'i.  and  fill  it  up  with 
distilled  water. 

Having  arranged  the  reflector  (S)  to  throw  artijiiinl  light  vertically  through 
both  compartments,  look  down  through  them,  and  move  the  wedge  of  glass  by  the 


Fig.  372. — Von  Fleischi  s  Hiemogiobinometer. 


milled  head  fT)  until  the  colour  of  the  two  is  identical.     Read  off  the  scale,  which  is 
so  con'^tructed  as  to  give  the  percentage  of  haemoglobin. 

Dr  George  Oliver's  Method  consists  in  comparing  a  specimen  of  blood 
suitably  diluted  in  a  shallow  white  palette  with  a  number  of  standard  tests  very 
carefully  prepared  by  the  use  of  Lovibond's  coloured  glasses.  These  standards  are 
much  better  matches  for  blood  in  various  degrees  of  dilution  than  in  most  colori- 
raetric  methods.  The  yellow  tint  of  diluted  haemoglobin  is  very  successfully 
imitated. 

Tests  for  Blood. — These  may  l»e  gathered  from  preceding  descrip- 
tions. Briefly,  they  are  microscopic,  spectroscopic,  and  chemical. 
The  best  chemical  test  is  the  formation  of  hsemin  crystals.  The  old 
test  with  tincture  of  guaiacum  and  hydrogen  peroxide,  the  blood 
causing  the  red  tincture  to  become  green,  is  very  untrustworthy 
(unless  performed  with  somewhat  elaborate  precautions),  as  it  is  also 
given  by  many  other  organic  substances. 

In  medico-legal  cases  it  is  often  necessary  to  ascertain  whether  or 
not  a  red  fluid  or  stain  upon  clothing  is  or  is  not  blood.  In  any  such 
case  it  is  advisable  not  to  rely  upon  one  test  only,  but  to  try  every 
means  of  detection  at  one's  disposal.  To  discover  whether  it  is  blood 
or  not  is  by  no  means  a  difficult  problem,  but  to  distinguish  human 
blood  from  that  of  the  common  mammals  is  possible  only  by  the 
"  biolosfical "  test  described  at  the  end  of  the  next  section. 


Cn.  XXVI.]  IMMUNITY  451 

Immunity. 

The  chemical  tlofeiices  of  the  body  agaiust  injury  and  disease  are 
numerous.  The  i)roperty  that  the  blood  possesses  of  coagulating  is 
a  defence  against  h?emorrhage ;  the  acid  of  the  gastric  juice  is  a  great 
protection  against  harmful  bacteria  introduced  with  food.  Bacterial 
activity  in  urine  is  inhibited  by  the  acidity  of  that  secretion. 

Far  more  important  and  widespread  in  its  effects  than  any  of  the 
foregoing  is  the  bactericidal  (i.e.  bacteria  killing)  action  of  the  blood 
and  lymph ;  a  study  of  this  question  has  led  to  many  interesting 
results  especially  in  connection  with  the  problem  of  immunity.  This 
subject  is  one  of  great  importance. 

It  is  a  familiar  fact  that  one  attack  of  many  infective  maladies 
protects  us  against  another  attack  of  the  same  disease.  The  person 
is  said  to  be  immune  either  partially  or  completely  against  that 
disease.  Vaccination  produces  in  a  patient  an  attack  of  cowpox  or 
vaccinia.  This  disease  is  either  closely  related  to  smallpox,  or 
maybe  it  is  smallpox  modified  and  rendered  less  malignant  by  passing 
through  the  body  of  a  calf.  At  any  rate,  an  attack  of  vaccinia  renders 
a  person  immune  to  smallpox,  or  variola,  for  a  certain  number  of 
years.  Vaccination  is  an  instance  of  what  is  called  protective  inoculation, 
which  is  now  practised  with  more  or  less  success  in  reference  to  other 
diseases,  such  as  plague  and  typhoid  fever.  The  study  of  immunity 
has  also  rendered  possible  what  may  be  called  curative  inoculation,  or 
the  injection  of  antitoxic  material  as  a  cure  for  diphtheria,  tetanus, 
snake  poisoning,  etc. 

The  leucocytes  or  phagocytes  destroy  bacteria  by  feeding  on 
them ;  but  the  fluid  part  of  the  blood  is  often  antagonistic  to  bacterial 
life,  and  this  power  was  first  discovered  when  the  effort  was  made  to 
grow  various  kinds  of  bacteria  in  it ;  it  was  looked  upon  as  probable 
that  blood-serum  would  prove  a  suitable  soil  or  medium  for  this 
purpose.  It  was  found  in  some  instances  to  have  exactly  the 
opposite  effect.  The  chemical  characters  of  the  substances  which  kill 
the  bacteria  are  not  fully  known ;  indeed,  the  same  is  true  for  most 
of  the  substances  we  have  to  speak  of  in  this  connection.  Absence 
of  knowledge  on  this  particular  point  has  not,  however,  prevented 
important  discoveries  from  l^eing  made. 

So  far  as  is  known  at  present,  the  substances  in  question  are 
protein  in  nature.  The  bactericidal  powers  of  blood  are  destroyed  by 
heating  it  for  an  hour  to  55°  C.  Whether  the  substances  are  derived 
from  the  leucocytes  is  a  disputed  point ;  the  balance  of  evidence 
appears  to  me  to  be  in  favour  of  this  view  in  many  cases  at  any 
rate,  and  phagocytosis  becomes  more  intelligible  if  this  view  is 
accepted.  The  substances,  whatever  be  their  source  or  their  chemical 
nature,  are  called  hactcrio-hjsins. 


452  THE   BLOOD  [CH.  XXVI. 

Closely  allied  to  the  bactericidal  power  of  blood,  or  blood-serum, 
is  its  globulicidal  power.  By  this  one  means  that  the  blood-serum  of 
one  animal  has  the  power  of  dissolving  the  red  blood-corpuscles  of 
another  species.  If  the  serum  of  one  animal  is  injected  into  the 
blood-stream  of  an  animal  of  another  species,  the  result  is  a  destruction 
of  its  red  corpuscles,  which  may  be  so  excessive  as  to  lead  to  the 
passing  of  the  liberated  hsemoglobin  into  the  urine  (hsemoglobinuria). 
The  substance  or  substances  in  the  serum  that  possess  this  property 
are  called  hcemolysins,  and  though  there  is  some  doubt  whether 
bacterio-lysins  and  hgemolysins  are  absolutely  identical,  there  is  no 
doubt  that  they  are  closely  related  substances. 

Normal  blood  possesses  a  certain  amount  of  substances  which  are 
inimical  to  the  life  of  our  bacterial  foes.  But  suppose  a  person  gets 
run  down ;  every  one  knows  he  is  then  liable  to  "  catch  anything." 
This  coincides  with  a  diminution  in  the  bactericidal  power  of  his 
blood.  But  even  a  perfectly  healthy  person  has  not  an  unlimited 
supply  of  bacterio-lysin,  and  if  the  bacteria  are  sufficiently  numerous 
he  will  fall  a  victim  to  the  disease  they  produce.  Here,  however, 
comes  in  the  remarkable  part  of  the  defence.  In  the  struggle  he 
will  produce  more  and  more  bacterio-lysin,  and  if  he  gets  well  it 
means  that  the  bacteria  are  finally  vanquished,  and  his  blood  remains 
rich  in  the  particular  bacterio-lysin  he  has  produced,  and  so  will 
render  him  immune  for  a  time  to  further  attacks  from  that  particular 
species  of  bacterium.  Each  bacteriimi  attacked  in  this  way  seems  to 
cause  the  development  of  a  specific  anti-substance. 

Immunity  can  more  conveniently  be  produced  gradually  in  animals, 
and  this  applies,  not  only  to  the  bacteria,  but  in  certain  cases  to  the 
toxins  they  form.  If,  for  instance,  the  bacilli  which  produce 
diphtheria  are  grown  in  a  suitable  medium,  they  produce  the 
diphtheria  poison,  or  toxin,  much  in  the  same  way  that  yeast-cells 
will  produce  alcohol  when  grown  in  a  solution  of  sugar.  Diphtheria 
toxin  is  associated  with  a  proteose,  as  is  also  the  case  with  the  poison 
of  snake  venom.  If  a  certain  small  dose  called  a  "  lethal  dose "  is 
injected  into  a  guinea-pig  the  result  is  death.  But  if  the  guinea-pig 
receives  a  smaller  dose  it  will  recover ;  a  few  days  after  it  will  stand 
a  rather  larger  dose ;  and  this  may  be  continued  until,  after  many 
successive  gradually  increasing  doses,  it  will  finally  stand  an  amount 
equal  to  many  lethal  doses  without  any  ill  effects.  The  gradual 
introduction  of  the  toxin  has  called  forth  the  production  of  an 
antitoxin.  If  this  is  done  in  the  horse  instead  of  the  guinea-pig  the 
production  of  antitoxin  is  still  more  marked,  and  the  serum  obtained 
from  the  blood  of  an  immunised  horse  may  be  used  for  injecting  into 
human  beings  suffering  from  diphtheria,  and  rapidly  cures  the  disease. 
The  two  actions  of  the  blood,  antitoxic  and  antibacterial,  are  fre- 
quently associated,  but  may  be  entirely  distinct. 


CH.  XXVI.]  THE   SIDE-CHAIN    THEORY  453 

Tho  antitoxin  is  also  a  protein  prol)al)ly  of  the  nature  of  a  globulin  ; 
at  any  rate  it  is  a  protein  of  larger  molecular  weight  than  a  proteose. 
This  suggests  a  practical  point.  In  the  case  of  snake-poisoning  the 
poison  gets  into  the  blood  rapidly  owing  to  the  comparative  ease  with 
which  it  diffuses,  and  so  it  is  quickly  carried  all  over  the  body.  In 
treatment  with  the  antitoxin  or  antivenin,  speed  is  everything  if  life 
is  to  be  saved ;  injection  of  this  material  under  the  skin  is  not  much 
good,  for  the  diffusion  into  the  l^lood  is  too  slow.  It  should  be 
injected  straight  away  into  a  blood-vessel. 

There  is  no  doubt  that  in  these  cases  the  antitoxin  neutralises  the 
toxin  much  in  the  same  way  that  an  acid  neutralises  an  alkali.  If 
the  toxin  and  antitoxin  are  mixed  in  a  test-tube,  and  time  allowed 
for  the  interaction  to  occur,  the  result  is  an  innocuous  mixture.  The 
toxin,  however,  is  merely  neutralised,  not  destroyed ;  for  if  the 
mixture  in  the  test-tube  is  heated  to  68"  C.  the  antitoxin  is  coagulated 
and  destroyed,  and  the  toxin  remains  as  poisonous  as  ever. 

Immunity  is  distinguished  into  active  and  passive.  Active  im- 
munity is  produced  by  the  development  of  protective  substances  in 
the  body ;  passive  immunity  by  the  injection  of  a  protective  serum. 
Of  the  two  the  former  is  the  more  permanent. 

Ricin,  the  poisonous  protein  of  castor-oil  seeds,  and  ahrin,  that 
of  the  Jequirity  bean,  also  produce,  when  gradually  given  to  animals, 
an  immunity,  due  to  the  production  of  anti-ricin  and  anti-abrin 
respectively. 

Ehrlich's  hypothesis  to  explain  such  facts  is  usually  spoken  of  as 
the  side-chain  theory  of  immunity.  He  considers  that  the  toxins  are 
capable  of  uniting  with  the  protoplasm  of  Hving  cells  by  possessing 
groups  of  atons  like  those  by  which  nutritive  proteins  are  united  to 
cells  during  normal  assimilation.  He  terms  these  haptophor  groups, 
and  the  groups  to  which  these  are  attached  in  the  cells  he  terms 
receptor  groups.  The  introduction  of  a  toxin  stimulates  an  excessive 
production  of  receptors,  which  are  finally  thrown  out  into  the  circula- 
tion, and  the  free  circulating  receptors  constitute  the  antitoxin.  The 
comparison  of  the  process  to  assimilation  is  justified  by  the  fact  that 
non-toxic  substances  like  milk  or  egg-white  introduced  gradually  by 
successive  doses  into  the  blood-stream  cause  the  formation  of  anti- 
substances  capable  of  coagulating  them. 

Up  to  this  point  I  have  spoken  only  of  the  blood,  but  month  by 
month  workers  are  bringing  forward  evidence  to  show  that  other 
cells  of  the  body  may  by  similar  measures  be  rendered  capable  of 
producing  a  corresponding  protective  mechanism. 

One  further  development  of  the  theory  I  must  mention.  At  least 
two  different  substances  are  necessary  to  render  a  serum  bactericidal 
or  globulicidal.  The  bacterio-lysin  or  hsemolysin  consists  of  these 
two  substances.     One  of  these^is  called  the  immune  body,  the  other 


454  THE   BLOOD  [CH.  XXVI. 

the  complement.  We  may  illustrate  the  use  of  these  terms  l)y  an 
example.  The  repeated  injection  of  the  blood  of  one  animal  {e.g.,  the 
goat)  into  the  blood  of  another  animal  {e.g.,  a  sheep)  after  a  time 
renders  the  latter  animal  immune  to  further  injections,  and  at  the 
same  time  causes  the  production  of  a  serum  which  dissolves  readily 
the  red  blood-corpuscles  of  the  first  animal.  The  sheep's  serum  is  thus 
hsemolytic  towards  goat's  blood-corpuscles.  This  power  is  destroyed 
by  heating  to  56°  C.  for  half  an  hour,  but  returns  when  the  fresh 
serum  of  any  animal  is  added.  The  specific  immunising  substance 
formed  in  the  sheep  is  called  the  immune  body;  the  ferment-like 
substance  destroyed  ))y  heat  is  the  complement.  The  latter  is  not 
specific,  since  it  is  furnished  by  the  blood  of  non-immunised  animals, 
but  it  is  nevertheless  essential  for  hsemolysis.  Ehrlich  believes  that 
the  immune  body  has  two  side  groups — one  which  connects  with  the 
receptor  of  the  red  corpuscles,  and  one  which  unites  with  the  hapto- 
phor  group  of  the  complement,  and  thus  renders  possible  the  ferment- 
like action  of  the  complement  on  the  red  corpuscles.  Various 
antibacterial  serums  which  have  not  been  the  success  in  treating 
disease  they  were  expected  to  be,  are  probably  too  poor  in  comple- 
ment, though  they  may  contain  plenty  of  the  immune  body. 

To  put  it  another  way :  the  cell-dissolving  substances  cannot  act 
on  their  objects  of  attack  without  an  intermediate  substance  to 
anchor  them  on  to  the  substance  in  question.  This  intermediary 
substance,  known  as  the  immune  body  or  amboceptor,  is  specific,  and 
varies  with  the  substance  to  be  attacked  (red  corpuscles,  bacterium, 
toxin,  etc.).  The  complement  may  be  compared  to  a  person  who 
wants  to  unlock  a  door;  to  do  this  effectively  he  must  be  provided 
with  the  proper  key  (amboceptor  or  immune  body). 

Quite  distinct  from  the  bactericidal,  globulicidal,  and  antitoxic 
properties  of  blood  is  its  agglutinating  action.  This  is  another  result 
of  infection  with  many  kinds  of  bacteria  or  their  toxins.  The  blood 
acquires  the  property  of  rendering  immobile  and  clumping  together 
the  specific  bacteria  used  in  the  infection.  The  test  apphed  to  the 
blood  in  cases  of  typhoid  fever,  and  generally  called  Widal's  reaction, 
depends  on  this  fact.  The  substances  that  produce  this  effect  are 
called  agglutinins.  They  also  are  probably  protein-like  in  nature, 
but  are  more  resistant  to  heat  than  the  lysins.  Prolonged  heating 
to  over  60''  C.  is  necessary  to  destroy  their  activity. 

We  thus  see  that  the  means  of  combating  our  bacterial  enemies 
are  various;  in  some  cases  they  are  rendered  immobile  by  agglu- 
tinins, and  in  other  cases,  killed  by  bacterio-lysins.  In  other 
instances,  their  toxins  are  neutralised  by  antitoxins,  and  in  others 
again  they  are  directly  devoured  by  phagocytes.  Metschnikoff's 
view,  which  is  shared  by  many  eminent  bacteriologists,  is  that 
phagocytosis   is   the   supreme   method,   and    the  others  are  merely 


CH.  XXVI.]  OPSONINS  455 

auxiliaries,  or  confined  to  a  small  number  of  cases.  If  a  foreign 
organism  is  destroyed  by  the  leucocytes,  it  produces  no  ill  effects 
when  it  enters  the  body  of  a  man  or  other  animal ;  but  if  it  is  not 
destroyed,  it  grows  and  produces  a  disease,  and  it  is  therefore  called 
pathogenic.  If  the  phagocytes  can  be  induced  to  feed  on  a  patho- 
genic organism,  it  is  at  once  rendered  non-pathogenic.  The  recent 
discovery  of  opsonins,  by  Sir  A.  E.  Wright,  emphasises  this  view  and 
shows  one  means  the  l)ody  possesses  of  persuading  the  leucocytes  to 
eat  bacteria,  which  would  otherwise  be  distasteful  to  them.  Washed 
bacteria  from  a  culture  are  usually  refused  by  leucocytes ;  but  if  the 
bacteria  had  been  previously  soaked  in  serum,  especially  if  that 
serum  has  been  obtained  from  the  blood  of  an  animal  previously 
immunised  against  that  special  bacterium,  then  the  leucocytes 
devour  them  eagerly.  Something  has  either  been  added  to  the 
bacterium  to  make  it  tasty,  or  something  removed  from  it  which 
previously  made  it  distasteful :  whichever  is  the  case,  the  action  is 
described  as  the  action  of  an  opsonin  (derived  from  a  Greek  word 
which  means  "  to  j^repare  the  feast "  ). 

We  may  take  the  specific  case  of  the  tubercle  bacillus  as  an 
instance  where  such  work  is  of  value.  All  of  us  are  breathing  in 
these  bacilli  every  day  of  our  lives,  but  many  of  us  escape  tubercu- 
losis because  the  opsonic  power  of  our  blood  is  sufficiently  high  to 
render  the  bacilli  an  easy  prey  to  leucocytes.  In  those  to  whom  the 
organism  is  pathoirenic,  the  modern  treatment  is  directed  to  enhanc- 
ing  nature's  cure  by  increasing  the  opsonic  power  of  the  j)atient's 
blood  by  good  food  and  pure  air,  or  the  injection  of  preparations  of 
the  required  opsonin. 

Lastly,  we  come  to  a  question  which  more  directly  appeals  to  the 
physiologist  than  the  preceding,  because  experiments  in  relation  to 
immunity  have  furnished  us  with  what  has  hitherto  been  lacking, 
a  means  of  distinguishing  human  blood  from  the  blood  of  other 
animals. 

The  discovery  was  made  by  Tchistovitch  (1899),  and  his  original 
experiment  was  as  follows: — Eabbits,  dogs,  goats,  and  guinea-pigs 
were  inoculated  with  eel-serum,  which  is  toxic :  he  thereby  obtained 
from  these  animals  an  antitoxic  serum.  But  the  serum  was  not  only 
antitoxic,  but  produced  a  precipitate  when  added  to  eel-serum,  but 
not  when  added  to  the  serum  of  any  other  animal.  In  other  words, 
not  only  has  a  specific  antitoxin  been  produced,  but  also  a  specific 
precipitin.  Numerous  observers  have  since  found  that  this  is  a 
general  rule  throughout  the  animal  kingdom,  including  man.  If,  for 
instance,  a  rabbit  is  treated  with  human  blood,  the  serum  ultimately 
obtained  from  the  rabbit  contains  a  specific  precipitin  for  human 
blood ;  that  is  to  say,  a  precipitate  is  formed  on  adding  such  a 
rabbit's  serum  to  human  blood,  but  not  on  adding  it  to  the  blood 


456  THE   BLOOD  [CH.  XXVI. 

of  any  other  animal.  There  may  be  a  slight  reaction  with  the 
blood  of  allied  animals ;  for  instance,  with  monkey's  blood  in  the 
case  of  man.  The  great  value  of  the  test  is  its  delicacy ;  it  will 
detect  the  specific  blood  when  it  is  greatly  diluted,  after  it  has  been 
dried  for  weeks,  or  even  when  it  is  mixed  with  the  blood  of  other 
animals. 


CHAPTEE  XXVII 

THE   ALIMENTAKY   CANAL 

The  alimentary  canal  consists  of  a  long  muscular  tube  lined  by 
mucous  membrane  beginning  at  the  mouth,  and  terminating  at  the 
anus.  It  comprises  the  mouth,  pharynx,  oesophagus,  stomach,  small 
intestine  and  large  intestine.  Opening  into  it  are  numerous  glands 
which  pour  juices  into  it;  these  bring  about  the  digestion  of  the  food 
as  it  passes  along.  Some  of  the  glands,  like  the  gastric  and  intestinal 
glands,  are  situated  in  the  mucous  membrane  which  lines  the  canal ; 
others,  like  the  salivary  glands,  liver,  and  pancreas,  are  situated  at  a 
distance  from  the  main  canal,  and  pour  their  secretion  into  it  by 
means  of  side  tubes  or  ducts. 

The  Mouth 

This  cavity  is  lined  by  a  mucous  membrane  consisting  of  a  corium 
of  fibrous  tissue  with  numerous  patches  of  lymphoid  tissue  in  it, 
especially  in  the  posterior  regions ;  and  an  epithelium  of  the  stratified 
variety  closely  resembhng  the  epidermis.  The  surface  layers,  like 
those  of  the  epidermis,  are  made  of  horny  scales.  Opening  into  the 
mouth  are  a  large  number  of  little  mucous  glands,  and  the  salivary 
glands  pour  their  secretion  into  the  mouth  also.  The  teeth  (p.  64) 
have  been  previously  studied.  The  tongue  will  be  considered  later 
in  connection  with  taste. 

The  Pharynx 

That  portion  of  the  alimentary  canal  which  intervenes  between 
the  mouth  and  the  oesophagus  is  termed  the  Pharynx.  It  is  con- 
structed of  a  series  of  three  muscles  with  striated  fibres  (constrictors), 
which  are  covered  by  a  thin  fascia  externally,  and  are  lined  internally 
by  a  strong  fascia  (pharyngeal  aponeurosis),  on  the  inner  aspect  of 
which  is  areolar  (submucous)  tissue  and  mucous  membrane,  con- 
tinuous with  that  of  the  mouth,  and,  as  regards  the  part  concerned 
in  swallowing,  identical  with  it  in  general  structure.  The  epithehum 
of  this  part  of  the   pharynx,  like   that  of   the  mouth,  is  stratified. 


458  THE    ALIMENTARY    CANAL  [CH.  XXVIL 

The  upper  portion  of  the  pharynx  into  which  tlie  nares  open  is  lined 
with  ciliated  epithelium. 

The  pharynx  is  well  sup2:»lied  with  mucous  glands. 

Between  the  anterior  and  posterior  arches  of  the  soft  palate  are 
situated  the  Tonsils,  one  on  each  side.  A  tonsil  consists  of  an  eleva- 
tion of  the  mucous  membrane  presenting  12  to  15  orifices,  which  lead 
into  crypts  or  recesses,  in  the  walls  of  which  are  placed  nodules  of 
lymphoid  tissue  (fig.  373).  These  nodules  are  enveloped  in  a  less 
dense  adenoid  tissue  which  reaches  the  mucous  surface.  The  surface 
is  covered  with  stratified  epithelium,  and  the  corium  may  present 
rudimentary  papillae  formed  of  adenoid  tissue.     The  tonsil  is  liounded 


5> 


"JEpithel. 


"-r^- 


'  Tunica 
,'  propria. 


Fig.  373. — Vertical  section  through  a  crypt  of  the  human  tonsil.  1,  entrance  to  the  crypt ;  2  and  3,  the 
framework  of  adenoid  tissue ;  4,  the  enclosing  fibrous  tissue ;  a  and  h,  lymphoid  notlules ;  5  and  6, 
blood-vessels.    (Stohr.) 

beneath  by  a  fibrous  capsule  (fig.  373,  4).     Into  the  crypts  open  the 
ducts  of  numerous  mucous  glands. 


The  (Esophagus  or  Gullet 

The  (Esophagus  or  Gullet,  the  narrowest  portion  of  the  alimentary 
canal,  is  a  muscular  tube,  nine  or  ten  inches  in  length,  which  extends 
from  the  lower  end  of  the  pharynx  to  the  cardiac  orifice  of  the 
stomach.  It  is  made  up  of  three  coats — viz.,  the  outer,  musndar ; 
the  middle,  suhmucoits ;  and  the  inner,  mucous.  The  muscular  coat 
is  covered  externally  by  a  varying  amount  of  loose  fibrous  tissue.  It 
is  composed  of  two  layers  of  fibres,  the  outer  being  arranged  longi- 
tudinally, and  the  inner  circularly.     At  the  upper  part  of  the  ceso- 


CIT.  XXVll.] 


THE    fRSOPIIAGUS 


459 


l)hagus  this  coat  is  made  up  principally  of  striated  muscle  fibres ; 
they  are  continuous  with  the  constrictor  muscles  of  the  pharynx ; 
but  lower  down  the  unstriated  fibres  become  more  and  more  numerous, 
and  towards  the  end  of  the  tube  form  the  entire  coat.  The  muscular 
coat  is  connected  with  the  mucous  coat  by  a  more  or  less  developed 
layer  of  areolar  tissue,  which  forms  the  sithnucous  coat,  in  which  are 
contained  in  the  lower  half  or  third  of  the  tube  many  mucous  glands, 
the  ducts  of  which,  passing  through  the  mucous  meml)rane,  open  on 


Fig.  374. — Section  of  the  mucniis  membrane  and  submuoons  coat  of  the  nesophagns. 


its  surface  (fig.  374).  In  the  deepest  part  of  the  mucous  membrane 
is  a  well-developed  layer  of  longitudinally  arranged  unstriated  muscle, 
called  the  muscularis  mucosae.  The  corium  of  the  mucous  membrane 
is  composed  of  fine  connective  tissue,  which,  towards  the  surface,  is 
elevated  into  papillae.  It  is  covered  with  a  stratified  epithelium,  of 
which  the  most  superficial  layers  are  composed  of  squamous  cells. 
The  epithelium  is  arranged  upon  a  basement  membrane. 

In  newly-born  children  the  corium  exhibits,  in  many  parts,  the 
structure  of  Ijonphoid  tissue  (Klein). 


460  the  alimentary  canal  [ch.  xxvtl 

The  Stomach 

The  stomach  is  a  dilatation  of  the  alimentary  canal  placed  between 
and  continuous  with  the  oesophagus,  which  enters  its  larger  or  cardiac 
end  on  the  one  hand,  and  the  small  intestine,  which  commences  at 
its  narrowed  end  or  pylorus,  on  the  other. 

Its  wall  is  composed  of  four  coats,  (1)  an  external  or  peritoneal, 
(2)  muscular,  (3)  submucous,  and  (4)  mucous  coat ;  with  blood-vessels, 
lymphatics,  and  nerves  distributed  in  and  between  them. 

(1)  The  peritoneal  coat  has  the  structure  of  serous  membranes  in 
general. 

(2)  The  muscular  coat  consists  of  three  separate  layers  or  sets  of 
fibres,  which,  according  to  their  several  directions,  are  named  the 
longitudinal,  circular,  and  oblique.  The  longitudinal  set  are  the 
most  superficial :  they  are  continuous  with  the  longitudinal  fibres  of 
the  oesophagus,  and  spread  out  in  a  diverging  manner  over  the  cardiac 
end  and  sides  of  the  stomach.  They  extend  as  far  as  the  pylorus, 
being  especially  distinct  at  the  lesser  or  upper  curvature  of  the  stomach, 
along  which  they  pass  in  several  strong  bands.  The  next  set,  the 
circular  or  transverse  fibres,  are  most  abundant  at  the  middle  and  in 
the  pyloric  portion  of  the  organ,  and  form  the  chief  part  of  the  thick 
projecting  ring  of  the  pylorus.  They  are  continuous  with  the  circu- 
lar layer  of  the  intestine.  The  deepest  set  of  fibres  are  the  oblique, 
continuous  with  the  circular  muscular  fibres  of  the  oesophagus :  they 
are  comparatively  few  in  number,  and  are  found  only  at  the  cardiac 
portion  of  the  stomach ;  they  form  a  sphincter  around  the  cardiac 
orifice.  The  muscular  fibres  of  the  stomach  and  of  the  intestinal 
canal  are  of  the  unstriated  or  plain  variety. 

(3)  The  submucous  coat  consists  of  loose  areolar  tissue,  which 
connects  the  muscular  coat  to  the  mucous  membrane.  It  contains 
blood-vessels  and  nerves ;  in  the  contracted  state  of  the  stomach  it  is 
thrown  into  numerous,  chiefly  longitudinal,  folds  or  rugae,  which  dis- 
appear when  the  organ  is  distended. 

(4)  The  mucous  membrane  is  composed  of  a  corium  of  fine  con- 
nective tissue,  which  approaches  closely  in  structure  to  adenoid 
tissue ;  this  tissue  supports  the  tubular  glands  of  which  the  super- 
ficial and  chief  part  of  the  mucous  membrane  is  composed,  and  pass- 
ing up  between  them  assists  in  binding  them  together.  The  glands 
are  separated  from  the  rest  of  the  mucous  membrane  by  a  very  fine 
homogeneous  basement  membrane.  The  corium  is  covered  with  a 
layer  of  columnar  epithelium,  which  passes  down  into  the  mouths  of 
the  glands. 

At  the  deepest  part  of  the  mucous  membrane  are  two  thin  layers 
(circular  and  longitudinal)  of  unstriped  muscular  fibres,  called  the 
mvscularis  mucoscc. 


CH.  XXVII.] 


THE   STOMACH 


461 


When  examined  with  a  lens,  the  internal  or  free  surface  of  the 
stomach  presents  a  peculiar  honeycomb  appearance,  produced  by- 
shallow  polygonal  depressions.  In 
the  bottom  of  these  little  pits,  and 
to  some  extent  between  them, 
minute  openings  are  visible,  which 
are  the  orifices  of  the  ducts  of 
perpendicularly  arranged  tubular 
glands  (fig.  375),  imbedded  side  by 
side  in  sets  or  bundles,  on  the 
surface  of  the  mucous  membrane, 
and  composing  nearly  the  whole 
structure. 

The    glands    of    the    mucous 
membrane  are  of  three  varieties. 


Fig.  376. — Transverse  section  through 
lower  part  of  fundus  glands  of  a  cat. 
a,  parietal  cells ;  h,  central  cells ; 
c,  transverse  section  of  capillaries. 
(Frey.) 

(a)  Cardiac,  (h)  Fundus,   and   (c) 
Pyloric. 

(a)  Cardiac  glands;  these  are 
simple  tubular  glands  lined  by 
short  columnar  granular  cells,  and 
are  only  found  quite  close  to  the 
cardiac  orifice. 

(b)  Fundus  glands  are  found 
throughout  the  remainder  of  the 
cardiac  half  and  fundus  of  the 
stomach.  They  are  arranged  in 
groups  of  four  or  five,  which  are 
separated    by    a    fine   connective 

tissue.  Two  or  three  tubes  open  into  one  duct,  which  forms  about  a 
third  of  the  whole  length  of  the  tube  and  opens  on  the  surface.  The 
ducts  are  lined  with  columnar  epithelium.  The  gland-tubes  are  lined 
with  coarsely  granular  polyhedral  cells  {central  cells)  which  are  con- 


FiG.  375.— From  a  vertical  section  through  the 
mucous  membrane  of  the  cardiac  end  of 
stomach.  Two  fundus  glands  are  shown 
with  a  duct  common  to  both,  a,  duct  with 
columnar  epithelium  becoming  shorter  as 
the  cells  are  traced  downward  ;  ?i,  neck  of 
gland  tubes,  with  central  and  parietal  cells  ; 
h,  base  with  curved  caecal  extremity — the 
parietal  cells  are  not  so  numerous  here. 
(Klein  and  Noble  Smith.) 


462 


THE    ALIMENTARY    CANAL 


[CH.  XXVII. 


tinuous  with  the  columnar  cells  of  the  duct.  Between  these  cells 
and  the  basement  membrane  of  the  tubes,  are  large  oval  or  spherical 
cells,  opaque  or  granular  in  appearance,  with  clear  oval  nuclei, 
bulging  out  the  basement  membrane ;  these  cells  are  called  parietal 
or  oxyntic  cells.     They  do  not  form  a  continuous  layer. 

(c)  Pjjloric  Glands. — These  glands  (fig.  377)  have  much  longer 
ducts  than  the  cardiac  glands.  Into  each  duct  two  or  three  tubes 
open  by  very  short  and  narrow  necks,  and  the  body  of  each  tube  is 
branched,  wavy,  and  convoluted.     The  lumen  is  large.     The  ducts  are 


mmsi  - 


Fio.  377.— Section  showing  the 
pyloric  glands,  s,  free  sur- 
face ;  (f ,  ducts  of  pyloric  glands  ; 
n,  neck  of  same ;  m,  the  gland 
tubules ;  7)!i)i,  muscularis  mu- 
coScP.    (Klein  and  Noble  Smith.) 


.  378.  — Plan  of  the  blood-vessels  of  the 
stomach,  as  they  would  be  seen  in  a 
vertical  section,  a,  arteries,  passing 
up  from  the  vessels  of  suijmucous 
coat ;  ?),  capillaries  branching  between 
and  around  the  tubes ;  c,  superficial 
plexus  of  capillaries  occupying  the 
ridges  of  the  mucous  membrane; 
d,  vein  formed  by  the  union  of  veins 
which,  having  collected  the  blood  of 
the  superficial  capillary  plexus,  are 
seen  passing  down  between  the  tubes. 
(Brinton.) 


lined  with  columnar  epithelium,  and  the  neck  and  body  with  shorter 
and  finely  granular  cubical  cells,  which  correspond  with  the  central 
cells  of  the  fundus  glands.  As  they  approach  the  duodenum  the 
pyloric  glands  become  larger,  more  convoluted  and  more  deeply 
situated.  They  are  directly  continuous  with  Brunner's  glands  in  the 
duodenum. 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a 
greater  or  less  extent.  Towards  the  base  of  the  fundus  glands  are 
found  masses  of  lymphoid  tissue,  which  may  appear  as  distinct 
follicles,  somewhat  like  the  solitary  glands  of  the  small  intestine. 


CH.  XXVII.] 


THE    INTKSTINKS 


463 


Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first  break 
up  in  the  submucous  tissue,  send  branches  upward  between  the 
closely  packed  glandular  tubes,  anastomosing  around  them  by  means 
of  a  fine  capillary  network,  with  oblong  meshes.  Continuous  with 
this  deeper  plexus,  or  prolonged  upwards  from  it,  is  a  more  superficial 
network  of  larger  capillaries,  which  branch  densely  around  the  orifices 
of  the  tubes,  and  form  the  framework  on  which  are  moulded  the 
small  elevated  ridges  of  mucous  membrane  bounding  the  minute, 
polygonal  pits  before  referred  to.  From  this  superficial  network  the 
veins  chiefly  take  their  origin.  Thence  passing  down  between  the 
tubes,  with  no  very  free  connection  with  the  deeper  inter-tubular 
capillary  plexus,  they  open  finally  into  the  venous  network  in  the 
submucous  tissue  (fig.  378). 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pneumo- 
gastric  and  sympathetic,  and  form  two  plexuses,  one  in  the  sub- 
mucous and  the  other  between  the  muscular  layers. 

These  plexuses  are  continuous  with  those  which  occur  in  the 
same  situations  in  the  intestine,  and  which  we  shall  again  refer  to 
there. 

The  Intestines. 

The  Intestinal  Canal  is  divided  into  two  chief  portions,  named, 
from  their  differences  in  diameter,  the  small  and  large  intestine. 
These  are  continuous  with  each  other,  and  communicate  by  means 
of  an  opening  guarded  by  a  valve,  the  ileo-ccecal  valve,  which  allows 
the  passage  of  the  products  of  diges- 
tion from  the  small  into  the  large 
bowel,  but  not,  under  ordinary  cir- 
cumstances, in  the  opposite  direction. 

The  Small  Intestine,  the  aver- 
age length  of  which  in  an  adult  is 
about  twenty  feet,  has  been  divided, 
for  convenience  of  description,  into 
three  portions,  viz.,  the  duodenum, 
which  extends  for  eight  or  ten  inches 
beyond  the  pylorus ;  the  jejunum, 
which  forms  two-fifths,  and  the  ileum, 
which  forms  three-fifths  of  the  rest 
of  the  canal. 

Like  the  stomach,  it  is  constructed 
of  four  coats,  viz.,  the  serous,  mus- 
cular, submucous,  and  mucous. 

(1)  The  serous  coat  is  formed  by  the  visceral  layer  of  the 
peritoneum,  and  has  the  structure  of  serous  membranes  in  general. 

(2)  The   7mcscular  coat  consists  of  an  internal  circular  and  an 


Fig.  379. — Horizontal  section  of  a  small  frag- 
ment of  the  mucous  membrane,  includ- 
ing one  entire  crypt  of  Lieberkiihn  and 
parts  of  several  others.  The  glands  are 
separated  by  loose  adenoid  tissue. 


464 


THE   ALIMENTARY   CANAL 


[CH.  XXVIL 


external  longitudinal  layer:  the  former  is  usually  considerably  the 
thicker.  Both  alike  consist  of  bundles  of  unstriped  muscle  supported 
by  connective  tissue.  They  are  well  provided  with  lymphatic 
vessels,  which  form  a  set  distinct  from  those  of  the  mucous 
membrane. 

Between  the  two  muscular  coats  is  a  nerve-plexus  (Auerbach's 
plexus)  (fig.  380),  similar  in  structure  to  Meissner's  (in  the  sub- 
mucous coat),  but  coarser  and  with  more  numerous  ganglia. 

(3)  Between  the  mucous  and  muscular  coats  is  the  submucous 
coat,  which  consists  of  connective  tissue  in  which  numerous  blood- 
vessels and  lymphatics  ramify.     A  fine  plexus,  consisting  mainly  of 


Fig.  380. — Auerbach's  nerve-plexus  in  small  intestine.    Ganglion-cells  are  imbedded  in  the  plexus  the 
whole  of  which  is  enclosed  in  a  nucleated  sheath.    (Kleiu.)  ' 

non-medullated  nerve-fibres,  Meissner's  plexus,  with  ganglion  cells  at 
its  nodes,  occurs  in  the  submucous  tissue  from  the  stomach  to  the 
anus. 

(4)  The  mucous  membrane  is  the  most  important  coat  in  relation 
to  the  function  of  digestion.  Its  general  structure  resembles  that 
of  the  stomach,  and,  like  it,  is  lined  on  its  inner  surface  by  columnar 
epithelium.  Adenoid  tissue  (fig.  379)  enters  largely  into  its  construc- 
tion ;  and  on  its  deep  surface  is  the  muscularis  mucosce  (m,  fig.  382), 
the  fibres  of  which  are  arranged  in  two  layers :  the  outer  longitudinal 
and  the  inner  circular. 

Valvulce  Conniventes. — The  valvulse  conniventes  (fig.  381)  com- 
mence in  the  duodenum,  about  one  or  two  inches  beyond  the 
pylorus,   and,   becoming    larger    and    more    numerous    immediately 


en.  XXVII.] 


THE    VILLI 


465 


beyond  the  entrance  of  the  bile  duct,  continue  well  developed 
throughout  the  jejunum ;  then,  gradually  diminishing  in  size  and 
number,  they  cease  near  the  middle  of  the  ileum.  They  are  formed 
by  a  doubling  inwards  of  the  mucous  membrane;  the  crescentic, 
nearly  circular,  folds  thus  formed  are  arranged  transversely  to  the 
axis  of  the  intestine,  but  each  individual  fold  seldom  extends  around 
more  than  ^  or  |  of  the  bowel's  circumference. 
Unlike  the  rugae  in  the  oesophagus  and  stomach, 
they  do  not  disappear  on  distension  of  the  canal. 
Their  function  is  to  afford  a  largely  increased 
surface  for  secretion  and  absorption.  They  are 
covered  with  villi. 

Villi.— The  villi  (figs.  382,  383,  and  384)  are 
confined  exclusively  to  the  mucous  membrane  of 
the  small  intestine.  They  are  minute  vascular 
processes,  from  ^jig  to  }  of  an  inch  ('5  to  3  mm.) 
in  length,  covering  the  surface  of  the  mucous 
membrane,  and  giving  it  a  peculiar  velvety,  fleecy 
appearance.  Krause  estimates  them  at  fifty  to 
ninety  in  number  in  a  square  line  at  the  upper 
part  of  the  small  intestine,  and  at  forty  to 
seventy  in  the  same  area  at  the  lower  part. 
They  vary  in  form  even  in  the  same  animal,  and 
differ  according  as  the  lymphatic  vessels  or 
lacteals  which  they  contain  are  empty  or  full ; 
being  usually,  in  the  former  case,  flat  and  pointed 
at  their  summits,  in  the  latter  cylindrical. 

Each  villus  is  a  small  projection  of  the  mucous  membrane; 
its  interior  consists  of  fine  adenoid  tissue,  which  forms  the  frame- 
work in  which  the  other  constituents  are  contained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  which 
rests  on  a  fine  basement  membrane;  while  within  this  are  found, 
reckoning  from  without  inwards,  blood-vessels,  fibres  of  the  muscularis 
mucosce,  and  a  lymphatic  or  lacteal  vessel  sometimes  looped  or 
branched  (fig.  384). 

The  epithelium  is  continuous  with  that  lining  the  other  parts  of 
the  mucous  membrane.  The  cells  are  arranged  with  their  long  axis 
radiating  from  the  surface  of  the  villus  (fig.  383),  and  their  smaller 
ends  resting  on  the  basement  membrane.  The  free  surface  of  the 
epithelial  cells  of  the  villi,  like  that  of  the  cells  which  cover  the 
general  surface  of  the  mucous  membrane,  is  surmounted  by  a  bright 
striated  border  (see  pp.  25-27). 

Immediately  beneath  the  basement  membrane  there  is  a  rich 
supply  of  blood-vessels.  Two  or  more  minute  arteries  are  distributed 
within  each  villus ;  and  from  their  capillaries,  which  form  a  dense 

2  Q 


Fig.  381.— Piece  of  small  in- 
testine (previously  dis- 
tended and  hardened  by 
alcohol),  laid  open  to 
show  the  normal  posi- 
tion of  the  valvulae 
conniventes.  Natural 
size. 


466 


THE   ALIMENTARY   CANAL 


[CH.  xxvn. 


network,  proceed  one  or  two  small  veins,  which  pass  out  at   the 

base  of  the  villus. 

The  layer  of  the  muscularis  mucosae 
in  the  villus  forms  a  kind  of  thin 
hollow  cone  immediately  around  the 
central  lacteal,  and  is,  therefore,  situ- 
ated beneath  the  blood-vessels.  It  is 
instrumental  in  the  propulsion  of  chyle 

W'W/^^'''\%.^^r^W         along  the  lacteal. 

Ui'jMSkmJ/'/^ 'yAy'i'-'^'M  The   lacteal   vessels    form    the    com- 

mencement of  the  intestinal  lymphatic 
system.  Each  begins  almost  at  the  tip 
of   the  villus   commonly   by   a    dilated 


'^W^M?§S^^ 


Fig.  383. — Vertical  section  of  a  villus  of 
the    small   intestine  of  a   cat.      a, 
Fig.  382.— Vertical  section  of  duode-  striated  border  of  the  epithelium  ;  b, 

num,  showing  o,  villi;  b,  crypts  columnar  epithelium  ;  c,  goblet  cells  ; 

of Lieberkilhn,  and  c,  Brunner's  d,  central   lymph-vessel;   e,  smooth 

glands  in  the  submucosa  s,  with  muscular  fibres  ;  /,  adenoid  stroma  of 

ducts,  d  ;  muscularis  mucosEe,  m  ;  the  villus  in  which  lymph  corpuscles 

and   circular  muscular   coat,  /.  lie.    (Klein.) 

(Schofield.) 

extremity.     In  the  larger  villi  there  may  be  two  small  lacteal  vessels 
which  join,   or    the   lac  teals   may   form   a   network   in    the   villus 

(fig.  384). 

Glands. — The  glands  are  of  two  kinds : — viz.,  those  of  Lieberkiihn 
and  of  Brunner.  Peyer's  patches  and  the  solitary  follicles  are  com- 
posed of  lymphoid  nodules.  Though  sometimes  called  glands,  they 
form  no  external  secretion. 

The  glands  or  crypts  of  Lieherkuhn  are  tubular  depressions  of  the 
intestinal  mucous  membrane,  thickly  distributed  over  the  whole 
surface  both  of  the  large  and  small  intestines.  In  the  small  intestine 
they  are  visible  only  with  the  aid  of  a  lens ;  and  their  orifices  appear 
as  minute  dots  scattered  between  the  villi.     They  are  larger  in  the 


CH.  XXVII.] 


INTESTINAL   GLANDS 


467 


large  intestine,  and  increase  in  size  the  nearer  they  approach  the 
anal  end  of  the  intestinal  tube ;  and  in  the  rectum  their  orifices  may 
be  visible  to  the  naked  eye.     In  length  they  vary  from   ,  io  to  ^  of 


Fig.  384.— a.  Villus  of  sheep.     B.  Villi  of  mem.    (Slightly  altered  from  Teichmann.) 

an  inch.  Each  tubule  (fig.  386)  is  constructed  of  a  fine  basement 
membrane,  lined  by  a  layer  of  columnar  epithelium,  many  of  the  cells 
of  which  are  goblet  cells. 

Brunner's  glands  (fig.  382)  are  confined  to  the  duodenum ;  they 
are  most  abundant  and  thickly  set  at  its  commencement,  and  diminish 
gradually  as  the  duodenum  advances.  They  are  situated  beneath  the 
muscularis  mucosae,  imbedded  in  the  submucous  tissue ;  each  gland 
is  a  branched  and  convoluted  tube,  lined  with  columnar  epithelium. 
In  structure  they  are  very  similar  to  the  pyloric  glands  of  the 
stomach,  but  they  are  more  branched  and  convoluted,  and  their  ducts 
are  longer.  The  duct  of  each  gland  passes  through  the  muscularis 
mucosae,  and  opens  on  the  surface  of  the  mucous  membrane. 

Peyer's  patches  are  found  in  greatest  abundance  in  the  lower  part 
of  the  ileum  near  to  the  ileo-csecal  valve.  They  consist  of  aggregated 
groups  of  lymphoid  nodules ;  they  vary  from  one  to  three  inches  in 


468 


THE   ALIMENTARY   CANAL 


[CH.  XXVIL 


length,  and  are  about  half-an-inch  in  width,  chiefly  of  an  oval  form, 
their  long  axes  being  parallel  with  that  of  the  intestine.  They  are 
almost  always  placed  opposite  the  attachment  of  the  mesentery. 


P^G.  385. — Transverse  section  through  four 
crypts  of  Lieberkiihn  from  the  large 
intestine  of  the  pig.  They  are  lined 
by  columnar  epithelial  cells,  the 
nuclei  being  placed  in  the  outer  part 
of  the  cells.  The  divisions  between 
the  cells  are  seen  as  lines  radiating 
from  L,  the  lumen  of  the  crypt ;  g, 
epithelial  cells,  which  have  become 
transformed  into  goblet  cells,  x  350. 
(Klein  and  Xoble  Smith.) 


Fig.  386.— a  gland 
of  Lieberkiihn  in 
longitudinal  sec- 
tion.   (Brinton.) 


When  the  lymphoid  nodules  occur  singly,  as  they  often  do  both  in 
small  and  large  intestines,  they  are  called  solitary  glands,  ov  follicles. 


Fig.  387.— Agminate  follicles,  or  Payer's  patch,  in  a  state  of  distension. 


(Boehm.) 


The  Large  Intestine  in  an  adult  is  from  about  4  to  6  feet  long ; 
it  is  subdivided  for  descriptive  purposes  into  three  portions,  viz. : — the 
ccecum,  a  short  wide  pouch,  communicating  with  the  lower  end  of  the 
small  intestine  through  an  opening,  guarded  by  the  ileo-ccecal  valve ; 
the  colon,  continuous  with  the  caecum,  w'hich  forms  the  principal 
part  of  the  large  intestine,  and  is  divided  into  ascending,  transverse, 
and  descending  portions;   and  the   rectum,  which,  after  dilating  at 


CH.  XXVII.]  THE   LARGE   INTESTINE  469 

its  lower  part,  again  contracts,  and  immediately  afterwards  opens 
externally  through  the  anus.  Attached  to  the  caecum  is  the  small 
appendix  vermiformis. 

Like  the  small  intestine,  the  large  intestine  is  constructed  of  four 
coats,  viz.,  the  serous,  muscular,  submucous,  and  mucous.  The  serous 
coat  has  connected  with  it  the  small  processes  of  peritoneum  containing 
fat,  called  appendices  epiploicce.  The  fibres  of  the  muscular  coat,  like 
those  of  the  small  intestine,  are  arranged  in  two  layers — the  outer 
longitudinal,  the  inner  circular.  In  the  caecum  and  colon,  the  longi- 
tudinal fibres,  instead  of  being,  as  in  the  small  intestine,  thinly  dis- 
posed in  all  parts  of  the  wall  of  the  bowel,  are  collected,  for  the  most 
part,  into  three  strong  bands,  which,  being  shorter,  from  end  to  end,  than 
the  other  coats  of  the  intestine,  hold  the  canal  in  folds,  bounding  in- 
termediate sacculi.  On  the  division  of  these  bands,  the  intestine  can 
be  drawn  out  to  its  full  length,  and  it  then  assumes  a  uniformly 
cylindrical  form.  In  the  rectum,  the  fasciculi  of  these  longitudinal 
bands  spread  out  and  mingle  with  the  other  longitudinal  fibres,  form- 
ing with  them  a  thicker  layer  of  fibres  than  exists  in  any  other  part 
of  the  intestinal  canal.  The  circular  muscular  fibres  are  spread  over 
the  whole  bowel,  but  are  somewhat  more  marked  in  the  intervals 
between  the  sacculi.  Towards  the  lower  end  of  the  rectum  they 
become  more  numerous,  and  at  the  anus  they  form  a  strong  ring 
called  the  internal  sphincter  muscle. 

The  mucous  membrane  of  the  large,  like  that  of  the  small  intestine, 
is  lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite 
destitute  of  villi,  and  is  not  projected  in  the  form  of  valvules  con- 
niventes.  It  is  bounded  below  by  the  muscularis  mucosae.  The 
arrangement  of  gangha  and  nerve-fibres  in  the  large  resembles  that 
in  the  small  intestine. 

Glands. — The  glands  with  which  the  large  intestine  is  provided 
are  simple  tubular  glands,  or  glands  of  Lieberkiihn ;  they  resemble 
those  of  the  small  intestine,  but  are  somewhat  larger  and  more 
numerous,  and  contain  a  very  great  number  of  goblet  cells ;  nodules  of 
adenoid  or  lymphoid  tissue  are  most  numerous  in  the  caecum  and 
vermiform  appendix.  They  resemble  in  shape  and  structure  the 
solitary  glands  of  the  small  intestine.  Peyer's  patches  are  not  found 
in  the  large  intestine. 

Heo-ccecal  Valve. — The  ileo-caecal  valve  is  situated  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any 
reflux  of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of 
two  semilunar  folds  of  mucous  membrane. 


CHAPTER  XXVIII 

FOOD 

The  chief  chemical  compounds  or  proximate  principles  in  food  are  : — 

1.  Proteins    .........         .'^ 

2.  Carbohydrates  ........  r  organic. 

3.  Fats J 

4.  Water 1  . 

:>.  Salts jinorganic. 

In  milk  and  in  eggs,  which  form  the  exclusive  foods  of  young 
animals,  all  varieties  of  these  proximate  principles  are  present  in 
suitable  proportions.  Hence  they  are  spoken  of  as  perfect  foods. 
Eggs,  though  a  perfect  food  for  the  developing  l»ird,  contain  too  little 
carbohydrate  for  a  mammal.  In  most  vegetable  foods  carbohydrates 
are  in  excess ;  while  in  animal  food,  like  meat,  the  proteins  are  pre- 
dominant. In  a  suitable  diet  these  should  be  mixed  in  proper  pro- 
portions, which  must  vary  for  herbivorous  and  carnivorous  animals. 

A  healthy  and  suitable  diet  must  possess  the  following  cha- 
racters : — 

1.  It  must  contain  the  proper  amount  and  proportion  of  the 
various  proximate  principles. 

2.  It  must  be  adapted  to  the  climate ;  to  the  age  and  weight  of 
the  individual,  and  to  the  amount  of  work  done  by  him. 

3.  The  food  must  contain  not  only  the  necessary  amoimt  of 
proximate  principles,  but  these  must  be  present  in  a  digestible  form. 
As  an  instance  of  this,  many  vegetables  (peas,  beans,  lentils)  contain 
even  more  protein  than  beef  or  mutton,  but  are  not  so  nutritious,  as 
they  are  less  digestible,  much  passing  off  in  the  faeces  unused. 

The  nutritive  value  of  a  diet  depends  chiefly  on  the  amount  of 
carbon  and  nitrogen  it  contains.  A  man  doing  a  moderate  amount  of 
work  and  taking  the  usual  diet  will  eliminate,  chiefly  from  the  lungs, 
in  the  form  of  carbonic  acid,  from  250  to  280  grammes  of  carbon  j9er 
diem.  During  the  same  time  he  will  eUminate,  chiefly  in  the  form 
of  urea  in  the  urine,  about  15  to  18  grammes  of  nitrogen.  These 
substances  are  derived  partly  from  the  food  and  partly  from  the 
metabolism  of  the  tissues,  various  forms  of  energy — mechanical  motion 

470 


CH.  XXVIII.]  CONSTRUCTION   OF   DIETARIES  471 

and  heat  being  the  chief — being  simultaneously  liberated.     During 

muscular  exercise  the  output  of  carbon  greatly  increases ;  the  increased 

excretion  of  nitrogen  is  not   nearly  so  marked.     Taking,  then,  the 

state  of  moderate  exercise,  it  is  necessary  that  the  waste  should  be 

replaced  by  fresh  material  in  the  form  of  food ;  and  the  proportion 

of  carbon  to  nitrogen  should  be  the  same  as  in  the  excretions :  250 

to  15,  or  166  to  1.    The  proportion  of  carbon  to  nitrogen  in  protein 

is,  however,  53  to  15,  or  3-5  to  1.     The  extra  supply  of  carbon  must 

come  from  non-nitrogenous  food — viz.,  fat  and  carbohydrate. 

Volt  gives  the  following  daily  diet : — 

Protein 120  grras. 

Fat 90     „ 

Carbohydrate 333     ,, 

Eanke's  diet  closely  resembles  Moleschott's ;  it  is  — 

Protein 100  grms. 

Fat 100     „ 

Carbohydrate 250     „ 

Such  typical  diets  as  these  must  not  be  considered  as  more  than 
rough  averages  of  what  is  necessary  for  a  man  in  the  course  of  the 
day.  Actual  experience  shows  that  in  the  diets  of  different  nations 
there  are  considerable  variations  from  this  standard  without  the 
production  of  ill  effects.  Age,  and  the  amount  of  work  done,  also 
influence  the  amount  of  food  necessary ;  growing  children,  for  instance, 
require  a  relatively  rich  diet ;  thus,  milk,  the  diet  of  the  infant,  is 
proportionally  twice  as  rich  in  proteins,  and  half  as  rich  again  in 
fats,  as  the  normal  diet  given  above.  During  work  more  food  is 
necessary  than  during  inactivity. 

Attention  has  recently  been  devoted  to  the  question  whether  as 
much  protein  as  100  to  120  grammes  daily  is  really  necessary,  and 
by  far  the  most  convincing  of  the  experiments  published  in  favour 
of  a  reduction  are  those  carried  out  by  Chittenden  on  himself,  his 
colleagues,  his  students,  and  on  soldiers  and  athletes,  over  compara- 
tively long  periods  of  time.  The  protein  intake  was  reduced  to  half 
and  sometimes  to  less  than  half  the  quantity  hitherto  regarded  as 
necessary.  The  deprivation  was  followed  by  no  untoward  results ; 
bodily  equilibrium  was  maintained ;  the  health  remained  perfect  or 
improved;  the  muscular  force  in  athletes  was  increased;  mental 
acuity  was  undiminished,  and  desire  for  richer  food  soon  disappeared. 

It  may  be  freely  admitted  that  the  majority  of  well-to-do  people 
eat  too  much  protein ;  there  are  not  many  who  limit  themselves 
even  to  Voit's  minimum,  and  in  those  who  are  prone  to  digestive  and 
uric  acid  diseases,  one  cannot  but  feel  that  improvement  in  body  and 
mind  would  be  the  result  of  more  temperate  habits. 

But  if  we  were  all  to  permanently  reduce  our  diet  to  the 
Chittenden  level,  we  might  be  living  perilously  near  the  margin ; 


472 


FOOD 


[CH.  XXVIII. 


any  unusual  strain,  such  as  privation  or  a  severe  illness,  would  then 
find  us  without  any  reserve  of  nutrient  energy,  and  we  should 
probably  suffer  more  severely  in  consequence.  The  poor  around  us 
have  had  nolens  volens  to  subsist  on  a  Chittenden  diet  for  years, 
whereas  Chittenden's  experiments  only  lasted  months,  and  nearly  all 
of  his  subjects  have  returned  now  to  their  previous  diet.  The 
underfed  condition  of  the  poor  is  apparent,  and  is  not  such  as  to 
make  others  inclined  to  follow  their  example.  In  countries  like 
India,  where  the  vegetarian  native  population  is  diluted  with  the 
meat-eating  white  races,  it  is  the  former  who  more  readily  succumb 
to  the  effects  of  disease.  The  recent  development  of  the  Japanese 
is  by  some  attributed  in  part  to  the  fact  that  they  are  accustoming 
themselves  to  a  richer  nitrogenous  diet  than  they  took  in  the  past. 

It  is  doubtful  if  the  minimum  is  also  the  optimum.  We  take  in 
protein,  and  rapidly  eliminate  most  of  its  nitrogen  as  urea,  without 
building  it  up  first  into  the  body  tissues ;  but  some  is  wanted  by  the 
body  tissues  to  repair  their  waste,  and  some  of  the  cleavage  products 
of  the  food-protein  are  especially  necessary  for  the  synthesis  of  tissue 
protein ;  it  is  in  order  to  obtain  a  sufficient  quantity  of  these 
scanty  cleavage  products  that  we  ingest  what  at  first  sight  is  an 
excess  of  the  proteins  which  yield  them.  But  after  our  study  of 
digestion  and  excretion,  we  shall  be  in  a  better  position  to  discuss 
this  question  more  fully,  and  we  shall  return  to  it  in  the  chapter 
on  Metabolism  (Chapter  XXXIX.). 

Milk. 

Milk,  which  we  have  already  spoken  of  as  a  perfect  food,  is  only 
so  for  young  children.     For  those  who  are  older,  it  is  so  voluminous 

that  unpleasantly  large  quantities  of 
it  would  have  to  be  taken  in  the 
course  of  the  day  to  ensure  the  proper 
supply  of  nitrogen  and  carbon.  More- 
over, it  is  relatively  too  rich  in  protein 
and  fat.  It  also  contains  too  little 
iron  (Bunge) :  hence  children  weaned 
late  become  anpemic. 

The  microscope  reveals  that  it  con- 
sists of  two  parts :  a  clear  fluid  and  a 
number  of  minute  particles  that  float 
in   it.      These   consist   of   minute   oil 
globules,   varying   in    diameter    from 
0-0015  to  0-005  millimetre  (fig.  388). 
The  milk  secreted  during  the  first 
few  days    of   lactation  is  called  colostrum.     It  contains  very  little 
caseinogen,  but  large  quantities  of  albumin  and  globulin  instead.     It 


\Q 


Fig.  388.— Globules  of  cow's  milk,     x  400. 


cir.  XXVIII.] 


MILK 


473 


coagulates  like  white  of  egg  when  boiled.  Microscopically,  cells 
from  the  acini  of  the  mammary  gland  are  seen,  which  contain  fat 
globules  in  their  interior ;  they  are  called  colostrum  corpuscles. 

Reaction  and  Specific  Gravity. — The  reaction  of  fresh  cow's 
milk  and  of  human  nulk  is  amphoteric ;  that  is,  it  turns  blue  litmus 
red,  and  rod  litmus  blue.  This  is  due  to  the  presence  of  both  acid  and 
alkaline  salts.  All  milk  readily  turns  acid  or  sour  as  the  result  of 
fermentative  change,  part  of  its  lactose  being  transformed  into  lactic 
acid.  The  specific  gravity  of  milk  is  usually  ascertained  with  the 
hydrometer.  That  of  normal  cow's  milk  varies  from  1028  to  1034. 
When  the  milk  is  skimmed  the  specific  gravity  rises,  owing  to  the 
removal  of  the  light  constituent,  the  fat,  to  1033  to  1037.  In  all 
cases  the  specific  gravity  of  water,  with  which  other  substances  are 
compared,  is  taken  as  1000. 

Composition. — Bunge  gives  the  following  table,  contrasting  the 
milk  of  woman,  and  the  cow : — 


Woman. 

Cow. 

Proteins  (chiefly  caseinogen) 

Butter  (fat) 

Lactose 

Salts 

Per  cent. 

1-7 
3-4 
6-2 
0-2 

Per  cent. 

3-5 
3-7 
4-9 
0-7 

Hence,  in  feeding  infants  on  cow's  milk,  it  is  necessary  to  dilute  it, 
and  add  sugar  and  a  little  cream  to  make  it  approximately  equal  to 
natural  human  milk. 

The  Proteins  of  Milk. — The  principal  protein  in  milk  is  called 
caseinogen ;  it  is  precipitdble  by  acids  such  as  acetic  acid,  and  also  by 
saturation  with  magnesium  sulphate,  or  half  saturation  with  ammonium 
sulphate,  so  resembling  globulins ;  it  is  coagulated  by  rennet  to  form 
casein.  Cheese  consists  of  casein  with  the  entangled  fat.  The  other 
protein  in  milk  is  an  albumin.  It  is  present  in  small  quantities  only ; 
it  differs  in  some  of  its  properties  (specific  rotation,  coagulation 
temperature,  etc.)  from  serum-albumin ;  it  is  called  lact-albumin. 

The  Coagulation  of  Milk. — Rennet  is  the  agent  usually  employed 
for  this  purpose :  it  is  a  ferment  secreted  by  the  stomach,  especially 
in  sucking  animals,  and  is  generally  obtained  from  the  calf. 

The  curd  consists  of  the  casein  and  entangled  fat:  the  liquid 
residue  called  whey  contains  the  sugar,  salts,  and  albumin  of  the  milk. 
There  is  also  a  small  quantity  of  a  new  protein  called  whey -protein, 
which  differs  from  caseinogen  by  not  being  convertible  into  casein ; 
this  is  produced  by  the  decomposition  of  the  caseinogen  molecule 
during  the  process  of  curdling. 


474  FOOD  [CH.  XXVIII. 

The  curd  formed  in  human  milk  is  more  finely  divided  than  that 
in  cow's  milk;  and  it  is  more  digestible.  In  feeding  children  and 
invalids  on  cow's  milk,  the  lumpy  condition  of  the  curd  may  be  ob- 
viated by  the  addition  of  lime  water  or  barley  water  to  the  milk. 
There  appears  to  be  no  chemical  difference  between  the  caseinogen  of 
human  and  that  of  cow's  milk ;  variations  in  the  amount  of  calcium 
salts  and  of  citric  acid  account  for  the  differences  described. 

The  addition  of  rennet  produces  coagulation  in  milk,  provided 
that  a  sufficient  amount  of  calcium  salts  is  present.  If  the  calcium 
salts  are  precipitated  by  the  addition  of  potassium  oxalate,  rennet 
causes  no  formation  of  casein.  The  process  of  curdling  in  milk  is  a 
double  one ;  the  first  action  due  to  rennet  is  to  produce  a  change  in 
caseinogen;  the  second  action  is  that  of  the  calcium  salt  which 
precipitates  the  altered  caseinogen  as  casein.  In  blood,  also,  calcium 
salts  are  necessary  for  coagulation,  but  there  they  act  in  a  different 
way,  namely,  in  the  production  of  fibrin  ferment  (see  p.  424). 

Caseinogen  is  a  phospho-protein  (see  p.  411).  In  milk  it  is  com- 
bined with  calcium  to  form  calcium  caseinogenate  ;  when  acetic  acid 
is  added  we  therefore  get  calcium  acetate  and  free  caseinogen. 

The  Pats  of  Milk. — The  chemical  composition  of  the  fat  of  milk 
(butter)  is  very  like  that  of  adipose  tissue.  It  consists  chiefly  of 
palmitin,  stearin,  and  olein.  There  are,  however,  smaller  quantities 
of  fats  derived  from  fatty  acids  lower  in  the  series,  especially  butyrin 
and  caproin.  The  relation  between  these  varies  somewhat,  but  the 
proportion  is  roughly  as  follows : — Olein,  f ;  palmitin,  J  ;  stearin,  ^  ; 
butyrin,  caproin,  and  caprylin,  y\-.  The  old  statement  that  each 
fat  globule  is  surrounded  by  a  film  of  caseinogen  is,  according  to 
Ramsden's  recent  observations,  correct.  Milk  also  contains  small 
quantities  of  lecithin,  a  phosphorised  fat;  of  cholesterin,  an  alcohol 
which  resembles  fat  in  its  solubihties,  and  a  yellow  fatty  pigment  or 
lipochrome. 

Milk  Sugar,  or  Lactose. — This  is  a  saccharose  (C^.^HooOn).  Its 
properties  have  already  been  described  in  Chap.  XXV.,  p.  394. 

Souring  of  Milk. — When  milk  is  allowed  to  stand  the  chief 
change  which  it  is  apt  to  undergo  is  a  conversion  of  a  part  of  its 
lactose  into  lactic  acid.  This  is  due  to  the  action  of  micro-organisms, 
and  would  not  occur  if  the  milk  were  contained  in  closed  sterilised 
vessels.  Equations  showing  the  change  produced  are  given  on  p.  395. 
When  souring  occurs,  the  acid  formed  precipitates  a  portion  of  the 
caseinogen.  This  must  not  be  confounded  with  the  formation  of 
casein  from  caseinogen  which  is  produced  by  rennet.  There  are, 
however,  some  bacteria  which,  like  rennet,  produce  true  coagula- 
tion. 

Alcoholic  Fermentation  in  Milk. — When  yeast  is  added  to  milk, 
the  sugar  does  not  readily  undergo  the  alcoholic  fermentation.     Other 


CH.  XXVIII.] 


THE  MAMMARY   GLANDS 


475 


somewhat  similar  fungoid  growths  are,  however,  able  to  produce  the 
change,  as  in  the  preparation  of  koumiss ;  the  milk  sugar  is  first 
inverted,  that  is  dextrose  and  galactose  are  formed  from  it  (see  p.  395), 
and  it  is  these  sugars  from  which  alcohol  and  carbonic  acid  originate. 
The  Salts  of  Milk.— The  principal  salt  present  is  calcium  phos- 
phate; a  small  quantity  of  magnesium  phosphate  is  also  present. 
The  other  salts  are  chiefly  chlorides  of  sodium  and  potassium. 


The  Mammary  Glands. 

The  mammary  glands  are  composed  of  large  divisions  or  lobes,  and  these  are 
again  divisible  into  lobules  ;  the  lobules  are  composed  of  the  convoluted  and  dilated 
subdivisions  of  the  main  ducts  held  together  by  connective  tissue.  Covering  the 
general  surface  of  the  gland,  with  the  exception  of  the  nipple,  is  a  considerable 
quantity  of  fat,  itself  lobulated  by  sheaths  and  processes  of  areolar  tissue  (fig.  389) 


Fig.  389. — Dissection  of  the  lower  half  of  the  female  mamma,  during  the  period  of  lactation.  §. — In  the 
left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially  unravelled  ;  and 
on  the  right-hand  side,  the  glandular  substance  has  been  removed  to  show  the  reticular  loculi  of 
the  connective  tissue  in  which  the  glandular  lobules  are  placed  :  1,  upper  part  of  the  mamilla  or 
nipple  ;  2,  areola  ;  3,  subcutaneous  masses  of  fat ;  4,  reticular  loculi  of  the  connective-tissue  which 
support  the  glandular  substance  and  contain  the  fatty  masses  ;  5,  one  of  three  lactiferous  ducts 
shown  passing  towards  the  mamilla  where  they  open ;  6,  one  of  the  sinus  lactei  or  reservoirs  ;  7, 
some  of  the  glandular  lobules  which  have  been  unravelled  ;  7 ',  others  massed  together.    (Luschka.) 

connected  both  with  the  skin  in  front  and  the  gland  behind ;  the  same  bond  of 
connection  extends  also  from  the  under  surface  of  the  gland  to  the  sheathing 
connective  tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The  main  ducts  of 
the  gland,  fifteen  to  twenty  in  number,  called  the  lactiferous  ducts,  are  formed  by 
the  union  of  the  smaller  (lobular)  ducts,  and  open  by  small  separate  orifices  through 
the  nipple.  At  the  points  of  junction  of  lobular  ducts  to  form  lactiferous  ducts,  and 
just  before  these  enter  the  base  of  the  nipple,  the  ducts  are  dilated ;  and  during  the 
period  of  active  secretion  by  the  gland,  the  dilatations  form  reservoirs  for  the  milk. 


476 


FOOD 


[CH.  XXVIII. 


which  collects  in  and  distends  them.  The  walls  of  the  gland-ducts  are  formed  of  areolar 
with  some  unstriped  muscular  tissue,  and  are  lined  internally  by  short  columnar  and 
near  the  nipple  by  flattened  epitheUum. 

The  nipple  is  composed  of  areolar  tissue,  and  contains  unstriped  muscular  fibres. 
Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  an  erectile  structure.  On 
its  surface  are  very  sensitive  papillae ;  and  around  it  is  a  small  area  or  areola  of 
pink  or  dark-tinted  skin,  on  which  are  to  be  seen  small  projections  formed  by 
minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to  the  mammary 
glands ;  the  cahbre  of  the  blood-vessels,  as  well  as  the  size  of  the  glands,  varies 
very  greatly  under  certain  conditions,  especially  those  of  pregnancy  and  lactation. 

The  alveoli  of  the  glands  during  the  secreting  periods  are  found  to  be  lined 
with  short  columnar  cells  (see  fig.  390).  The  edges  of  the  cells  towards  the  lumen 
may  be  irregular  and  jagged,  and  the  remainder  of  the  alveolus  is  filled  up  with  the 
materials  of  the  milk.  During  the  intervals  between  the  acts  of  discharge,  the 
cells  of  the  alveoli  elongate  towards  the  lumen,  their  nuclei  divide,  and  in  the 
part  of  the  cells  towards  the  lumen  a  collection  of  oil  globules  and  of  other 
materials  takes  place. 

The  next  stage  is  that  the  cells  divide  and  the  part  of  each  towards  the  lumen 
containing  a  nucleus  and  the  materials  of  the  secretion,  disintegrates  and  goes  to 
form  the  constituents  of  the  milk. 

In  the  earlier  days  of  lactation,  epithelial 
cells  only  partially  transformed  are  discharged  in 
the  secretion ;  these  are  termed  colostrum  cor- 
puscles. 

During  pregnancy  the  mammary  glands 
undergo  changes  {evolution)  which  are  readily 
observable.  They  enlarge,  become  harder,  and 
more  distinctly  lobulated ;  the  veins  on  the  sur- 
face become  more  prominent.  The  areola  becomes 
enlarged  and  dusky,  with  projecting  papillae ;  the 
nipple,  too,  becomes  more  prominent,  and  milk  can 
be  squeezed  from  the  orifices  of  the  ducts.  This  is 
a  very  gradual  process,  which  commences  about 
the  time  of  conception,  and  progresses  steadily 
during  the  whole  period  of  gestation.  In  the 
gland  itself  solid  colunms  of  cells  bud  off  from 
the  old  alveoli  to  form  new  alveoli.  But  these 
solid  columns  after  a  while  are  converted  into 
tubes  by  the  central  cells  becoming  fatty  and  being 
discharged  as  the  colostrum  corpuscles  above 
mentioned.  After  the  end  of  lactation,  the  mamma 
gradually  returns  to  its  original  size  {involution).  The  acini,  in  the  early  stages  of 
involution,  are  lined  with  cells  in  all  degrees  of  vacuolation.  As  involution  pro- 
ceeds, tlie  acini  diminish  considerably  in  size,  and  at  length,  instead  of  a  mosaic  of 
lining  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we  have  five  or  six  nuclei 
(some  with  no  surrounding  protoplasm)  lying  in  an  irregular  heap  within  the  acinus. 
No  secretory  nerves  of  the  mammary  gland  have  yet  been  discovered.  It  is 
possible  they  do  not  exist,  but  that  the  normal  stimulus  to  mammary  activity  is  a 
chemical  one  formed  by  the  foetus  during  its  residence  in  the  uterus.  Extracts  of 
fcEtal  tissues  injected  into  virgin  rabbits  leads  to  incomplete  evolution  of  the 
mammary  glands  (Starling  and  Lane-Claypon). 

Eggs. 

In  this  country  the  eggs  of  hens  and  ducks  are  those  particularly 
selected  as  foods.  The  chief  constituent  of  the  shell  is  calcium  car- 
bonate. The  white  is  composed  of  a  richly  albuminous  fluid  enclosed 
in  a  network  of  firmer  and  more  fibrous  material.     The  amount  of 


Fig.  390.— Section  of  mammary  gland 
of  bitch,  showing  acini,  lined 
with  epithelial  cells  of  a  short 
columnar  form,  x  200.  (V.  D. 
Harris.) 


CH.  XXVIII.]  MEAT  477 

solids  is  13-3  per  cent. ;  of  this,  12-2  is  protein  in  nature  (egg-albumin, 
with  smaller  quantities  of  egg-globulin,  and  of  a  mucinoid  sul)stance 
called  ovo-mucoid),  and  the  remainder  is  made  up  of  sugar  (0'5  per 
cent.),  traces  of  fats,  lecithin  and  cholesterin,  and  0'6  per  cent,  of 
inorganic  salts.  The  yolk  is  rich  in  food  materials  for  the  develop- 
ment of  the  future  embryo.  In  it  there  are  two  varieties  of  yolk- 
spherules,  one  kind  yellow  and  opaque  (due  to  admixture  with  fat 
and  a  yellow  Hpochrome),  and  the  other  smaller,  transparent  and 
almost  colourless ;  these  are  protein  in  nature,  consisting  of  the 
phospho-protein  called  vitellin.  Small  quantities  of  sugar,  lecithin, 
cholesterin  and  inorganic  salts  are  also  present. 

The  nutritive  value  of  eggs  is  high,  as  they  are  so  readily  digest- 
ible ;  but  the  more  an  egg  is  cooked  the  more  insoluble  do  its  protein 
constituents  become. 

Meat. 

This  is  composed  of  the  muscular  and  connective  (including  adipose) 
tissues  of  certain  animals.  The  flesh  of  some  animals  is  not  eaten ; 
in  some  cases  this  is  a  matter  of  fashion,  in  others,  owing  to  an 
unpleasant  taste,  such  as  the  flesh  of  carnivora  is  said  to  have ;  and 
in  other  cases  {e.g.  the  horse)  because  it  is  more  lucrative  to  use  the 
animal  as  a  beast  of  burden. 

Meat  is  the  most  concentrated  and  most  easily  assimilable  of 
nitrogenous  foods.  It  is  our  chief  source  of  nitrogen.  Its  chief  solid 
constituent  is  protein,  and  the  principal  protein  is  myosin.  In  addition 
to  the  extractives  and  salts  contained  in  muscle,  there  is  always  a 
certain  percentage  of  fat,  even  though  all  visible  adipose  tissue  is 
dissected  off.  The  fat-cells  are  placed  between  the  muscular  fibres, 
and  the  amount  of  fat  so  situated  varies  in  different  animals ;  it  is 
particularly  abundant  in  pork  ;  hence  the  indigestibility  of  this  form 
of  flesh :  the  fat  prevents  the  gastric  juice  from  obtaining  ready  access 
to  the  muscular  fibres. 

The  following  table  gives  the  chief  substances  in  some  of  the 
principal  meats  used  as  food : — 


Constituents. 

Ox. 

Calf. 

Pig. 

Horse. 

Fowl. 

1 
Pike. 

Water 

76-7 

75-6 

72-6 

74-3 

70-8 

79-3 

'  Solids 

23-3 

24-4 

27-4 

25-7 

29-2 

20-7 

'  Proteins,  including  gelatin* 

20-0 

19-4 

19-9 

21-6 

22-7 

18-3 

Fat 

1-5 

2-9 

6-2 

2-5 

4-1 

0-7 

Carbohydrate 

0-6 

0-8 

0-6 

0-6 

1-3 

0-9 

Salts 

1-2 

1-3 

1-1 

1-0 

1-1 

0-8 

1 

*  The  flesh  of  young  animals  is  richer  in  gelatin  than  that  of  old ;  thus  1000 
parts  of  beef  yield  6,  of  veal  50,  parts  of  gelatin. 


478 


FOOD 


[CH.  XXVIII. 


The  large  percentage  of  water  in  meat  should  be  particularly 
noted ;  if  a  man  wished  to  take  his  daily  supply  of  100  grammes  of 
protein  entirely  in  the  form  of  meat,  it  would  be  necessary  for  him 
to  consume  aboi>t  500  grammes  (i.e.,  a  little  more  than  1  lb.)  of  meat. 

Flour. 

The  best  wheat  flour  is  made  from  the  interior  of  wheat  grains, 
and  contains  the  greater  proportion  of  the  starch  of  the  grain  and 
most  of  the  protein.  Whole  flour  is  made  from  the  whole  grain 
minus  the  husk,  and  thus  contains  not  only  the  white  interior  but 
also  the  harder  and  browner  outer  portion  of  the  grain.  This  outer 
region  contains  a  somewhat  larger  proportion  of  the  proteins  of  the 
grain.  Whole  flour  contains  1  to  2  per  cent,  more  protein  than  the 
best  white  flour,  but  it  has  the  disadvantage  of  being  less  readily 
digested.  Brown  flour  contains  a  certain  amount  of  bran  in  addition  ; 
it  is  still  less  digestible,  but  is  useful  as  a  mild  laxative,  the  insoluble 
cellulose  mechanically  irritating  the  intestinal  canal  as  it  passes  along. 

The  best  flour  contains  very  little  sugar.  The  presence  of  sugar 
indicates  that  germination  has  commenced  in  the  grains.  In  the 
manufacture  of  malt  from  barley  this  is  purposely  allowed  to  go  on. 

When  mixed  with  water,  wheat  flour  forms  a  sticky,  adhesive  mass 
called  dough.  This  is  due  to  the  formation  of  gluten,  and  the  forms  of 
grain  poor  in  gluten  cannot  be  made  into  dough  (oats,  rice,  etc.).  Gluten 
is  a  mixture  of  several  proteins  (gliadin,  mucedin,  gluten-fibrin,  etc.). 

The  following  table  contrasts  the  composition  of  some  of  the  more 
important  vegetable  foods : — 


Constituents. 

Wheat. 

Barley. 

Oats. 

Rice. 

Lentils. 

Peas. 

Potatoes. 

Water . 

13-6 

13-8 

12-4 

13-1 

12-5 

14-8 

76-0 

Protein 

12-4 

11-1 

10-4 

7-9 

24-8 

23-7 

2-0 

Fat      . 

1-4 

2-2 

5-2 

0-9 

1-9 

1-6 

0-2 

Starch 

67-9 

64-9 

57-8 

76-5 

54-8 

49-3 

20-6 

Cellulose      . 

2-5 

5-3 

11-2 

0-6 

3-6 

7-5 

0-7 

Mineral  salts 

1-8 

2-7 

3-0 

1-0 

2-4 

3-1 

1-0 

We  see  from  this  table — 

1.  The  great  quantity  of  starch  always  present. 

2.  The  small  quantity  of  fat ;  that  bread  is  generally  eaten  with 
butter  is  a  popular  recognition  of  this  fact. 

3.  Protein,  except  in  potatoes,  is  pretty  abundant,  and  especially 
so  in  the  pulses  (lentils,  peas,  etc.).  The  protein  in  the  pulses  is  not 
gluten,  but  consists  of  vitellin  and  globulin-Kke  substances. 

In  the  mineral  matters  in  vegetables,  salts  of  potassium  and 
magnesium  are,  as  a  rule,  more  abundant  than  those  of  sodium  and 
calcium. 


CH.  XXVIII.]  BREAD  479 

Bread. 

Bread  is  made  by  cooking  the  dough  of  wheat  flour  mixed  with 
yeast,  salt,  and  flavouring  materials.  A  ferment  in  the  flour  acts  at 
the  commencement  of  the  process,  when  the  temperature  is  kept  a 
little  over  that  of  the  body,  and  forms  dextrin  and  sugar  from  the 
starch,  and  then  the  alcoholic  fermentation,  due  to  the  action  of  the 
yeast,  begins.  The  bubbles  of  carbonic  acid,  Ijurrowing  passages 
through  the  bread,  make  it  light  and  spongy.  This  enables  the 
digestive  juices  subsequently  to  soak  into  it  readily  and  affect  all 
parts  of  it.  In  the  later  stages,  viz.,  baking,  the  temperature  is  raised, 
the  gas  and  alcohol  are  expelled  from  the  bread,  the  yeast  is  killed, 
and  a  crust  forms  from  the  drying  of  the  outer  portions  of  the  dough. 

White  bread  contains,  in  100  parts,  7  to  10  of  protein,  55  of 
carbohydrates,  1  of  fat,  2  of  salts,  and  the  rest  water. 

Cooking  of  Food. 

The  cooking  of  foods  is  a  development  of  civilisation  and  serves 
many  useful  ends : — 

1.  It  destroys  all  parasites  and  danger  of  infection.  This  relates 
not  only  to  bacterial  growths,  but  also  to  larger  parasites,  such  as 
tapeworms  and  trichinae. 

2.  In  the  case  of  vegetable  foods  it  breaks  up  the  starch  grains, 
bursting  the  cellulose  and  allowing  the  digestive  juices  to  come  into 
contact  with  the  granulose. 

3.  In  the  case  of  animal  foods  it  converts  the  insoluble  collagen  of 
the  universally  distributed  connective  tissues  into  the  soluble  gelatin. 
The  loosening  of  the  fibres  is  assisted  by  the  formation  of  steam 
between  them.  By  thus  loosening  the  binding  material,  the  more 
important  elements  of  the  food,  such  as  muscular  fibres,  are  rendered 
accessible  to  the  gastric  and  other  juices.  Meat  before  it  is  cooked  is 
generally  kept  a  certain  length  of  time  to  allow  rigor  mortis  to  pass  off. 

Of  the  two  chief  methods  of  cooking,  roasting  and  boiling,  the 
former  is  the  more  economical,  as  by  its  means  the  meat  is  first  sur- 
rounded with  a  coat  of  coagulated  protein  on  its  exterior,  which  keeps 
in  the  juices  to  a  great  extent,  letting  little  else  escape  but  the  drip- 
ping (fat).  Whereas  in  boiling,  unless  both  bouillon  and  bouilli  are  used, 
there  is  considerable  waste.  Cooking,  especially  boiling,  renders  the 
proteins  more  insoluble  than  they  are  in  the  raw  state ;  but  this  is 
counterbalanced  by  the  other  advantages  that  cooking  possesses. 

In  making  leef  tea  and  similar  extracts  of  meat  it  is  necessary 
that  the  meat  should  be  placed  in  cold  water,  and  this  is  gradually 
and  carefully  warmed.  In  boiling  a  joint  it  is  usual  to  put  the  meat 
into  boiling  water  at  once,  so  that  the  outer  part  is  coagulated,  and 
the  loss  of  material  minimised. 


480  FOOD  [CU.  XXYIIL 

An  extremely  important  point  in  this  connection  is  that  beef  tea 
and  similar  meat  extracts  should  not  be  regarded  as  foods.  They  are 
valuable  as  pleasant  stimulating  drinks  for  invalids,  but  they  contain 
very  little  of  the  nutritive  material  of  the  meat,  their  chief  con- 
stituents, next  to  water,  being  the  salts  and  extractives  of  flesh. 

Soup  contains  the  extractives  of  meat,  a  very  small  proportion  of 
the  myosin,  and  the  principal  part  of  the  gelatin.  The  gelatin  is 
usually  increased  by  adding  bones  and  fibrous  tissue  to  the  stock.  It 
is  the  presence  of  this  substance  which  causes  soup  when  cold  to 
gelatinise. 

Accessories  to  Pood. 

Among  these  must  be  placed  alcohol,  the  value  of  which  within 
moderate  limits  is  not  as  a  food  but  as  a  stimulant;  condiments 
(mustard,  pepper,  ginger,  curry  powder,  etc.),  which  are  stomachic 
stimulants,  the  abuse  of  which  is  followed  by  dyspeptic  troubles; 
and  tea,  coffee,  cocoa,  and  similar  drinks.  These  are  stimulants 
chiefly  to  the  nervous  system ;  tea,  coSee,  mate  (Paraguay),  guarana 
(Brazil),  cola  nut  (Central  Africa),  bush  tea  (South  Africa),  and 
a  few  other  plants  used  in  various  countries  all  owe  their  chief 
property  to  an  alkaloid  called  theine  or  caffeine  (CgH^QlSr^Oo) ;  cocoa  to 
the  closely  related  alkaloid,  theobromine  (CjHgN^O.,) ;  coca  to  cocaine. 
These  alkaloids  are  all  poisonous,  and  used  in  excess,  even  in  the  form 
of  infusions  of  tea  and  coffee,  produce  over-excitement,  loss  of  diges- 
tive power,  and  other  disorders  well  known  to  physicians.  Coffee 
differs  from  tea  in  being  rich  in  aromatic  matters ;  tea  contains  a 
bitter  principle,  tannin;  to  avoid  the  injurious  solution  of  too  much 
tannin,  tea  should  only  be  allowed  to  infuse  (draw)  for  a  few  minutes. 
Cocoa  is  not  only  a  stimulant,  but  a  food  in  addition ;  it  contains 
about  50  per  cent,  of  fat,  and  12  per  cent,  of  protein.  In  manufac- 
tured cocoa,  the  amount  of  fat  is  reduced  to  30  per  cent.,  and  the 
amount  of  protein  rises  proportionately  to  about  20  per  cent.  The 
quantity  of  cocoa  usually  consumed  is  too  small  for  these  food 
materials  to  count  very  much  in  the  daily  supply.  The  amount  of 
protein  in  solution  (mainly  proteose)  in  a  breakfast  cup  of  cocoa  is 
under  half  a  gramme ;  most  of  the  food  stuffs  are  in  suspension,  for 
cocoa  is  drunk  "  thick,"  not  as  a  clear  infusion. 

Green  vegetables  are  taken  as  a  palatable  adjunct  to  other  foods, 
rather  than  for  their  nutritive  properties.  Their  potassium  salts  are, 
however,  abundant.  Cabbage,  turnips,  and  asparagus  contain  80  to 
92  water,  1  to  2  protein,  2  to  4  carbohydrates,  and  1  to  1"5  cellulose 
per  cent.  The  small  amount  of  nutriment  in  most  green  foods 
accounts  for  the  large  meals  made  by,  and  the  vast  capacity  of  the 
alimentary  canal  of,  herbivorous  animals. 


CHAPTEE    XXIX 

SECKETING   GLANDS 

Befoke  passing  on  to  the  action  of  the  digestive  secretions  on  foods, 
it  will  be  well  to  discuss  the  varieties  of  glands  by  means  of  which 
these  substances  are  formed. 

It  is  the  function  of  gland-cells  to  produce  by  the  metabolism  of 
their  protoplasm  certain  substances  called  secretions.  These  materials 
are  of  two  kinds,  viz.,  those  which  are  employed  for  the  purpose  of 
serving  some  ulterior  office  in  the  economy,  and  those  which  are  dis- 
charged from  the  body  as  useless  or  injurious.  In  the  former  case 
the  separated  materials  are  termed  secretions ;  in  the  latter  they  are 
termed  excretions. 

The  secretions,  as  a  rule,  consist  of  substances  which  do  not  pre- 
exist in  the  same  form  in  the  blood,  but  require  special  cells  and  a 
process  of  elaboration  for  their  formation,  e.g.,  the  liver  cells  for  the 
formation  of  bile,  the  mammary  gland-cells  for  the  formation  of  milk. 
The  excretions,  on  the  other  hand,  commonly  consist  of  substances 
which  exist  ready-formed  in  the  blood,  and  are  merely  abstracted 
therefrom.  If  from  any  cause,  such  as  extensive  disease  or  extirpa- 
tion of  an  excretory  organ,  the  separation  of  an  excretion  is  prevented, 
and  an  accumulation  of  it  in  the  blood  ensues,  it  frequently  escapes 
through  other  organs,  and  may  be  detected  in  various  fluids  of  the 
body.  An  instance  of  this  is  seen  after  the  kidneys  have  been 
removed.  Urea  then  accumulates  in  the  blood.  But  this  is  never  the 
case  with  secretions ;  for,  after  the  removal  of  the  special  organ  by 
which  each  of  them  is  manufactured,  the  secretion  is  no  longer  formed. 

The  circumstances  of  their  formation,  and  their  final  destination, 
are,  however,  the  only  particulars  in  which  secretions  and  excretions 
can  be  distinguished ;  for,  in  general,  the  structure  of  the  parts 
engaged  in  eliminating  excretions  is  as  complex  as  that  of  the  parts 
concerned  in  the  formation  of  secretions.  It  will,  therefore,  be 
sufficient  to  speak  in  general  terms  of  the  process. 

Every  secreting  apparatus  consists  essentially  of  a  layer  of  secret- 
ing cells  arranged  round  a  central  cavity ;  they  take  from  the  lymph 
.81  2  H 


482 


SECRETING   GLANDS 


[CH.  XXIX. 


which  bathes  them  the  necessary  material,  and  transform  it  into  the 
secretion  which  they  pour  at  high  pressure  into  the  cavity. 

The  principal  secreting  organs  are  the  following : — (1)  the 
synovial  membranes ;  (2)  the  mucous  membranes  with  their  special 
glands,  e.g.,  the  buccal,  gastric  and  intestinal  glands ;  (3)  the  salivary 
glands  and  pancreas ;  (4)  the  mammary  glands  ;  (5)  the  liver ;  (6)  the 
lacrimal  gland ;  (7)  the  kidney  and  skin ;  and  (8)  the  testes. 

The  synovial  membranes  line  the  joints  and  the  sheaths  of 
tendons  and  ligaments  with  which  we   may  include   the   synovial 

hursce.  The  contents  of  these 
sacs  is  called  synovia ;  it  lubri- 
cates the  surfaces  of  the  joint, 
and  so  ensures  an  easy  move- 
ment. Synovia  is  a  rich  lymph 
plus  a  mucinoid  material ;  and 
it  is  this  latter  constituent 
which  gives  the  secretion  its 
viscidity.  It  is  thus  a  true 
secretion ;  and  is  formed  by 
the  epithelial  cells  which  form 
an  imperfect  lining  to  the  sac, 
and  which  are  especially  accu- 
mulated on  the  processes  of 
the  synovial  fringes  (fig.  391). 
A  mucous  membrane 
consists  of  two  parts :  the 
epithelium  on  its  surface,  and 
the  corium  of  connective 
tissue  beneath.  The  epithe- 
lium generally  rests  on  a  base- 
ment membrane  which  is  usu- 
ally composed  of  clear  flattened 
cells  placed  edge  to  edge. 
The  name  mucous  is  derived  from  the  fact  that  nearly  all  these 
memljranes  secrete  mucin,  the  chief  constituent  of  mucus ;  this  may 
be  formed  from  the  surface  epithelium  cells  breaking  down  into  goblet 
cells  (see  p.  26),  or  an  analogous  process  may  occur  in  the  cells  of 
little  glands  called  mucous  glands,  situated  more  or  less  deeply 
under  the  epithelium,  and  opening  on  the  surface  by  ducts.  Many 
mucous  membranes  {e.g.,  that  of  the  stomach)  form  other  secretions 
as  well. 

3lucous  membranes  line  all  those  passages  by  wliich  internal  parts 
communicate  with  the  exterior.  The  principal  tracts  are  the  Digestive, 
Respiratory,  and  Genito -urinary. 

Secreting  glands  may  be  classifiod  according  to  certain    types, 


Fio.  391. — Section  of  synovial  membrane,  a,  epithelial 
covering;  of  the  elevations  of  the  membrane ; 
h,  underlying  tissue  containlnj;  fat  and  blood- 
vessels ;  c,  liKament  covered  by  the  synovial  mem. 
brane.    (Cadiat.) 


CH.  XXIX.] 


TYPES   OF   GLANDS 


483 


which  are  tho  followinj:^: — 1.  The  simple  tubular  gland  (a,  fig.  392), 
examples  of  which  are  furnished  by  the  crypts  of  Lieberkiihn  in  the 
intestinal  wall.  To  the  same  class  may  be  referred  the  elongated  and 
tortuous  sudoriferous  glands. 

2.  The   compound   tubular  glands   (d,    fig.    392)    form    another 


Fig.  302. — Diagram  of  types  of  secreting  glands,  a,  simple  glands,  viz.,  g,  straight  tube;  h,  sac;  ;, 
coiled  tube,  b,  multilocular  crypts;  k,  of  tubular  form;  I,  saccular,  c,  racemose,  or  saccular 
compound  gland  ;  m,  entire  gland,  showing  branched  duct  and  lobular  structure ;  n,  a  lobule, 
detached  with  o,  branch  of  duct  proceeding  from  it.    d,  compound  tubular  gland.    (Sharpey.) 

division.     These   consist   of    main    gland-tubes,   which    divide    and 
sub-divide. 

3.  The  racemose  glands  are  those  in  which  a  number  of  vesicles 
or  acini  are  arranged  in  groups  or  lobules  (c,  fig.  392).  The  Meibo- 
mian follicles  are  examples  of  this  kind  of  gland.  Some  glands,  like 
the  pancreas,  are  of  a  mixed  character,  combining  some  of  the  char- 
acters of  the  tubular  with  others  of  the  racemose  type ;  these  are 


484  SECKETING   GLANDS  [CH.  XXIX. 

called  tuhulo-racemose  or  tubulo-acinous  glands.  These  glands  differ 
from  each  other  only  in  secondary  points  of  structure,  but  all  have 
the  same  essential  character  in  consisting  of  rounded  groups  of 
vesicles  containing  gland-cells,  and  opening  by  a  common  central 
cavity  into  minute  ducts,  which  ducts  in  the  large  glands  converge 
and  unite  to  form  larger  and  larger  tubes,  and  at  length  open  by  one 
common  trunk  on  a  free  surface.  The  larger  racemose  glands,  like  the 
salivary  glands,  are  called  compound  racemose  glands. 

Electrical  Variations  in  Glands. 

These  have  been  studied  in  many  glandular  organs,  but  especially  in  the 
salivary  glands  and  skin. 

In  the  submaxillary  gland  the  hilus  is  electro-negative  to  the  external  surface 
of  the  organ  ;  a  current  therefore  passes  from  hilus  to  surface  through  the  galvano- 
meter. If  the  chorda  tympani  is  stimulated  by  rapidly  interrupted  shocks,  the 
surface  becomes  still  more  positive.  This  is  the  opposite  to  what  occurs  in  a 
muscle  ;  there  the  current  of  action  is  in  the  reverse  direction  to  the  demarcation 
current ;  the  change  in  the  gland  is  a  positive  variation  in  the  arithmetical  sense. 
This  is  abolished  by  a  small  dose  of  atropine ;  stimulation  then  causes  a  small 
negative  variation  which  is  abolished  by  a  larger  dose  of  atropine. 

If,  before  atropine  is  given,  slowly  interrupted  shocks  are  used,  or  rapidly 
interrupted  shocks  too  weak  to  excite  secretion  are  employed,  the  electrical  response 
of  the  organ  is  a  negative  variation.  The  same  is  true  for  stimulation  of  the 
sympathetic.  Single  induction  shocks  applied  to  the  chorda  tympani  cause  a 
diphasic  variation,  first  the  surface  of  the  gland  becoming  more  positive  and  then 
the  hilus. 

The  two  changes  are  believed  to  be  due  to  the  fact  that  secretory  nerves  are  of 
two  kinds  :  anabolic,  which  increase  the  building  up  of  the  glandular  protoplasm  ; 
and  katabolic,  which  increase  the  disintegrative  side  of  metabolism,  and  so  lead  to 
secretion. 

It  is  important  to  remember  the  existence  of  the  skin  currents,  for  they  interfere 
with  any  attempt  to  determine  the  electrical  change  in  muscles  through  the  intact 
skin.  This  interference  will  naturally  be  greater,  the  richer  the  portion  of  skin  is, 
in  secreting  glands. 

The  most' satisfactory  work  on  skin  currents  is  that  recently  carried  out  by 
Waller.  He  speaks  of  them  as  glandular  and  epithelial,  and  regards  them  as 
important  signs  of  life  here  as  in  other  tissues  (eye,  muscle,  nerve,  plant  tissues, 
etc.)  which  he  has  studied.  He  has  worked  with  the  skin  of  the  frog,  cat,  and 
other  animals,  including  fresh  human  skin  obtained  from  surgical  operations.  The 
skin  may  be  excited  either  directly  or  indirectly  through  the  nerves  that  supply  it. 
The  main  results  obtained  are  very  simple,  and  are  also  true  for  mucous  membranes, 
and  such  epithelial  structures  as  the  crystalHne  lens.  The  normal  current  of 
unexcited  living  skin  is  ingoing.  The  normal  response  of  excited  skin  is  outgoing. 
This  is  explained  in  the  following  way  :— In  a  passive  mass  of  living  animal 
material  acted  upon  by  its  environment,  there  must  be  most  change  occurring  on  its 
surface,  a  point  on  the  surface  will  therefore  be  electropositive  to  any  point  in  the 
interior.  If  the  same  mass  is  excited,  chemical  changes  will  be  greater  in  its 
interior  than  at  the  surface  ;  hence  internal  points  become  less  electronegative  than 
they  were  before,  or  even  electropositive  in  relation  to  the  external  surface,  hence 
the  current  of  action  through  the  mass  of  skin  is  outgoing,  and  will  therefore  pass 
through  the  galvanometer  from  the  external  to  the  internal  surface. 


CHAPTEE   XXX 


SALIVA 


The  saliva  is  formed  by  three  pairs  of  salivary  glands,  called  the 
parotid,  submaxillary,  and  sublingual  glands. 


The  Salivary  Glands. 

These  are  typical  secreting  glands.  They  are  made  up  of  lobules 
united  by  connective  tissue.  Each  lobule  is  made  of  a  group  of  tubulo- 
saccular  alveoli  or  acini,  from  which  a  duct  passes ;  this  unites  with 
other  ducts  to  form  larger  and  larger 
tubes,  the  main  duct  opening  into  the 
mouth. 

Each  alveolus  is  surrounded  by  a 
plexus  of  capillaries ;  the  lymph  which 
exudes  from  these  is  in  direct  contact 
with  the  basement  membrane  that  en- 
closes the  alveolus.  The  basement  mem- 
brane is  lined  by  secreting  cells  which 
surround  the  central  cavity  or  lumen. 
The  basement  membrane  is  thin  in 
many  places,  to  allow  the  lymph  more 
ready  access  to  the  secreting  cells ;  it 
is  continued  along  the  ducts. 

The  secreting  epitheUum  is  com- 
posed of  a  layer  of  polyhedral  cells. 

The  epithelium  of  the  ducts  is  columnar,  except  where  it  passes 
into  an  alveolus  ;  at  this  point  it  is  flattened.  The  columnar  epithelium 
cells  of  the  ducts  exhibit  striations  in  their  outer  part  (see  fig.  393) ; 
the  inner  zone  of  each  cell  is  made  of  granular  protoplasm.  The 
largest  ducts  have  a  wall  of  connective  tissue  outside  the  basement 
membrane,  and  a  few  unstriated  muscular  fibres. 

The  secreting  cells  differ  according  to  the  substance  they  secrete. 
In  alveoli  that  secrete  mucin  (such  as  those  in  the  dog's  submaxillary, 


%mm 


Fig.  393. — From  a  section  through  a 
salivary  gland,  a,  serous  or  albumi- 
nous alveoli ;  h,  intralobular  duct 
cut  transversely.  (Klein  and  Noble 
Smith.) 


486 


SALIVA 


[CH.  XXX. 


and  some  of  the  alveoli  in  the  human  submaxillary)  the  cells  after 
treatment  with  water  or  alcohol  are  clear  and  swollen  (fig.  395);  this 
is  the  appearance  they  usually  present  in  sections  of  the  organ.  But 
if  examined  in  their  natural  state  by  teasing  a  portion  of  the  fresh 


r^.^ '- 


Fio.  394. — Section  of  submaxillary  gland  of  dog.     Showing 

(Kiilliker.) 


gland-cells,  h,  and  a  duct,  a,  h,  in  section. 


gland  in  serum,  they  are  seen  to  be  occupied  by  large  granules  com- 
posed of  a  substance  known  as  mucigen  or  mucinogen.  When  the 
gland  is  active,  mucigen  is  transformed  into  mucin  and  discharged  as 
a  clear  droplet  of  that  substance  into  the  lumen  of  the  alveolus.  Out- 
side these  are  smaller,  highly 
granular  cells  containing  no 
mucigen ;  these  marginal  cells 
stain  darkly,  and  generally  form 
crescentic  groups  {crescents  or 
demilunes  of  Gianuzzi)  next  to 
the  basement  membrane.  They 
do  not  secrete  mucin,  but  are 
albuminous  cells.  After  secretion 
their  granules  are  lessened.  The 
demilunes  are  therefore  easily 
seen  in  the  gland  before  secretion 
owing  to  the  contrast  they  ex- 
hibit to  the  cells  loaded  with 
mucin. 

In  those  alveoli  which  do  not 
secrete  mucin,  but  a  watery  non-viscid  saliva  (parotid,  and  some  of 
the  alveoli  of  the  human  submaxillary),  the  cells  are  filled  with  small 
granules  of  albuminous  nature.  Such  alveoli  are  called  serous  or 
albuminous,  to  distinguish  them  from  the  mucous  alveoli  we  have  just 
described. 

These  yield  to  the  secretion  its  ferment,  ptyalin.     The  granular 


Fig.  395.— Section  through  a  mucous  gland 
hardened  in  alcohol.  The  alveoli  are  lined 
with  transparent  mucous  cells,  and  outside 
these  are  the  demilunes.    (Heidenhain.) 


CH.  XXX.] 


SECRETION    OF   SALIVA 


487 


substance  within  tlio  coll  is  tlio  mother  substance  of  the  ferment 
{zymogen),  not  the  ferment  itself.  It  is  converted  into  the  ferment 
in  the  act  of  secretion.  We  shall  study  the  question  of  zymogens 
more  fully  in  connection  with  the  gastric  glands  and  the  pancreas, 
where  they  have  been  separated  from  the  ferments  by  chemical  methods. 
In  the  case  of  saliva  we  may  term  the  zyiwogQW,  iJtyalinogen  provision- 
ally, but  it  has  never  been  satisfactorily  separated  chemically  from 
ptyalin. 

After  secretion,  due  to  the  administration  of  food  or  of  such  a 
drug  as  pilocarpine,  the  cells  shrink,  they  stain  more  readily,  their 


Fig.  306.— Alveoli  of  parotiii  gland.    A,  before  secretion  ;  B,  in  the  first  stage  of  secretion  ;  C,  after 
prolonged  secretion.     (Langley.) 

nuclei  become  more  conspicuous,  and  the  outer  part  of  each  cell  becomes 
clear  and  free  from  granules  (fig.  396). 


The  Secretory  Nerves  of  Salivary  Glands. 

The  Submaxillary  and  Sublingual  Glands.  —  These  glands 
have  l)een  mainly  studied  in  the  dog ;  they  receive  two  sets  of  nerve- 
fibres  ;  namely,  from  the  chordi  tympani  and  the  sympathetic. 

The  chorda  tympani  is  given  off  from  the  seventh  cranial  nerve  in 
the  region  of  the  tympanum.  After  quitting  the  temporal  bone  it 
passes  downwards  and  forwards,  and  joins  the  lingual  nerve,  with 
which  it  is  bound  up  for  a  short  distance.  On  leaving  the  lingual 
nerve  it  traverses  the  suhmaxillary  ganglion ;  it  then  runs  parallel  to 
the  duct  of  the  gland,  gives  off  a  branch  to  the  sublingual  gland,  and 
others  to  the  tongue.  The  main  nerve  enters  the  hilus  of  the  sub- 
maxillary gland,  where  it  traverses  a  scattered  collection  of  ganglion 
cells  concealed  within  the  substance  of  the  gland,  and  which  may 
be  called  after  its  discoverer,  Langley's  ganglion. 

The  sympathetic  branches  to  these  two  glands  are  derived  from  the 
plexus  around  the  facial  artery,  and  accompany  the  arteries  which 
supply  the  glands. 

Section  of  the  nerves  produces  no  immediate  result ;  but  after  a 
few  days  a  scanty  but  continuous  secretion  of  thin  watery  saliva. 


488 


SALIVA 


[CH.  XXX. 


takes  place ;  this  is  called  paralytic  secretion,  and  is  produced  either 
by  the  activity  of  the  local  nervous  mechanism,  which  is  then  uncon- 
trolled by  impulses  from  the  central  nervous  system ;  or  else  it  is  a 
degenerative  effect  analogous  to  the  fibrillar  contractions  which  occur 
in  degenerating  muscles  after  severance  of  their  nerves.  If  the  opera- 
tion is  performed  on  one  side,  the  glands  of  the  opposite  side  also 
show  a  similar  condition,  and  the  thin  saliva  secreted  there  is  called 
the  antilytic  secretion. 

Stimulation  of  the  peripheral  end  of  the  divided  chorda  tympani 
produces  an  abundant  secretion  of  saliva,  which  is  accompanied  by 

vaso-dilatation  (see  p.  306).  Stimu- 
lation of  the  peripheral  end  of  the 
divided  sympathetic  causes  a  scanty 
secretion  of  thick  viscid  saliva,  accom- 
panied by  vaso-constriction. 

The  abundant  secretion  of  saliva, 
which  follows  stimulation  of  the 
chorda  tympani,  is  not  merely  the 
result  of  a  filtration  of  fluid  from  the 
blood-vessels,  in  consequence  of  the 
largely  increased  circulation  through 
them.  This  is  proved  by  the  fact 
that,  when  the  main  duct  is  obstruc- 
ted, the  pressure  within  it  may  con- 
siderably exceed  the  blood-pressure  in 
the  arteries,*  and  also  that  when  into 
the  veins  of  the  animal  experimented 
upon,  some  atropine  has  been  pre- 
viously injected,  stimulation  of  the 
peripheral  end  of  the  divided  chorda 
produces  all  the  vascular  effects  as 
before,  without  any  secretion  of  sahva 
accompanying  them.  Again,  if  an 
animal's  head  is  cut  ofiF,  and  the  chorda  be  rapidly  exposed  and  stimu- 
lated with  an  interrupted  current,  a  secretion  of  saliva  ensues  for  a 
short  time,  although  the  blood-flow  is  necessarily  absent.  These 
experiments  serve  to  prove  that  the  chorda  contains  two  sets  of 
nerve-fibres,  one  set  (vaso-dilator)  which,  when  stimulated,  cause  the 
vessels  to  dilate ;  while  another  set,  which  are  paralysed  by  atropine, 
directly   stimulate   the   cells   themselves  to  activity,  whereby  they 


Fio.  397. — Diagram  of  secretory  nerves  of 
submaxillarj'  and  sublingual  glands. 
Two  fibres  of  the  chorda  tympani  (Oh.) 
are  shown,  one  of  which  supplies  the 
sublingual  gland,  of  which  an  acinus  is 
shown  ;  the  cell  station  for  this  is  in  S. 
G.,  the  so-called  submaxillary  ganglion. 
The  other  fibre  supplies  an  acinus  of  the 
submaxillary  gland  ;  its  cell  station  Is  in 
Langley's  ganglion  (L.  G.),  within  the 
substance  of  the  gland.  Sy  is  a  fibre  of 
the  sympathetic,  which  has  its  cell 
station  in  the  superior  cervical  ganglion, 
S.  C.  G.  (after  Dixon). 


*  The  student  should  not  suppose  that  the  sahva  is  normally  secreted  at 
such  high  pressure.  If  it  were  so  the  saliva  would  spurt  from  the  salivary  duct 
with  greater  force  than  the  blood  would  spurt  from  the  arteries  when  they  are 
cut.  The  high  pressure  alluded  to  in  the  text  only  occurs  when  the  duct  is 
obstructed,  and  indicates  what  enormous  force  the  secreting  cells  can  exercise. 


CH.  XXX.]  SECRETORY  NERVES  489 

secreto  and  discharge  the  constituents  of  the  saliva  which  they  pro- 
duce. On  the  other  hand,  the  sympathetic  fibres  are  also  of  two 
kinds,  vaso-constrictor  and  secretory,  the  latter  being  paralysed  by 
atropine.  The  chorda  tympani  nerve  is,  however,  the  principal  nerve 
through  which  efterent  impulses  proceed  from  the  central  nervous 
system  to  excite  the  secretion  of  these  glands. 

The  function  of  the  ganglia  has  been  made  out  by  Langley  by  the 
nicotine  method  (see  p.  302).  At  one  time  the  submaxillary  ganglion 
was  supposed  to  be  the  seat  of  reflex  action  for  the  secretion.  This, 
however,  is  not  the  case.  The  ganglia  are  cell-stations  on  the  course 
of  the  fibres  to  the  submaxillary  and  sublingual  glands.  Nicotine 
apphed  locally  has  the  power  of  paralysing  nerve-cells,  but  not  nerve- 
fibres.  If  the  submaxillary  ganglion  is  painted  with  nicotine,  and 
the  nerve  stimulated  on  the  central  side  of  the  ganglion,  secretion 
from  the  submaxillary  gland  continues,  but  that  from  the  subhngual 
gland  ceases.  The  paralysed  nerve-cells  in  the  ganglion  act  as  blocks 
to  the  propagation  of  the  impulse,  not  to  the  submaxillary,  but  to  the 
sublingual  gland.  The  cell  station  for  the  submaxillary  fibres  is  in 
Langley 's  ganglion  (see  fig.  397). 

The  differences  between  the  two  secretions  is  not  only  one  of  amount,  for  the 
"chorda  secretion  "'  is  continuous  as  long  as  the  nerve  is  stimulated  ;  it  is  like  the 
flow  of  fluid  from  a  tap.  The  "  sympathetic  secretion,"  on  the  other  hand,  stops 
after  about  fifteen  seconds,  and  may  be  compared  to  what  happens  when  one 
squeezes  a  sponge.  These  facts  are  in  accordance  with  observations  on  the  loss  of 
water  sustained  by  the  blood  when  the  nerves  are  stimulated.  In  an  actual  experi- 
ment, 19-8  c.c.  of  blood  left  the  gland  in  a  minute  during  chorda  stimulation. 
When  tested,  the  blood  was  found  to  be  more  concentrated  than  the  blood  which 
entered  the  gland.  The  concentration  was  determined  by  estimating  the  relative 
amount  of  haemoglobin  in  the  arterial  and  venous  bloods  ;  the  ratio  was  1000  :  1075. 
It  follows  that  for  each  10  c.c.  of  venous  blood  which  left  the  gland,  10'75  c.c.  of 
arterial  blood  entered  it;  or  for  19'8  c.c.  emerging,  19'8  ■  :{;;j^i  c.c.  =21'5  c.c. 
entered.  Hence  21  "5  minus  19-8  =  1-5  c.c.  of  fluid  left  the  blood  to  become  sahva, 
and  this  was  the  actual  amount  secreted.  In  similar  experiments  on  sympathetic 
saliva,  there  was  no  evidence  of  any  loss  of  water  from  the  blood.  Sympathetic 
saliva  comes  either  from  the  substance  of  the  cells,  or  from  the  ducts,  and  without 
going  into  the  evidence  at  length,  the  former  is,  at  anyrate  in  part,  the  correct 
explanation.  It  would  appear,  therefore,  that  the  fundamental  difference  between 
the  two  nerves  is  that  the  chorda  confers  upon  the  cells  the  power  of  recouping 
themselves  from  the  blood,  whilst  this  is  denied  to  the  sympathetic. 

This  is  the  salient  point,  but  it  is  certain  that  the  rate  of  blood-flow  can  modify 
the  rate  of  salivary  secretion  ;  thus  squeezing  the  artery  during  chorda  stimulation 
lessens  both  flow  of  blood  and  flow  of  saliva,  though  the  latter  still  remains  con- 
tinuous ;  and  in  the  cat  it  is  possible,  on  prolonged  stimulation  of  the  sympathetic, 
for  the  initial  constriction  of  the  arteries  to  pass  off,  and  yet  there  is  no  continuous 
secretion. 

Salivary  secretion  cannot  be  due  to  osmosis,  for  the  saliva  is  poorer  in  salts 
than  the  blood,  and  therefore  the  stream  of  water,  if  osmosis  existed,  would  be 
back  to  the  blood  from  the  saliva.  The  cells  of  the  salivary  glands  are  really 
doing  work,  or  can  be  made  to  do  so.  There  is  positive  evidence  of  increase 
of  work  by  the  increase  of  metabolism  which  occurs,  and  on  p.  387,  under  the 
subject  tissue  respiration,  figures  illustrating  this  are  given  ;  there  is  no  such 
evidence  of  increased  gaseous  metabolism  when  the  sympathetic  is  stimulated. 
(Barcroft. ) 


490  SALIVA  [CH.  XXX. 

Parotid  Gland. — This  gland  also  receives  two  sets  of  nerve-fibres 
analogous  to  those  we  have  studied  in  connection  with  the  submaxil- 
lary gland.  The  principal  secretory  nerve-fibres  are  glosso-pharyngeal 
in  origin ;  the  sympathetic  is  mainly  vaso-constrictor,  but  in  some 
animals  does  contain  a  few  secretory  fibres  also. 

Reflex  Secretion. — Under  ordinary  circumstances  the  secretion 
of  saliva  is  a  refiex  action.  The  principal  afferent  nerves  are  those  of 
taste ;  Imt  the  smell  or  sight  of  food  will  also  cause  "  the  mouth  to 
water  " ;  and  under  certain  circumstances,  as  before  vomiting,  irrita- 
tion of  the  stomach  has  a  similar  effect.  These  sensory  nerves  stimu- 
late a  centre  in  the  medulla  from  which  efferent  secretory  impulses 
are  reflected  along  the  secretory  nerves  (chorda  tympani,  etc.)  to  the 
glands. 

Pawlow  has  made  some  interesting  observations  on  the  salivary 
glands.  He  made  an  external  fistula  of  the  submaxillary  duct  in  the 
dog,  and  found  that  the  sight  of  food,  the  smell  of  food,  or  the 
administration  of  any  kind  of  food,  caused  secretion ;  acid  or  even 
sand  introduced  into  the  mouth  produced  a  similar  effect.  By  means 
of  similar  experiments  on  the  parotid  secretion,  very  different  results 
were  obtained.  If  the  dog  was  shown  meat,  or  the  meat  was  given 
to  it  to  eat,  there  was  practically  no  secretion.  If,  however,  the  meat 
was  given  as  a  dry  powder,  a  copious  secretion  followed ;  dry  bread 
produced  a  similar  effect ;  in  fact,  the  parotid  secretion  flows  freely 
if  dry  food  is  simply  shown  to  the  animal ;  of  course,  in  all  such 
experiments  the  dog  must  be  hungry. 

Such  observations  emphasize  the  psychical  element  involved  in 
secretion,  and  point  out  also  the  adaptation  of  the  secretory  process 
to  the  needs  of  the  animal ;  thus  the  submaxillary  saliva,  which  is 
mainly  a  lubricant  in  virtue  of  its  mucin,  flows  whatever  the  food 
may  be,  whereas  moist  food  requiring  no  watery  saliva  from  the 
parotid  excites  the  flow  of  none. 

Extirpation  of  the  Salivary  Glands. — These  may  be  removed 
without  any  harmful  effects  in  the  lower  animals. 

The  Saliva. 

The  saliva  is  the  first  digestive  juice  to  come  in  contact  with  the 
food.  The  secretions  from  the  different  salivary  glands  are  mixed  in 
the  mouth ;  the  secretion  of  the  minute  mucous  glands  of  the  mouth 
and  a  certain  number  of  epithelial  scales  and  the  so-called  "  salivary 
corpuscles "  derived  from  the  tonsils  are  added  to  it.  The  liquid  is 
transparent,  slightly  opalescent,  of  slimy  consistency,  and  may  con- 
tain lumps  of  nearly  pure  mucin.  On  standing  it  becomes  cloudy 
owing  to  the  precipitation  of  calcium  carbonate,  the  carbonic  acid, 
which  held  it  in  solution  as  bicarbonate,  escaping. 


U: 


ClI.  XXX.]  ACTION    OF    SALIVA  401 

Of  the  three  forms  of  saliva  which  contribute  to  the  mixture 
found  in  the  mouth  the  sublingual  is  richest  in  solids  (2'75  per  cent.). 
The  submaxillary  saliva  comes  next  (21  to  25  per  cent.).  The 
parotid  saliva  is  poorest  in  total  solids  (03  to  0'5  per  cent.),  and 
contains  no  mucin.  Mixed  saliva  contains  in  man  an  average  of 
about  0"5  per  cent,  of  solids :  it  is  alkaline  in  reaction,  due  to  the  salts 
in  it;  and  has  a  specific  gravity  of  1002  to  1006. 

The  solid  constituents  dissolved  in  saliva  may  be  classified  thus : 

f  a.  Mucin  :  this  may  be  precipitated  by  acetic  acid. 
_  .  J  h.  Ptyalin  :  an  amylolytic  ferment. 

rgan  c       •  \   ^    Protein  :  of  the  nature  of  a  globuhn. 
Potassium  sulphocyanide. 
Sodium  chloride  :  the  most  abundant  salt. 
Inorganic    .  -]  /.  Other  salts  :  sodium  carbonate,  calcium  phosphate  and 
{         carbonate ;  magnesium  phosphate  ;  potassium  chloride. 

The  action  of  saliva  is  twofold,  physical  and  chemical. 

The  physical  use  of  saliva  consists  in  moistening  the  mucous 
membrane  of  the  mouth,  assisting  the  solution  of  soluble  substances 
in  the  food,  and  in  virtue  of  its  mucin,  lubricating  the  bolus  of  food 
to  facilitate  swallowing. 

The  chemical  action  of  saliva  is  due  to  its  active  principle,  ptyalin. 
This  substance  belongs  to  the  class  of  unorganised  ferments,  which 
are  called  amylolytic  (starch  splitting)  or  diastatic  (resembling 
diastase,  the  similar  ferment  in  germinating  barley  and  other  grains). 

The  starch  is  first  split  into  dextrin  and  maltose ;  the  dextrin  is 
subsequently  converted  into  maltose  also :  this  occurs  more  quickly 
with  erythro-dextrin,  which  gives  a  red  colour  with  iodine,  than  with 
the  other  variety  of  dextrin  called  achroo-dextrin,  which  gives  no 
colour  with  iodine.  Brown  and  Morris  give  the  following  equa- 
tion : — 

10(C6HioO>    +   4nH,0 

[Starch.]  [Water.] 

=    4nq.3ooOn    +    (CoHioO,),.   +   (C,H,,0,)„. 

[Maltose.]  [Achroo-dextrin.]         [Erythro-dextrin.] 

Ptyalin  acts  in  a  similar  way,  but  more  slowly  on  glycogen :  it  has 
no  action  on  cellulose;  hence  it  is  inoperative  on  uncooked  starch 
grains,  for  in  them  the  cellulose  layers  are  intact. 

Ptyalin  acts  best  at  about  the  temperature  of  the  body  (35-40"  C). 
It  acts  best  in  a  neutral  medium ;  a  small  amount  of  alkali  makes 
but  little  difference ;  a  very  small  amount  of  acid  stops  its  activity. 
The  conversion  of  starch  into  sugar  by  swallowed  saliva  in  the 
stomach  continues  for  a  certain  time.  It  then  ceases  owing  to  the 
hydrochloric  acid  secreted  by  the  glands  of  the  stomach.  The  acid 
which  is  first  poured  out  neutralises  the  saliva,  and  combines  with 
the  proteins  of  the  food,  but  when  free  acid  appears  ptyalin  is  de- 
stroyed, and  so  it  cannot  resume  work  when  the  acid  is  neutralised 


492  SALIVA  [CH.  XXX. 

in  the  duodenum.  Another  amylolytic  ferment  contained  in  pan- 
creatic juice  (to  be  considered  later)  continues  the  digestion  of  starch 
in  the  intestine. 

Cannon  has  recently  shown  that  salivary  digestion  continues  in 
the  stomach  for  longer  than  one  supposed.  The  food  lying  in  the 
fundus  of  the  stomach  undergoes  amylolysis  for  at  least  two  hours, 
because  the  absence  of  peristalsis  in  this  region  until  quite  late 
stages  in  digestion  prevents  admixture  with  gastric  juice,  especially 
in  the  interior  of  the  swallowed  masses. 


CHAPTER    XXXI 

THE   GASTRIC   JUICE 

The  juice  secreted  by  the  glands  in  the  mucous  membrane  of  tlio 
stomach  varies  in  composition  in  the  different  regions,  but  the  mixed 
gastric  juice,  as  it  may  be  termed,  is  a  sohition  of  a  proteolytic 
ferment  called  pepsin  in  a  saline  solution,  which  also  contains  a  little 
free  hydrochloric  acid. 

The  gastric  juice  can  be  obtained  during  the  life  of  an  animal  by 
means  of  a  gastric  fistula.*  Gastric  fistulas  have  also  been  made  in 
human  beings,  either  by  accidental  injury  or  by  surgical  operations. 
The  most  celebrated  case  is  that  of  Alexis  St  Martin,  a  young 
Canadian,  who  received  a  musket  wound  in  the  abdomen  in  1822. 
Observations  made  on  him  by  Dr  Beaumont  formed  the  starting- 
point  for  our  correct  knowledge  of  the  physiology  of  the  stomach  and 
its  secretion. 

Artificial  gastric  juice  is  made  by  mixing  weak  hydrochloric  acid 
(0*2  per  cent.)  with  the  glycerin  extract  of  the  stomach  of  a  recently- 
killed  animal.     This  acts  like  the  normal  juice. 

Three  kinds  of  glands  are  distinguished  in  the  stomach,  which 
differ  from  each  other  in  their  position,  in  the  character  of  their 
epithelium,  and  in  their  secretion.  Their  structure  will  be  found 
described,  on  pp.  461  462.  We  may,  however,  repeat  that  the  fimdns 
or  oxyntic  glands  are  those  situated  in  the  fundus  and  nearly  the 
whole  of  the  cardiac  part  of  the  stomach :  their  ducts  are  short,  their 
tubules  long  in  proportion.  The  latter  are  filled  with  polyhedral 
cells,  only  a  small  lumen  being  left ;  they  are  more  coarsely  granular 
than  the  corresponding  cells  in  the  pyloric  glands.  They  are  called 
principal  or  central  cells.  Between  them  and  the  basement  membrane 
of  the  tubule  are  other  cells  which  stain  readily  with  aniUne  dyes. 
They  are  called  parietal  or  oxyntic  cells.     The  pyloric  glands,  in  the 

*  A  gastric  fistula  is  made  by  cutting  through  the  abdominal  wall  so  as  to 
expose  the  stomach.  The  stomach  is  then  attached  to  the  edges  of  the  abdominal 
wound,  and  a  small  orifice  is  finally  made  through  the  wall  of  the  stomach.  When 
the  wound  heals  there  is  then  a  free  communication  between  the  stomach  and  the 
exterior. 

4S3 


494  THE   GASTRIC   JUICE  [CH.  XXXL 

pyloric  part  of  the  stomach,  have  long  ducts  and  short  tubules  lined 
with  cubical  granular  cells.     There  are  no  parietal  cells. 

The  central  cells  of  the  fundus  glands  and  the  cells  of  the  pyloric 
glands  are  loaded  with  granules.  During  secretion  they  discharge 
their  granules,  those  that  remain  being  chiefly  situated  near  the  lumen, 
leaving  in  each  cell  a  clear  outer  zone.  These  are  the  cells  that 
secrete  the  pepsin.  Like  secreting  cells  generally,  they  select  certain 
materials  from  the  lymph  that  bathes  them;  these  materials  are 
worked  up  by  the  protoplasmic  activity  of  the  cells  into  the  secretion, 
which  is  then  discharged  into  the  lumen  of  the  gland.  The  most 
important  substance  in  a  digestive  secretion  is  the  ferment.  In  the 
case  of  the  gastric  juice  this  is  pepsin.  We  can  trace  an  intermediate 
step  in  this  process  by  the  presence  of  the  granules.  The  granules 
are  not,  however,  composed  of  pepsin,  but  of  a  mother-substance 
which  is  readily  converted  into  pepsin.  We  shall  find  a  similar 
ferment  precursor  in  the  cells  of  the  pancreas,  and  the  term  zymogen 
is  applied  to  these  ferment  precursors.  The  zymogen  in  the  gastric 
cells  is  cqX\q(\. pepsinogen.  The  rennet-ferment  that  causes  the  curdling 
of  milk  is  distinct  from  pepsin,  but  is  formed  by  the  same  cells. 
Pawlow's  view  that  the  curdling  is  only  a  phase  of  pepsin  action  has 
not  met  with  general  acceptance. 

The  parietal  cells  undergo  merely  a  change  of  size  during  secre- 
tion, being  at  first  somewhat  enlarged,  and  after  secretion  they  are 
somewhat  shrunken.  They  are  also  called  oxyntic  (acid-forming)  cells, 
because  they  secrete  the  hydrochloric  acid  of  the  juice.  Heidenhain 
succeeded  in  making  in  one  dog  a  cul-de-sac  of  the  fundus,  in  another 
of  the  pyloric  region  of  the  stomach ;  the  former  secreted  a  juice 
containing  both  acid  and  pepsin ;  the  latter,  parietal  cells  being 
absent,  secreted  a  viscid  alkaline  juice  containing  pepsin.  The  forma- 
tion of  a  free  acid  from  the  alkaline  blood  and  lymph  is  an  important 
problem.  There  is  no  doubt  that  it  is  formed  from  the  chlorides  of 
the  blood  and  lymph,  and  of  the  many  theories  advanced  as  to  its 
actual  mode  of  formation,  none  is  wholly  satisfactory. 

Some  theories  are  chemical  and  explain  the  formation  of  the  acid 
by  an  interaction  of  the  chlorides  and  phosphates.  Others  call  to 
their  assistance  the  law  of  "mass  action,"  and  we  certainly  know 
that  by  the  action  of  large  quantities  of  carbonic  acid  on  salts  of 
mineral  acids,  the  latter  may  be  liberated  in  small  quantities.  We 
know  further  that  small  quantities  of  acid  ions  may  be  continually 
formed  in  the  organism  by  ionisation.  But  in  every  case  we  can 
only  make  use  of  these  explanations  if  we  assume  that  the  small 
quantities  of  acid  are  carried  away  as  soon  as  they  are  formed,  and 
thus  give  room  for  the  formation  of  fresh  acid.  Even  then  we  are 
unable  to  explain  the  whole  process.  A  specific  action  of  the  cells  is 
no  doubt  exerted,  for  these  reactions  can  hardly  be  considered  to 


CH.  XXXI.] 


COMPOSITION    OF   GASTRIC    JUICE 


495 


occur  in  the  blood  generally,  but  rather  in  the  oxyntic  cells,  which 
possess  the  necessary  selective  powers  in  reference  to  the  saline 
constituents  of  the  blood,  and  the  hydrochloric  acid,  as  soon  as  it  is 
formed,  passes  into  the  secretion  of  the  gland  in  consequence  of  its 
high  power  of  diffusion. 


Composition  of  Gastric  Juice, 

The  following  table  gives  the  percentage  composition  of  the  gastric 
juice  of  man  and  the  dog : — 


Constituents. 

Human. 

Dog. 

Water 

99-44 

97-30 

Organic  substances  (chiefly  pepsin)    . 
HCl 

0-32 
0-20 

1-71 
0-40  to  0-60 

CaCl..   . 

0-006 

0-06 

NaCf    . 

0-14 

0-25 

KCl      . 

0-05 

0-11 

NH4CI. 

Ca,(P04)., 
Mg,(P04), 
FePO^ . 

I       0-01 

0-05 
0-17 
0-02 
0-008 

One  sees  from  this  how  much  richer  in  all  constituents  the  gastric 
juice  of  the  dog  is  than  that  of  man.  Carnivorous  animals  have  always 
a  more  powerful  gastric  juice  than  other  animals  ;  they  have  more 
work  for  it  to  do ;  but  the  great  contrast  seen  in  the  table  is,  no 
doubt,  partly  due  to  the  fact  that  the  persons  from  whom  it  has  been 
possible  to  collect  gastric  juice  have  been  invalids.  In  the  foregoing 
table  one  also  sees  the  great  preponderance  of  chlorides  over  other 
salts ;  apportioning  the  total  chlorine  to  the  various  metals  present, 
that  which  remains  over  must  be  combined  with  hydrogen  to  form 
the  free  hydrochloric  acid  of  the  juice. 

In  recent  years,  the  composition  and  action  of  the  gastric  juice 
has  been  studied  by  Pawlow.  By  an  ingenious  surgical  operation,  he 
succeeded  in  separating  from  the  stomach  of  dogs  a  diverticulum 
which  pours  its  secretion  through  an  opening  in  the  abdominal  wall; 
the  nerves  of  this  small  stomach  are  intact,  and  the  amount  of  juice 
that  can  be  collected  from  it  when  it  is  active  amounts  to  several 
hundred  cubic  centimetres  in  a  few  hours.  Pawlow  thus  obtained  a 
pure  gastric  juice,  which  enabled  him  to  study  its  action  and  com- 
position. It  is  clear,  colourless,  has  a  specific  gravity  of  1003 — 1006, 
and  is  feebly  dextro-rotatory.  It  contains  0'4  to  0"6  per  cent,  of 
hydrochloric  acid.  It  is  strongly  proteolytic,  and  inverts  cane  sugar. 
When  cooled  to  0^  C.  it  deposits  a  precipitate  of  pepsin,  and  this 
carries  down  with  it  the  acid  in  loose  combination,  especially  in  the 


496  THE   GASTRIC   JUICE  [CH.  XXXL 

layers  first  deposited.  Its  percentage  composition  is  very  similar 
to  that  of  a  protein,  only  it  contains  chlorine  in  addition  to  the  usual 
elements.  The  numbers  agree  closely  with  those  obtained  hj  Kiihne, 
who  used  ammonium  sulphate  as  the  precipitant. 

Pepsin  stands  apart  from  nearly  all  other  ferments  by  requiring 
an  acid  medium  in  order  that  it  may  act.  A  compound  of  the  two 
substances,  called  pepsin-hydrochloric  acid,  is  the  really  active  agent. 
Other  acids  may  take  the  place  of  hydrochloric  acid,  but  none  act  so 
well.  Lactic  acid  is  often  found  in  gastric  juice:  this  is  derived  by 
fermentative  processes  from  the  food. 

The  digestive  powers  of  the  acids  are  proportional  to  their  dissociation  and  the 
number  of  H  ions  liberated.  The  anions,  however,  modify  this  by  having  different 
powers  of  retarding  the  action.  The  greater  suitability  of  hydrochloric  over  lactic 
acid,  for  instance,  in  gastric  digestion  is  due  to  the  fact  that  the  former  acid  more 
readily  undergoes  dissociation. 

Hydrochloric  acid  is  absent  in  some  diseases  of  the  stomach,  notably  in 
cancer ;  the  best  colour  tests  for  it  are  the  following  : — 

((()  Gunsberg's  reagent  consists  of  2  parts  of  phloroglucinol,  1  part  of  vanillin, 
and  oO  parts  of  rectified  spirit.  A  drop  of  filtered  gastric  juice  is  evaporated  with 
an  equal  cjuantity  of  the  reagent.  Red  crystals  form,  or  if  much  peptone  is  present, 
there  will  be  a  red  paste.  The  reaction  takes  place  with  one  part  of  hydrochloric 
acid  in  10,000,     The  organic  acids  do  not  give  the  reaction. 

{h)  Tropacolin  test.  Drops  of  a  saturated  solution  of  tropaeolin  -00  in  94  per 
cent,  methylated  spirit  are  allowed  to  dry  on  a  porcelain  slab  at  40  C.  A  drop  of 
the  fluid  to  be  tested  is  placed  on  the  tropaeohn  drop,  still  at  40  C.  ;  and  if  hydro- 
chloric acid  is  present,  a  violet  spot  is  left  when  the  fluid  has  evaporated.  A  drop 
of  0'006  per  cent,  hydrochloric  acid  leaves  a  distinct  mark. 

((■)  Topfer's  test.  A  drop  of  dimethyl-amido-azo-benzol  is  spread  in  a  thin  film 
on  a  white  plate.  A  drop  of  dilute  hydrochloric  acid  (up  to  1  in  10,000)  strikes  with 
this  in  the  cold  a  bright  red  colour. 

Lactic  acid  is  soluble  in  ether,  and  is  generally  detected  by  making  an  ethereal 
extract  of  the  stomach  contents,  and  evaporating  the  ether.  If  lactic  acid  is  present 
in  the  residue  it  may  be  identified  by  the  following  way  : — 

A  solution  of  dilute  ferric  chloride  and  carbolic  acid  is  made  as  follows  : — 

10  c.c.  of  a  4-per-cent.  solution  of  carbohc  acid. 

20  c.c.  of  distilled  water. 

1  drop  of  the  liquor  ferri  perchloridi  of  the  British  Pharmacopoeia. 

On  mixing  a  solution  containing  a  mere  trace  (up  to  1  part  in  10,0o0)  of  lactic 
acid  with  this  violet  solution,  it  is  instantly  turned  yellow.  Larger  percentages  of 
other  acids  (for  instance,  more  than  0*2  per  cent  of  hydrochloric  acid)  are  necessary 
to  decolorise  the  test  solution,  but  they  do  not  turn  the  solution  yellow.  Another 
colour  test,  that  of  Hopkins,  is  performed  as  follows  : — 5  c.c.  of  sulphuric  acid  and 
3  drops  of  a  saturated  solution  of  copper  sulphate  are  added  to  a  few  drops  of 
lactic  acid  dissolved  in  alcohol.  The  mixture  is  placed  in  boiling  water  for  five 
minutes,  and  then  cooled;  2  drops  of  0*2  per  cent,  alcohohc  solution  of  thiophene 
are  then  added ;  on  replacing  the  tube  in  boiling  water,  a  cherry-red  colour 
develops. 

The  Innervation  of  the  Gastric  Glands. 

As  long  ago  as  1852  Bidder  and  Schmidt  showed  in  a  dog  with 
a  gastric  fistula  that  the  sight  of  food  caused  a  secretion  of  gastric 
juice;  and  in  1878  Kichet  observed  that  in  a  man  with  complete 
occlusion  of  the  gullet  the  act  of  mastication  caused  a  copious  flow 
of  gastric  juice.     There  could  therefore  have  been  no  doubt  that  the 


rH.  XXXI.]  INNERVATION    OF   GASTRIC    GLANDS  497 

glands  are  under  tho  control  of  the  nervous  system,  but  the  early 
attempts  to  discover  tho  secretory  nerves  of  the  stomach  were 
unsuccessful.  The  Russian  physiologist  Pawlow  solved  the  proltlem 
by  the  employment  of  new  methods.  He  experimented  on  dogs.  In 
the  first  place  he  separated  off  the  diverticulum,  which  we  have 
described  on  p.  495,  and  by  careful  experiments  he  showed  that 
the  secretion  of  this  small  stomach  is  an  exact  sample,  both  as  regards 
composition  and  rate  of  formation,  of  that  which  occurs  in  the  main 
stomach,  which  is  still  left  in  continuity  with  tlie  oesophagus  above 
and  the  duodenimi  below. 

Another  procedure  adopted  was  to  divide  the  oesophagus,  and  to 
attach  the  two  cut  ends  to  the  opening  in  the  neck.  The  animal  was 
fed  by  the  lower  segment,  but  any  food  taken  into  the  mouth,  or  any 
saliva  secreted  there,  never  reached  the  stomach,  but  fell  out  through 
the  opening  of  the  upper  segment.  These  animals  were  kept  alive 
for  months,  and  soon  accommodated  themselves  to  their  new  con- 
ditions of  life.  The  animals  could  thus  be  subjected  to,  (1)  real 
feeding,  (2)  sham  feeding,  by  allowing  them  to  eat  food  which  subse- 
quently tumbled  out  through  the  neck  opening,  and  (3)  psychical 
feeding,  in  which  the  animal  was  shown  the  food  but  was  not  allowed 
to  eat  it.     The  psychical  element  is  important. 

Mechanical  excitation  of  the  stomach  wall  produces  no  secretion. 
If  water  is  introduced  there  is  a  slight  flow,  and  even  if  meat  is 
introduced  into  the  main  stomach  without  the  knowledge  of  the  dog, 
the  juice  formed  is  scanty  and  of  feeble  digestive  power. 

There  is,  moreover,  no  connection  between  the  acts  of  mastication 
and  swallowing  with  that  of  gastric  secretion.  Sham  feeding  with 
stones,  butter,  salt,  pepper,  mustard,  extract  of  meat,  and  acid,  though 
it  excited  a  flow  of  saliva,  produced  no  effect  on  the  stomach.  If, 
however,  meat  was  used  for  the  sham  feeding,  an  abundant  and  active 
secretion  occurred  in  the  stomach  (that  of  the  small  stomach  was 
actually  examined)  after  a  latency  of  about  five  minutes.  The 
secretion  is  thus  adapted  to  the  kind  of  food  the  dog  has  to  digest ; 
the  larger  the  proportion  of  protein  in  the  diet,  the  more  abundant  is 
the  juice,  and  the  richer  both  in  pepsin  and  acid. 

Indeed,  if  the  animal  is  hungry  and  shown  the  meat  and  not 
allowed  to  swallow  it,  the  effect  is  almost  as  great.  The  following 
striking  experiment  also  shows  the  importance  of  the  psychical  element. 
Two  dogs  were  taken,  and  a  weighed  amount  of  protein  introduced  into 
the  main  stomach  of  each  without  their  knowledge ;  one  was  then  sham 
fed  on  meat,  and  one  and  a  half  hours  later  the  amount  of  protein 
digested  by  this  dog  was  five  times  greater  than  that  which  was 
digested  by  the  other. 

In  the  meat,  however,  it  is  not  the  protein  which  acts  most 
strongly  as  the  stimulus ;  egg-white,  for  instance,  is  not  a  stronger 

2  I 


498  THE   GASTRIC    JUICE  [CH.  XXXI. 

stimulus  than  water,  but  extract  of  meat  is  a  powerful  stimulus ; 
what  the  exact  extractives  are  that  act  in  this  way  is  not  yet  known, 
and  Herzen  has  since  shown  that  dextrin  acts  even  more  powerfully. 
Herzen  distinguishes  between  succagogues  (juice-drivers)  like  Liebig's 
extract,  and  peptogens  like  dextrin,  which  produce  not  only  an 
increased  flow,  but  a  juice  rich  in  pepsin -hydrochloric  acid.  The 
products  of  proteolysis  are  also  peptogenic,  so  that  when  once 
digestion  has  started,  a  stimulus  for  more  secretion  is  provided. 

If  the  vagi  are  cut  (below  the  origin  of  the  recurrent  laryngeal  to 
avoid  paralysis  of  the  larynx),  and  then  sham  feeding  is  performed 
with  meat,  no  secretion  is  obtained ;  the  vagi  therefore  contain  the 
secretory  fibres.  The  experiment  of  stimulating  the  peripheral  end 
of  the  cut  nerve  confirmed  this  h}'p)othesis.  The  nerve  was  cut  in 
the  neck  four  or  five  days  before  it  was  stimulated ;  in  this  time 
degeneration  of  the  cardio-inhibitory  fibres  took  place,  so  that 
stoppage  of  the  heart  did  not  occur  when  the  nerve  was  stimulated ; 
under  these  circumstances  a  secretion  was  obtained  with  a  long 
latency ;  the  latency  is  explained  by  the  presence  of  secreto-inhibitory 
fibres.  Atropine  abolishes  the  action  of  the  vagus.  In  other  animals 
the  spinal  cord  was  cut  at  the  level  of  the  first  cervical  nerve,  and  the 
animal  kept  alive  by  artificial  respiration ;  the  vagus  nerve  was  then 
cut,  and  its  peripheral  end  stimulated ;  an  abundant  secretion  usually 
followed.  Division  of  the  cord  renders  an  anaesthetic  unnecessary, 
and  also  prevents  the  afferent  impulses  set  up  by  the  operation  passing 
to  the  vagal  centres,  and  thus  exciting  the  inhibitory  impulses  which 
pass  down  the  vagus,  and  tend  to  prevent  secretion  under  ordinary 
circumstances. 

Pawlow  thinks  that  the  sympathetic  also  contains  some  secretory 
fibres,  but  this  has  not  yet  been  proved. 

Action  of  Gastric  Juice. 

The  principal  action  of  the  gastric  juice  consists  in  converting  the 
proteins  of  the  food  into  the  diffusible  peptones.  In  the  case  of  milk 
this  is  preceded  by  the  curdhng  due  to  rennet  (see  p.  473).  The 
prolonged  action  of  the  juice  leads  to  the  formation  from  the  peptones 
of  the  final  cleavage  products,  leucine,  tyrosine,  and  other  amino- 
acids.  But  the  usual  duration  of  gastric  digestion  is  so  short  that 
the  amount  of  these  that  are  formed  is  insignificant. 

There  is  a  still  further  action — that  is,  the  gastric  juice  is  anti- 
septic ;  putrefactive  processes  do  not  normally  occur  in  the  stomach, 
and  the  organisms  that  produce  such  processes,  many  of  which  are 
swallowed  with  the  food,  are  in  great  measure  destroyed,  and  thus  the 
body  is  protected  from  them. 

The  formation  of  peptones  is  a  process  of   hydrolysis;  peptones 


en.  XXXI.]  PROTEOSES    AND    PEPTONES  499 

may  be  formed  by  other  hydrolysing  agencies  such  as  superheated 
steam  or  heating  with  dihite  mineral  acids.  There  are  certain  inter- 
mediate steps  in  this  process :  the  intermediate  substances  are  called 
propeptones  or  proteoses.  The  word  "  proteose  "  includes  the  albumoses 
(from  albumin),  globuloses  (from  globulin),  vitelloses  (from  vitellin), 
etc.  Similar  substances  are  also  formed  from  gelatin  (gelatinoses) 
and  elastin  (elastoses). 

Another  intermediate  step  in  gastric  digestion  is  acid  albumin  or 
syntonin.  The  products  of  digestion  of  albumin  may  be  classified, 
according  to  the  order  in  which  they  are  formed,  as  follows : — 

1.  Acid  albumin. 

((a)  Proto-albumose        |  The  primary  albumoses,  /... 

2.  Propeptone  |  (h)  Heterc^lbuinose    J        ^'j^f   ^'"^'^   ^''^  ^o"!^^'^ 

\{(-)  Deutero-albumose 

3.  Peptone. 

Proteoses. — They  are  not  coagulated  by  heat;  they  are  precipi- 
tated but  not  coagulated  by  alcohol:  like  peptone  they  give  the 
biuret  reaction.  They  are  precipitated  by  nitric  acid,  the  precipitate 
being  soluble  on  heating,  and  reappearing  when  the  liquid  cools. 
This  last  is  a  distinctive  property  of  proteoses.  They  are  slightly 
diffusible. 

The  primary  proteoses  arc  precipitated  by  saturation  with 
magnesium  sulphate  or  sodium  chloride.  Deutero-proteose  is  not ; 
it  is,  however,  precipitated  by  saturation  with  ammonium  sulphate. 
Proto-  and  deutero-albumose  are  soluble  in  water ;  hetero-albumose  is 
not ;  it  requires  salt  to  hold  it  in  solution. 

Peptones. — They  are  soluble  in  water,  are  not  coagulated  by  heat, 
and  are  not  precipitated  by  nitric  acid,  copper  sulphate,  ammonium 
sulphate,  and  a  number  of  other  precipitants  of  proteins.  They  are 
precipitated  but  not  coagulated  by  alcohol.  They  are  also  precipi- 
tated by  tannin,  picric  acid,  potassio-mercuric  iodide,  phospho- 
molybdic  acid,  and  phospho-tungstic  acid. 

They  give  the  biuret  reaction  (rose-red  solution  with  a  trace  of 
copper  sulphate  and  caustic  potash  or  soda). 

Peptone  is  readily  diffusible  through  animal  membranes. 

The  annexed  table,  p.  500,  will  give  us  at  a  glance  the  chief  char- 
acters of  peptones  and  proteoses  in  contrast  with  those  of  the  native 
proteins,  albumins,  and  globulins. 

We  see  that  the  main  action  of  the  gastric  juice  is  upon  the 
proteins  of  the  food,  converting  them  into  more  soluble  and  diffusible 
products.  The  fats  are  not  chemically  altered  in  the  stomach,*  their 
protein  envelopes  are,  however,  dissolved,  and  the  solid  fats  are  melted. 

*  According  to  some  recent  observations,  a  small  amount  of  fat-splitting  does 
occur  in  the  stomach. 


500 


THE   GASTRIC   JUICE 


[CH.  XXXI. 


Starch  is  unaffected ;  but  cane  sugar  is  inverted.  The  inversion  of 
cane  sugar  is  largely  due  to  the  hydrochloric  acid  of  the  juice,  and  is 
frequently  assisted  by  inverting  ferments  contained  in  the  vegetable 
food  swallowed. 


Variety 

of 
proteid. 

Action 

of 
heat. 

Action 

of 
alcohol. 

Action 

of 

nitric  acid. 

Action  of 
ammonium 
sulphate. 

Action  of 

copper 

sulphate 

and  caustic 

potash. 

Diffusi- 
bility. 

Albumin 

Coagulated 

Precipitated, 
then    coagu- 
lated 

Precipitated 
in  the  cold; 
not    readily 
soluble      on 
heating 

Precipitated 
by  complete 
saturation 

Violet 
colour 

Nil 

Globulin 

Ditto. 

Ditto. 

Ditto. 

Precipitated 
by  half  satu- 
ration ;   also 
precipitated 
by  MgSO.. 

Ditto. 

Ditto. 

Proteoses 

Not 
coagulated 

Precipitated, 
but  not  co- 
agulated 

Precipitated 
in  the  cold  ; 
readily    sol- 
u  b 1 e       on 
heating;  the 
precipitate 
reappears  on 
cooling* 

Precipitated 
by      satura- 
tion 

Rose-red 
colour 
(biuret 
reaction) 

Slight 

Peptones 

Not 
coagulated 

Precipitated, 
but   not  co- 
agulated 

Not      precipi- 
tated 

Not      precipi- 
tated 

Rose-red 
colour 
(biuret 
reaction) 

Great 

*  In  the  case  of  deutero-albumose  this  reaction  only  occurs  in  the  presence  of  excess  of  salt. 

The  question  has  been  often  raised  why  the  stomach  does  not  digest  itself  during 
life.  The  mere  fact  that  the  tissues  are  alkaline  and  pepsin  requires  an  acid 
medium  in  which  to  act  is  not  an  explanation,  but  only  opens  up  a  fresh  difficulty 
as  to  why  the  pancreatic  juice  which  is  alkaline  does  not  digest  the  intestinal  wall. 
To  say  that  it  is  the  vital  properties  of  the  tissues  that  enable  them  to  resist 
digestion  only  shelves  the  difficulty  and  gives  no  real  explanation  of  the  mechanism 
of  defence.  Recent  studies  on  the  important  question  of  immunity  (see  p.  451) 
have  furnished  us  with  the  key  to  the  problem ;  just  as  poisons  introduced  from 
without  stimulate  the  cells  to  produce  antitoxins,  so  harmful  substances  produced 
within  the  body  are  provided  with  anti-substances  capable  of  neutralising  their 
eflPects  ;  for  this  reason  the  blood  does  not  normally  clot  within  the  blood-vessels, 
and  Weinland  has  shown  that  the  gastric  epithelium  forms  an  antipepsin,  the 
intestinal  epithelium  an  antitrypsin,  and  so  on.  The  bodies  of  parasitic  worms  that 
live  in  the  intestine  are  particularly  rich  in  these  anti-bodies. 


Mett's  Tubes. 

A  method  which  is  now  generally  employed  for  estimating  the  proteolytic 
activity  of  a  digestive  juice  is  one  originally  introduced  by  Mett  Pieces  of 
capillary  glass  tubing  of  known  length  are  filled  with  white  of  egg.  This  is  set  into 
a  solid  by  heating  to  95°  C.  They  are  then  placed  in  the  digestive  fluid  at  36°  C, 
and  the  coagulated  egg-white  is  digested.  After  a  given  time  the  tubes  are 
removed  ;  and  if  the  digestive  process  has  not  gone  too  far,  only  a  part  of  the  little 
column  of  coagulated  proteid  will  have  disappeared ;  the  length  of  the  remaining 


CII.  XXXI.]  SCHUTZ'    LAW  501 

column  is  easily  measured,  and  the  length  that  has  been  digested  is  a  measure  of 
the  digestive  strength  of  the  Huid. 

Hamburger  has  used  the  same  method  in  investigating  the  digestive  action  of 
juices  on  gelatin.  The  tubes  are  filled  with  warm  gelatin  solution,  and  this  jellies 
on  cooling.  They  are  placed  as  before  in  the  digestive  mixture,  and  the  length  of 
the  column  that  disappears  can  be  easily  measured.  These  experiments  must,  how- 
ever, be  performed  at  room  temperature,  for  the  usual  temperature  (3tr — 40°  C.)  at 
which  artificial  digestion  is  usually  carried  out  would  melt  the  gelatin.  He  has  also 
used  the  same  method  for  estimating  amylolytic  activity,  by  filling  the  tubes  with 
thick  starch  paste. 

Sohtitz'  Law. 

E.  Schiitz  stated  in  1885  that  the  amount  of  peptic  activity  is  proportional  to  the 
square  root  of  the  amount  of  pepsin.  This  was  confirmed  by  Borissow,  who  used 
Mett's  capillary  tube  method.  An  example  (taken  from  the  work  of  E.  Schiitz,  who 
estimated  the  amount  of  the  digestive  products  in  solution  by  means  of  nitrogen 
determinations)  will  suffice. 


Amount  of  Solution 

Digested  Nitroij 

;en  in  Grammes. 

of  Pepsin  in 

Cubic  Centimetres. 

Found. 

Calculated. 

1 

0-0230 

0-0223 

4 

0-0427 

0-0446 

9 

0-0686 

0-0669 

16 

0-0889 

0-0892 

This  work  was  an  early  attempt  to  deal  with  enzyme  action  on  exact  mathemati- 
cal lines,  a  branch  of  the  subject  now  being  extensively  studied.  Some  have  stated 
that  the  law  holds  more  or  less  exactly  for  other  enzymes  ;  in  other  cases  the  rela- 
tionship is  different.  The  usual  method  now  adopted  is  to  estimate  the  velocity  of 
reaction,  that  is,  the  time  occupied  by  the  ferment  in  accomphshing  a  given  end  on 
a  fixed  amount  of  material.  If,  for  instance,  one  takes  a  series  of  tubes,  each  con- 
taining the  same  araoimt  of  milk,  and  adds  to  each  different  known  amounts  of 
rennet,  the  time  occupied  in  producing  curdling  is  accurately  noted.  In  this  case, 
and  in  similar  experiments  with  blood  or  blood-plasma  and  fibrin  ferment,  the 
amount  of  ferment  multiplied  by  the  coagulation  time  is  constant ;  thus,  if  two  drops 
of  rennet  produce  coagulation  in  30  seconds,  four  drops  will  curdle  the  same  amount 
of  milk  in  15  seconds.  The  same  simple  relationship  also  probably  holds  for  the 
action  of  invertin,  erepsin,  and  trypsin. 


CHAPTER  XXXIl 


DIGESTION    IN   THE   INTESTINES 


Here  we  have  to  consider  the  action  of  pancreatic  juice,  of  bile,  and  of 
the  succus  entericus. 

The  Pancreas. 

This  is  a  tubulo-racemose  gland  closely  resembling  the  salivary 

glands  in  structure.     The  principal  differences  are  that  the  alveoli  or 

acini  are  more  tubular  in  character ; 
the  connective  tissue  between  them 
is  looser,  and  in  it  are  small  groups 
of  epithelium-like  cells  (islets  of 
Langerhans)  which  are  supplied  by  a 
close  network  of  capillaries  (fig.  399). 
The  secreting  cells  of  the 
pancreas  are  polyhedral.  When 
examined  in  the  fresh  condition,  or 
in  preparations  preserved  by  osmic 
acid,  their  protoplasm  is  seen  to  be 
tilled  in  the  inner  two-thirds  with 
small  granules ;  but  the  outer  third 
is  left  clear,  and  stains  readily  with 
protoplasmic  dyes  (fig.  398). 

During  secretion  the  granules  are 
discharged ;  the  clear  zone  conse- 
quently becomes  wider,  and  the 
granular  zone  narrower. 

These  granules  indicate  the 
presence   of    a   zymogen   which    is 

called    trypsinogen ;    that    is,   the    precursor   of    trypsin,   the   most 

important  ferment  of  the  pancreatic  juice. 

In  the  centre  of  the  acini,  spindle-shaped  cells  {centro-acinar  cells) 

are  often  seen ;  theii-  function  and  origin  are  unknown. 


Fig.  398.— Section  of  the  pancreas  of  a  dog 
during  digestion,  o,  Alveoli  lined  with 
cells,  the  clear  outer  zone  of  which  is  well 
stained  with  haematoxylin  ;  d,  duct  lined 
with  short  cubical  cells,  x  350.  (Klein 
and  Noble  Smith.) 


ClI.  XXXII.]  COMPOSITION    OF    PAXCUEATIC    JUICE  503 

Composition  and  Action  of  Pancreatic  Juice, 

The  pancreatic  juice  may  be  obtained  by  a  fistula  in  animals,  a 
cannula  being  inserted  into  the  main  pancreatic  duct ;  but  as  in  the 
case  of  gastric  juice,  experiments  on  the  pancreatic  secretion  are  usu- 
ally performed  with  an  artificial  juice  made  by  mixing  a  weak  alkaline 
solution  (1  per  cent,  sodium  carbonate)  with  a  glycerin  extract  of 
pancreas.     The  pancreas  should  be  treated  with  dilute  acid  for  a  few 


Fig.  399.— Section  of  the  pancreas  of  armadillo,  showing  alveoli  and  an  islet  of  Langerhans  in  the 
connective  tissue.     (V.  D.  Harris.) 

hours  before  the  glycerin  is  added.     This  ensures  a  conversion  of  the 
trypsinogen  into  trypsin. 

Quantitative  analysis  of  human  pancreatic  juice  gives  the  follow- 
ing results : — 

Water 97*6  per  cent. 

Organic  solids 1  '8         „ 

Inorganic  salts 0"6         ,, 

In  the  dog  the  amount  of  solids  is  much  greater. 

The  organic  substances  in  pancreatic  juice  are — 

{a)  Ferments.     These  are  the  most  important  both  quantitatively 
and  functionally.     They  are  four  in  number : — 
i.  Trypsin,  a  proteolytic  ferment, 
ii.  Amylopsin  or  pancreatic  diastase,  an  amylolytic  ferment. 

iii.  Steapsin  or  lipase,  a  fat-splitting  or  lipolytic  ferment. 

iv.  A  milk-curdhng  ferment. 

(&)  A  small  amount  of  protein  matter,  coagulable  by  heat. 

(c)  Traces  of  leucine,  tyrosine,  xanthine,  and  soaps. 

The  inorganic  substances  in  pancreatic  juice  are — 

Sodium  chloride,  which  is  the  most  abundant,  and  smaller  quan- 
tities of  potassium  chloride,  and  phosphates  of  sodium,  calcium,  and 


504  DIGESTION    IN    THE    INTESTINES  [CH.  XXXII. 

magnesium.     The  alkalinity  of  the  juice  is  due  to  phosphates  and  car- 
bonates, especially  of  sodium. 

1.  Action  of  Trypsin. — Trypsin  acts  like  pepsin,  but  with  certain 
differences,  which  are  as  follows : — 

(a)  It  acts  in  an  alkaline,  pepsin  in  an  acid  medium. 

(b)  It  acts  more  rapidly  than  pepsin ;  deutero-proteoses  can  be 
detected  as  intermediate  products  in  the  formation  of  peptone ;  the 
primary  proteoses  have  not  been  detected. 

(c)  Alkali-albumin  is  formed  in  place  of  the  acid-albumin  of 
gastric  digestion. 

(d)  It  acts  more  powerfully  on  certain  proteins  (such  as  elastin) 
which  are  difficult  of  digestion  in  gastric  juice.  It  does  not,  however, 
digest  collagen. 

(e)  Acting  on  solid  proteins  like  fibrin,  it  eats  them  away  from  the 
surface  to  the  interior ;  there  is  no  preliminary  swelling  as  in  gastric 
digestion. 

(/)  Trypsin  acts  further  than  pepsin,  on  prolonged  action  decom- 
posing the  peptone  which  has  left  the  stomach  into  simpler  products, 
of  which  the  most  important  are  polypeptides,  leucine,  tyrosine, 
arginine,  aspartic  acid,  glutamic  acid,  hexone  bases,  ammonia,  and  a 
substance  called  tryptophan  [indole-amino-propionic  acid],  which 
gives  a  red  colour  with  chlorine  or  bromine  water,  and  also  the 
Adamkiewicz  reaction.  (For  the  constitution  and  properties  of  these 
cleavage  products,  see  pp.  400  to  404.) 

The  action  of  proteolytic  enzymes  is,  by  a  process  of  hydrolysis, 
to  split  the  heavy  protein  molecule  into  smaller  and  smaller 
molecules;  first,  we  get  proteoses,  then  peptones  and  polypeptides, 
and,  finally,  simple  products  such  as  leucine  and  tyrosine.  A  variable 
fraction  of  the  protein  molecule  is  broken  off  with  comparative  ease, 
but  the  whole  breakdown  is  more  easily  performed  by  the  powerful 
tryptic  enzyme  than  by  pepsin-hydrochloric  acid.  The  latter  agent, 
however,  is  not  entirely  inactive  in  this  direction,  for  although 
leucine  and  tyrosine  and  other  amino-acids  are  not  found  to  any 
great  extent  in  a  peptic  digest,  unless  the  action  has  been  very 
prolonged,  yet  there  is  usually  a  small  amount  of  such  substances, 
and  this  amount  increases  the  more  time  is  allowed.  The  essential 
difference  between  pepsin  and  trypsin  is  one  of  velocity  of  action,  or 
in  other  words,  trypsin  is  the  more  powerful  catalyst  (see  p.  418). 

2.  Action  of  Amylopsin. — The  conversion  of  starch  into  maltose 
is  the  most  rapid  of  all  the  actions  of  the  pancreatic  juice.  Its  power 
in  this  direction  is  much  greater  than  that  of  saliva,  and  it  will  act 
even  on  unboiled  starch.  The  absence  of  this  ferment  in  the  pancreatic 
juice  of  infants  is  an  indication  that  milk,  and  not  starch,  is  their 
natural  diet. 

3.  Action  on  Pats. — The  action  of  pancreatic  juice  on  fats  is  a 


CH.  XXXII. ]  MECHANISM   OF    PANCREATIC   SECRETION  505 

double  one :  it  forms  an  emulsion,  and  it  decomposes  the  fats  into 
fatty  acids  and  glycerin  by  means  of  its  fat-splittiiig  ferment  steapsin. 
The  fatty  acids  unite  with  the  alkaline  bases  to  form  soaps  {saponifi- 
cation). The  chemistry  of  this  is  described  on  p,  399.  The  fat- 
splitting  power  of  pancreatic  juice  cannot  be  studied  with  a  glycerin 
extract,  as  steapsin  is  not  soluble  in  glycerin :  either  the  fresh  juice 
or  a  watery  extract  of  pancreas  must  be  used. 

The  formation  of  an  emulsion  may  be  studied  in  the  following 
w^ay :  if  olive  oil  and  water  are  shaken  up  together,  and  the  mixture 
is  allowed  to  stand,  the  finely  divided  oil  globules  soon  separate,  run 
together,  and  form  a  layer  which  floats  on  the  surface  of  the  water. 
But  if  olive  oil  is  shaken  up  with  a  solution  of  soap,  the  conditions  of 
surface  tension  are  such  that  the  oil  globules  remain  as  such  in  the 
mixture,  and  a  white  milky  fluid  called  an  emulsion  is  the  result. 
The  emulsion  is  still  more  permanent  if  a  colloid  material  like  gum  or 
albumin  is  also  present.  Pancreatic  juice  possesses  all  the  necessary 
qualifications  for  the  formation  of  an  emulsion ;  it  is  alkaline,  and  so 
liberates  fatty  acids  from  the  fat ;  these  acids  form  soap  with  the  alkali 
present ;  moreover,  it  is  viscous  from  the  presence  of  protein. 

4.  Milk-curdling  Ferment. — The  addition  of  pancreatic  extracts 
or  pancreatic  juice  to  milk  causes  clotting;  but  this  action  (which 
differs  in  some  particulars  from  the  clotting  caused  by  rennet)  can 
hardly  ever  be  called  into  play,  as  the  milk  upon  which  the  juice  has 
to  act  has  been  already  curdled  by  the  rennin  of  the  stomach. 

The  so-called  Peripheral  Reflex  Secretion  of  the  Pancreas. 

One  of  the  most  effective  ways  of  producing  a  flow  of  pancreatic 
juice  is  to  introduce  acid  into  the  duodenum.  Popielski  and 
Wertheimer  and  Le  Page  showed  that  this  flow  still  occurs  when  the 
nerves  supplying  the  duodenum  and  pancreas  have  been  cut  through. 
Wertheimer  also  mentions  that  the  flow  can  be  excited  by  injection 
of  acid  into  the  jejunum,  but  not  when  it  is  injected  into  the  lower 
part  of  the  ileum.  These  authors  concluded  that  the  secretion  is  a 
local  reflex,  the  centres  being  situated  in  the  scattered  ganglia  of  the 
pancreas,  or,  in  the  case  of  the  jejunum,  in  the  ganglia  of  the  solar 
plexus. 

This  subject  has  been  re-investigated  by  Starling  and  Bayliss,  and 
the  results  they  have  obtained  are  most  noteworthy.  They  consider 
that  the  secretion  cannot  be  reflex,  since  it  occurs  after  extirpation  of 
the  solar  plexus,  and  destruction  of  all  nerves  passing  to  an  isolated 
loop  of  intestine.  Moreover,  atropine  does  not  paralyse  the  secretory 
action.  It  must  therefore  be  due  to  direct  excitation  of  the  pancreatic 
cells,  by  a  substance  or  substances  conveyed  to  the  gland  from  the 
bowel  by  the  blood-stream.     So  many  of  the  connections  between 


506  DIGESTION   IN   THE   INTESTINES  [CH.  XXXII. 

organs  are  made  by  nerves  (the  telegraphic  service  of  the  body),  that 
we  are  apt  to  forget  the  other  messenger,  the  blood,  whom  we  may 
compare  to  the  postman. 

The  exciting  substance  is  not  acid;  injection  of  04  per  cent,  of 
hydrochloric  acid  into  the  blood-stream  has  no  influence  on  the 
pancreas.  The  su1)stance  in  question  must  be  produced  in  the 
intestinal  mucous  membrane  under  the  influence  of  the  acid.  This 
conclusion  was  confirmed  by  experiment.  If  the  mucous  membrane 
of  the  jejunum  or  duodenum  is  exposed  to  the  action  of  0'4  per  cent, 
hydrochloric  acid,  a  body  is  produced  which,  when  injected  into  the 
blood-stream  in  minimal  doses,  produces  a  copious  secretion  of  pan- 
creatic juice  and  also,  but  to  a  less  extent,  of  bile.  This  substance  is 
termed  secretin.  It  is  associated  with  another  substance  which  lowers 
arterial  blood-pressure.  The  two  substances  are  not  identical,  since 
acid  extracts  of  the  lower  end  of  the  ileum  produce  a  lowering  of 
blood-pressure,  but  have  no  excitatory  influence  on  the  pancreas. 

Secretin  is  split  off  from  a  precursor,  "prosecretin,  which  is  present 
in  relatively  large  amounts  in  the  duodenal  mucous  membrane,  and 
gradually  diminishes  as  we  descend  the  intestine.  Pro-secretin  can 
be  dissolved  out  of  the  mucous  membrane  by  normal  saline  solution. 
It  has  no  influence  on  the  pancreatic  secretion.  Secretin  can  be  split 
off  from  it  by  boiling  or  by  treatment  with  acid. 

What  secretin  is  chemically  we  do  not  yet  know.  It  is  soluble  in 
alcohol  and  ether.  It  is  not  a  protein,  but  probably  is  an  organic 
substance  of  low  molecular  weight.  It  is,  moreover,  the  same  sub- 
stance in  all  animals,  and  not  specific  to  different  kinds  of  animals. 

Pawlow  by  experiments  of  a  similar  nature  to  those  which  led 
him  to  the  discovery  of  the  secretory  nerves  of  the  gastric  mucous 
membrane,  thought  he  had  also  discovered  the  secretory  nerves  of 
the  pancreas  in  the  vagus,  and  to  a  less  extent  in  the  splanchnic 
nerves.  His  failure  to  produce  this  result  in  some  experiments  he 
explained  by  the  concomitant  stimulation  of  secreto-inhibiting  fibres. 
It  is  quite  possible  that  nerves  of  this  nature  exist ;  but  Pawlow's 
experiments  do  not  prove  their  existence,  because  the  passage  of  acid 
chyme  into  the  duodenum  was  not  excluded,  and  so  he  may  only 
have  been  dealing  with  a  production  of  secretin,  the  chemical 
stimulus  to  pancreatic  activity. 

Starling's  work  on  secretion  naturally  led  him  and  others  to  seek 
for  other  chemical  messengers  employed  in  the  regulation  of  the 
activities  of  the  body,  and  it  has  already  been  established  that 
secretin  is  by  no  means  a  solitary  instance  of  such.  The  general 
name  given  to  these  agents  is  that  of  Iwrmone.  The  chemical 
substances  secreted  by  such  glands  as  the  thyroid  and  suprarenal 
must  be  included  under  tliis  term,  and  the  part  played  by  carbonic 
acid  in  the  regulation  of  breathing  (see  p.  363)  also  comes  into  the 


en.  XXXII.]  THE   INTESTINAL  JUICE  507 

same  category.  In  our  study  of  gastric  digestion,  we  have  seen  the 
powerful  peptogenic  action  of  dextrin,  a  substance  prepared  during 
the  salivary  digestion  of  starch ;  Edkins  has  given  the  name  gastrin 
to  the  special  hormone  which  is  the  result  of  the  action  of  the 
sali\ary  prochicts  on  the  gastric  mucous  membrane.  Another 
e.xaniple  of  a  hormone  is  furnished  by  the  material  formed  by  the 
ovum  especially  during  its  development  in  u/ero,  and  which,  passing 
into  the  maternal  blood-stream,  stimulates  the  mammary  gland  to 
action  (see  p.  476). 

Adaptation  of  the.  Pancreas.  -To  a  certain  degree  it  cannot  be  doubted  that 
the  pancreas  adapts  its  secretion  to  the  work  it  has  to  do.  Thus,  whereas  gastric 
juice  has  a  maximal  flow  soon  after  the  ingestion  of  food,  the  pancreative  How 
does  not  attain  its  full  force  until  some  hours  later,  that  is,  when  it  is  wanted.  The 
view  that  this  is  due  to  the  hormone  named  secretin,  which  is  not  formed  until 
the  gastric  contents  enter  the  intestine,  fully  explains  the  reason  for  the  delay. 

But  Pawlow  went  further  than  this,  and  stated  that  the  proportion  of  the 
various  enzymes  of  the  juice  was  adapted  to  the  proportions  of  proteins,  carbo- 
hydrates, and  fats  in  the  food  taken.  Considerable  doubt  has  been  cast  on  these 
results,  because  of  the  failure  to  confirm  one  of  the  most  remarkable  instances  of 
such  adaptation ;  this  is  the  power  of  the  pancreas  to  secrete  lactase  (a  ferment 
capable  of  hydrolysing  lactose  into  glucoses).  Normal  pancreatic  juice  contains 
no  lactase,  but  certain  observers  stated  that  by  feeding  an  animal  on  milk,  the 
pancreas  could  be  educated  to  secrete  it.  Careful  experiments  by  Plinimer  have 
recently  shown  this  is  not  really  so,  and  so  much  more  stringent  experimental 
conditions  will  have  to  be  imposed  before  the  other  cases  of  adaptation  can  be 
considered  proven. 

The  Succus  Entericus. 

Succus  entericus  has  been  obtained  free  from  other  secretions  by 
means  of  a  fistula.  Thiry's  method  is  to  cut  the  intestine  across  in 
two  places;  the  loop  so  cut  out  is  still  supplied  with  blood  and 
nerves,  as  its  mesentery  is  intact ;  this  loop  is  emptied,  one  end  is 
sewn  up,  and  the  other  stitched  to  the  abdominal  wound,  and  so  a 
cul-de-sac  from  which  the  secretion  can  be  collected  is  made.  The 
continuity  of  the  remainder  of  the  intestine  is  restored  by  fastening 
together  the  upper  and  lower  portions  of  the  bowel  from  which  the 
loop  has  been  removed.  Vella's  method  resembles  Thiry's,  except  that 
both  ends  of  the  loop  are  sutured  to  the  wound  in  the  abdomen.  Fig. 
400  illustrates  the  two  methods. 

The  succus  entericus  possesses  to  a  slight  extent  the  power  of  con- 
verting starch  into  sugar.  Its  best  known  action  is  due  to  a  ferment 
called  invertase,  which  inverts  saccharoses — that  is,  it  converts  cane 
sugar  and  maltose  into  glucose.  The  original  use  of  the  term  "  inver- 
sion "  has  been  explained  on  p.  394.  It  may  be  extended  to  include 
the  shnilar  hydrolysis  of  other  saccharoses,  although  there  may  be  no 
formation  of  levo-rotatory  substances.  There  are  probably  numerous 
inverting  ferments,  each  of  which  acts  on  a  different  saccharose. 

Up  till  a  year  or  two  ago  little  or  nothing  was  known  regarding 
the  action  of    the   intestinal  juice    beyond    this,  but  investigations 


508 


DIGESTION    IN   THE   INTESTINES 


[CH.  XXXII. 


published  quite  recently  have,  however,  altered  this  state  of  things, 
and  in  the  light  of  these  the  succus  entericus  appears  to  be  a  juice  of 
the  highest  importance. 

Pawlow  was  the  first  to  show  that  one  of  its  main  actions  is  to 
reinforce  and  intensify  the  action  of  the  pancreatic  juice,  especially 
in  reference  to  its  proteolytic  power.  Fresh  pancreatic  juice  has 
practically  no  digestive  power  on  proteins.  Claude  Bernard,  the 
earliest  to  study  the  pancreatic  secretion,  entirely  missed  its  tryptic 
action.  On  standing,  the  juice  very  slowly  acquires  proteolytic 
activity.  Vernon  has  shown  that  much  the  same  is  true  for  extracts 
of  the  pancreas.     There  is  no  doubt  that  what  the  fresh  juice  con- 


FiG.  400 —Diagram  of  intestiual  ttstula.    I.,  Thiry's  method  ;  II.,  Vella's  method.    A,  Abdominal  wall ; 
B,  intestine,  with  mesentery;  0,  separated  loop  of  intestine,  with  attached  mesentery. 

tains  is  trypsinogen,  and  this  is  slowly  transformed  into  the  active 
enzyme  trypsin. 

If  fresh  pancreatic  and  intestinal  juices  are  mixed  togetlier,  the 
result  is  a  powerful  proteolytic  mixture,  though  neither  juice  by  itself 
has  any  proteolytic  activity. 

Pawlow  speaks  of  the  substance  in  the  intestinal  juice  which  has 
this  action  as  a  "  ferment  of  the  ferments,"  and  has  named  it  entero- 
kinase.  It  mainly  reinforces  tryptic  activity,  but  also  has  a  similar 
though  slighter  energising  influence  on  the  fat-splitting  ferment. 

Starling,  like  Pawlow,  worked  with  dogs,  and  has  confirmed  his 
main  results.  A  valuable  contribution  to  the  same  subject  has  also 
been  made  by  Hambm-ger.  He  has  had  the  unusual  opportunity  of 
examining  human  succus  entericus.  It  became  necessary  in  a  patient 
for  surgical  reasons  to  isolate  a  loop  of  the  small  intestine,  and  this 
loop  continued  to  discharge  intestinal  juice  to  the  exterior  for  some 
time  after  the  operation.  He  finds  that  this  juice,  like  that  of  the 
dog,  contains  a  substance  which  renders  pancreatic  juice  active.  He 
could  not  find  that  it  exercised  any  energising  influence  on  the 
fat-splitting  and  amylolytic  ferments  of  the  pancreas,  but  its  action 


CH.  XXXII.]  ENTEROKINASE   AND    EREPSIN  509 

on  the  tryptic  forineiit  was  most  marked.  His  quantitutixo  experi- 
ments do  not  bear  out  Pavvlow's  view  that  the  active;  substance 
in  the  intestinal  juice  is  a  forniont,  for  it  is  unable  like  a  ferment  to 
act  on  an  unlimited  amount  of  pancreatic  juice.  Delezenne  also 
thinks  it  is  not  a  ferment,  but  compares  it  to  the  immune  l^ody  or 
amboceptor  which  enables  hsemolysins  to  become  effective  (see  p.  454). 
Starling,  however,  supports  Pawlow's  view  ;  provided  sufficient  time 
is  allowed  to  elapse,  it  will  activate  any  amount  of  pancreatic  juice. 

Another  discovery  in  connection  with  succus  entericus  has  been 
made  by  Otto  Cohnheim.  The  juice  has  no  action  on  native  proteins 
such  as  iibrin  and  egg-white,*  but  it  acts  on  proteoses  and  peptone. 
It  rapidly  breaks  them  up  into  simpler  substances,  of  which  ammonia, 
leucine,  tyrosine,  and  the  hexone  bases  have  been  identified.  Cohn- 
heim has  named  the  ferment  to  which  this  is  due  erepsin.  Ham- 
burger found  that  erepsin  is  also  present  in  the  human  juice ;  it  is 
not  identical  with  enterokinase  because  erepsin  is  destroyed  by  heat- 
ing the  juice  to  59°  C.  for  three  hours ;  enterokinase  is  not  destroyed 
until  the  temperature  is  raised  to  67°  C.  Other  observers  have  con- 
firmed the  discovery  of  erepsin,  but  have  found  that  it  or  a  similar 
ferment  is  present  in  most  tissues;  it  is  most  abundant  in  the 
kidney  (Vernon). 

The  bile,  as  we  shall  find,  has  little  or  no  digestive  action  by 
itself,  but  combined  with  pancreatic  juice  it  assists  the  latter  in  all 
its  actions.  This  is  true  for  the  digestion  of  starch  and  of  protein, 
but  most  markedly  so  for  the  digestion  of  fat.  Occlusion  of  the  bile- 
duct  by  a  gall-stone  or  by  inflammation  prevents  bile  entering  the 
duodenum.  Under  these  circumstances  the  faeces  contain  a  large 
amount  of  undigested  fat. 

The  importance  of  the  work  of  Pawlow,  and  the  other  physi- 
ologists whose  names  have  been  mentioned,  arises  from  the  entirely 
new  light  thrown  upon  the  digestion  process  as  a  whole.  We  have 
been  too  apt  to  think  of  the  occurrences  in  the  alimentary  canal  as  a 
series  of  isolated  phenomena.  We  now  see  that  each  step  follows  in 
an  orderly  manner  as  the  result  of  the  previous  steps.  For  example, 
the  acid  gastric  juice  reaches  the  small  intestine,  and  there  produces 
secretin  from  its  forerunner ;  the  secretin  is  taken  by  the  blood- stream 
to  the  pancreas,  where  it  excites  a  flow  of  pancreatic  juice;  this  juice 
arrives  in  the  duodenum  ready  to  act  on  starchy  substances  and  on 
fat.     With  the  assistance  of  the  bile,  fatty  acid  is  liberated  which  in 

*  Cohnheim  has  investigated  the  action  of  erepsin  on  a  large  number  of  proteins  ; 
it  acts  energetically  on  proteoses,  peptone,  and  protamines :  on  histone,  which 
occupies  an  intermediate  place  between  protamines  and  the  other  proteins,  it  has  a 
slight  action.  On  the  other  native  proteins  it  has  no  action,  with  the  single  excep- 
tion of  caseinogen,  which  is  speedily  broken  up  into  simple  substances  ;  this  opens 
up  the  interesting  physiological  possibility  that  the  suckling  infant  is  able  to  digest 
its  protein  nutriment  even  if  pepsin  and  trypsin  are  absent 


510  DIGESTION    IN   THE   INTESTINES  [CH.  XXXII. 

its  turn  forms  more  secretin,  and  so  more  pancreatic  juice.  The 
pancreatic  juice,  however,  cannot  act  on  proteins  without  enterokinase, 
which  is  supplied  by  the  succus  entericus  ;  *  this  sets  free  the  trypsin  ; 
and  trypsin  with  the  assistance  of  erepsin  effectively  carries  out 
digestive  proteolysis. 

Bacterial  Action. 

The  gastric  juice  is  an  antiseptic;  the  pancreatic  juice  is  not. 
An  alkaline  fluid  like  pancreatic  juice  is  just  the  most  suitable  medium 
for  bacteria  to  flourish  in.  Even  in  an  artificial  digestion  the  fluid 
is  very  soon  putrid,  unless  special  precautions  to  exclude  or  kill 
bacteria  are  taken.  It  is  often  difficult  to  say  where  pancreatic 
action  ends  and  bacterial  action  begins,  as  many  of  the  bacteria  that 
grow  in  the  intestinal  contents  (having  reached  that  situation  in 
spite  of  the  gastric  juice)  act  in  the  same  way  as  the  pancreatic  juice. 
Some  form  sugar  from  starch,  others  peptone,  leucine,  and  tyrosine 
from  proteins,  while  others,  again,  break  up  fats.  There  are,  how- 
ever, certain  actions  that  are  entirely  due  to  these  putrefactive 
organisms. 

i.  On  carbohydrates.  The  most  frequent  fermentation  they  set 
up  is  the  lactic  acid  fermentation  :  this  may  go  further  and  result  in 
the  formation  of  carbonic  acid,  hydrogen  and  butyric  acid  (see  p. 
395).  Cellulose  is  broken  up  into  carbonic  acid  and  methane.  This 
is  the  chief  cause  of  the  gases  in  the  intestine,  the  amount  of  which 
is  increased  by  vegetable  food. 

ii.  On  fats.  In  addition  to  acting  like  steapsin,  they  produce 
lower  acids  (valeric,  butyric,  etc.).  The  formation  of  acid  products 
from  fats  and  carbohydrates  gives  to  the  intestinal  contents  an  acid 
reaction.  Kecent  researches  show  that  the  contents  of  the  intestine 
become  acid  much  higher  up  than  was  formerly  supposed.  Organic 
acids  do  not,  however,  hinder  pancreatic  digestion. 

iii.  On  proteins.  Fatty  acids  and  amino-acids,  especially  leucine 
and  tyrosine,  are  produced ;  but  these  putrefactive  organisms  have  a 
specially  powerful  action  in  liberating  substances  having  an  evil 
odour,  like  indole  (CgHyN),  skatole  (C9H9N),  and  phenol  (C^jH^.O). 
There  are  also  gaseous  products  in  some  cases. 

If  excessive,  putrefactive  processes  are  harmful ;  if  within  normal 
limits,  they  are  useful,  helping  the  pancreatic  juice,  and,  further, 
preventing  the  entrance  into  the  body  of  poisonous  products.  It  is 
possible  that,  in  digestion,  poisonous  alkaloids  are  formed.  Certainly 
this  is  so  in  one  well-known  case.  Lecithin,  a  material  contained  in 
small  quantities  in  many  foods,  and  in  large  quantities  in  egg-yolk 

*  The  mixture  of  pancreatic  and  intestinal  juice  is  extraordinarily  powerful. 
If  secretin  is  administered  to  a  fasting  animal  the  juice  secreted,  having  no  food  to 
act  upon,  will  produce  erosion  and  inflammation  of  the  intestinal  wall.     (Starling.) 


en.  XXXII.] 


LEUCINE    AND    TYROSINE 


111 


and  brain,  is  broken  up  by  the  pancreatic  juice  into  glycerin, 
phosphoric  acid,  fatty  acids,  and  an  alkaloid  called  choline.  We 
are,  however,  protected  from  the  poisonous  action  of  choline  by  the 
bacteria,  which  lireak  it  up  into  carbonic  acid,  methane,  and  ammonia. 

Leucine  and  Tyrosine. 

These  two  substances  have  been  frequently  mentioned  in  the 
preceding  pages.  They  are  important  as  types  of  the  final  cleavage 
products  of  proteins. 

Leucine  is  usually  the  most  abundant  of  these  products,  and 
hitherto  we  have  spoken  of  it  as  amino-caproic  acid  (see  p.  401). 

But  according  to  the  way  in  which  the  amino-group  is  linked,  a 
large  number  of  isomeric  amino-caproic  acids,  all  with  the  same 
empirical  formula,  are  theoretically  possible.  Some  of  these  have 
been  actually  prepared  in  the  laboratory ;  and  chemical  research  has 
shown  that  the  amino-caproic  acid  called  leucine  formed  during  diges- 
tion should  be  more  accurately  named  r/-amino-isobutylacetic  acid 
(CHJ,CH.CH.,CH(NH.,)COOH. 

Tyrosine  is  a  little  more  complicated,  and  not  nearly  so  abund- 
ant ;  its  importance  arises  from  its  being  a  type  of  amino-acids  which 


Fig.  401.— Crystals  of  leucine  and  tyrosine 


contain  an  aromatic  radical.  The  constitution  of  tyrosine  or 
oxyphenyl-amino-propionic  acid  is  fully  explained  on  p.  403.  Leucine 
and  tyrosine  are  both  crystalline ;  the  former  crystallises  in  the  form 
of  spheroidal  clumps  of  crystals,  the  latter  in  collections  of  fine  silken 
needles  (fig.  401). 

Extirpation  of  the  Pancreas. 

Complete  removal  of  the  pancreas  in  animals  and  diseases  of  the 
pancreas  in  man  prqduce  a  condition  of  diabetes,  in  addition  to  the 
loss  of  pancreatic  action  in  the  intestines.     Grafting  the  pancreas 


512  DIGESTION    IN    THE   INTESTINES  [CII.  XXXII. 

from  another  animal  into  the  abdomen  of  tlio  animal  from  which  the 
pancreas  has  been  removed  relieves  the  dialjetic  condition. 

How  the  pancreas  acts  other  than  in  producing  the  pancreatic 
juice  is  not  known.  It  must,  however,  have  other  functions  related 
to  the  general  metabolic  phenomena  of  the  body,  which  are  disturbed 
by  removal  or  disease  of  the  gland.  This  is  an  illustration  of  a 
universal  truth — viz.,  that  each  part  of  the  body  does  not  merely  do 
its  own  special  work,  but  is  concerned  in  the  great  cycle  of  changes 
which  is  called  general  metabolism.  Interference  with  any  organ 
upsets  not  only  its  specific  function,  but  causes  disturbances  through 
the  body  generally.  The  interdependence  of  the  circulatory  and 
respiratory  systems  is  a  well-known  instance.  Kemoval  of  the  thyroid 
gland  upsets  the  whole  body,  producing  widespread  changes  known  as 
myxoedema.  Kemoval  of  the  testes  produces  not  only  a  loss  of  the 
spermatic  secretion,  but  changes  the  whole  growth  and  appearance 
of  the  animal.  The  precise  way  in  which  these  glands  are  related  to 
the  general  body  processes  is,  however,  a  subject  of  which  we  know 
as  yet  very  little.  The  theory  at  present  most  in  favour  is  that 
certain  glands  produce  an  internal  secretion,  which  leaves  them  vid 
the  lymph,  and  is  then  distributed  to  minister  to  parts  elsewhere. 
The  question  of  the  internal  secretions  of  the  thyroid  and  suprarenal 
capsules  is  discussed  in  Chap.  XXIII.  In  the  case  of  the  pancreas, 
the  theory  has  been  propounded  that  its  internal  secretion,  stoppage 
of  which  in  some  way  leads  to  diabetes,  is  produced  in  the  islets  of 
Langerhans  (see  fig.  399,  p.  503),  but  if,  as  Dale  and  others  have 
shown,  these  are  only  phases  in  the  life-history  of  the  secreting  acini, 
it  is  difficult  to  accept  this  exclusive  view. 


CHAPTEE  XXX III 


THE   LIVER 


The  Liver,  the  largest  gland  in  the  body,  situated  in  the  abdomen  on 
the  right  side  chietiy,  is  an  extremely  vascular  organ,  and  receives  its 
supply  of  blood  from  two  distinct  sources,  viz.,  from  the  portal  vein 
and  from  the  hepatic  artery,  while  the  blood  is  returned  from  it  into 


Fin.  40-2.— The  under  surface  of  the  liver,  i;.  h.,  gall-bladder  ;  h.  d.,  common  bile-duct ;  h.  a.,  hepatic 
artery;  v.  p.,  portal  vein  ;  l.  y.,  lobulus  ciuadratus  ;  L.  s.,  lobulus  spigelii ;  l.  c.,  lobuluscaudatus  ; 
D.  v.,  ductus  venosus  ;  u.  v.,  umbilical  vein.     (Noble  Smith.) 

the  vena  cava  inferior  by  the  hepatic  veins.  Its  secretion,  the  hile,  is 
conveyed  from  it  by  the  hepatic  duct,  either  directly  into  the  intestine, 
or,  when  digestion  is  not  going  on,  into  the  cystic  duct,  and  thence 
into  the  gall-bladder,  where  it  accumulates  until  required.  The 
portal  vein,  hepatic  artery,  and  hepatic  duct  branch  together  through- 
out the  liver,  while  the  hepatic  veins  and  their  tributaries  run  by 
themselves. 

On  the  outside,  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over 
the  whole  surface  of    the  organ.     At   the    transverse   fissure  it   is 
'''  2    Iv 


514 


THE    LIVER 


[CH.  XXXIII. 


merged  in  the  areolar  investment  called  Glisson's  capsule,  which, 
surroundini,'  the  portal  vein,  hepatic  artery,  and  hepatic  duct,  accom- 
panies them  in  their  Ijranchings  through  the  substance  of  the  liver. 

Strudarc. — The  liver  is  in  origin  a  tubular  gland,  but  as  develop- 
ment progresses  it  soon  loses  all  resemblance  to  the  tubular  'glands 
found  elsewhere.  It  is  made  up  of  small  roundish  or  oval  portions 
called  lobules,  each  of  which  is  about  ^  of  an  inch  (about  1  mm.)  in 
diameter,  and  composed  of  the  liver  cells,  between  which  the  blood- 
vessels and  bile-vessels  ramify.  The  hepatic  cells  (fig.  406),  which 
form  the  glandular  or  secreting  part  of  the  liver,  are  of  a  spheroidal 

form,  somewhat  polygonal  from 
mutual  pressure,  about  g^  to 
-Y-^jfij  inch  (about  3V  to  -^  mm.) 
in  diameter,  possessing  a  nuc- 
leus, sometimes  two.  The  cell 
protoplasm  contains  numerous 
fatty  particles,  as  well  as  a 
variable  amount  of  glycogen. 
They  are  held  together  by  a 
very  delicate  sustentacular 
tissue,  continuous  with  the 
inter-lobular  connective  tissue. 
To  understand  the  distri- 
bution of  the  blood-vessels  in 
the  liver,  it  will  be  well  to 
trace,  first,  the  two  blood- 
vessels which  enter,  and  the 
duct  which  leaves  the  organ 
on  the  under  surface  at  the 
transverse  fissure,  viz.,  the 
portal  vein,  hepatic  artery,  and 
hepatic  duct.  As  before  re- 
marked, all  three  rim  in  com- 
pany, and  their  appearance  on 
longitudinal  section  is  shown  in  fig.  403.  Eunning  together  through 
the  substance  of  the  liver,  they  are  contained  in  small  channels  called 
portal  canals,  their  immediate  investment  being  a  sheath  of  areolar 
tissue  continuous  with  Glisson's  capsule. 

To  take  the  distribution  of  the  portal  vein  first : — In  its  course 
through  the  liver  this  vessel  gives  off  small  branches  which  divide 
and  subdivide  between  the  lobules  surrounding  them  and  limiting 
them,  and  from  this  circumstance  called  inter -lohn\a.T  veins.  From 
these  vessels  a  dense  capillary  network  is  prolonged  into  the  substance 
of  the  lobule,  and  this  network  converges  to  a  single  small  vein, 
occupying  the  centre  of  the  lobule,  and  hence  called  intra-\ohu.\a.T. 


Fig.  403. — Longitudinal  section  of  a  portal  canal,  con- 
taining a  portal  vein,  hepatic  artery  and  hejjatic 
duct,  from  the  pig.  p,  branch  of  vena  portae, 
situated  in  a  portal  canal  amongst  the  lobules  of 
the  liver;  I,  I,  and  giving  off  interlobular  veins; 
there  are  also  seen  within  the  large  portal  vein 
numerous  orifices  of  interlobular  veins  arising 
directly  from  it ;  a,  hepatic  artery ;  d,  bile  duct. 
X  5.    (Kiernan.) 


CH.  XXXIII.] 


STRUCTURE   OF   THE   LlVEIi 


515 


This  arrangement  is  well  seen  in  fig.  404,  which  represents  a  section 

of  a  small  ])ioco  of  an  injocted  livor. 


Fid.  404.— Caiiillary  network  of  the  lobules  of  tlie  rabbit's  liver.  The  figure  is  taken  from  a  very 
successful  injection  of  the  liver  veins,  made  by  Harting  :  it  shows  nearly  the  whole  of  two  lobules, 
and  parts  of  three  others  ;  p,  interlobular  (portal)  branches  running  in  the  interlobular  spaces  ;  h, 
intralobular  (hepatic)  veins  occupying  the  centre  of  the  lobules.  The  interlobular  and  intralobular 
vessels  are  connected  by  radiating  capillaries,     x  45.     (KuUiker.) 

The  small  intra-lohiilsiT  veins  discharge  their  contents  into  veins 
called  SM6-lobular  (h  h  h,  fig.  405);  while  these,  again,  by  their  union. 


'^^. 


Fio.  405. — Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic  vein,  from 
the  pig.  H,  hepatic  venous  trunk,  against  which  the  sides  of  the  lobules  (i)  are  applied;  h,  h,  h, 
sublobular  hepatic  veins,  on  which  the  bases  of  the  lobules  rest,  and  through  the  coats  of  which 
they  are  seen  as  polygonal  figures ;  i,  mouth  of  the  intralobular  veins,  opening  into  the  sublobular 
veins  ;  i',  intralobular  veins  shown  passing  up  the  centre  of  some  divided  lobules  ;  I,  I,  cut  surface  of 
th«  liver;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  jjolygonal  bases  of  the  lobules, 
X  5.    (Kieman.) 


516 


THE   LIVEK 


[CH.  XXXIII. 


form  the  main  branches  of  the  hepatic  veins,  which  leave  the  posterior 
border  of  the  liver  to  end  by  two  or  three  principal  trunks  in  the 
inferior  vena  cava,  just  before  its  passage  through  the  diaphragm. 

The  sub-ldbular  and  hepatic  veins,  unlike  the 
portal  vein  and  its  companions,  have  little 
or  no  areolar  tissue  around  them,  and  their 
coats  are  very  thin. 

The  hepatic  artery,  the  chief  function  of 
which  is  to  distribute  blood  for  nutrition 
to  Glisson's  capsule,  the  walls  of  the  ducts 
and  blood-vessels,  and  other  parts  of  the 
liver,  is  distributed  in  a  very  similar  manner 
to  the  portal  vein,  its  blood  being  returned 
by  small  branches  which  pass  into  the  capil- 
lary plexus  of  the  lobules  which  connects 
the  inter-  and  m^ra-lobular  veins. 

The  hepatic  duct  divides  and  subdivides 
in  a  manner  very  like  that  of  the  portal  vein 
and  hepatic  artery,  the  larger  branches  being 
lined  by  columnar,  and  the  smaller  by  small 
polygonal  epithelium. 

The  bile  capillaries  commence  between 
the  hepatic  cells,  and  are  bounded  by  a  deli- 
cate membranous  wall  of  their  own.  They 
are  always  bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated 
from  the  nearest  blood  capillary  by  at  least  the  breadth  of  one  cell 
(figs.  406  and  407). 


Fio.  406.— Portion  of  a  lobule  of 
liver,  a,  bile  capillaries  be- 
tween liver-cells,  the  network 
in  which  is  well  seen ;  b,  blood 
capillaries,  x  350.  (Klein 
and  Noble  Smith.) 


Fio.  407. — Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months  old.  Both  figures 
represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule.  The  red  corpuscles  of 
the  blood  are  recognised  by  their  circular  contour  ;  vp,  corresponds  to  an  interlobular  vein  in 
immediate  proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts,  to  which,  at  the  lower 
part  of  the  figures,  the  much  larger  hepatic  cells  suddenly  succeed.     (E.  Hering.) 

To  demonstrate  the  intercellular  network  of  bile  capillaries, 
Chrzonszezewsky  employed  a  method  of  natural  injection.  A 
saturated  aqueous  solution  of  sulph-indigotate  of  soda  is  introduced 


CH.  xxxm.] 


THE   LIVER -CELLS 


517 


into  the  circulation  of  dogs  and  pigs  by  the  jugular  vein.  The 
animals  are  killed  an  hour  and  a  half  afterwards,  and  the  blood-vessels 
washed  free  from  blood,  or  injected  with  gelatin  stained  with  carmine. 
The  bile-ducts  are  then  seen  filled  with  blue,  and  the  blood-vessels 
with  red  material.  If  the  animals  are  killed  sooner  than  this,  the 
pigment  is  found  within  the  hepatic  cells,  thus  demonstrating  it  was 
through  their  agency  that  the  canals  were  filled. 

Pfliiger  and  Kupffer  have  since  this  shown  that  the  relation 
between  the  hepatic  cells  and  the  bile  canaliculi  is  even  more 
intimate,  for  they  have  demonstrated  the  existence  of  vacuoles  in  the 
cells  communicating  by  minute  intracellular  channels  with  the  adjoin- 
ing bile  canaliculi   (fig.    408).     It   is  important  to  notice  that  the 


Fig.  408. — Sketches  illustrating  the  mode  of  commencement  ol  the  bile  canaliculi  withiu  the  liver- 
cells  (Heidenhain,  after  Kupfter).    A,  rabbit's  liver,  injected  from  hepatic  duct  with  Berlin  blue. 

The  intercellular  canaliculi  give  off  minute  twigs  which  penetrate  into  the  liver-cells,  and  there 
terminate  in  vacuole-like  enlargements.  B,  frog's  liver  naturally  injected  witli  sulph-indigotate  of 
soda.    A  similar  aj)pearance  is  obtained,  but  the  communicating  twigs  are  ramified. 

bile  canaliculi  are  always  separated  by  at  least  a  portion  of  a  cell  from 
the  nearest  blood  capillaries,  and  that  the  formation  of  bile  is  no  mere 
transudation  from  the  blood  or  lymph.  The  liver-cells  take  certain 
materials  from  the  plasma  and  elaborate  the  constituents  of  the  bile, 
the  bile-salts  and  the  bile  pigments.  There  can  be  no  doubt  that 
these  substances  are  formed  by  the  hepatic  cells,  for  they  are  not 
found  in  the  blood  nor  in  any  other  organ  or  tissue ;  and  after  extirpa- 
tion of  the  liver  they  do  not  accumulate  in  the  blood. 

Intracellular  canaliculi  in  the  liver-cells  are  not  unique.  Eecent 
research  by  Golgi's  method  has  shown  that  in  the  salivary  and 
gastric  glands,  and  in  the  pancreas,  there  is  a  similar  condition. 

Schiifer  has  further  shown  that  the  Kver-cells  contain  not  only 
the  intracellular  bile  canaliculi,  but  also  intracellular  blood  canaliculi 
passing  into  the  cells  from  the  capillaries  between  them.  These 
are  too  minute  to  admit  blood-corpuscles. 


518  THE   LIVER  [CH.  XXXIIl. 

The  Gall-bladder  (g.  b.,  fig.  402)  is  a  pear-shaped  bag,  attached  to 
the  under  surface  of  the  liver.  Its  smaller  end  contracts  into  the 
cystic  duct.  Its  wall  is  constructed  of  three  coats.  (1)  Externally 
(excepting  that  part  which  is  in  contact  with  the  liver)  is  the  serous 
coat,  which  has  the  same  structure  as  the  peritoneum  with  which  it  is 
continuous.  Within  this  is  (2)  the  fibrous  or  areolar  coat,  with  which 
is  mingled  a  considerable  number  of  plain  muscular  fibres,  both 
longitudinal  and  circular.  (3)  Internally  the  gall-bladder  is  lined  by 
mucous  membrane  and  a  layer  of  columnar  epithelium.  The  gall- 
bladder and  all  the  main  biliary  ducts  are  provided  with  mucous 
glands,  which  open  on  their  internal  surface. 

Functions  of  the  Liver. 

The  functions  of  the  liver  are  connected  with  the  general  meta- 
bolism of  the  body,  especially  in  connection  with  the  metabohsm  of 
carbohydrates  (glycogenic  function) ;  and  in  connection  with  the 
metabolism  of  nitrogenous  material  (formation  of  urea  and  uric  acid). 
This  second  function  we  shall  discuss  with  the  urine.  The  third 
function  is  the  formation  of  bile,  which  it  will  be  convenient  to  take 
first. 

Bile. 

Bile  is  the  secretion  of  the  liver  which  is  poured  into  the  duo- 
denum :  it  has  been  collected  in  living  animals  by  means  of  a  biliary 
fistula ;  the  same  operation  has  occasionally  been  performed  in  human 
beings.  After  death  the  gall-bladder  yields  a  good  supply  of  bile 
which  is  more  concentrated  than  that  obtained  from  a  fistula. 

Bile  is  being  continuously  poured  into  the  intestine,  but  there 
is  an  increased  discharge  immediately  on  the  arrival  of  food  in  the 
duodenum ;  there  is  a  second  increase  in  secretion  a  few  hours  later. 

Though  the  chief  blood  supply  of  the  liver  is  by  a  vein  (the 
portal  vein),  the  amount  of  blood  in  the  liver  varies  with  its  needs, 
being  increased  during  the  periods  of  digestion.  This  is  due  to  the 
fact  that  in  the  area  from  which  the  portal  vein  collects  blood — 
stomach,  intestine,  spleen,  and  pancreas  —  the  arterioles  are  all 
dilated,  and  the  capillaries  are  thus  gorged  with  blood.  The  active 
peristalsis  of  the  intestine  and  the  pumping  action  of  the  spleen  are 
additional  factors  in  driving  more  blood  onwards  to  the  liver. 

The  bile  is  secreted  from  the  portal  blood  at  much  lower  pressure 
than  one  finds  in  glands  such  as  the  salivary  glands,  the  blood  supply 
of  which  is  arterial.  Heidenhain  found  that  the  pressure  in  the  bile 
duct  of  the  dog  averages  15  mm.  of  mercury,  which  is  nearly  double 
that  in  the  portal  vein.  This  fact  illustrates  the  general  truth  that 
secretion  is  not  a  mere  process  of  passive  filtration,  but  that  the  cells 
exercise  secretory  force. 


CH.  XXXITI.]  THE    BILE  519 

The  second  increase  in  the  flow  of  bile — that  which  occurs  some 
hours  after  the  arrival  of  the  semi-digested  f(jod  (chyme)  in  the 
intestine — appears  to  be  due  to  the  effect  of  the  digestive  products 
carried  by  the  blood  to  the  liver,  stimulating  the  hepatic  cells  to 
activity:  this  is  supported  by  the  fact  that  protein  food  increases 
the  quantity  of  bile  secreted,  whereas  fatty  food  which  is  absorbed, 
not  by  the  portal  vein,  but  by  the  lacteals,  has  no  such  effect.  It  is, 
however,  possible  that  the  increased  flow  is  due  to  the  action  of 
secretin,  for  this  material  stimulates  the  liver  as  well  as  the 
pancreas. 

The  chemical  process  by  which  the  constituents  of  the  bile  are 
formed  is  obscure.  We,  however,  know  that  the  biliary  pigment  is 
produced  by  the  decomposition  of  htemoglobin.  Bilirubin  is,  in  fact, 
identical  with  the  iron-free  derivative  of  hsemoglobin  called  haema- 
toidin,  which  is  found  in  the  form  of  crystals  in  old  blood-clots  such 
as  occur  in  the  brain  after  cerebral  haemorrhage  (see  p.  443). 

An  injection  of  hfemoglobin  into  the  portal  vein  or  of  substances 
such  as  water  which  liberate  haemoglobin  from  the  red  blood-corpuscles 
produces  an  increase  of  bile  pigment.  If  the  spleen  takes  any  part 
in  the  elaboration  of  bile  pigment,  it  does  not  proceed  so  far  as  to 
liberate  hsemoglolnn  from  the  corpuscles.  No  free  hsemoglobin  is 
discoverable  in  the  blood  plasma  in  the  splenic  vein. 

The  amount  of  bile  secreted  is  differently  estimated  by  different 
observers ;  the  amount  secreted  daily  in  man  varies  from  500  c.c.  to 
a  litre  (1000  c.c). 

The  constituents  of  the  bile  are  the  bile  salts  proper  (tauro- 
cholate  and  glycocholate  of  soda),  the  bile  pigments  (bilirubin, 
biliverdin),  a  mucinoid  substance,  small  quantities  of  fats,  soaps, 
cholesterin,  lecithin,  urea,  and  mineral  salts,  of  which  sodium  chloride 
and  the  phosphates  of  iron  and  calcium  are  the  most  important. 

Bile  is  a  yellowish,  reddish-brown,  or  green  fluid,  according  to  the 
relative  preponderance  of  its  two  chief  pigments.  It  has  a  musk-like 
odour,  a  bitter-sweet  taste,  and  a  neutral  or  faintly  alkaline  reaction. 

The  specific  gravity  of  human  bile  from  the  gall-bladder  is  1026 
to  1032;  that  from  a  fistula,  1010  to  1011.  The  greater  concentra- 
tion of  gall-bladder  bile  is  partly  but  not  wholly  explained  by  the 
addition  to  it  from  the  walls  of  that  cavity  of  the  mucinoid  material 
it  secretes. 

The  amount  of  solids  in  gall-bladder  bile  is  from  9  to  14  per 
cent.,  in  fistula  bile  from  1"5  to  3  per  cent.  The  following  table  shows 
that  this  low  percentage  of  solids  is  almost  entirely  due  to  want  of  bile 
salts.  This  can  be  accounted  for  in  the  way  first  suggested  by  Schiff 
— that  there  is  normally  a  bile  circulation  going  on  in  the  body,  a 
large  quantity  of  the  bile  salts  that  pass  into  the  intestine  being  first 
split  up,  then    reabsorbed  and  again  secreted.     Such  a  circulation 


520 


THE    LIVER 


[CH.  XXXIII. 


would  obviously  be  impossible  in  cases  where  all  the  bile  is  dis- 
charged to  the  exterior. 

The  following  table  gives  some  important  analyses  of  human  bile : — 


Constituents. 

Fistula  bile 

(healthy  woman. 

Copeman  and 

Winston). 

Fistula  bile  (case 
of  cancer.     Yeo 
and  Herroun). 

Normal  bile 
(Prerichs). 

Sodium  glycocholate 
Sodium  tauroc'holate 
Cholesterin,  lecithin,  fat  . 
Mucinoid  material    . 
Pigment   .... 
Inorganic  salts 

1        0-6280     1 

0-0990 
0-1725 
0-0725 
0-4510 

0-165 
0-055 
0-038 

1         0-148 

0-878 

1          9-14 
1-18 
2-98 
0-78 

Total  solids 
Water  (by  difference) 

1-4230 
98-5570 

1-284 
98-716 

14-08 
85-92 

Bile  Mucin. — There  has  baen  considerable  diversity  of  opinion 
as  to  whether  bile  mucin  is  really  mucin.  The  most  recent  work  in 
Hammarsten's  laboratory  shows  that  differences  occur  in  different 
animals.  Thus  in  the  ox  there  is  very  little  true  mucin,  but  a  great 
amount  of  nucleo-protein ;  in  human  bile,  on  the  other  hand,  there 
is  very  little  if  any  nucleo-protein ;  the  mucinoid  material  present 
there  is  really  mucin. 

The  Bile  Salts. — The  bile  contains  the  sodium  salts  of  complex 
amino-acids  called  the  bile  acids.  The  two  acids  most  frequently 
found  are  glycocholic  and  taurocholic  acids.  The  former  is  the  more 
abundant  in  the  bile  of  man  and  herbivora ;  the  latter  in  carnivorous 
animals,  like  the  dog.  The  most  important  difference  between  the 
two  acids  is  that  taurocholic  acid  contains  sulphur,  and  glycocholic 
acid  does  not. 

Glycocholic  acid  (C^eH^gNOg)  is  by  the  action  of  dilute  acids  and 
alkalis,  and  also  in  the  intestine,  hydrolysed  and  split  into  glycine  or 
amino-acetic  acid  and  cholalic  acid. 

C.^gH^gNOg   +    H.,0    =    CoH.NO,   +    C.,,H,(,0,. 

[Glycocholic  acid.]  [Glycine.]"  [Cholalic  acid.] 

The  glycocholate  of  soda  has  the  formula  C26H4.,]SraNOg. 
Taurocholic  acid  (C.26H45NO-S)  similarly  splits  into  taurine  or 
amino-isethionic  acid  and  cholalic  acid. 


C,,H,,NO.S    +    H.3O 

[Taurocholic  acid.] 


CH.NO.S    +    C,,,H,,0. 


[Taurine.] 


[Cholalic  acid.] 


The  taurocholate  of  soda  has  the  formula  CoGH44lSraN07S, 

The  colour  reaction  called  Pettenkofer's  reaction  is  due  to  the 


CH.  XXXIII.]  THE   BILE  521 

presence  of  cholalic  acid.  Small  quantities  of  cane  sugar  and  strong 
sulphuric  acid  are  added  to  the  bile.  The  sulphuric  acid  acting  on 
sugar  forms  a  small  quantity  of  a  substance  called  furfuraldehyde,  in 
addition  to  other  products.  The  furfuraldehydo  gives  a  brilliant 
purple  colour  with  cholalic  acid. 

The  Bile  Pigments — The  two  chief  bile  pigments  are  bilirubin 
and  biliverdin.  Bile  which  contains  chiefly  the  former  (such  as  dog's 
bile)  is  of  a  golden  or  orange-yellow  colour,  while  the  bile  of  many 
herbivora,  which  contains  chiefly  biliverdin,  is  either  green  or  bluish- 
green.  Human  bile  is  generally  described  as  containing  chiefly 
bilirubin,  but  there  have  been  some  cases  described  in  which  biliverdin 
was  in  excess.  The  bile  pigments  show  no  absorption  bands  with 
the  spectroscope ;  they  originate  from  the  blood  pigment  (see  p.  519). 

Bilirubin  has  the  formula  C^gHigNoOg :  it  is  thus  an  iron-free 
derivative  of  haemoglobin.  The  iron  is  apparently  stored  up  in  the 
liver  cells,  perhaps  for  future  use  in  the  manufacture  of  new  haemo- 
globin.    The  bile  contains  only  a  trace  of  iron. 

Biliverdin  has  the  formula  CjeH^gN.^O^  {i.e.,  one  atom  of  oxygen 
more  than  in  bilirubin):  it  may  occur  as  such  in  bile;  it  may  be 
formed  by  simply  exposing  red  bile  to  the  oxidising  action  of  the 
atmosphere ;  or  it  may  be  formed  as  in  G-melin's  test  by  the  more 
vigorous  oxidation  produced  by  fuming  nitric  acid. 

Gmelin's  test  consists  in  a  play  of  colours — green,  blue,  red,  and 
finally  yellow,  produced  by  the  oxidising  action  of  fuming  nitric  acid 
(that  is,  nitric  acid  containing  nitrous  acid  in  solution).  The  end  or 
yellow  product  is  called  clioletelin,  Q^^-^^X)^. 

Hydrobilirubin. — If  a  solution  of  bilirubin  or  biliverdin  in  dilute 
alkali  is  treated  with  sodium  amalgam  or  allowed  to  putrefy,  a 
brownish  pigment,  which  is  a  reduction  product,  is  formed  called 
hydrobilirubin,  C32H4oN"407.  With  the  spectroscope  it  shows  a  dark 
absorption  band  between  h  and  F,  and  a  fainter  band  in  the  region 
of  the  D  line. 

This  substance  is  interesting  because  a  similar  substance  is  formed 
from  the  bile  pigment  by  reduction  processes  in  the  intestine,  and 
constitutes  stercobilin,  the  pigment  of  the  faeces.  Some  of  this  is 
absorbed  and  ultimately  leaves  the  body  in  the  urine  as  one  of  its 
pigments  called  urobilin.  A  small  quantity  of  urobilin  is  sometimes 
found  preformed  in  the  bile.  The  identity  of  urobilin  and  stercobihn 
has  been  frequently  disputed,  but  the  recent  work  of  Garrod  and 
Hopkins  has  confirmed  the  old  statement  that  they  are  the  same 
substance  with  different  names.  Hydrobilirubin  differs  from  urobilin 
in  containing  more  nitrogen  (9"2  instead  of  4*1  per  cent.). 

Cholesterin. — This  substance  is  contained  not  only  in  bile,  but 
very  largely  in  nervous  tissues.  Like  lecithin,  it  is  an  abundant 
constituent  of  the  white  substance  of  Schwann,     It   is  found  also 


522  THE   LIVER  [CII.  XXXIII. 

in  blood-corpuscles.  lu  bile  it  is  normally  present  in  small  quanti- 
ties only,  but  it  may  occur  in  excess,  and  form  the  concretions 
known  as  gall-stones,  which  are  usually  more  or  less  tinged  with 
bilirubin. 

Though  its  solubihties  remind  one  of  a  fat,  cholesterin  is  not  a 
fat.  It  is,  in  fact,  chemically  speaking,  a  monatomic  alcohol  probalily 
of  the  terpene  series.     Its  formula  is  C.,7H45HO. 

From  alcohol  or  ether  containing  water  it  crystallises  in  the  form 
of  rhombic  tables,  which  contain  one  molecule  of  water  of  crystal- 
lisation :    these   are   easily  recognised 
under  the  microscope  (see  fig.  409). 

It  gives  the  following  colour 
tests : — 

1.  Heated  with  sulphuric  acid  and 
water  (5  : 1),  the  edges  of  the  crystals 
turn  red. 

2.  A  solution  of  cholesterin  in 
chloroform,  shaken  with  an  equal 
amount  of  concentrated  sulphuric  acid, 
turns  red,  and  ultimately  purple,  the 
subjacent  acid  acquiring  a  green  fluores- 

FiG.409.— CostaUinescalesofcholesterm.        COnce.       (Salkowski's  reaction.) 

3.  If  acetic  anhydride  is  added  to 
a  chloroformic  solution  of  cholesterin,  and  then  sulphuric  acid,  drop 
by  drop,  a  red  coloration,  which  changes  to  bluish-green,  is  produced. 
(Liebermann's  reaction). 

The  physiological  significance  of  cholesterin  is  entirely  unknown. 

A  substance  called  iso-cholesterin,  isomeric  with  ordinary  chole- 
sterin, is  found  in  the  fatty  secretion  of  the  skin  (sebum) ;  it  is 
largely  contained  in  the  preparation  called  lanoline  made  from  sheep's- 
wool  fat.  It  does  not  give  Salkowski's  reaction  with  chloroform  and 
sulphuric  acid  just  described. 

The  Uses  of  Bile. — Bile  is  doubtless,  to  a  certain  extent, 
excretory.  Some  state  that  it  has  a  slight  action  on  fats  and  carbo- 
hydrates, but  its  principal  action  is  as  a  coadjutor  to  the  pancreatic 
juice  (especially  in  the  digestion  of  fat).  In  some  animals  it  has  a 
feeble  diastatic  power. 

Bile  is  said  to  be  a  natural  antiseptic,  lessening  the  putrefactive 
processes  in  the  intestine.  This  is  very  doubtful.  Though  the  bile 
salts  are  weak  antiseptics,  the  bile  itself  is  readily  putrescible,  and 
the  power  it  has  of  diminishing  putrescence  in  the  intestine  is  due 
chiefly  to  the  fact  that  by  increasing  absorj^tion  it  lessens  the  amount 
of  putrescible  matter  in  the  bowel. 

When  the  bile  meets  the  chyme  the  turbidity  of  the  latter  is 
increased  owing  to  the  precipitation  of  unpeptonised  protein.     Tliis 


ctt.  XXXIII.]  THE  bile:  523 

is  an  action  due  to  the  bile  salts,  and  it  has  been  surmised  that  this 
conversion  of  the  chyme  into  a  more  viscid  mass  is  to  hinder  some- 
w^hat  its  progress  through  the  intestines ;  it  clings  to  the  intestinal 
wall,  thus  allowing  absorption  to  take  place. 

Bile  is  alkaline ;  it  therefore  assists  the  pancreatic  juice  in  neutral- 
ising the  acid  mixture  that  leaves  the  stomach. 

Bile  assists  the  absorption  of  fats,  as  we  shall  see  in  studying  that 
subject.     It  is  also  a  solvent  of  fatty  acids. 

We  have  seen  that  fistula  bile  is  poor  in  solids  as  compared  with 
normal  bile,  and  that  this  is  explained  on  the  supposition  that  the 
normal  bile  circulation  is  not  occurring — the  liver  cannot  excrete 
what  it  does  not  receive  back  from  the  intestine.  Schiff  was  the  first 
to  show  that  if  the  bile  is  led  back  into  the  duodenum,  or  even  if  the 
animal  is  fed  on  bile,  the  percentage  of  solids  in  the  bile  excreted  is 
at  once  raised.  It  is  on  these  experiments  that  the  theory  of  a  bile 
circulation  is  mainly  founded.  The  bile  circulation  relates,  however, 
chiefly,  if  not  entirely,  to  the  bile  salts :  they  are  found  but  sparingly 
in  the  fgeces ;  they  are  only  represented  to  a  slight  extent  in  the  urine : 
hence  it  is  calculated  that  seven-eighths  of  them  are  re-absorbed  from 
the  intestine.  Small  quantities  of  cholalic  acid,  taurine,  and  glycine 
are  found  in  the  faeces ;  the  greater  part  of  these  products  of  the  decom- 
position of  the  bile  salts  is  taken  by  the  portal  vein  to  the  Liver,  where 
they  are  once  more  synthesised  into  the  bile  salts.  Some  of  the  taurine 
is  absorbed  and  excreted  as  tauro-carbamic  acid  in  the  urine.  Some  of 
the  absorbed  glycine  may  be  excreted  as  urea  or  uric  acid.  The 
cholesterin  and  mucus  are  found  in  the  faeces ;  the  pigment  is  changed 
into  stercobilin  (see  p.  521). 

The  bile-expelling  mechanism  must  be  carefully  distinguished 
from  the  bile-secreting  action  of  the  liver-cells.  The  bile  is  forced 
into  the  ducts,  and  ultimately  into  the  duodenum,  by  the  pressure  of 
newly-formed  bile  pressing  on  that  previously  in  the  ducts,  and  this 
is  assisted  by  the  contraction  of  the  plain  muscular  fibres  of  the 
larger  ducts  and  gall-bladder,  which  occurs  reflexly  when  the  food 
enters  the  duodenum.  In  cases  of  obstruction,  as  by  a  gall-stone,  in 
the  ducts,  this  action  becomes  excessive,  and  gives  rise  to  the  intense 
pain  known  as  hepatic  colic. 

Many  cholagogues  (bile-drivers),  such  as  calomel,  act  on  the  bile- 
expelling  mechanism  and  increase  the  peristalsis  of  the  muscular 
tissue ;  they  do  not  really  cause  an  increased  formation  of  bile. 

Jaundice. — The  commonest  form  of  jaundice  is  produced  by 
obstruction  in  the  bile  ducts  preventing  the  bile  entering  the 
intestine.  A  very  small  amount  of  obstruction,  for  instance,  a 
plug  of  mucus  produced  in  excess  owing  to  inflammatory  pro- 
cesses, will  often  be  sufficient,  as  the  bile  is  secreted  at  such  low 
pressure.     Under  these  circumstances,  the  faeces  are  whitish  or  clay 


524  THE   LIVEE  [CH.  XXXIII. 

coloured,  and  the  bile  passing  backwards  into  the  lymph,*  enters 
the  blood  and  is  thus  distributed  over  the  body,  causing  a  yellow 
tint  in  the  skin  and  mucous  membranes,  and  colouring  the  urine 
deeply. 

In  some  cases  of  jaundice,  however  {e.g.,  produced  by  various 
poisons),  there  is  no  obvious  obstruction;  the  causes  of  non- 
obstructive, or  blood -jaundice,  form  a  pathological  problem  of  some 
interest.  A  few  years  ago  it  was  believed  that  the  bile  pigment  was 
actually  produced  in  the  blood.  But  all  recent  work  shows  that  the 
liver  is  the  only  place  where  production  of  bile  occurs,  and  that  in  all 
cases  of  so-called  non-obstructive  jaundice,  the  bile  is  absorbed  from 
the  liver.  There  may  be  obstruction  present  in  the  smaller  ducts,  or 
the  functions  of  the  liver  may  be  so  upset  that  the  bile  passes  into 
the  lymph  even  when  there  is  no  obstruction. 

The  Glycogenic  Function  of  the  Liver, 

The  important  fact  that  the  liver  normally  forms  sugar,  or  a 
substance  readily  convertible  into  it,  was  discovered  by  Claude 
Bernard  in  the  following  way:  he  fed  a  dog  for  seven  days  with  food 
containing  a  large  quantity  of  sugar  and  starch;  and,  as  might  be 
expected,  found  sugar  in  both  the  portal  and  hepatic  blood.  But 
when  this  dog  was  fed  with  meat  only,  to  his  surprise,  sugar  was  still 
found  in  the  blood  of  the  hepatic  veins.  Eepeated  experiments  gave 
invariably  the  same  result ;  no  sugar  was  found,  under  a  meat  diet, 
in  the  portal  vein,  if  care  were  taken,  by  applying  a  ligature  on  it  at 
the  transverse  fissure,  to  prevent  reflux  of  blood  from  the  hepatic 
venous  system.  Bernard  found  sugar  also  in  the  substance  of  the 
liver.  It  thus  seemed  certain  that  the  liver  formed  sugar, even  when, 
from  the  absence  of  carbohydrates  in  the  food,  none  could  have  been 
brought  directly  to  it  from  the  stomach  or  intestines. 

Bernard  found,  subsequently,  that  a  liver,  removed  from  the 
body,  and  from  which  all  sugar  had  been  completely  washed  away  by 
injecting  a  stream  of  water  through  its  blood-vessels,  contained  sugar 
in  abundance  after  the  lapse  of  a  few  hours.  This  post-mortem  pro- 
duction of  sugar  was  a  fact  which  could  only  be  explained  on  the 
supposition  that  the  liver  contained  a  substance  readily  convertible 
into  sugar;  and  this  theory  was  proved  to  be  correct  by  the  dis- 
covery of  a  substance  in  the  liver  allied  to  starch,  and  now  termed 
glycogen  or  animal  starch.  We  are  thus  led  to  the  conclusion  that 
glycogen  is  formed  first  and  stored  in  the  liver  cells,  and  that  the 
sugar,  when  present,  is  the  result  of  its  transformation. 

Source  of  Glycogen. — Although  the  greatest  amount  of   glycogen 

*  The  absorption  is  by  the  lymph,  because  if  jaundice  is  produced  in  an 
animal  by  ligature  of  the  bile  duct,  it  will  cease  when  the  thoracic  duct  is  tied. 


CH.  XXXIII.]  GLYCOGENIC    FUNCTION  525 

is  produced  by  the  liver  upon  a  diet  of  starch  or  sugar,  a  certain 
quantity  is  produced  upon  a  protein  diet.  It  must,  then,  be  produced 
by  protoplasmic  activity  within  the  cells.  The  glycogen  when  stored 
in  the  liver  cells  may  readily  be  demonstrated  in  sections  of  liver 
containing  it  by  its  reaction  (red  or  port-wine  colour)  with  iodine,  and 
moreover,  when  the  hardened  sections  are  soaked  in  water  in  order  to 
dissolve  out  the  glycogen,  the  protoplasm  of  the  cell  is  so  vacuolated 
as  to  appear  little  more  than  a  framework.  In  the  liver  of  a  hiber- 
nating frog  the  amount  of  glycogen  stored  up  in  the  outer  parts  of 
the  liver  cells  is  very  considerable. 

Averayp,  Amount  of  Glycogen  in  tha  Liver  of  Doys  under  various  Diets  (Pavy). 

Amount  of 
Diet.  Glycogen  in  Liver. 

Animal  food         ........       7*19  per  cent. 

Animal  food  with  sugar  (about  1-lb  of  sugar  daily)     .     14*5  ,, 

Vegetable  diet  (potatoes,  with  bread  or  barley-meal) .     17  "23        ,, 

The  dependence  of  the  formation  of  glycogen  on  the  kind  of  food 
taken  is  also  well  shown  by  the  following  results,  obtained  by  the 
same  experimenter : — 

Average  Quantity  of  Glycoyen  found  in  the  Liver  of  Rahhits  after  Fastiny,  and 
after  a  Diet  of  Starch  and  Suyar  respectively. 

Average  amount  of 
Glycogen  in  Liver. 

After  fasting  for  three  days Practically  absent. 

,,     diet  of  starch  and  grape-sugar      .         .         .     15 '4  per  cent. 
,,  ,,      cane-sugar  .....     16'9         ,, 

The  diet  most  favourable  to  the  production  of  a  large  amount  of 
glycogen  is  a  mixed  diet  containing  a  large  amount  of  carbohydrate, 
but  with  some  portein.  Fats  taken  in  as  food  do  not  increase  the 
amount  of  glycogen  in  the  cells,  although  glycerin  may  do  so. 

Destination  of  Glycogen. — There  are  two  chief  theories  as  to  the 
destination  of  hepatic  glycogen.  (1.)  That  the  glycogen  is  converted 
into  sugar  during  life  by  the  agency  of  a  ferment  (liver  diastase)  also 
formed  in  the  liver ;  and  that  the  sugar  is  conveyed  away  by  the 
blood  of  the  hepatic  veins,  to  undergo  combustion  in  the  tissues.  (2.) 
That  the  conversion  into  sugar  only  occurs  after  death,  and  that 
during  life  no  sugar  exists  in  healthy  livers,  glycogen  not  undergoing 
this  transformation. 

The  first  view  is  that  of  Claude  Bernard,  and  has  been  adopted  by 
the  majority  of  physiologists.  The  second  view  is  that  of  Pavy: 
he  denies  that  the  liver  is  a  sugar-forming  organ,  he  regards  it  as  a 
sugar-destroying  organ;  the  sugar  is  stored  as  animal  starch,  but 
never  again  leaves  the  liver  as  sugar  during  life.  He  has  been  unable 
to  find  more  sugar  in  the  hepatic  blood  than  in  the  portal  blood. 
Other  observers  have  found  an  increase  in  the  sugar  of  the  blood 
leaving  {^the   liver,  but   the   estimation   of   sugar  in  a  fluid  rich  in 


526  THE   LIYER  [CH.  XXXIII. 

proteins  is  a  matter  of  great  difficulty.  Even  if  the  increase  is  so 
small  as  hardly  to  be  detected,  it  must  be  remembered  that  the 
whole  blood  of  the  body  passes  through  the  liver  about  once  a 
minute,  so  that  a  very  small  increase  each  time  would  mount  up  to 
a  large  total. 

Pavy  further  denies  that  i\iQ  post-mortem  formation  of  sugar  from 
glycogen  that  occurs  in  an  excised  liver  is  a  true  picture  of  what 
occurs  during  life,  but  is  due  to  a  ferment  which  is  only  formed  after 
death.  During  life,  he  regards  the  glycogen  as  a  source  of  other 
substances,  like  fat  and  protein.  It  is  certainly  a  fact  that  increase 
of  carbohydrate  food  leads  to  the  formation  of  fat  in  the  body  and  in 
the  liver-cells.  In  support  of  the  theory  that  glycogen  may  also  con- 
tribute to  the  formation  of  proteins,  he  has  shown  that  many  proteins 
contain  a  carbohydrate  radical. 

The  whole  question  is  under  keen  discussion  at  present.  "We 
may  state,  however,  that  the  prevalent  opinion  is  that  the  liver- 
cells  may  be  able  to  convert  part  of  the  store  of  glycogen  into  fat, 
but  that  most  of  the  glycogen  leaves  the  liver  as  sugar  (dextrose),  so 
justifying  the  name  (literally,  mother  substance  of  sugar)  given  to 
it  by  Bernard. 

Diabetes. — In  certain  disorders  of  metabolism,  excess  of  sugar 
occurs  in  the  blood,  and  leaves  the  body  by  the  urine  (jcjlycosuria). 
This  may  be  due  to  temj)orary  causes,  as  for  instance  in  what  is 
called  "  alimentary  glycosuria";  in  this  condition  the  diet  contains 
too  much  carbohydrate  for  the  liver  to  store  as  glycogen,  and  the 
excess  passes  into  the  blood;  it  is  most  readily  produced  in  conditions 
where  the  liver  is  inactive,  and  may  be  remedied  by  reducing  the 
carbohydrate  ingested,  or  by  improving  tlie  condition  of  the  liver. 
In  other  cases,  as  in  puncture  diabetes,  immediately  to  be  described, 
it  is  due  to  an  excessive  action  of  the  liver  cells  converting  glycogen 
into  sugar.  In  other  cases,  again,  it  is  due  to  an  inability  of  the 
organism  to  burn  {i.e.  utilise)  sugar,  and  this  is  the  usual  condition  in 
diabetes  mellitus  in  man.  A  similar  condition  may  be  produced  in 
animals  by  removal  of  the  pancreas.  In  most  of  these  cases  the 
diabetic  condition  may  be  removed  by  rigid  abstention  from  starchy 
and  saccharine  food.  In  other  cases  diet  makes  little  or  no  difference ; 
in  this  condition  the  sugar  must  come  from  the  metabolism  of  the 
protein  constituents  of  protoplasm ;  40  per  cent,  or  more  of  the 
katabolised  protein  may  leave  the  body  as  sugar,  certain  of  its 
cleavage  products  (for  instance,  alanine,  see  p.  597)  acting  as  inter- 
mediate sul)Stances  in  sugar  formation. 

The  principal  ways  in  which  diabetes  may  be  produced  in  animals 
are  the  following : — 

(1)  By  diabetic  ^juncture. — C.  Bernard  was  the  first  to  show  that 
injury  to  the  floor  of  the  fourth  ventricle  in  tlie  region  of  the  vaso- 


CH.  XXXIII.]  DIABETES  527 

motor  centre  leads  to  glycosuria.  In  man,  also,  disease  of  the  bulb  is 
frequently  associated  with  glycosuria.  These  observations  led  to  the 
erroneous  conclusion  that  diabetes  is  always  of  nervous  origin.  The 
diabetes  produced  in  this  way  cannot  be  wholly  due  to  vaso-motor 
disturbances,  but  is  more  probably  due  to  an  influence  on  the  nerves 
of  the  liver  which  control  its  glycogenic  function  (see  p.  528),  for  the 
glycosuria  only  occurs  when  the  liver  has  within  it  a  store  of  glycogen. 

(2)  By  exti'rpation  of  the  pancreas. — (See  also  p.  511).  It  is 
probable  that  in  diabetes,  the  oxidative  powers  of  the  body-cells  are 
lessened.  Nevertheless,  other  diseases  in  which  diminished  oxidation 
occurs  are  n(jt  necessarily  accompanied  with  glycosuria.  The  diffi- 
culty in  diabetes  probably  lies  in  an  impairment  of  the  capacity  of 
the  cells  of  the  body  to  prepare  the  sugar  for  oxidation.  In  this 
process  the  sugar  or  its  derivative  glycnronic  acid  is  split  into 
smaller  molecules  and  ultimately  into  water  and  carbon  dioxide. 
The  close  relationship  of  sugar  and  glycuronic  acid  is  shown 
by  the  following  formulae: — 

COH  COH 

(CHOH)^  (CHOH)^ 

CHoOH  COOH 

[Dextrose.]  [Glycuronic  acid.] 

That  is  two  hydrogen  atoms  in  the  CHoOH  group  are  replaced  by 
one  of  oxygen.  This  oxidation  is  readily  brought  about  in  the  body, 
and  glycuronic  acid  is  usually  found  in  diabetic  urine;  but  the 
further  oxidation  into  water  and  carbon  dioxide  is  a  more  difficult 
task,  because  it  involves  the  disruption  of  the  linkage  of  the  carbon 
atoms.  Perhaps  it  is  here  that  the  internal  secretion  of  the  pancreas 
is  effective.  This,  however,  is  at  present  a  mere  theory,  and  certainly 
Lepine's  idea  that  the  ferment  of  the  pancreatic  internal  secretion  is 
one  which  initiates  glycolysis  or  sugar-splitting  in  the  Hood,  has  been 
abundantly  disproved.  It  may  be  that  the  active  principle  of  the 
pancreatic  internal  secretion  stimulates  the  glycolytic  action  of  the 
tissue-cells. 

(3)  By  administration  of  phloridzin. — Many  poisons  produce 
temporary  glycosuria,  but  the  most  interesting  and  powerful  of  these 
is  phloridzin.  Phloridzin  is  a  glucoside,  but  the  sugar  passed  in  the 
urine  is  too  great  to  be  accounted  for  by  the  small  amount  of  sugar 
derivable  from  the  drug.  Besides  that,  phloretin,  a  derivative  of 
phloridzin,  free  from  sugar,  produces  the  same  results. 

Phloridzin  produces  diabetes  in  starved  animals,  or  in  those  in 
which  any  carbohydrate  store  must  have  been  got  rid  of  by  the 
previous  administration  of  the  same  drug.  Phloridzin-diabetes  is 
therefore  analogous  to  those  intense  forms  of  diabetes  in  man  in  which 
the  sugar  must  be  derived  from  protoplasmic  metabolism. 

A  puzzling  feature  is  the  absence  of  an  increase  of  sugar  in  the 


528  THE   LIVER  [CH.  XXXIII. 

blood;  if  the  phloridzin  is  directly  injected  into  one  renal  artery, 
sugar  rapidly  appears  in  the  secretion  of  that  kidney ;  the  sugar  is 
formed  within  the  kidney  cells  from  some  substance  in  the  blood, 
and  that  substance  is  probably  protein.  In  these  cases  the  ratio  of 
dextrose  to  nitrogen  in  the  urine  is  3"6  : 1 ;  if  such  a  ratio  occurs  in 
man  when  carbohydrates  are  absent  from  the  food,  a  very  serious 
condition  is  revealed ;  Graham  Lusk  calls  it  the  fatal  ratio. 

(4)  By  administration  of  adrenaline. — This  drug  also  produces  a 
diabetic  condition,  but  in  this  case  there  is  excess  of  sugar  in  the 
blood  also. 

Acetonaemia. — Death  in  diabetic  patients  is  usually  preceded  by 
deep  coma,  or  unconsciousness.  Some  poison  must  be  produced  that 
acts  soporifically  upon  the  brain.  The  breath  and  urine  of  these 
patients  smell  strongly  of  acetone ;  hence  the  term  acetoncemia.  This 
apple-like  smell  should  always  suggest  the  possible  onset  of  coma  and 
death,  but  it  is  quite  certain  that  acetone  (which  can  certainly  be 
detected  in  the  urine)  is  not  the  true  poison ;  ethyl-diacetic  acid, 
which  accompanies,  and  is  the  source  of  the  acetone,  was  regarded 
for  a  time  as  the  actual  poison,  but  this  substance,  when  introduced 
into  the  circulation  artificially,  does  not  cause  any  serious  symptoms. 
The  principal  poison  is  hydroxybutyric  acid  or  an  amino-derivative 
of  the  same.  The  alkalinity  and  carbonic  acid  of  the  blood  are 
decreased,  and  the  ammonia  of  the  urine  is  increased ;  this  indicates 
an  attempt  of  the  body  to  neutrahse  the  poisonous  acids. 

The  Nerves  of  the  Liver. 

Claude  Bernard  observed  that  an  increase  of  sugar  in  the  blood  is 
brought  about  by  stimulation  of  the  central  and  peripheral  ends  of 
the  divided  vagus,  and  that  on  the  section  of  both  vagi  sugar  dis- 
appears from  the  blood,  and  glycogen  from  the  liver  and  tissues 
generally.  These  results  have  been  confirmed  in  recent  experiments, 
and  it  has  been  in  addition  found  that  stimulation  of  the  coeliac 
plexus  also  leads  to  a  loss  of  glycogen  in  the  liver,  with  a  correspond- 
ing production  of  glucose  that  passes  into  the  blood.  The  disappear- 
ance of  glycogen  from  the  liver  cells  after  the  stimidation  of  these 
nerves  can  also  be  seen  histologically  (Cavazzani).  These  results  are 
due  to  a  direct  influence  of  the  nerves  on  the  liver  cells,  for  they  are 
obtained  after  the  circulation  is  stopped  by  ligature  of  the  aorta  and 
portal  vein  (Morat  and  Dufourt). 

Vaso-motor  nerves. — The  vaso-constrictor  fibres  for  the  portal  vein 
leave  the  spinal  cord  in  the  third  to  the  eleventh  thoracic  nerves 
inclusive  (Bayliss  and  Starling).  The  nerves  of  the  hepatic  artery 
are  constrictors  contained  in  the  splanchnic,  and  dilators  in  both 
splanchnic  and  vagus, 


CHAPTER  XXXIV 

THE   ABSORPTION    OF   FOOD 

Food  is  digested  in  order  that  it  may  be  absorbed.  It  is  absorbed  in 
order  that  it  may  be  assimilated,  that  is,  become  an  integral  part  of 
the  living  material  of  the  body.  The  digested  food  thus  diminishes 
in  quantity  as  it  passes  along  the  alimentary  canal,  and  the  fseces 
contain  the  undigested  or  indigestible  residue. 

In  the  mouth  and  oesophagus  the  thickness  of  the  epithelium  and 
the  quick  passage  of  the  food  through  these  parts  reduce  aljsorption 
to  a  minimum.  Absorption  takes  place  very  slightly  in  the  stomach : 
the  small  intestine  with  its  folds  and  villi  to  increase  its  surface  is 
the  great  place  for  absorption ;  in  the  large  intestine,  absorption 
(mainly  of  water)  occurs  also,  but  to  a  less  extent. 

Foods  such  as  water  and  soluble  salts  like  sodium  chloride  are 
absorbed  unchanged.  The  organic  foods  are,  however,  considerably 
changed,  colloid  materials  such  as  starch  and  protein  being  converted 
respectively  into  the  diffusible  materials  sugar  and  amino-acids. 

There  are  two  channels  of  absorption,  the  blood-vessels  (portal 
capillaries)  and  the  lymphatic  vessels  or  lacteals. 

Absorption,  however,  is  no  mere  physical  process  of  osmosis  and 
filtration.  We  must  also  take  into  account  the  fact  that  the  cells 
through  which  the  absorbed  substances  pass  are  living,  and  in  virtue 
of  their  inherent  activity  not  only  select  materials  for  absorption,  but 
also  change  those  substances  while  in  contact  with  them.  These  cells 
are  of  two  kinds — (1)  the  columnar  epithelium  that  covers  the  surface ; 
and  (2)  the  lymph  cells  in  the  lymphoid  tissue  beneath.  It  is  now 
generally  accepted  that  of  the  two  the  former,  the  columnar  epithelium, 
is  the  more  important. 

Absorption  of  Carbohydrates. — Though  the  sugar  formed  from 
starch  by  ptyalin  and  amylopsin  is  maltose,  that  found  lq  the  blood 
is  glucose.  Under  normal  circumstances  little,  if  any,  is  absorbed  by 
the  lacteals.  The  glucose  is  formed  from  the  maltose  by  the  succus 
entericus,  aided  by  the  action  of  the  epithelial  cells  through  which  it 

02.  2   L 


500  THE   AIJSOUPTION    OF   FOOD  [CH.  XXXIV. 

passes.  Cano  sugar  and  milk  sugar  are  also  converted  into  glucoses 
before  absorption. 

The  carbohydrate  food  which  enters  the  blood  as  glucose  is  taken 
to  the  liver,  and  there  stored  up  in  the  form  of  glycogen — a  reserve 
store  of  carbohydrate  material  for  the  future  needs  of  the  body. 
Glycogen,  however,  is  found  in  animals  who  take  no  carbohydrate 
food.  It  must,  then,  be  formed  by  the  protoplasmic  activity  of  the 
liver  cells  from  their  protein  constituents  (see  preceding  chapter). 
Glucose  is  the  only  sugar  from  which  the  liver  is  capable  of  forming 
glycogen.  If  other  carbohydrates  such  as  cane  sugar  or  lactose  are 
injected  into  the  blood-stream  direct,  they  are  unaltered  by  the  liver, 
and  finally  leave  the  body  by  the  urine. 

Absorption  of  Proteins. — It  is  possible  for  the  alimentary  canal 
to  absorb  soluble  protein  in  an  unchanged  condition.  Thus,  after 
taking  a  large  number  of  eggs,  egg-albumin  is  found  in  the  urine. 
Patients  fed  jpcr  rectum  derive  nourishment  from  protein  food, 
although  proteolytic  enzymes  are  absent  from  that  part  of  the 
intestine.  But  such  occurrences  are  exceptional;  they  are  merely 
illustrations  of  the  fact  that  under  unusual  conditions  certain  parts 
of  the  body  can  rise  to  the  occasion  and  perform  unusual  feats. 

The  normal  course  of  events  is  that  the  food  proteins  are  broken 
up  into  their  constituent  amino-acids,  and  it  is  in  this  form  that 
they  are  absorbed.  If  an  animal  receives,  instead  of  protein,  the 
final  cleavage  products  of  pancreatic  digestion,  it  continues  to 
maintain  its  health  and  nitrogenous  equilibrium;  that  is  to  say, 
the  cells  of  the  body  are  able  to  synthesise  tissue-proteins  from  the 
fragments  of  the  food  proteins. 

Not  many  years  ago,  it  was  held  that  proteins  were  mainly 
absorbed  as  peptone,  and  that  the  absence  of  proteoses  and  peptones 
in  the  blood-stream  was  due  to  the  fact  that  the  intestinal 
epithelium  had  the  power  of  resynthesising  the  blood-proteins  from 
the  peptone ;  and  that  this  protected  us  from  the  poisonous  effects 
which  "  peptone  "  exercises  when  it  gets  into  the  circulation. 

Recent  research  has  failed  to  substantiate  such  views,  and  the 
intestinal  epithelium  does  not  possess  the  exclusive  power  of  build- 
ing up  heavy  moleculed  proteins  either  from  "peptones"  or  from 
amino-acids. 

It  is  certainly  difficult  to  find  the  amino-acids  in  the  blood 
during  absorption,  for  several  reasons :  (1)  the  absorption  during 
any  given  time  is  slow,  and  the  products  are  diluted  with  the  whole 
volume  of  the  blood ;  (2)  the  presence  of  coagulable  proteins  in  the 
blood  in  large  quantity  renders  a  search  for  the  amino-acids  difficult ; 
and  (3)  when  the  amino-acids  get  into  the  blood  they  do  not 
accumulate  there,  but  are  rapidly  removed  by  the  cells  of  the  tissues. 
In  spite  of  these  difficulties,  Leathes  and,  later,  Howell  have  sue- 


CH.  XXXIV.]  ABSORPTION   OF   PROTEINS  531 

ceeded  in  demonstrating  that  during  absorption  the  non-protein 
(that  is  the  amino-acid)  nitrogen  of  the  blood  increases. 

There  is  something  very  attractive  in  this  view,  because  it  affurds 
a  rational  explanation  of  why  it  is  that  the  organism  can  construct 
the  proteins  peculiar  to  itself  and  maintain  its  chemical  individu- 
ality, although  the  food  taken  varies  so  widely  in  composition. 

If  a  man  wants  to  build  a  house  from  the  bricks  of  another 
previously  built  house,  he  naturally  takes  the  latter  to  pieces  first, 
and  uses  the  bricks  most  suitable  for  his  purpose,  and  arranges  them 
in  a  dififerent  way  to  their  previous  arrangement.  The  Germans 
have  recently  coined  the  expression  Bausteine  (or  building  stones) 
for  the  final  products  of  proteolysis  with  the  same  underlying  idea ; 
these  fragments  are  rearranged  by  the  tissue  cells  into  tissue- 
protein,  which  is  different  architecturally  from  the  food-protein. 

Abderhalden  has  published  a  very  striking  experiment  in  confirmation  of  this 
view.  He  collected  the  blood  of  a  horse,  separated  out  the  various  proteins  of  the 
plasma,  and  estimated  in  each  the  yield  of  certain  cleavage  products  (glutamic  acid 
and  tyrosine)  which  resulted  from  hydrolysis.  He  then  fed  the  horse  so  that  it 
formed  new  blood,  but  the  only  protein  given  was  gliadin,  a  vegetable  product, 
which  is  remarkable  for  its  high  percentage  yield  (31-5)  of  glutamic  acid.  But  in 
the  regenerated  blood  proteins  the  percentage  yield  of  glutamic  acid  was  not 
increased  at  ail ;  they  exactly  resembled  the  proteins  previously  present. 

It  is  a  far  cry  from  the  highly  specialised  organism  of  the  horse  to  the  proto- 
plasm of  the  simple  mould  known  as  Aspergillus  niger ;  nevertheless,  the  same 
general  rule  holds ;  the  protein  matter  present  yields  on  hydrolysis,  glycine, 
alanine,  leucine,  glutamic  and  aspartic  acids,  but  aromatic  products,  such  as 
tyrosine  and  phenylalanine,  were  not  discovered.  The  mould  was  then  cultivated 
on  media  of  widely  varying  composition,  but  the  protein  formed  in  the  living 
protoplasm  remained  constant  in  composition,  and  is  thus  independent  of  the 
composition  of  the  nutritive  medium. 

What,  then,  if  this  is  the  case,  would  be  the  fate  of  food  proteins  introduced 
directly  into  the  blood-stream  without  the  intervention  of  the  alimentary  digestive 
processes  r  This  is  a  question  to  which  Mendel  and  Rockwood  have  been  attempt- 
ing to  find  an  answer.  If  the  preliminary  cleavage  in  the  gastro-intestinal  tract  is 
absolutely  necessary,  one  would  anticipate  that  a  foreign  food  protein  (such  as 
edestin  from  hemp  seed,  or  excelsin  from  Brazil  nuts)  administered  by  intravenous 
or  intraperitoneal  injection  would  not  be  assimilated,  but  would  be  cast  out  of  the 
body  in  one  or  more  of  the  excretions.  But  Mendel  and  Rockwood  found  that 
they  were  not  eliminated  in  either  urine  or  bile.  In  some  cases,  a  proteose  was 
found  in  small  quantities  in  the  urine,  but  the  greater  part  of  the  protein  adminis- 
tered was  retained  in  the  body,  especially  if  the  injection  was  slowly  performed. 

The  fact  that  proteins  are  retained  after  this  method  of  administration  and 
apparently  used  in  the  body  does  not  really  militate  against  the  theory  that 
proteins  under  normal  conditions  are  more  or  less  completely  broken  down  in  the 
alimentary  tract.  It  is  more  than  probable  that  cleavage  is  absolutely  necessary 
for  assimilation,  and  here  the  enzymes  present  in  the  tissue-cells  step  in  ;  they  are 
capable  of  occasionally  taking  the  place  of  the  pancreatic  trypsin  and  intestinal 
erepsin  and  doing  their  work.  The  presence  of  a  proteose  in  urine  in  some  of 
Mendel  and  Rockwood's  experiments  points  in  this  direction,  and  this  view  is 
supported  also  by  Vernon's  recent  discover}^  that  every  tissue  of  the  body  has  an 
ereptic  action,  and  that  in  some  tissues  this  power  is  even  greater  than  in  the 
intestinal  mucous  membrane. 

It  must  not,  however,  be  supposed  that  all  the  building  stones  of 


532  THE   ABSORPTION   OF   FOOD  [CH.  XXXIV. 

the  food-protein  are  utilised  in  this  way.  The  body  is  remarkable 
for  its  economical  use  of  the  tissue-proteins,  and  quite  a  small 
quantity  relatively  is  used  up  in  our  daily  activities,  and  so  repair 
is  only  necessary  to  the  same  small  extent.  We  may  again  get 
some  assistance  from  our  example  of  the  man  building  a  house. 
When  he  takes  the  first  house  to  pieces,  there  will  be  a  lot  of 
useless  bricks  and  other  rubbish,  and  if  the  house  he  wants  to  build 
is  a  smaller  one  than  the  one  he  has  destroyed,  he  will  have  to  dis- 
card also  many  bricks  which  are  not  rubbish.  So  it  is  with  the 
fragments  of  the  food-protein,  wliich,  on  usual  diets,  are  more  abun- 
dant than  is  necessary  for  the  building  of  tissue-protein.  The  excess 
is  carried  to  the  liver,  and  there  rapidly  converted  into  urea,  which 
is  finally  discharged  from  the  body  by  the  kidneys. 

It  should  be  further  noted  that  the  nitrogen  of  the  protein  is 
split  off  from  it  by  hydrolysis,  not  by  oxidation,  so  that  the  products 
of  breakdown  retain  almost  intact  the  previous  energy  of  the 
protein,  and  the  non-nitrogenous  residue,  in  particular,  is  thus 
available  for  calorific  process  in  the  same  way  that  the  non- 
nitrogenous  foods  (carbohydrates  and  fat)  are. 

Absorption  of  Fats. — The  fats  undergo  in  the  intestine  two 
changes :  one  a  physical  change  (emulsification),  the  other  a  chemical 
change  (saponification).  The  lymphatic  vessels  are  the  great  channels 
for  fat  absorption,  and  their  name  lacteals  is  derived  from  the  milk- 
like appearance  of  their  contents  {chyle)  during  the  absorption  of  fat. 

The  course  which  the  minute  fat-globules  take  may  be  studied  by 
killing  animals  at  varj'ing  periods  after  a  meal  of  fat,  and  making 
osmic  acid  microscopic  preparations  of  the  vilK.  Figs.  410  and  411 
illustrate  the  appearances  observed. 

The  columnar  epithelium  cells  become  first  filled  with  fatty 
globules  of  varying  size,  which  are  generally  larger  near  the  free 
border.  The  globules  pass  down  the  cells,  the  larger  ones  breaking 
up  into  smaller  ones  during  the  journey ;  they  are  then  transferred 
to  the  amoeboid  cells  of  the  hmiphoid  tissue  beneath  :  these  ultimately 
penetrate  into  the  central  lacteal,  where  they  either  disintegrate  or 
discharge  their  cargo  into  the  lymph-stream.  The  globules  are  by 
this  time  divided  into  immeasurably  small  ones,  the  molecular  basis 
of  chyle.  The  chyle  enters  the  blood-stream  by  the  thoracic  duct, 
and  after  an  abundant  fatty  meal  the  blood-plasma  is  quite  milky ; 
the  fat  droplets  are  so  small  that  they  circiilate  without  hindrance 
through  the  capillaries.  The  fat  in  the  blood  after  a  meal  is  even- 
tually stored  up  especially  in  the  cells  of  adipose  tissue.  It  must, 
however,  be  borne  in  mind  that  the  fat  of  the  body  is  not  exclusively 
derived  from  the  fat  of  the  food,  but  it  may  originate  from  carbo- 
hydrate, and  according  to  some  observers  from  protein  also. 

The  great  difficulty  in  fat  absorption  was  to  explain  how  the  fat 


CH.  XXXIY.] 


ABSORPTION   OF   FATS 


533 


first  gets  into  the  columnar  epithelium:  these  cells  will  not  take  up 

other  particles,  and  it  is  certain    that    the  epithelial   cells  do  not 

protrude  pseudopodia  from 

their  borders  (this,  however, 

does  occur  in  the  endoderm 

of   some   of   the   lower  in- 

verteljrates) ;  moreover,  fat 

particles  have  never   been 

seen  in  the  striated  border 

of  the  cells. 

Although  granules  really 

protoplasmic  in  nature  are 

apt  to  be  mistaken  for  fat 

granules,  there  is  no  doubt 

that  the  particles  found  in 

the  cells  during  fat  absorp- 
tion  are   composed  of   fat. 

There  is  also  no  doubt  that 

the  epithelial  cells  have  the 

power  of  forming  fat  out  of 

the  fatty  acids  and  glycerin 

into  which  fats  have  been 

broken  up  in  the  intestine. 

Munk,  who  has  performed  a 

large  number  of  experiments 

on  the  subject,  showed  that 

the    splitting   of    fats   into 

glycerin  and  fatty  acids  occurs  to  a  much  greater  extent  than  was 

formerly   supposed  ;    these    substances,  being   soluble,  pass   readily 

into  the  epithelium  cells;  and  these 
cells  perform  the  synthetic  act  of 
building  them  into  fat  once  more, 
the  fat  so  formed  appearing  in  the 
form  of  small  globules,  surrounding 
or  becoming  mixed  with  the  proto- 
plasmic granules  that  are  ordinarily 
present.  Another  remarkable  fact 
which  he  made  out  is  that  after 
feeding  an  animal  on  fatty  acids 
the  chyle  contains  fat.  The  neces- 
sary glycerin  must  have  been  formed 
by  protoplasmic  activity  during  ab- 
sorption.    The  more  recent  work  of 

Moore  and  Eockwood   has  shown  that   fat  is  absorbed  entirely  as 

fatty  acid  or  soap  and  glycerin ;  and  that  preliminary  emulsification, 


Fig.  410. — Section  of  the  villus  of  a  rat  killed  during  fat 
absorption,  cp,  epithelium;  str,  striated  border; 
c,  lymph-cells ;  c',  lymph-cells  in  the  epithelium ; 
I,  cential  lacteal  containing  disintegrating  lymph- 
corpuscles.    (E.  A.  Schiifer.) 


Fig.  411. — Mucous  membrane  of  frog's  intes- 
tine during  fat  absorption,  ep,  epithe- 
lium; str,  striated  border;  C,  lymph 
corpuscles  ;  I,  lacteal.    (E.  A.  Schafer.) 


534  THE   ABSORPTION   OF   FOOD  [CH.  XXXIV. 

though  advantageous  for  the  formation  of  these  substances,  is  not 
essential. 

Bile  aids  the  digestion  of  fat,  in  virtue  of  its  being  a  solvent  of 
fatty  acids,  and  it  probably  assists  fat  absorption  by  reducing  the 
surface  tension  of  the  intestinal  contents;  membranes  moistened 
with  bile  allow  fatty  materials  to  pass  through  them  more  readily 
than  would  otherwise  be  the  case.  In  cases  of  disease  in  which  bile 
is  absent  from  the  intestines,  a  large  proportion  of  the  fat  in  the  food 
passes  into  the  fseces. 

The  fseces  are  alkaline,  and  contain  the  following  substances  : — 

1.  Water :  in  health  from  68  to  82  per  cent. ;  in  diarrhoea  it  is 
more  abundant  still. 

2.  Undigested  food;  that  is,  if  food  is  taken  in  excess,  some 
escapes  the  action  of  the  digestive  juices.  On  a  moderate  diet 
unaltered  protein  is  never  found. 

3.  Indigestible  constituents  of  the  food  :  cellulose,  keratin,  mucin, 
chlorophyll,  gums,  resins,  cholesterin. 

4.  Constituents  digestible  with  difficulty :  uncooked  starch, 
tendons,  elastin,  various  phosphates,  and  other  salts  of  the  alkaline 
earths. 

5.  Products  of  decomposition  of  the  food :  indole,  skatole,  phenol, 
acids  such  as  fatty  acids,  lactic  acid,  etc. ;  hsematin  from  haemoglobin ; 
insoluble  soaps  like  those  of  calcium  and  magnesium. 

6.  Bacteria  of  all  sorts,  and  dSbris  from  the  intestinal  wall ;  cells, 
nuclei,  mucus,  etc.     This  forms  a  very  large  contribution. 

7.  Bile  residues :  mucus,  cholesterin,  traces  of  bile  acids  and  their 
products  of  decomposition,  stercobilin  from  the  bile  pigment. 

The  average  quantity  of  solid  fsecal  matter  passed  by  the  human 
adult  ^67'  diem  is  6  to  8  ounces. 

Meconium  is  the  name  given  to  the  greenish-black  contents  of 
the  intestine  of  new-born  children.  It  is  chiefly  concentrated  bile, 
with  dt^hris  from  the  intestinal  wall.  The  pigment  is  a  mixture  of 
bilirubin  and  biliverdin,  not  stercobilin. 


CHAPTEK  XXXV 

THE   MECHANICAL   PROCESSES    OF   DIGESTION 

Under  this  head  we  shall  study  the  neuro-muscular  mechanism  of  the 
alimentary  canal,  which  has  for  its  object  the  onward  movement  of 
the  food,  and  its  thorough  admixture  with  the  digestive  juices.  We 
shall  therefore  have  to  consider  mastication,  deglutition,  the  move- 
ments of  the  stomach  and  intestines,  defsecation,  and  vomiting. 

Mastication. 

The  act  of  mastication  is  performed  by  the  biting  and  grinding 
movement  of  the  lower  range  of  teeth  against  the  upper.  The 
simultaneous  movements  of  the  tongue  and  cheeks  assist  partly  by 
crushing  the  softer  portions  of  the  food  against  the  hard  palate  and 
gums,  and  thus  supplement  the  action  of  the  teeth,  and  partly  by 
returning  the  morsels  of  food  to  the  teeth  again  and  again,  as 
they  are  squeezed  out  from  between  them,  until  they  have  been 
sufficiently  chewed. 

The  act  of  mastication  is  much  assisted  by  the  saliva,  and  the 
intimate  incorporation  of  this  secretion  with  the  food  is  called 
insalivation. 

Mastication  is  much  more  thoroughly  performed  by  some  animals 
than  by  others.  Thus,  dogs  hardly  chew  their  food  at  all,  but  the 
oesophagus  is  protected  from  abrasion  by  a  thick  coating  of  very 
viscid  saliva  which  lubricates  the  pieces  of  rough  food. 

In  vegetable  feeders,  on  the  other  hand,  insalivation  is  a  much 
more  important  process.  This  is  especially  so  in  the  ruminants ;  in 
these  animals,  the  grass,  etc.,  taken,  is  hurriedly  swallowed,  and  passes 
into  the  first  compartment  of  their  four-chambered  stomach.  Later 
on,  it  is  returned  to  the  mouth  in  small  instalments  for  thorough 
mastication  and  insalivation ;  this  is  the  act  of  rumination,  or 
"  chewing  the  cud " ;  it  is  then  once  more  swallowed  and  passes 
on  to  the  digestive  regions  of  the  stomach. 

In  man,  mastication  is  also  an  important  process,  and  in  people 


536  THE   MECHANICAL   PROCESSES    OF   DIGESTION        [CH.  XXXV. 

who  have  lust  their  teeth  severe  dyspepsia  is  often  produced,  which 
can  be  cured  by  a  new  set  of  teeth. 

Deglutition. 

When  properly  masticated,  the  food  is  transmitted  in  successive 
portions  to  the  stomach  by  the  act  of  deglutition  or  swallowing. 
This,  for  the  purpose  of  description,  may  be  divided  into  three  acts. 
In  the  first,  particles  of  food  collected  as  a  bolus  are  made  to  glide 
between  the  surface  of  the  tongue  and  the  palatine  arch,  till  they 
have  passed  the  anterior  arch  of  the  fauces ;  in  the  second,  the  morsel 
is  carried  through  the  pharynx;  and  in  the  third,  it  reaches  the 
stomach  through  the  oesophagus.  These  three  acts  follow  each  other 
rapidly.  (1.)  The  first  act  is  voluntary,  although  it  is  usually  per- 
formed unconsciously ;  the  morsel  of  food  when  sufficiently  masti- 
cated, is  pressed  between  the  tongue  and  palate,  by  the  agency  of  the 
muscles  of  the  former,  in  such  a  manner  as  to  force  it  back  to  the 
entrance  of  the  pharynx.  (2.)  The  second  act  is  theniost  complicated, 
because  the  food  must  go  past  the  posterior  orifice  of  the  nose  and 
the  upper  opening  of  the  larynx  without  entering  them.  When  it 
has  been  brought,  by  the  first  act,  between  the  anterior  arches  of  the 
palate,  it  is  moved  onwards  by  the  movement  of  the  tongue  backwards, 
and  by  the  muscles  of  the  anterior  arches  contracting  on  it  and  then 
behind  it.  The  root  of  the  tongue  being  retracted,  and  the  larynx 
being  raised  with  the  pharynx  and  carried  forwards  under  the  base 
of  the  tongue,  the  epiglottis  is  pressed  over  the  upper  opening  of  the 
larynx,  and  the  morsel  glides  past  it;  the  closure  of  the  glottis  is 
additionally  secured  by  the  simultaneous  contraction  of  its  own 
muscles :  so  that,  even  when  the  epiglottis  is  destroyed,  there  is  little 
danger  of  food  passing  into  the  larynx  so  long  as  its  muscles  can  act 
freely.  In  man,  and  some  other  animals,  the  epiglottis  is  not  drawn 
as  a  lid  over  the  larynx  during  swallowing.  At  the  same  time,  the 
raising  of  the  soft  palate,  so  that  its  posterior  edge  touches  the  back 
part  of  the  pharynx,  and  the  approximation  of  the  sides  of  the 
posterior  palatine  arch,  which  move  quickly  inwards  like  side  curtains, 
close  the  passage  into  the  upper  part  of  the  pharynx  and  the  posterior 
nares,  and  form  an  inclined  plane,  along  the  under  surface  of  which 
the  morsel  descends ;  then  the  pharynx,  raised  up  to  receive  it,  in  its 
turn  contracts,  and  forces  it  onwards  into  the  oesophagus.  The  passage 
of  the  bolus  of  food  through  the  three  constrictors  of  the  pharynx  is 
the  last  step  in  this  stage.  (3.)  In  the  third  act,  in  which  the  food 
passes  through  the  oesophagus,  every  part  of  that  tube,  as  it  receives 
the  morsel  and  is  dilated  by  it,  is  stimulated  to  contract :  hence  an 
undulatory  or  peristaltic  contraction  of  the  oesophagus  occurs,  which 
is  easily  observable  through  the  skin  in  long-necked  animals  like  the 


CH.  XXXV.]  DEGLUTITIOX  537 

swau.  If  we  suppose  the  bolus  to  b(3  at  one  particular  place  in  the 
tube,  it  acts  stimulatingly  on  the  circular  muscular  fibres  behind  it, 
and  inhibitin^•ly  on  those  in  front ;  the  contraction  therefore  squeezes 
it  into  the  dilated  portion  of  the  tube  in  front,  where  the  same 
process  is  repeated,  and  this  travels  along  the  whole  length  of 
the  tube.  The  second  and  third  parts  of  the  act  of  deglutition 
are  involuntary.  The  action  of  these  parts  is  more  rapid  than 
peristalsis  usually  is.  This  is  due  to  the  large  amount  of  striated 
muscular  tissue  present.  It  serves  the  useful  purpose  of  getting 
the  bolus  as  quickly  as  possible  past  the  opening  of  the  respiratory 
tract. 

Nervous  Mechanis7n. — The  nerves  engaged  in  the  reflex  act  of 
deglutition  are : — sensory,  branches  of  the  fifth  cranial  nerve  supplying 
the  soft  palate  and  tongue;  glosso-pharyngeal,  supplying  the  tongue 
and  pharynx ;  the  superior  laryngeal  branch  of  the  vagus,  supplying 
the  epiglottis  and  the  glottis ;  while  the  motor  fibres  concerned  are : — 
branches  of  the  fifth,  supplying  part  of  the  digastric  and  mylo-hyoid 
muscles,  and  the  muscles  of  mastication ;  the  bulbar  part  of  the 
spinal  accessory  through  the  pharyngeal  plexus,  supplying  the  levator 
palati,  probably  by  rootlets  which  are  glosso-pharyngeal  in  origin  ;  the 
glosso-pharyngeal  and  vagus,  and  possibly  the  bulbar  part  of  the  spinal 
accessory,  supplying  the  muscles  of  the  pharynx  through  the  phar- 
yngeal plexus ;  the  vagus,  in  virtue  of  its  spinal  accessory  roots, 
supplying  the  muscles  of  the  larynx  through  the  inferior  laryngeal 
branch ;  and  the  hypo-glossal,  the  muscles  of  the  tongue.  The  nerve- 
centre  by  which  the  muscles  are  harmonised  in  their  action,  is  situated 
in  the  medulla  oblongata. 

Stimulation  of  the  vagi  gives  rise  to  peristalsis  of  the  oesophagus. 
The  cell  stations  of  these  fibres  are  in  the  ganglion  trunci  vagi. 
Division  of  both  pneumogastric  nerves  gives  rise  to  paralysis  of  the 
oesophagus  and  stomach,  and  firm  contraction  of  the  cardiac  orifice. 
These  nerves  therefore  normally  supply  the  oesophagus  with  motor, 
and  the  cardiac  sphincter  with  inhibitory  fibres.  If  food  is  swallowed 
after  these  nerves  are  divided,  it  accumulates  in  the  gullet  and  never 
reaches  the  stomach. 

In  discussing  peristalsis  on  a  previous  occasion  (p.  158),  we 
arrived  at  the  conclusion  that  it  is  an  inherent  property  of  muscle 
rather  than  of  nerve;  though  normally  it  is  controlled  and  influenced 
by  nervous  agency.  This  nervous  control  is  especially  marked  in  the 
oesophagus;  for  if  that  tube  is  divided  across,  leaving  the  nerve 
branches  intact,  a  wave  of  contraction  will  travel  from  one  end  to  the 
other  across  the  cut. 

Swallowing  of  Fluids. — The  swallowing  both  of  solids  and 
liquids  is  a  muscular  act,  and  can,  therefore,  take  place  in 
opposition  to  the  force  of  gravity.     Thus,  horses  and  many  other 


538  THE  MECHANICAL   PROCESSES   OF   DIGESTION        [CH.  XXXV. 

animals  habitually  drink  up-hill,  and  the  same  feat  can  be 
performed  by  jugglers. 

In  swallowing  liquids  the  two  mylo-hyoid  muscles  form  a 
diaphragm  below  the  anterior  part  of  the  mouth.  The  stylo-glossi 
draw  the  tongue  backwards  and  elevate  its  base ;  the  two  hyo-glossi 
act  with  these,  pulling  the  tongue  backwards  and  downwards.  The 
action  of  these  muscles  resembles  that  of  a  force-pump  projecting  the 
mass  of  fluid  down  into  the  oesophagus ;  it  reaches  the  cardiac  orifice 
with  great  speed,  and  the  pharyngeal  and  oesophageal  muscles  do  not 
contract  on  it  at  all,  but  are  inhibited  during  the  passage  of  the  fluid 
through  them  (Kronecker). 

This  is  proved  in  a  striking  way  in  cases  of  poisoning  by  corrosive 
substances,  such  as  oil  of  vitriol ;  the  mouth  and  tongue  are  scarred 
and  burnt,  but  the  pharynx  and  oesophagus  escape  serious  injury,  so 
rapidly  does  the  fluid  pass  along  them;  the  cardiac  orifice  of  the 
stomach  is  the  next  place  to  show  the  effects  of  the  corrosive. 

There  is,  however,  no  hard-and-fast  line  between  the  swallowing 
of  solids  and  fluids :  the  more  liquid  the  food  is,  the  more  does  the 
force-pump  action  just  described  manifest  itself. 

Movements  of  the  Stomach. 

The  gastric  fluid  is  assisted  in  accomplishing  its  share  in  digestion 
by  the  movements  of  the  stomach.  In  graminivorous  birds,  for 
example,  the  contraction  of  the  strong  muscular  gizzard  affords  a 
necessary  aid  to  digestion,  by  grinding  and  triturating  the  hard 
seeds  which  constitute  their  food.  But  in  the  stomach  of  man  and 
other  Mammalia  the  movements  of  the  muscular  coat  are  too  feeble 
to  exercise  any  such  mechanical  force  on  the  food ;  neither  are 
they  needed,  for  mastication  has  already  done  the  mechanical  work 
of  a  gizzard ;  and  it  has  been  demonstrated  that  substances  are 
digested  even  when  enclosed  in  perforated  tubes,  and  consequently 
protected  from  mechanical  influence. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly  con- 
tracted, its  orifices  not  more  firmly  than  the  rest  of  its  walls ;  but, 
if  examined  shortly  after  the  introduction  of  food,  it  is  found  closely 
encircling  its  contents,  and  its  orifices  are  firmly  closed  by  sphincters. 
The  cardiac  orifice,  every  time  food  is  swallowed,  opens  to  admit  its 
passage  into  the  stomach,  and  immediately  again  closes.  The  pyloric 
orifice,  during  the  first  part  of  gastric  digestion,  is  usually  so  com- 
pletely closed,  that  even  when  the  stomach  is  separated  from  the 
intestines,  none  of  its  contents  escape.  But  towards  the  termination 
of  the  digestive  process,  the  pylorus  offers  less  resistance  to  the 
passage  of  substances  from  the  stomach ;  first  it  yields  to  allow  the 
successively  digested  portions  to  go  through  it ;  and  then  it  allows 


CH.  XXXV.]  MOVEMENTS    OF   THE   STOMACH  539 

the  transit  even  of  undigested  substances.  The  peristaltic  action 
of  the  muscular  coat,  whereby  the  digested  portions  are  gradually 
moved  towards  the  pylorus,  also  ensures  thorough  admixture  with 
the  gastric  juice.  The  movements  increase  as  the  process  of  chymi- 
fication  advances,  and  are  continued  until  it  is  completed. 

The  contraction  of  the  fibres  situated  towards  the  pyloric  end  of 
the  stomach  is  more  energetic  and  more  decidedly  peristaltic 
than  those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of 
St  Martin,  that  when  the  bulb  of  a  thermometer  was  placed  about 
three  inches  from  the  pylorus,  through  the  gastric  fistula,  it  was 
tightly  embraced  from  time  to  time,  and  drawn  towards  the  pyloric 
orifice  for  a  distance  of  three  or  four  inches.  The  object  of  this 
movement  appears  to  be,  as  just  said,  to  carry  the  food  towards  the 
pylorus  as  fast  as  it  is  formed  into  chyme,  and  to  propel  the  chyme 
into  the  duodenum ;  the  undigested  portions  of  food  are  kept  back 
until  they  are  also  reduced  into  chyme,  or  until  all  that  is  digestible 
has  passed  out.  The  action  of  these  fibres  is  often  seen  in  the  con- 
tracted state  of  the  pyloric  portion  of  the  stomach  after  death,  when 
it  alone  is  contracted  and  firm,  while  the  cardiac  portion  forms  a 
dilated  sac.  Sometimes,  by  a  predominant  action  of  strong  circular 
fibres  placed  between  the  cardia  and  pylorus,  the  two  portions,  or 
ends,  as  they  are  called,  of  the  stomach,  are  partially  separated  from 
each  other  by  a  kind  of  hour-glass  contraction. 

The  subject  has  recently  been  taken  up  by  Cannon.  He  gave 
an  animal  food  mixed  with  bismuth  subnitrate,  and  obtained  by  the 
Rontgen  rays  shadow  photographs  of  the  stomach,  because  the  bismuth 
salt  renders  its  contents  opaque.  His  results  mainly  confirm  those 
of  the  earlier  investigators;  the  principal  peristalsis  occurs  in  the 
pyloric  portion  of  the  stomach.  The  cardiac  portion  (including  the 
fundus)  presses  steadily  on  its  contents,  and  as  they  become  chymified, 
urges  them  onwards  towards  the  pyloric  portion ;  the  latter  empties 
itself  gradually  through  the  pylorus  into  the  duodenum,  and  in  the 
later  stages  of  digestion  the  cardiac  part  also  is  constricted  into  a 
tube. 

Under  ordinary  circumstances,  three  or  four  hours  may  be  taken 
as  the  average  time  occupied  by  the  digestion  of  a  meal  in  the 
stomach.  But  the  digestibility  and  quantity  of  the  meal,  and  the 
state  of  body  and  mind  of  the  individual,  are  important  causes  of 
variation.  The  pylorus  usually  opens  for  the  first  time  about  twenty 
minutes  after  digestion  begins ;  it,  however,  quickly  closes  again. 
The  acid  chyme  provides  a  chemical  stimulus  for  pancreatic  secretion, 
and  the  strongly  alkaline  pancreatic  juice  neutralises  it;  as  soon  as 
the  intestinal  contents  are  neutral,  the  pylorus  again  opens,  more 
acid  chyme  is  thrust  into  the  duodenum ;  more  pancreatic  juice 
provided ;  and  so  on.  until  the  stomach  is  finally  emptied. 


540  THE   MECHANICAL   PROCESSES    OF   DIGESTION        [CH.  XXXV, 

Influence  of  the  Nervous  System. — -The  normal  movements  of 
the  stomach  during  gastric  digestion  are  in  part  controlled  by  the 
plexuses  of  nerves  and  ganglia  contained  in  its  walls.  The  stomach 
is  also  connected  with  the  higher  nerve-centres  by  means  of 
branches  of  the  vagi  and  of  the  splanchnic  nerves  through  the  solar 
plexus. 

The  vagi  (especially  the  left)  contain  the  accelerator  nerves  of  the 
stomach  ;  when  they  are  stimulated  the  result  is  peristaltic  move- 
ment. The  sympathetic  fibres  are  inhibitory ;  when  they  are  stimu- 
lated peristalsis  ceases.  The  cell  stations  on  the  course  of  the  vagus 
fibres  are  in  the  ganglion  trunci  vagi ;  the  post-ganglionic  fibres  that 
issue  from  this  ganglion  are  non-medullatecl. 

The  sympathetic  fibres  leave  the  spinal  cord  by  the  anterior  roots 
of  the  spinal  nerves  from  the  fifth  to  the  eighth  thoracic.  They  pass 
into  the  sympathetic  system,  have  cell  stations  in  the  coeliac  ganglion, 
and  ultimately  pass  to  the  stomach  by  the  splanchnic  nerves. 

It  seems  probable  that  automatic  rhythmical  contraction  is  inherent 
in  the  muscular  coat  of  the  stomach,  and  that  the  central  nervous 
system  is  only  employed  to  regulate  it  by  impulses  passing  down  by 
the  vagi  or  splanchnic  nerves. 

The  secretory  nerves  of  the  gastric  glands  are  treated  on  p.  496. 

Vomiting. 

The  expulsion  of  the  contents  of  the  stomach  in  vomiting,  like 
that  of  mucus  or  other  matter  from  the  lungs  in  coughing,  is  preceded 
by  an  inspiration  ;  the  glottis  is  then  closed,  and  immediately  after- 
wards the  abdominal  muscles  strongly  act ;  but  here  occurs  the 
difference  in  the  two  actions.  Instead  of  the  vocal  cords  yielding  to 
the  action  of  the  abdominal  muscles,  they  remain  tightly  closed. 
Thus  the  diaphragm,  being  unable  to  go  up,  forms  an  unyielding 
surface  against  which  the  stomach  can  be  pressed.  At  the  same 
time  the  cardiac  sphincter  being  relaxed,  and  the  orifice  which  it 
naturally  guards  being  dilated,  while  the  pylorus  is  closed,  and  the 
stomach  itself  also  contracting,  the  action  of  the  abdominal  muscles 
expels  the  contents  of  the  organ  through  the  CBSophagus,  pharynx, 
and  mouth.  The  reversed  peristaltic  action  of  the  oesophagus 
possibly  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite 
passive  during  vomiting,  and  that  the  expulsion  of  its  contents  is 
effected  solely  by  the  pressure  exerted  upon  it  when  the  capacity  of 
the  abdomen  is  diminished  by  the  contraction  of  the  diaphragm,  and 
subsequently  of  the  abdominal  muscles.  The  experiments  and 
observations,  however,  which  are  supposed  to  confirm  this  statement, 
only  show  that  the  contraction  of  the  abdominal  muscles  alone  is 


CH.  XXXV.]  MOVEMENTS    OF   THE    INTESTINES  541 

sufficient  to  expel  matters  from  an  unresisting  bag  through  the 
oesophagus ;  and  that,  under  very  abnormal  circumstances,  the  stomach, 
by  itself,  cannot  expel  its  contents.  They  by  no  means  show  that  in 
ordinary  vomiting  tlie  stomach  is  passive,  for  there  are  good  reasons 
for  believing  the  contrary.  In  some  cases  of  violent  vomiting  the 
contents  of  the  duodenum  are  passed  by  anti-peristalsis  into  the 
stomach,  and  are  then  vomited.  Where  there  is  obstruction  to  the 
intestine,  as  in  strangulated  hernia,  the  total  contents  of  the  small 
intestine  may  be  vomited. 

Nervous  mechanism. — Some  few  persons  possess  the  power  of 
vomiting  at  will,  or  the  power  may  be  acquired  by  effort  and  practice. 
But  normally  the  action  is  a  reflex  one. 

The  afferent  nerves  are  principally  the  fifth,  and  glosso-pharyngeal 
(as  in  vomiting  produced  by  tickling  the  fauces),  and  the  vagus  (as 
in  vomiting  produced  by  gastric  irritants) ;  but  vomiting  may  occur 
from  stimulation  of  other  sensory  nerves,  e.g.,  those  from  the  kidney, 
uterus,  testicle,  etc.  The  centre  may  also  be  stimulated  by  im- 
pressions from  the  cerebrum  and  cerebellimi,  producing  so-called 
central  vomiting  occurring  in  diseases  of  those  parts. 

The  centre  for  vomiting  is  in  the  medulla  oblongata,  and  coincides 
with  the  centres  of  the  nerves  concerned. 

The  efferent  (motor)  impulses  are  carried  by  the  vagi  to  the 
stomach,  by  the  phrenics  to  the  diaphragm,  and  by  various  other 
spinal  nerves  to  the  abdominal  muscles. 

Emetics. — Some  emetics  produce  vomiting  by  irritating  the 
stomach ;  others,  like  tartar  emetic,  apomorphine,  etc.,  by  stimulating 
the  vomiting  centre. 

Movements  of  the  Intestines. 

The  movement  of  the  intestines  is  peristaltic  or  vermicular,  and  is 
effected  by  the  alternate  contractions  and  dilatations  of  successive 
portions  of  the  muscular  coats.  The  contractions,  which  may 
commence  at  any  j)oint  of  the  intestine,  extend  in  a  wave-like  manner 
along  the  tube.  They  are  sunilar  to  what  we  have  described  in  the 
oesophagus.  In  any  given  portion,  the  longitudinal  muscular  fibres 
contract  first,  or  more  than  the  circular ;  they  draw  a  portion  of  the 
intestine  upwards,  over  the  substance  to  be  propelled,  and  then  the 
circular  fibres  of  the  same  portion  contracting  in  succession  from 
above  downwards,  press  the  substance  into  the  portion  next  below,  in 
which  at  once  the  same  succession  of  actions  next  ensues.  These 
movements  take  place  slowly,  and,  in  health,  commonly  give  rise  to 
no  sensation ;  but  they  are  pjerceptible  when  they  are  accelerated 
under  the  influence  of  any  irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde ;  and 


542  THE   MECHANICAL   PROCESSES    OF   DIGESTION        [CH.  XXXV. 

there  is  no  hindrance  to  the  backward  movement  of  the  contents  of 
the  small  intestine,  as  in  cases  of  violent  vomiting  just  referred  to. 
But  almost  complete  security  is  afforded  against  the  passage  of  the 
contents  of  the  large  into  the  small  intestine  by  the  ileo-ceecal  valve. 

Proceeding  from  above  downwards,  the  muscular  fibres  of  the 
large  intestine  become,  on  the  whole,  stronger  in  direct  proportion 
to  the  greater  strength  required  for  the  onward  moving  of  the  faeces, 
which  are  gradually,  owing  to  the  absorption  of  water,  becoming 
firmer.  The  greatest  strength  is  in  the  rectum,  at  the  termination  of 
which  the  circular  unstriped  muscular  fibres  form  a  strong  band 
called  the  internal  sphincter ;  while  an  external  sphincter  muscle 
with  striped  fibres  is  placed  rather  lower  down,  and  more  externally, 
and  holds  the  orifice  closed  by  a  constant  slight  tonic  contraction. 

Nervous  mechanism. — Experimental  irritation  of  the  brain  or 
cord  produces  no  evident  or  constant  effect  on  the  movements  of  the 
intestines  during  life ;  yet  in  consequence  of  certain  mental  conditions 
the  movements  are  accelerated  or  retarded;  and  in  paraplegia  the 
intestines  appear  after  a  time  much  weakened  in  their  power,  and 
costiveness,  with  a  tympanitic  condition,  ensues. 

As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic 
movements  of  the  intestines  may  be  directly  set  up  in  the  muscular 
fibres  by  the  presence  of  food  or  chyme  acting  as  the  stimulus.  Few 
or  no  movements  occur  when  the  intestines  are  empty. 

The  small  intestine  is  connected  with  the  central  nervous  system 
by  the  vagi  and  by  the  splanchnic  nerves.  The  fibres  which  leave 
the  medulla  in  the  vagal  rootlets  are  fine  medullated  ones :  they 
arborise  around  cells  in  the  ganglion  trunci,  whence  non-medullated 
fibres  continue  the  impulse  to  the  intestinal  walls ;  they  pass  through 
the  solar  plexus,  but  are  not  connected  with  nerve-cells  in  that  plexus. 
In  animals  stimulation  of  the  pneumogastric  nerves  induces  peri- 
staltic movements  of  the  intestines.  If  the  intestines  are  contracting 
peristaltically  before  the  stimulus  is  applied,  the  movements  are 
inhibited  for  a  brief  period,  after  which  they  are  greatly  augmented. 
The  sympathetic  fibres  leave  the  cord  as  fine  medullated  fibres  by 
the  anterior  roots  from  the  sixth  thoracic  to  the  first  lumbar,  pass 
through  the  lateral  chain,  but  do  not  reach  their  cell-stations  until 
they  arrive  at  the  superior  mesenteric  ganglia :  thence  they  pass  as 
non-medullated  fibres  to  the  muscular  coats.  Stimulation  of  these 
fibres  causes  inhibition  of  any  peristaltic  movements  that  may  be 
present.  These  nerves  also  contain  vaso-motor  fibres,  and  section  of 
these  leads  to  vaso-dilatation  and  a  great  increase  of  very  watery 
succus  entericus. 

Peristalsis  in  the  small  intestine  can  be  excited  artificially  even 
when  all  nerves  running  to  it  from  the  central  nervous  system  have 
been   cut  through.     After  pinching  any  particular  spot  a  wave  of 


CH.  XXXV.]  MOVEMENTS    OF   THE   INTESTINES  543 

iuhibition  travels  downwards,  and  a  wave  of  contraction  upwards. 
(Starling.) 

In  the  case  of  the  large  intestine  there  is  no  supply  from  the  vagus. 
The  inferior  mesenteric  nerves  are  inhibitory  in  function,  and  the 
pelvic  nerves  take  the  place  of  the  vagal  fibres  as  excitatory :  this 
refers  to  both  coats  of  the  muscular  wall.  If  one  pinches  any  parti- 
cular spot,  the  upward  wave  of  contraction  is  not  so  marked  as  in 
the  small  intestine,  but  the  downward  travelling  wave  of  inhibition 
is  well  seen. 

Duration  of  Intestinal  Digestion. — The  time  occupied  by  the 
journey  of  a  given  portion  of  food  from  the  stomach  to  the  anus, 
varies  considerably  even  in  health,  and  on  this  account  probably  it  is 
that  such  different  .opinions  have  been  expressed  in  regard  to  the 
subject.  About  twelve  hours  are  occupied  by  the  journey  of  an 
ordinary  meal  through  the  small  intestine,  and  twenty-four  to  thirty- 
six  hours  by  the  passage  through  the  large  bowel. 

Drugs  given  for  relief  of  diarrhoea  or  constipation  act  in  various 
ways :  some  influence  the  amount  of  secretion  and  thus  increase  or 
diminish  the  fluidity  of  the  intestinal  contents;  others  acting  on  the 
muscular  tissue  or  its  nerves  increase  or  diminish  peristalsis. 

The  description  just  given  of  the  intestinal  movements  relates  to  the  principal 
movement  observable,  and  which  is  of  a  peristaltic  character.  The  rate  of  propa- 
gation of  the  peristaltic  wave  is  slow  but  variable ;  it  may  be  as  small  as  1  centi- 
metre per  minute. 

Starling  in  his  recent  work  on  the  subject  has  called  attention  to  another  kind  of 
movement  which  he  terms  swai/iitr/  ov  pendulum  movement.  These  movements,  and 
also  the  true  peristaltic  waves,  may  be  seen  in  the  small  intestine  in  a  warm  saline  bath 
even  after  all  the  nerves  connecting  them  to  the  central  nervous  system  have  been 
cut  through  ;  the  pendulum  movements  consist  of  slight  waves  of  contraction  affect- 
ing both  muscular  coats,  and  these  are  rapidly  propagated  at  the  rate  of  2  to  5  centi- 
metres per  second.  They  cause  a  movement  of  tiie  intestines  from  side  to  side,  and 
occur  at  regular  intervals  of  5  or  6  seconds.  Their  use  appears  to  bring  about  a 
mixing  of  the  intestinal  contents  ;  they  are  not  able  to  move  the  contents  onwards. 

They  differ  from  the  true  peristaltic  waves  in  being  m_i/o(/enic  :  that  is,  they  are 
due  to  the  rhythmicality  of  the  muscular  fibres  themselves,  and  are  propagated  from 
one  muscular  fibre  to  another.  They  are  not  abolished  by  painting  the  intestine 
with  cocaine,  or  by  an  injection  of  nicotine.  The  true  peristaltic  waves  cease  under 
these  circumstances,  and  they  are,  therefore,  co-ordinated  reflex  actions,  but  as  they 
continue  after  all  nerves  connecting  the  intestines  to  the  central  nervous  system  are 
severed,  they  must  be  carried  out  by  the  local  nervous  mechanism.  This  is  the  only 
example  known  of  a  true  reflex  action  dependent  on  peripheral  nervous  structures. 

Intestinal  Oncometer. — To  study  the  volume  changes  of  vascula.r  origin,  a 
loop  of  intestine  is  enclosed  in  an  oncometer  like  that  described  on  p.  152  (fig.  179). 
This  is  a  most  valuable  application  of  plethysmography,  for  the  loop  gives  an 
accurate  record  of  what  is  occurring  in  the  splanchnic  area. 

Defaecation. — The  act  of  the  expulsion  of  faeces  is  in  part  due  to 
an  increased  reflex  peristaltic  action  of  the  lower  part  of  the  large 
intestine,  namely,  of  the  sigmoid  flexure  and  rectum,  and  in  part  to 
the  action  of  the  abdominal  muscles.  In  the  case  of  active  voluntary 
efforts,  there  is  usually,  first,  an  inspiration,  as  in  the  case  of  coughing, 


544  THE   MECHANICAL   PROCESSES    OF   DIGESTION        [CH.  XXXV. 

sneezing,  and  vomiting ;  the  glottis  is  then  closed,  and  the  diaphragm 
fixed.  The  abdominal  muscles  are  contracted,  as  in  expiration  ;  but 
as  the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised  on  the 
abdominal  contents.  The  sphincter  of  the  rectum  being  relaxed,  the 
evacuation  of  its  contents  takes  place  accordingly,  the  effect  being 
increased  by  the  peristaltic  action  of  the  intestine. 

Nervous  Mechanism. — The  anal  sphincter  muscle  is  normally  in  a 
state  of  tonic  contraction.  The  nervous  centre  which  governs  this 
contraction  is  situated  in  the  lumbar  region  of  the  spinal  cord,  inas- 
much as  in  cases  of  division  of  the  cord  above  this  region  the  sphinc- 
ter regains,  after  a  time,  to  some  extent  the  tonicity  which  is  lost 
immediately  after  the  operation.  By  an  effort  of  the  will,  acting  on 
the  centre,  the  contraction  may  be  relaxed  or  increased.  Such  volun- 
tary control  over  the  act  is  obviously  impossible  when  the  cord  is 
divided.  In  ordinary  cases  the  apparatus  is  set  in  action  by  the 
gradual  accumulation  of  faeces  in  the  sigmoid  flexure  and  rectum, 
pressing  by  the  peristaltic  action  of  these  parts  of  the  large  intestine 
against  the  sphincter,  and  causing  by  reflex  action  its  relaxation ; 
this  sensory  impulse  acts  upon  the  brain  and  refiexly  through  the 
spinal  centre.  At  the  same  time  that  the  sphincter  is  inhibited  or 
relaxed,  impulses  pass  to  the  muscles  of  the  lower  intestine  increas- 
ing their  peristalsis,  and  to  the  abdominal  muscles  as  well. 

Both  inhibitory  and  motor  fibres  for  the  lower  part  of  the  intes- 
tine leave  the  cord  by  anterior  roots  lower  than  those  which  contain 
the  fibres  for  the  small  intestine.  The  cell-stations  are  situated  in 
the  inferior  mesenteric  ganglia,  or  along  the  course  of  the  colonic  or 
hypogastric  nerves.  The  lower  portion  of  the  large  intestine  resembles 
the  oesophagus  in  being  more  under  external  nervous  control  than 
the  small  intestine. 


CHAPTEE  XXXVI 


THE   UKINARY   APPARATUS 


This  consists  of  the  kidneys ;  from  each  a  tube  called  the  ureter  leads 
to  the  bladder  in  which  the  urine  is  temporarily  stored ;  from  the 
bladder  a  duct  called  the  urethra 
leads  to  the  exterior. 

The  Kidneys  are  situated  deeply 
in  the  lumbar  region  of  the  abdomen 
on  either  side  of  the  spinal  column 
behind  the  peritoneum.  In  man  each 
is  about  4  inches  long,  2^  inches 
broad,  and  1^  inch  thick,  and  weighs 
about  4i  oz. 

Structure. — The  kidney  is  covered 
by  a  fibrous  capsule,  which  is  slightly 
attached  at  its  inner  surface  to  the 
proper  substance  of  the  organ  by 
means  of  very  fine  bundles  of  areolar 
tissue  and  minute  blood-vessels. 
From  the  healthy  kidney,  therefore, 
it  may  be  easily  torn  off  without 
much  injury  to  the  subjacent  cor- 
tical portion  of  the  organ.  At  the 
hilus  of  the  kidney,  it  becomes  con- 
tinuous with  the  external  coat  of  the 
upper  and  dilated  part  of  the  ureter 
(fig.  412). 

On  dividing  the  kidney  into  two 
equal  parts  by  a  section  carried 
through  its  long  convex  border  it  is  seen  to  be  composed  of  two 
portions  called  respectively  cortical  and  medullary;  the  latter  is 
composed  of  about  a  dozen  conical  bundles  of  urinary  tubules,  each 
bundle  forming  what  is  called  a  pyramid.  The  upper  part  of  the 
515  2  li 


412. — Plan  of  a  longitudinal  section 
through  the  pelvis  and  substance  of  the 
right  kidney,  ^  :  a,  the  cortical  sub- 
stance ;  h,  h,  broad  part  of  the  pyramids 
of  Malpighi ;  c,  c,  the  divisions  of  the 
pelvis  named  calyces,  laid  open  ;  c',  one 
of  those  unopened  ;  d,  summit  of  the 
pyramid  projecting  into  calyces  ;  e,  e, 
section  of  the  narrow  part  of  two 
pyramids  near  the  calyces  ;  p,  pelvis 
or  enlarged  portion  of  the  ureter 
within  the  kidney  ;  m,  the  ureter  ;  s,  the 
sinus  ;  h,  the  hilus. 


U6 


THE  URINARY  APPARATUS 


[CH.  XXXVI. 


ureter  or  duct  of  the  organ  is  dilated  into  the  pelvis ;  and  this, 
again,  after  separating  into  two  or  three  principal  divisions,  is 
finally  subdivided  into  still  smaller  portions,  varying  in  number 
from  about  8  to  12,  called  calyces.  Each  of  these  little  calyces  or 
cups  receives  the  pointed  extremity  or  papilla  of  a  pyramid.  The 
number  of  pyramids  varies  in  different  animals;  in  some  there  is 
only  one. 

The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical 
and  medullary  portions  are  composed  of  tubes,  the  tuhuli  uriniferi, 
which,  by  one  extremity,  in  the  cortical  portion,  commence  around 

tufts  of  capillary  blood-vessels,  called  Mal- 
pighian  bodies,  and,  by  the  other,  open 
through  the  papillae  into  the  pelvis  of  the 
kidney,  and  thus  discharge  the  urine  which 
flows  through  them.  They  are  bound 
together  by  connective  tissue. 

In  the  pyramids  the  tubes  are  straight 
— uniting  to  form  larger  tubes  as  they  de- 
scend through  these  from  the  cortical  por- 
tion ;  while  in  the  latter  region  they  spread 
out  more  irregularly,  and  become  much  con- 
voluted. But  in  the  houndary  zone  between 
cortex  and  medulla,  small  collections  of 
straight  tubes  called  medullary  rays  project 
into  the  cortical  region. 

Tuhuli   Uriniferi. — The  tubuli  uriniferi 
(fig.  417)  are  composed  of  a  basement  mem- 
i)rane,  lined  internally  by  epithelium.    They 
vary  considerably  in  size  in  different  parts 
of  their  course,  but  are,  on  an  average,  about 
of  an  inch  (^V  mm.)  in  diameter,  and  are  found  to  be  made  up 
of  "several  distinct  portions   which   differ   from   one   another   very 
markedly,  both  in  situation  and  structure. 

Each  begins  in  the  cortex  as  a  dilatation  called  the  Capsule  of 
Bowman ;  this  encloses  a  tuft  or  glomerulus  of  capillaries  called  a 
Malpighian  corpuscle.  The  tubule  leaves  the  capsule  by  a  neck,  and 
then  becomes  convoluted  (first  convoluted  tubule),  but  soon  after 
becomes  nearly  straight  or  slightly  spiral  (spiral  tubule) ;  then  rapidly 
narrowing  it  passes  down  into  the  medulla  as  the  descending  tubule  of 
Henle;  this  turns  round,  forming  a  loop  (loop  of  Henle),  and  passes 
up  to  the  cortex  again  as  the  ascending  tubule  of  Henle.  It  then 
becomes  larger  and  irregularly  zigzag  (zigzag  tubule)  and  again  con- 
voluted (second  convoluted  tubule).  Eventually  it  narrows  into  a 
junctional  tubule,  which  joins  a  straight  or  collecting  tubule.  This 
passes  straight  through  the  medulla,  where  it  joins  with  others  to 


Fig.  413.— a.  Purtion  of  a  secreting 
tubule  from  the  cortical  sub- 
stance of  the  kidney,  b.  The 
epithelial  or  gland-cells,  x  700 
times. 


_1 

eolf 


Cir.  XXXVI.]  STRUCTURE   OF   THE   KIDNEY  547 

form  Olio  of  the  ducts  of  Bellini  that  open  at  the  apex  of  the  pyramid. 
These  parts  are  all  shown  in  fig.  414. 


Fig.   414. — A    diagram    of    the    uviiiiftruu.s    tubes.     A,  cortex    limited    externally    by    the    capsule ; 

•  a,  subcapsular  layer  not  containing  Malplghian  corpuscles  ;  a' ,  inner  stratum  of  cortex,  also  without 
JIalpighian  capsules  ;  B,  bound;iry  layer;  C,  medullary  part  next  the  boundary  layer;  1,  Bowman's 
capsule  of  Malpighian  corpuscle  ;  2,  neck  of  capsule  ;  3,  first  convoluted  tubule  ;  4,  spiral  tubule ; 
5,  descending  limb  of  Henle's  loop  ;  G,  the  loop  proper ;  7,  thick  part  of  the  ascending  limb  ;  8,  spiral 
part  of  ascending  limb  ;  9,  narrow  ascending  limb  in  the  medullary  ray  ;  10,  the  zigzag  tubule  ;  11, 
the  second  convoluted  tubule ;  12,  the  junctional  tubule  ;  13,  the  collecting  tubule  of  the  medullary 
ray  ;  14,  the  collecting  tube  of  the  boundary  layer ;  15,  duct  of  Bellini.    (Klein.) 

The  character  of  the  epithelium  that  lines  these  several  parts  of 
the  tubules  is  as  follows : — 


548 


THE    URINARY    APPARATUS 


[CH.  XXXVL 


In  the  capsule,  the  epithelium  is  flattened  and  reflected  over  the 
glomerulus. 

The  way  in  which  this  takes  place  in  process  of  development  is 
shown  in  figs.  415  and  416. 


Fig.  415. — Transverse  section  of  a  deve- 
loping Malpighian  capsule  and  tuft 
(human),  x  300.  From  a  foetus  at 
about  the  fourth  month  ;  a,  flattened 
cells  growing  to  form  the  capsule ; 
h,  more  rounded  cells ;  continuous 
with  the  above,  reflected  round  c,  and 
finally  enveloping  it ;  c,  mass  of  em- 
bryonic cells  which  will  later  become 
developed  into  blood-vessels.  (W. 
Pye.) 


Fig.  416. — Epithelial  elements  of  a  Malpi- 
ghian capsule  and  tuft,  with  the  com- 
mencement of  a  urinary  tubule  show- 
ing the  aff'erent  and  efferent  vessel ;  a, 
layer  of  flat  epithelium  forming  the 
capsule  ;  b,  similar,  but  rather  larger 
epithelial  cells,  placed  in  the  walls  of 
the  tube  ;  c,  cells,  covering  the  vessels 
of  the  capillary  tuft ;  d,  commence- 
ment of  the  tubule,  somewhat  nar- 
rower than  the  rest  of  it.    (W.  Pye.) 


In  the  neck  the  epithelium  is  still  flattened,  but  in  some  animals, 
such  as  frogs,  where  the  neck  is  longer,  the  epithelium  is  ciliated. 

In  thQ  first  convoluted  and  spiral  tubules,  it  is  thick,  and  the  cells 
show  a  fibriUated  structure,  except  around  the  nucleus,  where  the 
protoplasm  is  granular.  The  cells  interlock  laterally  and  are  difficult 
to  isolate.  In  some  animals  they  are  described  as  ciliated.  In  the 
narrovj  descending  tubule  of  Henle  and  in  the  loop  itself,  the  cells  are 
clear  and  flattened  and  leave  a  considerable  lumen ;  in  the  ascending 
limb  they  again  become  striated  and  nearly  fill  the  tubule.  In  the 
zigzag  and  second  convoluted  tubules  the  fibrillations  become  even  more 
marked.  The  junctional  tubule  has  a  large  lumen,  and  is  Lined  by 
clear  flattened  cells ;  the  collecting  tubules  and  ducts  of  Bellini  are 
lined  by  clear  cubical  or  columnar  cells. 

Blood-vessels  of  Kidney. — The  renal  artery  enters  the  kidney 
at  the  hilus,  and  divides  into  branches  that  pass  towards  the  cortex, 
then  turn  over  and  form  incomplete  arches  in  the  region  between 
cortex  and  medulla.     From  these  arches  vessels  pass  to  the  surface 


CH.  XXXVI.] 


STRUCTURE   OF   THE    KIDNEY 


549 


llll||l|ji^i|]l|ll|IBI||l||l|]JI[l|||[l|l'lllt;i|(|||i[]iM(i;.||i™iiil!1^J^ 


33Cl-'MII3B?mTT»l'''nT«"^'i»'r»-^-^-»fc 

Fig.  417. — From  a  vertical  section  through  the  kidney  of  a  dog — the  capsule  of  which  is  supposed  to  be 
on  the  right,  a,  the  capillaries  of  the  Malpighian  corpuscle,  which  are  aiTanged  in  lobules  ;  71,  neck 
of  capsule  ;  c,  convoluted  tubes  cut  in  various  directions  ;  h,  zigzag  tubule ;  d,  e,  and  /,  are  straight 
tubes  in  a  medidlary  ray;  d,  collecting  tube;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb. 
X  380.    (Klein  and  Noble  Smith.) 


Fig.  418. — Transverse  section  of  a  renal  papilla  :  a,  large  tubes  or  ducts  of  Bellini ;  6,  c,  and  d,  smaller 
tubes  of  Henle ;  e,  /,  blood  capillaries,  distinguished  by  their  flatter  epithelium.    (Cadiat.) 


550 


THE  URINARY  APPARATUS 


[CH.  XXXVI. 


which  are  called  the  interlohular  arteries ;  they  give  off  vessels 
at  right  angles,  which  are  the  afferent  vessels  of  the  glomeruli;  a 
glomerulus    is  made  up  of  capillaries  as  previously  stated.     From 

each,  a  smaller  vessel  {the  efferent 
vessel  of  the  glomeridus)  passes 
out,  and  like  a  portal  vessel  on 
a  small  scale,  breaks  up  once 
more  into  capillaries  which 
ramify  between  the  convoluted 
tubules.  These  unite  to  form 
veins  {interlobular  veins)  which 
accompany  the  interlobular  arte- 
ries ;  they  pass  to  venous  arches, 
parallel  to,  but  more  complete 
than,  the  corresponding  arterial 
arches ;  they  ultimately  unite  to 
form  the  renal  vein  that  leaves 
the  hilus.  These  veins  receive 
also  others  which  have  a  stellate 
arrangement  near  the  capsule 
{vence  stelhdoi). 

The  medulla  is  supplied  by 
pencils  of  fine  straight  arterioles 
which  arise  from  the  arterial 
arches.  They  are  called  arterice 
redce.  The  efferent  vessels  of 
the  glomeruli  nearest  the  me- 
dulla may  also  break  up  into 
similar  vessels  which  are  called 
false  arterice  rectm.  The  veins 
{venm  rectm)  take  a  similar  course 
and  empty  themselves  into  the 
venous  arches.  In  the  boundary 
zone  groups  of  vasa  recta  alter- 
nate with  groups  of  tubules,  and 
give  a  striated  appearance  to 
this  portion  of  the  medulla. 

The  Ureters. — The  duct  of 
each  kidney,  or  ureter,  is  a  tube 
about  the  size  of  a  goose-quill, 
and  from  twelve  to  sixteen  inches 
in  length,  which,  continuous  above  with  the  pelvis,  ends  below  by 
perforating  obliquely  the  walls  of  the  bladder,  and  opening  on  its 
internal  surface. 

It  is  constructed  of  three  coats :  {a)  an  outer  fibrous  coat ;  (&)  a 


Fir..  419. — Vascular  supply  of  kidney,  a,  part  of 
arterial  arch ;  h,  interlobular  artery ;  r,  glo- 
merulus ;  d,  efl'erent  vessel  passing  to  the 
medulla  as  false  arteria  recta ;  c,  capillaries  of 
cortex  ;  /,  capillaries  of  medulla ;  g,  venous 
arch ;  h,  straight  veins  of  medulla  ;  i,  inter- 
lobular vein  ;  j,  vena  stellula.    (Cadiat.) 


CII.  XXXVI.] 


TIIR    DLADDEi;    AND    Tti.'ETIIRA 


551 


middle  muscular  coat,  of  which  tho  fibres  are  imstriped,  and  arranged 
in  three  hiyors — tho  fibres  of  tho  central  layer  being  circular,  and 
those  of  tho  other  two  longitudinal  in  direction ;  the  outermost 
longitudinal  layer  is,  however,  present  only  in  tho  lower  part  of 
the  ureter ;  and  (c)  a  mucous  memhrane  continuous  with  that  of 
the  pelvis  above,  and  of  the  urinary  bladder  below.  It  is  com- 
posed of  areolar  tissue  lined  by  transitional 
epitholiuni. 

The  Urinary  Bladder,  which  forms  a 
recei)tacle  for  the  temporary  lodgment  of  the 
urine,  is  pyriform ;  its  widest  part,  which  is 
situate  above  and  behind,  is  termed  the 
fundus;  and  the  narrow  constricted  portion 
in  front  and  below,  by  which  it  becomes  con- 
tinuous with  the  urethra,  is  called  its  cervix 
or  neck. 

It  is  constructed  of  four  coats, — serous, 
muscular,  areolar  or  submucous,  and  mucous. 
{a)  The  serous  coat,  which  covers  only  the 
posterior  and  upper  part  of  the  bladder,  has 
the  same  structure  as  the  peritoneum,  with 
which  it  is  continuous,  {h)  The  fibres  of  the 
muscular  coat,  which  are  unstriped,  are 
arranged  in  three  layers,  of  which  the  exter- 
nal and  internal  have  a  general  longitudinal, 
and  the  middle  layer  a  circular  direction. 
The  latter  are  especially  developed  around 
the  cervix  of  the  organ  and  form  the  sphincter 
vesicce.  (c)  The  areolar  or  submucous  coat  is  constructed  of  connec- 
tive-tissue with  a  large  admixture  of  elastic  fibres,  {d)  The  mucous 
membrane  is  like  that  of  the  ureters.  It  is  provided  with  mucous 
glands,  which  are  most  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  hloocl-  and  lyn^ph-vessels,  and 
with  nerves.  The  latter  consist  of  branches  from  the  sacral  and  hypo- 
gastric plexuses.  Ganglion  cells  are  found,  here  and  there,  on  the 
course  of  the  nerve-fibres. 

The  Urethra. — This  occupies  the  centre  of  the  corpus  spongiosum 
in  the  male.  As  it  passes  through  the  prostate  it  is  lined  by  transi- 
tional, but  elsewhere  by  columnar  epithelium,  except  near  the  orifice, 
where  the  epithelium  is  stratified  like  the  epidermis  with  which  it 
becomes  continuous.  The  female  urethra  has  stratified  epithelium 
throughout.  The  epithelium  rests  on  a  vascular  corium,  and  this  is 
covered  by  submucous  tissue  containing  an  inner  longitudinal  and 
an  outer  circular  muscular  layer.  Outside  this  a  plexus  of  veins 
passes  insensibly  into  the  surrounding  erectile  tissue. 


Fig.  420.— Diagram  showing  tlie 
relation  of  tlie  jMal])ighian 
body  to  tlie  uriniferous  ducts 
and  blood-vessels,  o,  one  of 
the  interlobular  arteries  ;  a', 
afferent  artery  passing  into 
the  glomerulus  ;  c,  eupsule  of 
the  Malpighian  body,  form- 
Ingthecommencemejit  of  and 
continuous  with  t,  the  urini- 
ferous tube ;  e',  e',  efferent 
vessels  which  subdivide  and 
form  a  plexus,  p,  surround- 
ing the  tube,  and  linally 
terminate  in  the  branch  of 
the  renal  vein  e.  (After  Bow- 
]jjan.) 


552 


THE  URINAKY  APPARATUS 


[CH.  XXXVI. 


Into  the  urethra  open  a  number  of  oblique  recesses  or  lacunce,  a 
number  of  small  mucous  glands   (glands  of  Littre),  two  compound 


Fia.  421.— Jlalpighian  corpuscle,  injected  througli  the  renal  artery  with  coloured  gelatin  ;  a,  glomerular 
vessels ;  h,  capsule ;  c,  anterior  capsule ;  d,  afferent  vessel  of  glomerulus ;  e,  efferent  vessels  ; 
/,  epithelium  of  tubes.    (Cadiat.) 

racemose  glands  (Cowper's  glands),  the  glands  of  the  prostate,  and 
the  vas  deferens.     The  prostate,  which  surrounds  the  commencement 


-<?,., 


Fig.  422.— Section  of  a   small  portion  of  the  prostate,     a,  gland  duct  cut  across  obliquely;   h,  gland 
structure;  c,  prostatic  calculus.    (Cadiat.) 


CH.  XXXVI.]         THE  NERVES  OF  THE  KIDNEY  553 

of  the  male  urethra,  is  a  muscular  and  glandular  mass.     Its  glands 
are  tubular  and  lined  by  columnar  epithelium. 

The  Functions  of  the  Kidneys. 

The  main  function  of  the  kidneys  is  to  separate  the  urine  from 
the  blood.  The  true  secreting  part  of  the  kidney  is  ih  ^  glandular 
epithelium  that  lines  the  convoluted  portions  of  the  tubules ;  there 
is,  in  addition  to  this,  what  is  usually  termed  the  filtering  apparatus : 
we  have  already  seen  that  the  tufts  of  capillary  blood-vessels  called 
the  Malpighian  glomeruli  are  supplied  with  afferent  vessels  from  the 
renal  artery ;  the  efferent  vessels  that  leave  these  have  a  smaller 
calibre,  and  thus  there  is  high  pressure  in  the  Malpighian  capillaries. 
Certain  constituents  of  the  blood,  especially  water  and  salts,  pass 
through  the  thin  walls  of  these  vessels  into  the  surrounding  Bowman's 
capsule  which  forms  the  commencement  of  each  renal  tubule.  Though 
the  process  which  occurs  here  is  generally  spoken  of  as  a  filtration, 
yet  it  is  no  purely  mechanical  process  ;  but  the  cells  exercise  a  secretory 
and  a  selective  influence,  and,  among  other  things,  prevent  the 
albuminous  constituents  of  the  blood  from  escaping.  During  the 
passage  of  the  water,  which  leaves  the  blood  at  the  glomerulus,  through 
the  rest  of  the  renal  tubule,  it  gains  the  constituents  urea,  urates,  etc., 
which  are  poured  into  it  by  the  secreting  cells  of  the  convoluted 
tubules. 

The  term  excretion  is  better  than  secretion  as  applied  to  the  kidney, 
for  the  constituents  of  the  urine  are  not  actually  formed  in  the  kidney 
itself  (as,  for  instance,  the  bile  is  formed  in  the  liver),  but  they  are 
formed  elsewhere;  the  kidney  is  simply  the  place  where  they  a,re 
picked  out  from  the  blood  and  eliminated  from  the  body. 

The  Nerves  of  the  Kidney. 

These  are  derived  from  the  renal  plexus  of  each  side.  The  renal 
plexus  consists  of  both  medullated  and  non-medullated  nerve-fibres, 
with  collections  of  ganglion  cells.  Fibres  from  the  anterior  roots  of 
the  eleventh,  twelfth,  and  thirteenth  dorsal  nerves  (in  the  dog)  pass 
into  this  plexus.  They  are  both  vaso-constrictor  and  vaso-dilator  in 
function.  The  nerve-cells  on  the  course  of  the  constrictor  fibres  are 
situated  in  the  cceliac,  mesenteric,  and  renal  ganglia ;  the  nerve-cells 
on  the  course  of  the  dilator  fibres  are  placed  in  the  solar  plexus  and 
renal  ganglia.  These  nerves  are  thus  vaso-motor  in  function ;  we 
have,  at  present,  no  knowledge  of  true  secretory  nerves  to  the 
kidney,  and  the  amount  of  urine  is  influenced,  to  a  certain  extent 
at  any  rate,  by  the  blood-pressure  in  its  capillaries.  We  shall,  a 
few  pages  hence,  however,  see  that  the  amount  of  urine  does  not 
depend  wholly  on  the  height  of  the  blood-pressure ;  and  one  very 


r)54 


THE  URINARY  APPARATUS 


[CH.  XXXVI. 


striking  fact  in  this  relation  may  be  mentioned  now, — namely,  that  if 
the  blood-pressure  is  increased  without  allowing  the  blood  to  flow, 
the  amount  of  urine  formed  is  not  increased;  this  can  be  done  by 
ligaturing  the  renal  vein  ;  the  blood-pressure  within  the  kidney  then 
rises  enormously,  but  the  flow  of  urine  stops. 


The  Kidney  Oncometer. 

This  is  an  instrument  constructed  on  plethysmographic  principles, 
by  means  of  which  the  volume  of  the  kidney  is  registered.  The 
general  characters  of  this  instrument  are  described  in  the  diagrams 
on  p.  309.  The  special  form  introduced  by  Hoy  for  the  kidney  is 
shown  in  fig.  423.     Roy's  instrument,  however,  is  but  seldom  used  at 


Fig.  423. — Oncometers  for  kidneys  of  different  sizes. 

the  present  day.  An  air  oncometer,  connected  with  a  Marey's 
tambour  or  a  bellows  recorder  (like  that  figured  for  the  spleen  on 
p.  152),  is  much  less  complicated,  and  gives  better  results. 


Fig.  424. — Curve  taken  by  renal  oncometer  compared  \vilh  that  of  ordinary  blood-pressure,     a,  Kidney 
curve;  I/,  blood-pressure  curve.     (Roy.) 

It  is  found  that  the  effect  on  the  volume  of  the  organ  of  dividing 
or   stimulating  nerves  corresponds    to  blood-pressure.     If  a  rise  of 


CII.  XXXTI.J  THE   RENAL    EPITHELIUM  555 

pressure  in  the  renal  artery  is  produced  l)y  constriction  of  the  renal 
arterioles,  this  is  accompanied  by  a  fall  of  pressure  in  the  renal 
capillaries  and  a  shrinkage  of  the  kidney.  Increase  in  the  volume 
of  the  kidney  is  produced  by  the  opposite  circumstances. 

The  accompanying  tracing  (fig.  424)  shows  that  in  a  normal 
oncometric  curve  from  the  kidney  there  is  a  rise  of  volume,  due  to 
each  heart-beat,  and  larger  waves,  which  accompany  respiration.  In 
some  cases  larger  sweeping  waves  (Traube-Hering  curves)  are  seen 
as  well,  but  they  are  absent  in  the  tracing  reproduced.  If  the 
kidney  curve  is  compared  with  the  tracing  of  arterial  pressure,  it 
will  be  seen  that  the  rise  of  pressure  is  simultaneous  with  the  fall  in 
kidney  volume  due  to  constriction  of  the  renal  vessels. 

Activity  of  Renal  Epithelium. 

It  is  now  about  seventy  years  since  Bowman  set  forth  his  views 
concerning  the  functions  of  the  renal  epithelium.  These  views  have 
been  subjected  to  very  searching  criticism,  but  they  may  be  accepted 
at  the  present  time  with  considerable  confidence.  Two  contributions 
of  great  importance  were  made  by  this  observer : — (1)  By  means  of 
injection  he  found  that,  in  the  frog,  the  renal  arteries  supplied  both 
the  glomeruli  and  the  tubules  of  the  kidney,  whilst  the  renal  portal 
vein  carried  blood  only  to  the  tubules.  (2)  From  inspection  of  the 
nature  of  the  epithelium  in  different  situations,  he  inferred  that  the 
flat  cells  of  the  capsule  surrounding  the  glomeruli  were  such  as 
would  serve  for  the  ready  passage  of  water  and  saline  substances. 
The  somewhat  opaque  cubical  cells  of  the  convoluted  tubules  would 
be  likely  to  serve  the  purpose  of  secreting  the  more  complex  nitro- 
genous constituents  of  the  urine. 

Activity  of  Tubules. — Very  many  researches  have  been  carried 
out  on  lines  which  really  had  their  origin  in  the  researches  of 
Bowman.  Inasmuch  as  the  renal  portal  system  of  the  frog  supplies 
the  tubules  only,  it  is  possible  to  study  the  functions  of  the  tubules 
by  ligature  of  the  renal  arteries.  This  experiment  was  first  per- 
formed by  Xussbaum.  It  resulted  in  the  discovery  that  the  flow  of 
urine  ceased  when  the  glomeruli  were  deprived  of  their  blood-supply, 
but  that  a  flow — scanty,  it  is  true — could  be  re-established  by  the 
injection  of  urea ;  on  the  other  hand,  injection  of  such  substances  as 
peptone  did  not  set  up  a  flow  of  urine.  The  urine  which  resulted 
from  injection  of  urea  was  particularly  rich  in  this  substance. 
Xussbaum  concluded  then  that  the  normal  flow  of  water  was  a 
glomerular  flow,  and  that  such  substances  as  urea  were  secreted  by 
the  tubules,  whilst  other  substances  (salts  and  peptone)  were  not  so 
secreted. 

Much  doubt  was  cast  upon  the  validity  of  the  above  experiment 


556  THE  UEINARY  APPARATUS  [CH.  XXXVI. 

by  certain  unsuccessful  attempts  to  repeat  it.  Eecent  researches,* 
carried  on  along  quite  different  lines,  but  giving  rise  to  identical 
conclusions,  appear,  however,  to  have  entirely  established  N'ussbaum's 
contentions.  In  the  former  of  these  investigations,  the  original 
experiment  was  repeated  almost  exactly  after  Nussbaum's  fashion, 
and  it  was  found  that  a  secretion  of  urea  could  always  be  evoked 
from  the  tubules,  provided — and  this  proN^ision  is  of  great  importance 
— that  the  kidney  received  sufficient  oxygen  for  the  maintenance  of 
the  functional  activity  of  the  cells.  This  was  accomplished  by  keep- 
ing the  frogs  in  an  atmosphere  of  oxygen.  In  the  second  research, 
the  legs  of  the  frog  were  ligatured  below  the  junction  of  the  renal 
portal  with  the  femoral  vein;  fluid  injected  into  the  anterior 
abdominal  vein  would  pass,  therefore,  down  the  femorals,  up  the 
renal  portals,  and  to  the  tubules  of  the  kidney.  In  this  way  an 
artificial  circulation  of  fluid  was  kept  up.  The  fluid  was  of  approxi- 
mately the  same  saline  content  as  frog's  blood.  Such  a  circulation 
evoked  no  flow  of  urine ;  but  if  certain  diuretics,  such  as  urea,  or 
caffeine,  or  phloridzin,  were  mixed  in  suitable  doses  with  the  saline, 
a  flow  of  urine  was  set  up.  This  flow  could  at  any  time  be  stopped 
by  re-establishing  a  circulation  of  saline  which  contained  no  urea  or 
other  stimulating  substance.  Finally,  it  appeared  that  the  flow  of 
urine  was  accompanied  by  increased  metabolism  of  the  kidney-cells 
in  the  case  of  caffeine  and  dilute  urea  solutions.  This  is  shown  by 
the  fact  that  much  more  of  the  oxygen  dissolved  in  the  saline  was 
removed  by  the  kidney  during  the  secretion  of  the  urine  than  had 
previously  been  the  case.  Example — Oxygen  taken  up  by  resting 
tubules,  "002  c.c.  per  minute;  during  caffeine  diuresis,  010  c.c.  per 
minute. 

In  the  mammalian  kidney,  the  function  of  the  tubules,  as  opposed 
to  the  glomeruli,  must  be  studied  by  a  different  method.  The  flow 
of  urine  from  the  capsules  must  be  eliminated  here  also ;  but  this 
cannot  be  done,  as  in  the  frog,  by  ligaturing  the  renal  arteries ;  it  can, 
however,  be  compassed  by  lowering  the  arterial  blood-pressure.  A 
research  of  great  importance  has  been  performed  along  this  line  by 
Heidenhain.  By  cutting  the  spinal  cord,  he  removed  the  arterial 
tone  from  the  whole  \'isceral  area,  and  consequently  produced  a 
blood-pressure  so  low  that  the  flow  of  urine  ceased.  Into  the  animal 
he  then  injected  a  nitrogenous  body,  sulphindigotate  of  soda,  which 
was  known  to  be  readily  secreted,  and  which  can  easily  be  seen  by 
reason  of  its  blue  colour.  Subsequent  examination  of  microscopical 
sections  of  the  kidney  showed  the  pigment  in  the  lumen,  and  in  the 
cells  of  those  parts  of  the  kidney  tubule  to  which  Bowman  ascribed 
a  secreting  fiinction,  but  never  in  the  glomeruli.     This  experiment 

*  By   Beddard   and  Bainbridge  at  Guy's  Hospital,  and  by  Brodie,   Barcroft, 
Hamill,  and  Miss  Ciillis  at  the  London  School  of  Medicine  for  Women. 


CH.  XXXVI.]  THE   ACTIVITY   OF   GLOMEFtULI  557 

loses  much  of  its  interest  if  sulphindigotate  of  soda  cannot  be 
taken  as  a  type  of  nitrogenous  bodies  generally,  especially  of 
urea. 

Urea  itself  is  a  very  difficult  substance  to  trace  in  this  way, 
because  it  does  not  leave  a  coloured  trail  behind  it.  In  birds,  the 
place  of  urea  is  taken  by  uric  acid,  and  the  urates  can  actually  be 
traced,  because  they  are  depcjsited  as  crystals  and  can  be  seen  in  the 
cells  and  convoluted  tubules  in  much  the  same  way  as  Heidenhain's 
blue  pigment. 

Activity  of  Glomendi. — What  we  have  said  not  only  shows  that 
the  tubules  have  an  excretory  function  for  urea  and  certain  other 
nitrogenous  substances  (to  these  we  may  add,  in  a  more  qualified 
way,  phosphates  and  nitrates),  but  it  clears  the  way  for  a  study  of 
the  functions  of  the  glomerulus.  Already  we  have  shown  that 
sulphates  and  chlorides,  and  saline  substances  generally  (except 
phosphates  and  nitrates)  are  not  secreted  by  the  tubules,  and  water 
only  seems  to  be  so  secreted  under  special  circumstances.  The 
elimination  of  these  substances  must,  therefore,  be  relegated  to  the 
glomeruli.  The  point  of  greatest  interest,  with  regard  to  the 
glomerular  mechanism,  is  how  far  it  is  a  filtration  merely  and  how 
far  it  is,  in  the  more  restricted  sense,  a  secretion. 

Generally  speaking,  those  changes  in  the  general  arterial  blood- 
pressure  which  we  should  exi:)ect  to  cause  an  increased  filtrate  are, 
in  fact,  accompanied  by  diuresis.  Thus,  the  cajjillary  pressure  may 
be  increased  in  the  following  ways: — 

(1)  By  increase  in  the  force  and  frequency  of  the  heart-beat. 

(2)  By  constriction  of  the  arterioles  of  areas  other  than  that  of 
the  kidney,  as  in  cold  weather  when  the  cutaneous  capillaries  are 
constricted.* 

Local  changes,  which  give  rise  to  a  high  pressure  in  the 
glomerular  capillaries,  are  also  associated  with  increased  flow  of 
urine  ;  for  instance : — 

(1)  If  the  renal  nerves  are  divided,  the  renal  arterioles  relax,  and 
the  pressure  in  the  renal  capillaries  rises ;  this  leads  to  an  increased 
flow  of  urine,  which  is  accompanied  by  an  increase  in  the  volume  of 
the  kidney,  as  shown  by  the  oncometer.  Stimulation  of  the  divided 
nerves  produces  diminution  in  the  flow  of  urine,  and  a  shrinkage  of 
the  kidney  due  to  constriction  of  its  blood-vessels.f  [If  the 
splanchnic  nerves  are  experimented  with  instead  of  the  renal,  the 
effects  are  not  so  marked,  as  these  nerves  have  a  wide  distribution, 
and  section  leads  to  vascular  dilatation  in  the  whole  splanchnic  area ; 

*  The  reciprocal  action  between  skin  and  kidneys  will  be  discussed  more  fully 
in  the  chapter  on  the  skin. 

t  These  nerves  also  contain  vaso-dilator  fibres,  which  are  excited  when  a  slow 
rate  of  stimulation  is  used  (see  p.  307). 


558  THE  URINARY  APPARATUS  [CH.  XXXVI. 

hence  the  increase  of  pressure  in  the  renal  capillaries  is  not  so 
noticeable.] 

(2)  Puncture  of  the  floor  of  tlie  fourth  ventricle  in  the  neighbour- 
hood of  the  vaso-niotor  centre  (close  to  the  spot,  puncture  of  which 
produces  glycosuria)  leads  to  relaxation  of  the  renal  arterioles  and  a 
consequent  large  increase  of  urine. 

Whilst  these  facts  clearly  iudicate  a  connection  between  the 
capillary  pressure  and  the  urinary  flow,  there  are  numerous  observa- 
tions which  are  difficult  to  explain  on  such  a  simple  mechanical 
hypothesis.  Experimentally,  it  may  be  shown  that  an  increased 
kidney  volume  on  the  one  hand,  or  an  increased  flow  of  urine  on  the 
other,  may  take  place  without  an  increased  blood-flow  through  the 
kidneys.  Nor,  indeed,  is  there  always  an  increased  kidney  volume 
with  an  increased  flow  of  urine. 

Adhering  to  the  view  that  the  flow  of  urine  produced  by  saline 
diuretics  (such  as  sodium  sulphate)  is  essentially  a  glomerular  flow, 
we  would  point  out  that  there  are  difficulties  in  finding  a  ready 
explanation  of  a  sodium  sulphate  diuresis  as  the  result  of  purely 
vascular  changes : 

(1)  This  salt  is  much  more  rapidly  eliminated  than  others. 

(2)  It  causes  hydremic  plethora;  by  this  means  it  increases 
the  water  in,  and  so  the  total  volume  of,  the  blood ;  it  does  not,  how- 
ever, appreciably  increase  the  arterial  pressure ;  and  if  we  niay  accept 
the  analogy  of  the  intestinal  and  liver  capillaries  to  the  glomerular 
and  tubular  capillaries  of  the  kidney  respectively,  hydremic  plethora, 
though  it  would  markedly  increase  the  pressure  in  the  capillaries 
surrounding  the  tubules,  would  not  cause  greatly  increased  exudation 
from  the  vessels  of  the  glomeruli. 

(3)  Sodium  sulphate  diuresis  (and,  indeed,  all  forms  of  diuresis 
which  have  been  investigated)  is  accompanied  with  a  great  increase 
of  oxygen  used  by  the  kidney,  even  in  cases  where  the  urine  is  very 
dilute. 

(4)  It  has  also  been  shown  that  if  the  pressure  of  urine  in  the 
ureter  is  artificially  raised,  as  by  partially  blocking  it,  injection  of 
the  salt  causes  an  increase  of  the  output  of  sodium  sulphate,  and 
frequently  of  the  total  output  of  urine. 

Another  fact  which  is  out  of  harmony  with  the  idea  that  filtra- 
tion alone  will  account  for  the  functions  of  the  glomerulus,  is  the 
extreme  ease  with  which  the  kidney  may  be  asphyxiated.  Heiden- 
hain  has  shown  that  clamping  the  renal  artery  for  ten  seconds  may 
produce  suppression  of  urine  for  a  long  period. 

Again,  it  is  possible  to  obtain  urine  which  is  much  more  watery 
even  than  the  plasma. 

To  sum  up  our  knowledge  of  the  kidney,  we  may  say  that : — 

(1)  The  function  of  the  glomerulus  is  concerned  with  the  elimina- 


CII.  XXXVI.]  THE   WORK    OF   THE    KIDNEY  559 

tion   ol"  water  and  salts,  and  perhaps  a   trifling  (quantity  of    urea 
washed  through  witli  the  water. 

(2)  That  both  physical  and  secretory  factors  enter  into  this 
function. 

(3)  That  the  function  of  the  tubules  is  a  purely  secretory  one, 
and  deals  with  the  elimination  of  urea  and  certain  other  nitrogenous 
substances,  as  well  as  phosphates  and  nitrates. 

It  should  be  mentioned  that  Ludwig  held  that  reabsorption  of  some  of  the  water 
and  salts  which  escape  at  the  glomeruli  takes  place  in  the  tubules.  This  view  has 
been  revived  by  the  recent  work  of  Meyer  and  of  Cushny,  and  a  good  deal  of  con- 
troversy is  taking  place  whether  such  a  view  is  correct.  In  my  opinion,  however,  the 
main  function  of  the  tubules  is  undoubtedly  secretion  as  just  stated,  not  absorption. 

Diuretics. — We  have  gone  very  fully  into  the  functions  of  the 
kidney,  for  it  frequently  happens  that  drugs  must  be  prescribed  for 
the  purpose  of  promoting  these  functions.  Such  drugs  are  called 
diuretics.  They  act  in  different  ways,  some  locally  on  the  kidney, 
such  as  caffeine,  and  in  our  view  some  of  the  saline  diuretics ; 
others,  such  as  digitalis,  act  upon  the  general  blood-pressure.  It  is  im- 
portant, in  prescribing  these  drugs,  not  to  lose  sight  of  the  fact  that 
whilst  the  greatest  benefit  may  attend  their  action,  it  is  doubtful 
whether  any  of  them  (the  digitalis  group  excepted)  can  be  regarded 
as  doing  their  work  without  throwing  a  greater  or  less  strain  upon 
some  portion  of  the  renal  epithelium. 

The  V/ork  done  toy  the  Kidney. 

We  can  estimate  the  energy  transformed  by  the  kidney  in  more 
than  one  way.  The  urine  is  much  more  concentrated,  as  regards 
crystalline  constituents,  than  the  plasma  from  which  it  was  produced. 
Thus,  urine  contains  about  2  per  cent,  of  urea  on  an  average,  plasma 
0'03  per  cent.,  and  the  same  is  true  in  different  degrees  for  other  sub- 
stances. It  follows  that  if  urine  were  placed  inside  an  osmometer  and 
an  unlimited  supply  of  plasma  outside,  water  would  be  sucked  into 
the  osmometer  until  a  column  of  fluid  of  great  height  had  been 
established  and  much  work  had  been  performed  in  raising  it.  In  a 
specific  instance,  the  blood-plasma  had  an  osmotic  pressure  equivalent 
to  a  0'92  per  cent,  solution,  and  the  urine  to  a  4  per  cent,  solution,  of 
sodium  chloride.  From  these  data,  and  from  the  amount  of  urine 
secreted,  it  is  possible  to  make  a  calculation  of  the  work  performed 
by  the  kidney.  In  other  words,  the  energy  used  by  the  kidney  in 
secreting  the  urine  cannot  be  less  than  what  is  given  by  this  purely 
physical  consideration. 

The  maximum  energy  used  up  by  the  kidney  may  be  calculated 
in  quite  another  way.  Estimations  have  been  made  of  the  amount 
of  oxygen  used  by  the  kidney  in  secreting  urines  of  known  concen- 
tration ;  this  oxygen  may  be  taken  as  a  measure  of  the  amount  of 


560  THE  URENAEY  APPARATUS  [CH.  XXXVI. 

kidney  material  used  up.  If  the  amount  of  metabolism  be  thus 
determined,  we  can  arrive  at  the  amount  of  energy  used  up  by  a 
knowledge  of  the  heat  produced  by  the  decomposition  of  this  amount 
of  kidney  material. 

The  kidney  cannot  be  doing  more  work  than  its  raetabolisni  accounts  for.  If 
we  suppose  the  kidney  living  on  protein  (and  the  figures  would  not  differ  greatly  if 
we  supposed  it  to  be  living  on  carbohydratej,  we  may  sbirt  with  the  following 
constants  :  1  c.c.  of  oxygen  oxidises  1  milligramme  of  protein,  and  forms  water, 
carbon  dioxide,  urea,  etc.  In  doing  so,  it  gives  out  4  heat-units  or  calories  (see 
Chapter  XL.),  and  this  is  equivalent  to  170,000  gramme-centimetres  of  work.  In  a 
typical  experiment  during  diuresis,  the  kidney  used  4  c.c.  of  oxygen  per  minute ; 
this  was,  therefore,  equivalent  to  f380,000  gramme-<:entimetres  of  work,  and  the 
energy  transformed  from  potential  to  kinetic  energy  by  the  kidney  cannot  have 
been  less  than  this.  Let  us  consider  what  evidence  there  is  of  mechanical  work 
which  the  organ  does  as  an  offset  against  this ;  one  way  in  which  the  work 
manifests  itself  is  in  the  concentration  of  the  urine ;  this  fluid  is  many  times  more 
concentrated  than  the  blood-plasma.  The  degree  of  concentration  can  be  calcu- 
lated from  a  knowledge  of  the  freezing-points  of  the  blood  and  urine ;  the  greater 
the  concentration  of  a  solution  of  a  crystalline  substance,  the  lower  is  its  freezing- 
point  (see  p.  y25).  In  this  way,  it  was  calculated  that  14,700  gramme-centimetres  of 
work  was  done  in  the  case  just  referred  to.  If  the  calculation  is  made  for  each 
salt  separately,  a  higher  figure  than  this  would,  however,  be  obtained  ;  but  even 
then,  much  of  the  energy  of  the  kidney  is  left  unaccounted  for  ;  and  in  all  probabihty 
the  transference  even  of  water  at  a  rapid  rate  through  protoplasm  is  a  process 
involving  the  active  metabolism  of  cells. 

Extirpation  of  the  Kidneys. 

Extirpation  of  one  kidney  for  stone,  etc.,  is  a  common  operation. 
It  is  not  followed  by  any  untoward  result.  The  remaining  kidney 
enlarges  and  does  the  work  previously  shared  between  the  two. 

Extirpation  of  both  kidneys  is  fatal ;  the  urea,  etc.,  accumulate  in 
the  blood,  and  the  animal  dies  in  a  few  days;  uraemic  convulsions 
(see  p.  569)  do  not  occur  in  such  experiments. 

Ligature  of  both  renal  arteries  amounts  to  the  same  thing 
as  extirpation  of  the  kidneys,  and  leads  to  the  same  result.  If  the 
ligature  is  released  the  kidney  after  a  time  again  sets  to  work,  but  the 
urine  secreted  at  first  is  albuminous,  owing  to  the  epithelium  having 
been  impaired  by  being  deprived  for  a  time  of  its  blood  supply.  The 
ease  with  which  the  kidney  can  be  injured  l)y  asphyxiation  has 
already  been  alluded  to  (pp.  556,  558). 

Bradford  stated  that  in  dogs  removal  of  one  kidney,  followed  at  a  later  period 
by  removal  of  a  half  or  two-thirds  of  the  other,  produced  the  surprising  result  that 
the  animals  after  the  second  operation  secreted  an  increased  quantity  of  urine,  and 
this  contained  usually  a  quantity  of  urea  in  excess  of  the  normal ;  the  animals 
wasted  rapidly  and  died  within  a  few  weeks.  From  these  experiments  wide- 
reaching  conclusions  were  drawn,  one  of  which  was  that  the  kidney  plays  (perhaps 
by  means  of  an  internal  secretion)  an  important  role  in  nitrogenous  metabolism 
apart  from  merely  excreting  waste  substances.  Great  caution  should,  however,  be 
exercised  in  jumping  to  conclusions  at  present,  especially  because  recent  attempts 
to  obtain  the  same  results  in  cats  have  failed  to  confirm  Bradford's  statements. 


CII.  XXXVI.]  MICTUKITION  561 

The  Passage  of  Urine  into  the  Bladder. 

As  each  portion  of  urine  is  secreted  it  propels  that  which  is 
already  in  the  uriniferous  tubes  onwards  into  the  pelvis  of  the 
kidney.  Thence  through  the  ureter  the  urine  passes  into  the  bladder, 
into  which  its  rate  and  mode  of  entrance  has  been  watched  in  cases 
of  ectopia  vesicce,  i.e.  of  such  fissures  in  the  anterior  and  lower  part  of 
the  walls  of  the  abdomen,  and  of  the  front  wall  of  the  bladder,  as 
expose  to  view  its  hinder  wall  together  with  the  orifices  of  the  ureters. 
The  urine  does  not  enter  the  bladder  at  any  regular  rate,  nor  is  there 
a  synchronism  in  its  movement  through  the  two  ureters.  During  fast- 
ing, two  or  three  drops  enter  the  bladder  every  minute ;  each  drop  as 
it  enters  first  raises  up  the  little  papilla  through  which  the  ureter 
opens,  and  then  passes  slowly  through  its  orifice,  which  at  once  again 
closes  like  a  sphincter.  In  the  recumbent  posture,  the  urine  collects 
for  a  little  time  in  the  ureters,  then  flows  gently,  and,  if  the  body  is 
raised,  runs  from  them  in  a  stream  till  they  are  empty.  Its  flow  is 
aided  by  the  peristaltic  contractions  of  the  ureters,  and  is  increased 
in  deep  inspiration,  or  by  straining,  and  in  active  exercise,  and  in 
fifteen  or  twenty  minutes  after  a  meal.  The  urine  is  prevented  from 
regurgitation  into  the  ureters  by  the  mode  in  which  these  pass 
through  the  walls  of  the  bladder,  namely,  by  their  lying  for  between 
half  and  three-quarters  of  an  inch  between  the  muscular  and  mucous 
coats  before  they  turn  rather  abruptly  forwards,  and  open  through 
the  latter  into  the  interior  of  the  bladder. 


Micturition. 

The  contraction  of  the  muscular  walls  of  the  bladder  may  by 
itself  expel  the  urine  with  little  or  no  help  from  other  muscles.  In 
so  far,  however,  as  it  is  a  voluntary  act,  it  is  performed  by  means  of 
the  abdominal  and  other  expiratory  muscles,  which  in  their  contrac- 
tion press  on  the  abdominal  viscera,  the  diaphragm  being  fixed,  and 
cause  the  expulsion  of  the  contents  of  those  whose  sphincter  muscles 
are  at  the  same  time  relaxed.  The  muscular  coat  of  the  bladder 
co-operates,  in  micturition,  by  reflex  involuntary  action,  with  the 
abdominal  muscles ;  and  the  act  is  completed  by  the  accelerator  urince, 
which,  as  its  name  implies,  quickens  the  stream,  and  expels  the  last 
drop  of  urine  from  the  urethra.  The  act,  so  far  as  it  is  not  directed 
by  volition,  is  under  the  control  of  a  nervous  centre  in  the  lumbar 
spinal  cord,  through  which,  as  in  the  case  of  the  similar  centre  for 
defaecation,  the  various  muscles  concerned  are  harmonised  in  their 
action.  It  is  well  known  that  the  act  may  be  reflexly  induced,  e.g., 
in  children  who  suffer  from  intestinal  worms,  or  other  such  irritation. 
Generally,  the  afferent  impulse  which  calls  into  action  the  desire  to 

2  N 


562  THE  URINARY  APPARATUS  [CH.  XXXVI. 

micturate  is  excited  by  over-distension  of  the  bladder,  or  even  by  a 
few  drops  of  urine  passing  into  the  urethra.  The  impulse  passes  up 
to  the  lumbar  centre,  and  produces,  on  the  one  hand,  inhibition  of  the 
sphincter,  and  on  the  other  hand,  contraction  of  the  necessary  muscles 
for  the  expulsion  of  the  contents  of  the  bladder.  The  tonic  action  of 
the  lumbar  centre  can  also  be  inhibited  by  the  will. 

The  bladder  receives  nerves  from  two  sources: — (1)  from  the 
lower  dorsal  and  upper  lumbar  nerves ;  these  fibres  pass  to  the 
sympathetic  chain,  from  here  to  the  inferior  mesenteric  ganglion, 
and  ultimately  reach  the  bladder  by  the  hypogastric  nerves.  Stimu- 
lation of  these  nerves  causes  contraction  of  the  circular  fibres  of  the 
bladder,  including  the  sphincter;  (2)  from  the  second  and  third 
sacral  nerves;  these  run  to  the  bladder  by  the  nervi  erigentes. 
Stimulation  of  these  nerves  causes  relaxation  of  the  sphincter  and 
contraction  of  the  detrusor  urinae.  (Zeissl.)  Langley  and  Anderson 
find,  however,  that  stimulation  of  both  sets  of  nerves  causes  contrac- 
tion of  both  longitudinally  and  circularly  arranged  muscle  bundles. 


CHAPTER  XXXVII 

THE   URINE 

Quantity. — A  man  of  average  weight  and  height  passes  from  1400 
to  IGOO  C.C.,  or  about  50  oz.  daily.  This  contains  about  50  grammes 
(lA  oz.)  of  solids.  For  analytical  purposes  it  should  be  collected  in 
a  tall  glass  vessel  capable  of  holding  3000  c.c,  which  should  have  a 
smooth-edged  neck  accurately  covered  by  a  ground-glass  plate  to 
exclude  dust  and  prevent  evaporation.  The  vessel,  moreover,  should 
be  graduated  so  that  the  amount  may  be  easily  read  off.  From  the 
total  quantity  thus  collected  in  the  twenty-four  hours,  samples  should 
be  drawn  off  for  examination. 

Colour. — This  is  some  shade  of  yellow  which  varies  considerably 
in  health  with  the  concentration  of  the  urine.  It  is  due  to  a  mixture 
of  pigments ;  of  these,  urobilin  is  the  one  of  which  we  have  the  most 
accurate  knowledge.  Urobilin  has  a  reddish  tint,  and  is  ultimately 
derived  from  the  blood  pigment,  and,  like  bile  pigment,  is  an  iron- 
free  derivative  of  haemoglobin.  The  bile  pigment  in  the  intestines 
is  converted  into  stercobilin ;  most  of  the  stercobilin  leaves  the  body 
with  the  faeces ;  some,  however,  is  reabsorbed  and  is  excreted  with  the 
urine  as  urobilin  (see  p.  521).  Normal  urine,  however,  contains  very 
little  urobilin.  The  actual  body  present  is  a  chromogen  or  mother 
substance  called  urobilinogen,  which  by  oxidation — for  instance, 
standing  exposed  to  the  air — is  converted  into  the  pigment  proper. 
In  certain  diseased  conditions  the  amount  of  urobilin  is  considerably 
increased. 

The  most  abundant  urinary  pigment  is  a  yellow  one,  named 
urochrome.  It  shows  no  absorption  bands.  It  is  probably  an  oxida- 
tion product  of  urobilin.     (Riva,  A.  E.  Garrod.) 

Reaction. — The  reaction  of  normal  urine  is  acid.  This  is  not  due 
to  free  acid,  as  the  uric  and  hippuric  acids  in  the  urine  are  combined 
as  urates  and  hippurates  respectively.  The  acidity  is  due  to  acid 
salts,  of  which  acid  sodium  phosphate  is  the  most  important.  Under 
certain  circumstances  the  urine  becomes  less  acid  and  even  alkaline ; 
the  most  important  of  these  are  as  follows : — 

1.  During  digestion.     Here  there  is  a  formation  of  free  acid  in 

563 


564  THE   URINE  [CH.  XXXVII. 

the  stomach,  and  a  corresponding,'  liljeration  of  bases  in  the  blood, 
which,  passing  into  the  urine,  diminish  its  acidity,  or  even  render  it 
alkaHue.  This  is  called  the  alkaline  tide ;  the  opposite  condition,  the 
acid  tide,  occurs  after  a  fast — for  instance,  before  breakfast. 

2.  In  herbivorous  animals  and  vegetarians.  The  food  here  con- 
tains excess  of  alkaline  salts  of  acids  such  as  tartaric,  citric,  malic,  etc. 
These  acids  are  oxidised  into  carbonates,  which,  passing  into  the  urine, 
give  it  an  alkaline  reaction. 

Specific  Gravity. — This  should  be  taken  in  a  sample  of  the 
twenty-four  hours'  urine  with  a  urinometer. 

The  specific  gravity  varies  inversely  as  the  quantity  of  urine 
passed  under  normal  conditions  from  1015  to  1025.  A  specific 
gravity  below  1010  should  excite  suspicion  of  hydruria;  one  over 
1030,  of  a  febrile  condition,  or  of  diabetes,  a  disease  in  which  it  may 
rise  to  1050.  The  specific  gravity  has,  however,  been  known  to  sink 
as  low  as  1002  (after  large  potations,  urina  potus),  or  to  rise  as  high 
as  1035  (after  great  sweating)  in  perfectly  healthy  persons. 

Composition. — The  following  table  gives  the  average  amounts  of 
the  urinary  constituents  passed  by  a  man  taking  an  ordinary  diet 
containing  about  100  grammes  of  protein  in  the  twenty-four  hours : — 

Total  quantity  of  urine 1500 "00  grammes. 

Water       .      ' 1440-00 

Solids 60-00 

Urea 35-00 

Uric-  acid          ........  0-75  ,, 

Sodium  chloride       .         .         .         .         .         .         .  16-5  ,, 

Phosphoric  acid -j'o  „ 

Sulphuric  acid 2*0  ,, 

Ammonia          ........  0"65  ,, 

Creatinine         ........  0-9  „ 

Chlorine 11  "O 

Potassium 2-5  ,, 

Sodmm    .........  5-5  ,, 

Calcium 0-26 

Magnesium 0*21  ,, 

The  most  abundant  constituents  of  the  urine  are  water,  urea,  and 
sodium  chloride.  In  the  foregoing  table  one  must  not  be  misled  by 
seeing  the  names  of  the  acids  and  metals  separated.  The  acids  and 
the  bases  are  combined  to  form  salts,  such  as  urates,  chlorides, 
sulphates,  phosphates,  etc. 

Urea. 

Urea,  or  Carbamide,  CO(NH.2).2,  is  isomeric  (that  is,  has  the  same 
empirical,  but  not  the  same  structural  formula)  with  ammonium 
cyanate  (NH^;  CNO,  from  which  it  was  first  prepared  synthetically 
by  Wohler  in  1828.  Since  then  it  has  been  prepared  synthetically 
in  other  ways.     Wohler's  observation  derives  interest  from  the  fact 


CH.  XXXVII.] 


U1!EA 


565 


that  this  was  tho  first  organic  substance  which  was  prepared  syntheti- 
cally by  chemists.* 

When  crystallised  out  from  the  urine  it  is  found  to  be  readily 
soluble  both  in  water  and  alcohol :  it  has  a  saltish  taste,  and  is  neutral 
to  litmus  })aper,  Tho  form  of  its 
crystals  is  shown  in  fig.  425. 

When  treated  with  nitric  acid, 
nitrate  of  urea  (C0N.,H,.HN03)  is 
formed ;  this  crystallises  in  octahedra, 
lozenge-shaped  tablets  or  hexagons  (fig. 
426).  When  treated  with  oxalic  acid, 
flat  or  prismatic  crystals  of  urea  oxa- 
late (C0N"oH,.H..C.,04  +  H.,0)are  formed 
(fig.  427)." 

These  crystals  may  be  readily  ob- 
tained by  adding  excess  of  the  respective 
acids  to  urine  which  has  been  concen- 
trated to  a  third  or  a  quarter  of  its  bulk. 

Under  the  influence  of  an  organised  ferment,  the  micrococcus 
ureae,  which  grows  readily  in  stale  urine,  urea  takes  up  water, 
and  is  converted  into  ammonium  carbonate  [CON2H4-I- 211^0  = 
(NHj)oC03].     Hence  the  ammoniacal  odour  of  putrid  urine. 

By  means  of  nitrous  acid,  urea  is  broken  up  into  carbonic  acid, 
water   and    nitrogen,   CON,H4  +  2HNO,  =  CO.,-H3H20-f2N.,.       The 


Fig.  425.— Crj'stals  of  Urea. 


Fig.  426. — CrystaLs  of  Urea  nitrate. 


Fig.  427. — Crystals  of  Urea  oxalate. 


evolution  of  gas  bubbles  which  takes  place  on  the  addition  of  fuming 
nitric  acid  may  be  used  as  a  test  for  urea. 

Hypobromite  of  soda  decomposes  urea  in  the  following  way  : — 


CON.H^   +    SNaBrO    = 

=    CO,    +    No    +    2H.,0    +    3NaBr. 

[Urea.]                   [Sodium 

[Carbonic  [Nitrogen.]     [Water.]             [Sodium 

hypobromite.] 

acid.]                                                      bromide.] 

This  reaction  is  important,  for  on  it  one  of  the  readiest  methods 
for   estimating  urea  depends.     There  have  been   various   pieces   of 

*  Meldola  has  pointed  out  that  the  English  chemist  Henry  Hennell  prepared 
alcohol  from  olefiant  gas  simultaneously  with  Wohler's  synthesis  of  urea.  The 
honour  of  founding  the  science  of  organic  chemistry  must,  therefore,  be  shared 
between  the  two  men. 


566 


THE   URINE 


[CH.  XXXVII. 


apparatus  invented  for  rendering  the  analysis  easy ;  but  the  one 
described  below  is  the  best.  If  the  experiment  is  performed  as 
directed,  nitrogen  is  the  only  gas  that  comes  off,  the  carbonic  acid 
being  absorbed  by  excess  of  soda.  The  amount 
of  nitrogen  is  a  measure  of  the  amount  of  urea. 

Dupre's  apparatus  (fig.  428)  consists  of  a  bottle  (A) 
united  to  a  measuring  tube  by  indiarubber  tubing.  The 
noeasuring  tube  (C)  is  placed  within  a  cylinder  of  water 
(D),  and  can  be  raised  and  lowered  at  will.  Measure 
25  c.c.  of  alkaline  solution  of  sodium  hypobromite 
(made  by  mixing  2  c.c.  of  bromine  with  23  c.c.  of  a  40 
per  cent,  solution  of  caustic  soda)  into  the  bottle  A. 
Measure  5  c.c.  of  urine  into  a  small  tube  (B),  and  lower 
it  carefully,  so  that  no  urine  spills,  into  the  bottle. 
Close  the  bottle  securely  with  a  stopper  perforated  by 
a  glass  tube  ;  this  glass  tube  (the  bulb  blown  on  this 
tube  prevents  froth  from  passing  into  the  rest  of  the 
apparatus)  is  connected  to  the  measuring  tube  by  india- 
rubber  tubing  and  a  T-piece.  The  third  limb"  of  the 
T-piece  is  closed  by  a  piece  of  indiarubber  tubing  and 
a  pinch-cock,  seen  at  the  top  of  the  figure.  Open  the 
pinch-cock  and  lower  the  measuring  tube  until  the  sur- 
face of  the  water  with  which  the  outer  cyhnder  is  filled 
is  at  the  zero  point  of  the  graduation.  Close  the  pinch- 
cock,  and  raise  the  measuring  tube  to  ascertain  if  the 
apparatus  is  air-tight.  Then  lower  it  again.  Tilt  the 
bottle  A  so  as  to  upset  the  urine,  and  shake  well  for  a 
minute  or  so.  During  this  time  there  is  an  evolution 
of  gas.  Then  immerse  the  bottle  in  a  large  beaker  con- 
taining water  of  the  same  temperature  as  that  in  the 
cylinder.  After  two  or  three  minutes  raise  the  measur- 
ing tube  until  the  surfaces  of  the  water  inside  and  out- 
side it  are  at  the  same  level.  Read  off  the  amount  of 
gas  (nitrogen)  evolved.  SFri  c.c.  of  nitrogen  are  jielded 
by  0*1  gramme  of  urea.  From  this  the  quantity  of  urea 
in  the  5  c.c.  of  urine  and  the  percentage  of  urea  can  be 
calculated.  If  the  total  urea  passed  in  the  twenty-four 
hours  is  to  be  ascertained,  the  twenty-four  hours'  urine 
must  be  carefully  measured  and  thoroughly  mixed. 
A  sample  is  then  taken  from  the  total  for  analysis  ;  and 
then,  by  a  simple  sum  in  proportion,  the  total  amount 
of  urea  is  ascertained. 
A  more  accurate  determination  can  be  best  made  by  the  method  introduced  by 
Morner  and  Sjoquist.  The  following  reagents,  etc.,  are  wanted  : — (i.)  A  saturated 
solution  of  barium  chloride  containing  .">  per  cent,  of  barium  hydrate  :  (ii.)  A  mixture 
of  alcohol  and  ether  in  the  proportion  2:1;  (iii.)  The  apparatus,  etc.,  necessary  for 
carrying  out  Kjeldahrs  method  of  estimating  nitrogen.  5  c.c.  of  urine  are  mixed 
with  .")  c.c.  of  the  barium  mixture,  and  100  c.c.  of  the  ether-alcohol  mixture.  By 
this  means  all  nitrogenous  substances  except  urea  are  precipitated.  Twenty-four 
hours  later  this  is  filtered  off,  and  the  precipitate  is  washed  with  "jO  c.c.  of  the  ether- 
alcohol  mixture.  The  washings  are  added  to  the  filtrate,  and  a  little  magnesia  is 
added  to  drive  off  ammonia.  The  fluid  is  then  evaporated  down  at  55°  C.  until  its 
volume  is  about  10  c.c,  and  the  nitrogen  in  this  estimated  by  Kjeldahl's  method. 
The  nitrogen  found  is  multiplied  by  2"143,  and  the  result  is  the  amount  of  the  urea. 
Kjeldahl's  method  of  estimating  nitrogen  consists  in  boiling  the  material  under 
investigation  with  strong  sulphuric  acid.  The  nitrogen  present  is  by  this  means 
converted  into  ammonia.     Excess  of  soda  is  then  added,  and  the  ammonia  distilled 


Fig.  428.— Dupre's  Urea 
Apparatus. 


en.  XXXVII.]  FOHMATION   OF   UllEA  567 

over  into  a  known  volume  of  standard  acid.  The  amount  of  diminution  of  acidity 
in  the  standard  cnabks  one  to  calculate  the  amount  of  ammonia,  and  thence  the 
amount  of  nitrop:en. 

The  quantity  of  urea  is  variable,  the  chief  cause  of  variation 
being  the  amount  of  protein  food  ingested.  In  a  man  in  a  state  of 
nitrogenous  equilibrium,  taking  daily  100  grammes  of  protein  in  his 
food,  the  quantity  of  urea  secreted  daily  is  about  33  to  35  grammes 
(500  grains).  The  percentage  in  human  urine  would  then  be  2  per 
cent. ;  but  this  also  varies,  because  the  concentration  of  the  urine 
varies  considerably  in  health.  In  dogs  it  may  be  10  per  cent. 
The  excretion  of  urea  is  usually  at  a  maximum  three  hours  after  a 
meal,  especially  after  a  meal  rich  in  proteins.  If,  therefore,  people 
adopt  the  Chittenden  diet,  which  contains  about  half  the  quantity  of 
protein  which  is  present  in  the  more  usual  Yoit  dietary,  their  urine 
will  naturally  show  a  nitrogenous  output  of  half  of  that  which  is  now 
regarded  as  normal.  In  those  who  adopt  such  a  reduced  diet,  Folin 
has  shown  that  the  decrease  in  urinary  nitrogen  falls  mainly  on  the 
urea  fraction,  and  in  some  cases  the  urea  excreted  accounted  for  only 
66  per  cent,  of  the  total  nitrogen.  The  other  nitrogenous  katabolites 
of  the  urine  alter  comparatively  little  under  such  circumstances,  and 
the  creatinine  in  particular  remains  remarkably  constant  in  amount. 

In  our  study  of  protein  absorption  (p.  530),  we  have  already 
indicated  that  the  amino-acid  fragments  of  the  food-protein  are 
utilised  in  two  ways.  A  small  part  is  used  by  the  tissue  cells  for 
the  reconstruction  of  their  protein  which  has  undergone  katabolism. 
In  time  this  will  in  turn  be  katabolised,  and  the  waste  products 
discharged  as  ammonia,  creatinine,  and  probably  a  certain  amount 
of  urea.  This  form  of  metabolism  may  be  termed  tissue  or  endofjenous 
metabolism,  and  its  amount  is  constant  and  independent  to  a  great 
extent  of  the  food.  The  other  and  larger  part  of  the  cleavage  pro- 
ducts of  the  food  protein  are  not  made  use  of  thus,  but  are  rapidly 
converted  into  urea  by  the  liver,  and  discharged  by  the  kidney. 
This  part  of  metabolism  may  be  termed  eo:ogenous ;  it  is  variable  in 
amount,  and  depends  on  the  quantity  of  ingested  protein. 

That  the  liver  is  the  organ  where  urea  is  made  is  shown  by  the 
following  considerations : — 

1.  After  removal  of  the  liver  in  such  animals  as  frogs,  urea 
formation  almost  ceases,  and  ammonia  is  found  in  the  urine  instead. 

2.  In  mammals,  the  extirpation  of  the  liver  is  such  a  severe 
operation  that  the  animals  do  not  live.  But  the  liver  of  mammals 
can  be  very  largely  thrown  out  of  gear  by  connecting  the  portal  vein 
directly  to  the  inferior  vena  cava  (Eck's  fistula).  This  experiment 
has  been  done  successfully  in  dogs ;  the  amount  of  urea  in  the  urine 
is  lessened,  and  its  place  is  taken  by  ammonia. 

3.  When  degenerative  changes  occur  in  the  liver,  as  in  cirrhosis 


568  THE    URINE  [CH.  XXXVII. 

of  that  organ,  the  urea  formed  is  much  lessened,  and  its  place  is 
taken  by  ammonia.  In  acute  yellow  atrophy  urea  is  almost  absent  in 
the  urine,  and,  again,  there  is  considerable  increase  in  the  ammonia. 
In  this  disease  leucine  and  tyrosine  are  also  found  in  the  urine ; 
they  originate  in  the  intestine,  and,  escaping  further  decomposition 
in  the  degenerated  liver,  pass  as  such  into  the  urine. 

That  the  amino-acids  are  the  substance  from  which  the  liver 
forms  urea  is  shown  by  the  fact  that  if  such  amino-acids  as  glycine, 
leucine,  arginine,  etc.,  are  administered  by  the  mouth,  or  injected 
into  the  blood-stream,  the  excretion  of  urea  is  correspondingly  raised. 

The  transformation  of  arginine  into  urea  is  a  subject  on  which  we 
have  more  accurate  information  than  in  the  case  of  any  other  amino- 
acids,  for  there  is  no  doubt  that  the  change,  which  can  be  brought 
about  in  a  test-tube,  is  also  accomplished  in  the  organism.  If  the 
account  of  arginine  given  on  p.  401  is  referred  to,  it  will  be  seen  to 
consist  of  a  urea  radical  and  a  substance  called  ornithine.  On 
hydrolysis  we  therefore  get  urea  and  ornithine  (di-amino-valeric 
acid),  and  this  in  the  body  is  accomplished  by  a  special  enzyme 
called  arginase  (Kossel  and  Dakin)  which  is  more  abundant  in  the 
liver  than  in  any  other  tissue.  The  actual  yield  of  urea  is,  however, 
greater  than  one  would  anticipate,  and  so  it  must  be  supposed  that 
the  ornithine  in  its  turn  is  broken  up  and  urea  is  the  result.  If  we 
glance  at  the  formula  of  ornithine,  and  compare  it  with  that  of  certain 
other  amino-acids  which  are  also  undoubted  urea  forerunners,  we 
have  the  following  : — 

Glycine CoHgNOo 

Leucine CgHigNC)., 

Ornithine C5H12N.3O2 

In  all  cases,  the  atoms  of  carbon  are  more  numerous  than  those  of 
nitrogen.  In  urea  (CONoHJ  the  reverse  is  the  case.  The  amino- 
acids  must  therefore  be  split  into  simpler  compounds  which  unite 
with  one  another  to  form  urea.  Urea  formation  is  thus,  in  part, 
synthetic.  These  simpler  compounds  are  ammonium  salts.  Schroder's 
work,  which  has  been  confirmed  by  subsequent  investigators,  proves 
that  ammonium  carbonate  is  one  of  the  urea  precursors,  if  not  the 
principal  one.  The  equation  which  represents  the  reaction  is  as 
follows : — 

(NHJ.COg   =   CON,H^   +    2U.p. 

[Ammonium  [Urea. ) 

carbonate.] 

Schroder's  principal  experiment  was  this :  a  mixture  of  blood  and 
ammonium  carbonate  was  injected  into  the  liver  by  the  portal  vein ; 
the  blood  leaving  the  liver  by  the  hepatic  vein  was  found  to  contain 
urea  in  great  abundance.  This  does  not  occur  when  the  same  experi- 
ment  is   performed    with   any  other   organ   of    the    body,   so   that 


CH.  XXXVII.]  URAEMIA  569 

Schrr»der's  experiments  also  prove  the  great  importance  of  the  liver 
in  urea  formation.  Similar  results  were  obtained  by  Nencki  with 
ammonium  carbamate. 

The  importance  of  ammonia  is  accentuated  when  we  remember 
that  ammonia  is  one  of  the  products  of  pancreatic  digestion,  and 
probably  also  of  endogenous  protein  metabolism.  The  ammonia, 
whether  it  is  formed  directly  or  through  the  intermediate  stage  of 
amino-acid,  will  combine  with  the  carbonic  acid  of  the  blood  to  form 
ammonium  carbonate  or  carbamate,  and  the  following  structural 
formulae  exhibit  the  close  relationship  between  these  substances  and 
urea.  The  loss  of  one  molecule  of  water  from  ammonium  carbonate 
produces  ammonium  carbamate;  the  loss  of  a  second  molecule  of 
water  produces  urea — 

O  =  C     0.NH4  O  =  C\O.N'H^  ^  =    XNH^ 

[Ammonium  carbonate.]  [Ammonium  carbamate.]  [Urea  or  carbamide.] 

Urea  is  absent,  or  nearly  so,  from  the  muscles,  and  its  place  there 
is  taken  by  the  substance  called  creatine.  This  substance,  however, 
is  eliminated  not  as  urea  but  as  creatinine.  The  fact  that  muscular 
work  does  not  appreciably  increase  protein  katabolism  is  intelligible, 
when,  in  light  of  recently  acquired  knowledge,  we  realise  that  protein 
katabolism,  in  so  far  as  its  nitrogen  is  concerned,  is  independent  of 
the  oxidations  which  give  rise  to  heat,  or  to  the  energy  which  is 
converted  into  work.  Whether  severe  work  will  have  any  effect  on 
the  endogenous  protein  metabolism  of  muscle  cannot  be  shown  by 
investigating  urea  excretion;  determinations  of  creatinine  are  more 
likely  to  yield  satisfactory  results  in  the  study  of  this  question  (see 
Creatinine). 

UrcBmia. — The  older  authors  considered  that  urea  was  formed  in  the  kidneys, 
just  as  they  also  erroneously  thought  that  carbonic  acid  was  formed  in  the  lungs. 
Prevost  and  Dumas  were  the  first  to  show  that  after  complete  extirpation  of  the 
kidneys  the  formation  of  urea  goes  on,  and  that  it  accumulates  in  the  blood  and 
tissues.  Similarly,  in  those  cases  of  disease  in  which  the  kidneys  cease  work,  urea 
is  still  formed  and  accumidates.  This  condition  is  called  urcemia,  and  unless  the 
products  of  nitrogenous  breakdown  be  discharged  from  the  body  the  patient  dies 
in  a  condition  of  coma  preceded  by  convulsions. 

This  term  was  originally  applied  on  the  erroneous  supposition  that  it  is  urea  or 
some  antecedent  of  urea  which  acts  as  the  poison.  There  is  no  doubt  that  the 
poison  is  not  any  constituent  of  normal  urine  ;  if  the  kidneys  of  an  animal  are 
extirpated,  the  animal  dies  in  a  few  days,  but  there  are  no  symptoms  of  uraemia. 
In  man,  also,  if  the  kidneys  are  healthy,  or  approximately  so,  and  suppression  of 
urine  occurs  from  the  simultaneous  blocking  of  both  renal  arteries  by  clot,  or  of  both 
ureters  by  stones,  again  uraemia  does  not  follow.  On  the  other  hand,  uraemia  may 
occur  even  while  a  patient  with  diseased  kidneys  is  passing  a  considerable  amount 
of  urine.  What  the  poison  is  that  is  responsible  for  the  convulsions  and  coma,  is 
unknown.  It  is  doubtless  some  abnormal  katabolic  product,  but  whether  this  is 
produced  by  the  diseased  kidney  cells,  or  in  some  other  part  of  the  body,  is  also 
unknown. 


570  THE   UEINE  [CH.  XXXVII. 

Ammonia. 

A  small  quantity  of  ammonia  always  slips  through  into  the  urine, 
because  a  portion  of  the  ammonia-containing  blood  passes  through 
the  kidney  before  reaching  the  organs  that  are  capable  of  converting 
it  into  urea.  In  man  the  daily  amount  of  ammonia  excreted  varies 
between  0"3  and  1*2  grammes;  the  average  is  0'7  gramme.  The 
ingestion  of  ammonium  carbonate  does  not  increase  the  amount  of 
ammonia  in  the  urine,  but  increases  the  amount  of  urea,  into  which 
substance  the  ammonium  carbonate  is  easily  converted.  But  if  a 
mora  stable  salt,  like  ammonium  chloride,  is  given,  it  appears  as  such 
in  the  urine. 

Under  normal  circumstances  the  amount  of  ammonia  depends  on 
the  adjustment  between  the  production  of  acid  substances  in  meta- 
bolism and  the  supply  of  bases  in  the  food.  Ammonia  formation  is 
the  physiological  remedy  for  deficiency  of  bases. 

When  the  production  of  acids  is  excessive  (as  in  diabetes),  or 
when  mineral  acids  are  given  by  the  mouth  or  injected  into  the 
blood-stream,  the  result  is  an  increase  of  the  physiological  remedy, 
and  excess  of  ammonia  passes  over  into  the  urine.  Under  normal 
circumstances  ammonia  is  kept  at  a  minimum,  being  finally  converted 
into  the  less  toxic  substance  urea,  which  the  kidneys  easily  excrete. 
The  defence  of  the  organism  against  acids  which  are  very  toxic,  is  an 
increase  of  ammonia  formation,  or,  to  put  it  more  correctly,  less  of 
the  ammonia  formed  is  converted  into  urea. 

Under  the  opposite  conditions,  namely,  excess  of  alkali,  either  in 
food  or  given  as  such,  the  ammonia  disappears  from  the  urine,  all 
being  converted  into  urea.  Hence  the  diminution  of  ammonia  in  the 
urine  of  man  on  a  vegetable  diet,  and  its  absence  in  the  urine  of 
herbivorous  animals. 

Not  only  is  this  the  case,  but  if  ammonium  chloride  is  given  to  a 
herbivorous  animal  such  as  a  rabbit,  the  urinary  ammonia  is  but  little 
increased.  It  reacts  with  sodium  carbonate  in  the  tissues,  forming 
ammonium  carbonate  (which  is  excreted  as  urea)  and  sodium  chloride. 
Herbivora  also  suffer  much  more  from,  and  are  more  easily  killed  by, 
acids  than  carnivora,  their  organisation  not  permitting  a  ready  supply 
of  ammonia  to  neutralise  excess  of  acids. 

Creatinine. 

The  creatinine  of  the  urine  is,  next  to  urea,  its  most  abundant, 
nitrogenous  constituent.  It  originates  from  the  substance  known  as 
creatine,  and  creatine  is  in  muscle  the  principal  representative  of 
nitrogenous  katabolism. 

Creatine,  like  arginine,  contains  a  urea  radical,  and  by  boiling 


CII.  XXXVII.]  URIC    ACID  571 

with  baryta  it  splits  into  urea  and  sarcosine  (or  methyl-glycine),  as 
shown  in  the  following  equation : — 

C,H„\,0.,   +    H,0   =    CON,H,    +    C3H-NO.. 

[•'reatiiit'.]  "  [Water.)  [Urea.)  [Sarcosine.]' 

The  same  decomposition  is  shown  graphically  on  p.  401. 

Here  we  have  an  instance  of  a  reaction  which  occurs  in  vitro,  but 
which  is  not  carried  out  in  vivo.  There  is  no  evidence  that  creatine 
in  the  living  body  is  a  precursor  of  urea.  Indeed,  all  the  evidence 
points  the  other  way,  for  if  creatine  is  given  to  an  animal  either  by 
the  mouth,  or  injected  into  the  blood-stream,  there  is  no  increase  in 
the  urea  of  the  urine.  Whether  creatinine  (C\H-NyO,  that  is  creatine 
viinus  water)  is  increased  under  such  conditions  is  also  extremely 
doubtful,  unless  creatine  is  given  in  very  large  amounts.  Even  then 
the  rise  in  creatinine  is  insignificant,  and  a  good  deal  of  the  creatine 
is  excreted  as  such.  If  only  small  amounts  of  creatine  are  given, 
they  are  retained  in  the  body.  Creatinine  thus  appears  to  be  a  sub- 
stance of  almost  wholly  endogenous  origin  (Folin).  Its  amount 
varies  somewhat  in  different  individuals  and  animals,  but  is  remark- 
ably constant  in  the  same  individual  or  the  same  animal,  whatever 
be  the  diet.  Under  ordinary  circumstances  also,  it  is  not  increased 
by  muscular  work,  but  if  the  work  is  excessive,  and  especially  if  the 
muscle  is  not  receiving  a  due  supply  of  carbohydrate  and  fatty  food, 
which  are  the  normal  sources  of  muscular  energy,  the  amount  excreted 
increases,  showing  that  under  such  circumstances  there  is  a  per- 
ceptible increase  in  the  endogenous  protein  katabolism. 


Uric  Acid. 

Uric  Acid  (CjN^H^Os)  is,  in  mammals,  the  medium  by  which  a 
very  small  quantity  of  nitrogen  is  excreted  from  the  body.  It  is, 
however,  in  birds  and  some  reptiles  the  principal  nitrogenous  con- 
stituent of  their  urine.  It  is  not  present  in  the  free  state,  but  is 
combined  with  bases  to  form  urates. 

It  may  be  obtained  from  human  urine  by  adding  5  c.c.  of  hydro- 
chloric acid  to  100  c.c.  of  the  urine,  and  allowing  the  mixture  to 
stand  for  twelve  to  twenty-four  hours.  The  crystals  which  form  are 
deeply  tinged  with  urinary  pigment,  and  though  by  repeated  solution 
in  caustic  soda  or  potash,  and  precipitation  by  hydrochloric  acid, 
they  may  be  obtained  fairly  free  from  pigment,  pure  uric  acid  is  more 
readily  obtained  from  the  solid  urine  of  a  serpent  or  bird,  which 
consists  principally  of  the  acid  ammonium  urate.  This  is  dissolved 
in  soda,  and  then  the  addition  of  hydrochloric  acid  produces  as  before 
the  crystallisation  of  uric  acid  from  the  solution. 


572  THE   URINE  [CH.  XXXVIl. 

The  pure  acid  crystallises  in  colourless  rectangular  plates  or 
prisms.  In  striking  contrast  to  urea  it  is  a  most  insoluble  substance, 
requiring  for  its  solution  1900  parts  of  hot  and  15,000  parts  of  cold 
water.  The  forms  which  uric  acid  assumes  when  precipitated  from 
human  urine,  either  by  the  addition  of  hydrochloric  acid  or  in  certain 
pathological  processes,  are  very  various,  the  most  frequent  being  the 
whetstone  shape ;  there  are  also  bundles  of  crystals  resembling 
sheaves,  barrels,  and  dumb-bells  (see  fig.  429). 

The  murexide  test  is  the  principal  test  for  uric  acid.  The  test 
has  received  the  name  on  account  of  the  resemblance  of  the  colour 
to  the  purple  of  the  ancients,  which  was  obtained  from  certain  snails 
of  the  genus  Murex.  It  is  performed  as  follows :  place  a  little  uric 
acid  or  a  urate  in  a  capsule ;  add  a  little  dilute  nitric  acid  and 
evaporate  to  dryness.     A  yellowish-red  residue  is  left.     Add  a  little 

ammonia  carefully,  and  the  residue 
turns  violet;  this  is  due  to  the  forma- 
tion of  purpurate  of  ammonia.  On  the 
addition  of  potash  the  colour  becomes 
bluer. 

Another  reaction  that  uric  acid  un- 
dergoes (though  it  is  not  applicable  as 
a  test)  is,  that  on  treatment  with 
certain  oxidising  reagents  urea  and 
oxalic  acid  can  be  obtained  from 
it.  Alloxan  (C4H._>ISr204)  or  allantoin 
(C^HyN^Og)  are  intermediate  products. 
It  is,  however,  doubtful  whether  a 
"crystaisr*"  "  similar  oxidation  occurs  in  the  normal 

metabolic  processes  of  the  body. 
Uric  acid  is  dibasic,  and  thus  there  are  two  classes  of  urates — 
the  normal  urates  and  the  acid  urates.  A  normal  urate  is  one  in 
which  two  atoms  of  the  hydrogen  are  replaced  by  two  of  a  monad 
metal  like  sodium ;  an  acid  urate  is  one  in  which  only  one  atom  of 
hydrogen  is  thus  replaced.     The  formulae  would  be — 

051141^403   =   uric  acid. 
CgHgNaN^Og  =   acid  sodium  urate. 
OgHoNa.^lSr^Og   =   normal  sodium  urate. 

The  acid  sodium  urate  is  the  chief  constituent  of  the  pinkish  deposit 
of  urates,  which  often  occurs  in  urine,  and  is  called  the  lateritious 
deposit. 

If  uric  acid  is  represented  by  HoU,  the  normal  urates  may  be  represented  by 
MoU,  and  the  acid  urates  by  MHU.  Bence  Jones,  and  later  Sir  W.  Roberts, 
considered  that  the  urates  actually  occurring  in  urine  are  what  are  termed  quadri- 
urates  MHU.H.,U.  There  is  much  doubt  whether  such  compounds  really  exist ;  if 
they  do,  they  are  readily  decomposed  into  acid  urate,  MHU,  and  free  uric  acid,  HoU. 


Fig.  429. — Various  forms  of  uric  acid 


CH.  XXXVII.]  OltlCrIN   OF    UUIC    ACID  573 

The  quantity  of  uric  acid  excreted  by  an  adult  varies  from  7  to 
10  grains  (0"5  to  0'75  gramme)  daily. 

The  best  method  for  determining  the  quantity  of  uric  acid  in 
the  urine  is  that  of  Hopkins.  Ammonium  chloride  in  crystals  is 
added  to  the  urine  until  no  more  will  dissolve.  This  saturation 
completely  precipitates  all  the  uric  acid  in  the  form  of  ammonium 
urate.  After  standing  for  two  hours  the  precipitate  is  collected  on 
a  filter,  washed  with  saturated  solution  of  ammonium  chloride,  and 
then  dissolved  in  weak  alkali.  From  this  solution  the  uric  acid  is 
precipitated  by  neutralising  with  hydrochloric  acid.  The  precipitate 
of  uric  acid  is  collected  on  a  weighed  filter,  dried,  and  weighed ;  or 
the  crystals  may  be  dissolved  in  sodium  carbonate  solution,  and 
titrated  with  standard  solution  of  potassium  permanganate,  until  a 
diffused  pink  flush  appears  throughout  the  solution. 

Origin  of  Uric  Acid. — Uric  acid  is  not  made  by  the  kidneys ; 
when  these  organs  are  removed,  uric  acid  continues  to  be  formed, 
and  accumulates  in  the  organs,  especially  in  the  liver  and  the  spleen. 
After  extirpation  of  the  liver  in  birds  (in  which  animals  uric  acid  is 
such  an  important  katabolite),  the  formation  of  uric  acid  practically 
ceases,  and  its  place  is  taken  by  ammonia  and  lactic  acid,  and  the 
conclusion  is  therefore  drawn  that  in  these  animals,  ammonia  and 
lactic  acid  are  normally  synthesised  in  the  liver  to  form  uric  acid. 

But  in  mammals,  this  is  not  the  history  of  uric  acid  formation ; 
in  these  animals,  including  man,  uric  acid  is  the  end  product  of  the 
metabolism  of  nuclein,  from  the  bases  of  which  it  arises  by  oxidation. 

Nuclein,  the  main  constituent  of  the  nuclei  of  cells  (see  p.  412), 
yields,  on  decomposition,  certain  products  ca,\led  purine  substances, 
and  their  close  relationship  to  uric  acid  is  shown  by  their  formulae : — 

Purine C5H4N4 

f  Hypoxanthine  (monoxypurine)     .        .  CgHjNjO 

Purine  bases  J  Xanthine  (dioxypurine)  .        .        .  C5H4N4O,, 

^""^  "^^^^i  Adenine  (amino-purine)         .        .        .  C5H.jN4.NH0 

\^ Guanine  (amino-oxypurine)  .        .  C5H^N40.NH2 

Uric  acid  (trioxypurine)         .        .        ,  C5H4N4O3 

Just  as  the  ordinary  protein  metabolism  is  both  exogenous  and 
endogenous,  so  is  it  the  case  with  nuclein  metabolism.  There  are 
certain  kinds  of  food  (such  as  liver  and  sweetbread)  which  are  rich 
in  nuclei,  and  others,  such  as  meat,  which  are  rich  is  purine  bases 
(especially  hypoxanthine).  The  increase  in  uric  acid  excretion  after 
partaking  of  such  food  is  exogenous,  and  those  liable  to  uric  acid 
disorders  should  avoid  such  articles  of  diet.  Other  forms  of  diet 
lead  to  an  increase  in  uric  acid  formation  by  increasing  the  number 
of  leucocytes  in  the  blood,  and  there  is  a  consequent  increase  in  the 
metabolism  of  their  nuclei.  Increase  in  leucocytes  may  occur,  how- 
ever, independently  of  diet,  and  in  the  disease  known  as  leucocy- 


574  THE   URINE  [CH.  XXXVII. 

thremia,  this  occurs  to  a  marked  degree ;  in  such  cases  uric  acid 
formation  increases.  Although  special  attention  has  been  directed 
to  the  nuclei  of  leucocytes  because  these  can  readily  be  examined 
during  life,  it  must  be  remembered  that  the  nuclein  metabolism  of 
all  cells  may  contribute  to  imc  acid  formation.  Uric  acid,  which 
originates  by  metabolism,  is  spoken  of  as  endogenous. 

We  must  next  consider  the  mechanism  by  which  the  tissue  cells 
form  uric  acid  from  nuclein.  This  question  is  not  only  of  interest 
in  itself,  but  also  because  it  illustrates  a  general  truth  concerning 
the  importance  of  the  tissue  enzymes.  The  ferment  of  the  liver 
which  turns  glycogen  into  sugar  is  the  oldest  known  example  of 
these;  in  more  recent  times,  the  importance  of  tissue  erepsins 
(see  p.  531)  and  arginase  (see  p.  568)  has  been  recognised.  In  uric 
acid  formation,  we  have  the  very  striking  example  of  the  action  of 
a  succession  of  enzymes ;  these  have  been  studied  in  the  extracts  of 
different  organs,  and  their  distribution  varies  a  good  deal ;  speaking 
generally,  however,  they  appear  to  be  most  abundant  in  spleen  and 
liver.  The  first  of  these  is  called  nuclease ;  this  liberates  the  purine 
bases  from  nuclein.  The  next  to  come  into  play  are  certain  de- 
amidising  ferments ;  one  of  these,  called  adenase,  converts  adenine 
into  hypoxanthine,  and  another,  called  guanase,  converts  guanine 
into  xanthine.  Finally,  oxidases  step  in,  which  convert  hypoxan- 
thine into  xanthine,  and  xanthine  into  uric  acid.  But  even  that 
does  not  bring  the  list  to  a  conclusion,  for  in  many  organs  there  is 
a  capacity  to  destroy  uric  acid  after  it  is  formed,  and  so  we  are 
protected  from  a  too  great  accvmiulation  of  this  substance.  What 
exactly  happens  to  the  uric  acid  is  not  certain,  although  it  is  clear 
that  the  products  of  its  breakdown  are  not  so  harmful  as  uric  acid 
itself.  The  ferment  responsible  for  uric  acid  destruction  is  called 
the  uricolytic  ferment.  The  uric  acid  which  ultimately  eacapes  as 
urates  (normally)  in  the  urine  is  the  undestroyed  residue. 

In  gout  and  allied  disorders  there  may  be  increased  formation  of 
uric  acid,  or  a  smaller  amount  of  that  formed  may  be  destroyed ; 
the  excess  may  pass  into  the  urine,  partly  as  free  uric  acid  or  excess 
of  urates,  and  so  there  is  a  liability  to  concretions  (calculi,  gravel, 
etc.),  forming  in  the  kidney  or  bladder.  There  is  also  a  tendency 
to  the  deposition  of  urates  in  certain  parts,  and  the  joint  cartilages 
in  particular  are  liable  to  these  concretions.  The  uric  acid  diathesis 
is,  however,  much  too  large  a  subject  to  treat  in  a  physiological  text- 
book, and  medical  students,  when  they  come  to  the  study  of 
pathology,  will  discover  that  many  views  are  held  in  relation  to  it. 

Hippuric  Acid. 

Hippuric  Acid  (C9H9NO3),  combined  with  bases  to  form  hip- 
purates,  is  present  in  small  quantities  in  human  urine,  but  in  large 


CH.  XXXVII.] 


THE   SALTS    OF   THE   IJIUNE 


575 


quantities  in  tho  urine  of  herbivora.  This  is  due  to  the  food  of 
herbivora  containing  substances  belonging  to  the  aromatic  group — 
the  benzoic  acid  series.  If  benzoic  acid  is  given  to  a  man,  it  unites 
with  glycine  with  the  elimination  of  a  molecule  of  water,  and  is 
excreted  as  hippuric  acid — 


CH,.NH,     CH.NH.CO.C.H, 


CgHj.COOH 


[Benzoic  acid.] 


+     I 


COOH 

[Glycine.] 


COOH 

[Hippuric  acid.] 


+    H,0 


[Water.; 


This  is  a  well-marked  instance  of  synthesis  carried  out  in  the 
animal  body,  and  experimental  investigation  shows  that  it  is  accom- 
plished by  the  living  cells  of  the  kid- 
ney itself ;  for  if  a  mixture  of  glycine, 
benzoic  acid,  and  blood  is  injected 
through  the  kidney  (or  mixed  with  a 
minced  kidney  just  removed  from  the 
body  of  an  animal),  their  place  is  found 
to  have  been  taken  by  hippuric  acid. 


Fig.  4.30.— Crystals  of  hippuric  acid. 


The  Inorganic  Constituents  of 
Urine. 

The  inorganic  or  mineral  constitu- 
ents of  urine  are  chiefly  chlorides, 
phosphates,  sulphates,  and  carbonates ; 
the  metals  with  which  these  are  in 
combination  are  sodium,  potassium,  ammonium,  calcium,  and  mag- 
nesium. The  total  amount  of  these  salts  varies  from  19  to  25 
grammes  daily.  The  most  abundant  is  sodium  chloride,  which 
averages  in  amount  10  to  16  grammes  per  diem.  These  substances 
are  derived  from  two  sources — first  from  the  food,  and  secondly  as 
the  result  of  metabolic  processes.  The  chlorides  and  most  of  the 
phosphates  come  from  the  food ;  the  sulphates  and  some  of  the  phos- 
phates, as  a  result  of  metabolism. 

Chlorides. — The  chief  chloride  is  that  of  sodium.  The  ingestion 
of  sodium  chloride  is  followed  by  its  appearance  in  the  urine,  some 
on  the  same  day,  some  on  the  next  day.  Some  is  decomposed  to  form 
the  hydrochloric  acid  of  the  gastric  juice.  The  salt,  in  passing 
through  the  body,  fulfils  the  useful  office  of  stimulating  metabolism 
and  secretion. 

Sulphates. — The  sulphates  in  the  urine  are  principally  those  of 
potassium  and  sodium.  Only  the  smallest  trace  enters  the  body  with 
the  food.  Sulphates  have  an  unpleasant  bitter  taste  (for  instance, 
Epsom  salts) :  hence  we  do  not  take  food  that  contains  them.  The 
sulphates  vary  in  amount  from  1"5  to  3  gramnaes  daily. 


576  THE   URINE  [CH.  XXXVII. 

They  are  derived  from  the  metabolism  of  proteins,  and  the 
excretion  of  sulphates,  though  it  occurs  earlier  than  that  of  urea, 
runs  parallel  with  it.  The  sulphates  are  therefore  like  urea  the 
result  of  exogenous  protein  metabolism.  The  sulphur  of  the  protein, 
which  is  endogenously  katabolised,  is  not  converted  into  ordinary 
sulphates  to  any  great  extent,  but  reappears  in  the  urine  partly  as 
ethereal  sulphates,  and  partly  in  the  form  of  certain  obscure  but 
not  fully  oxidised  sulphur  compounds,  and  is  usually  spoken  of  as 
neutral  sulphur. 

The  ethereal  sulphates  just  mentioned  form  about  a  tenth  of  the 
total  sulphates.  They  are  combinations  of  sulphuric  acid  with 
organic  radicals,  and  the  greater  part  of  them  originate  from  putre- 
factive changes  in  the  intestine.  The  chief  of  these  ethereal 
sulphates  are  phenyl  sulphate  of  potassium  and  indoxyl  sulphate  of 
potassium.  The  latter  originates  from  the  indole  formed  in  the 
intestine,  and  as  it  yields  indigo  when  treated  with  certain  reagents 
it  is  sometimes  called  indican.  It  is  very  important  to  remember 
that  the  indican  of  urine  is  not  the  same  thing  as  the  indican  of 
plants,  which  is  a  glucoside.  Both  yield  indigo,  but  there  the  resem- 
blance ceases. 

The  formation  of  these  sulphates  is  somewhat  important;  the 
aromatic  substances  liberated  by  putrefactive  processes  in  the 
intestine  are  poisonous,  but  their  conversion  into  ethereal  sulphates 
renders  them  harmless. 

The  equation  representing  the  formation  of  potassium  phenyl-sulphate  is  as 
follows  : — 

CeH,,OH  +  SO,<^gg    =   SO /g^fi"^  +   H,,0. 

[Phenol.]  [Potassium  [Potassium  [Water.] 

hydrogen         phenyl-sulphate.] 
sulphate.] 

Indole  (CgH^N)  on  absorption  is  converted  into  indoxyl : — 
f,„/C.OH:CH 

The  equation  representing  the  formation  of  potassium  indoxyl-sulphate  is  as 
follows  : — 

CgH-NO  +  SO./g^    =   SO^/qJ^^^s^   +   H.,0. 

[Indoxyl.]  [Potassium  [Potassium  [Water.] 

hydrogen  indoxyl-sulphate.] 

sulphate.] 

Carbonates. — Carbonates  and  bicarbonates  of  sodium,  calcium, 
magnesium,  and  ammonium  are  only  present  in  alkaline  urine. 
They  arise  from  the  carbonates  of  the  food,  or  from  vegetable  acids 
(malic,  tartaric,  etc.)  in  the  food.  They  are,  therefore,  found  in  the 
urine  of  herbivora  and  vegetarians,  whose  urine  is  thus  rendered 
alkaline.     Urine  containing  carbonates  becomes,  like  saliva,  cloudy 


CH.  XXXVII.] 


THE   PHOSPHATES    IN    URINE 


577 


on  standing,  the  precipitate  consisting  of  calcium  carbonate,  and 
also  phosphates. 

Phosphates. — Two  classes  of  phosphates  occur  in  normal  urine : — 

(1)  Alkaline  phosphates — that  is,  phosphates  of  sodium  (abundant) 
and  potassium  (scanty). 

(2)  Earthy  phosphates — that  is,  phosphates  of  calcium  (abundant) 
and  magnesium  (scanty). 

The  composition  of  the  phosphates  in  urine  is  lial)le  to  variation. 
In  acid  urine  the  acidity  is  due  to  the  acid  salts.  These  are 
chiefly: — 

Sodium  dihydrogen  phosphate,  ]SraH.,P04,  and  calcium  dihydrogen 
phosphate,  CaQIoPO^).,. 

In  neutral  urine,  in  addition,  disodium  hydrogen  phosphate 
(Na.jHPOJ,  calcium  hydrogen  phosphate,  CaHP04,  and  magnesium 


Fig.  4.S1. — Urinary  sediment  of  triple  phos- 
phates (large  prismatic  crystals)  and 
urate  of  ammonium,  from  urine  which 
had  undergone  alkaline  fermentation. 


Fig.  432. — Mucus  deposited  from  urine. 


hydrogen  phosphate,  MgHP04,  are  found.  In  alkaline  urine  there 
may  be  instead  of,  or  in  addition  to,  the  above,  the  normal  phosphates 
of  sodium,  calcium,  and  magnesium  [Na3P04,  Ca3(P04).^,  Mg3(P04)2]. 

The  earthy  phosphates  are  precipitated  by  rendering  the  urine 
alkaline  by  ammonia.  In  decomposing  urine,  ammonia  is  formed 
from  the  urea:  this  also  precipitates  the  earthy  phosphates.  The 
phosphates  most  frequently  found  in  the  white  creamy  precipitate 
which  occurs  in  decomposing  urine  are : — 

(1)  Triple  phosphate  or  ammonio  -  magnesium  phosphate 
(]SrH4MgP04  +  6H.30).  This  crystallises  in  "coffin-lid  "  crystals  (see 
fig.  431)  or  feathery  stars. 

(2)  Stellar  phosphate,  or  calcium  phosphate ;  this  crystallises  in 
star-like  clusters  of  prisms. 

As  a  rule  normal  urine  gives  no  precipitate  when  it  is  boiled ; 
but  sometimes  neutral,  alkaline,  and  occasionally  faintly  acid  urines 

2  O 


578  THE   URINE  [CH.  XXXVIL 

give  a  precipitate  of  calcium  phosphate  when  boiled :  this  precipitate 
is  amorphous,  and  is  liable  to  be  mistaken  for  albumin.  It  may  be 
distinguished  readily  from  albumin,  as  it  is  soluble  in  a  few  drops  of 
acetic  acid,  whereas  coagulated  protein  does  not  dissolve. 

The  phosphoric  acid  in  the  urine  chiefly  originates  from  the  phos- 
phates of  the  food,  but  is  partly  a  decomposition  product  of  the  phos- 
phorised  organic  materials  in  the  body,  such  as  lecithin  and  nuclein. 
The  amount  of  P..O5  in  the  twenty-four  hours'  urine  varies  from  2'5 
to  3"5  grammes,  of  which  the  earthy  phosphates  contain  about  half 
(1  to  1-5  gr.). 

Tests  for  the  Inorganic  Salts  of  Urine. 

Chlorides. — Acidulate  with  nitric  acid  and  add  silver  nitrate  ;  a  white  precipitate 
of  silver  chloride,  soluble  in  ammonia,  is  produced.  The  object  of  acidulating  with 
nitric  acid  is  to  prevent  phosphates  being  precipitated  by  the  silver  nitrate. 

Sulphates. — Acidulate  with  hydrochloric  acid,  and  add  barium  chloride.  A 
white  precipitate  of  barium  sulphate  is  produced.  Hydrochloric  acid  is  again  added 
first,  to  prevent  precipitation  of  phosphates. 

Phosphates. — i.  Add  ammonia;  a  white  crystalline  precipitate  of  earthy  (that 
is,  calcium  and  magnesium)  phosphates  is  produced.  This  becomes  more  apparent 
on  standing.  The  alkaline  (that  is,  sodium  and  potassium)  phosphates  remain  in 
solution,  ii.  Mix  another  portion  of  urine  with  half  its  volume  of  nitric  acid  ;  add 
ammonium  molybdate,  and  boil.  A  yellow  crystalline  precipitate  falls.  This  test  is 
given  by  both  classes  of  phosphates. 

Quantitative  estimation  of  the  salts  is  accomplished  by  the  use  of  solutions  of 
standard  strength,  which  are  run  into  the  urine  till  the  formation  of  a  precipitate 
ceases.  The  standards  are  made  of  silver  nitrate,  barium  chloride,  and  uranium 
nitrate  or  acetate  for  chlorides,  sulphates,  and  phosphates  respectively. 

Urinary  Deposits. 

The  different  substances  that  may  occur  in  urinary  deposits  are 
formed  elements  and  chemical  substances. 

The  formed  or  anatomical  elements  may  consist  of  blood 
corpuscles,  pus,  mucus,  epithelium  cells,  spermatozoa,  casts  of  the 
urinary  tubules,  fungi,  and  entozoa.  All  of  these,  with  the  exception 
of  a  small  quantity  of  mucus,  which  forms  a  flocculent  cloud  in  the 
urine,  are  pathological,  and  the  microscope  is  chiefly  employed  in 
their  detection. 

The  chemical  substances  are  uric  acid,  urates,  calcium  oxalate, 
calcium  carbonate,  and  phosphates.  Earer  forms  are  leucine,  tyrosine, 
xanthine,  and  cystin.  We  shall,  however,  here  only  consider  the 
commoner  deposits,  and  for  their  identification  the  microscope  and 
chemical  tests  must  both  be  employed. 

Deposit  of  Uric  Acid. — This  is  a  sandy  reddish  deposit  resembling 
cayenne  pepper.  It  may  be  recognised  by  its  crystalline  form  (fig. 
429,  p.  572)  and  the  murexide  reaction.  The  presence  of  these 
crystals  generally  indicates  an  increased  formation  of  uric  acid,  and, 
if  excessive,  may  lead  to  the  formation  of  stones  or  calculi  in  the 
bladder. 


cn.  XXXVII.] 


URINARY    DEPOSITS 


579 


Deposit  of  Urates.— This  is  much  commoner,  and  may,  if  the 
urine  is  concentrated,  occur  in  normal  urine  when  it  cools.  It  is 
generally  found  in  the  concentrated  urine  of  fevers ;  and  there 
appears  to  be  a  kind  of  fermentation,  called  the  acid  fermentation, 
which  occurs  in  the  urine  after  it  has  been  passed,  and  which  leads 
to  the  same  result.  The  chief  constituent  of  the  deposit  is  the  acid 
sodium  urate,  the  formation  of  which  from  the  normal  sodium  urate 
of  the  urine  may  be  represented  by  the  equation : — 


2CH,Na.N,0.,    +    H,0    +    CO., 


2C,H3NaN,P3    +    Na.,C03. 

[Normal  soiliiiiu  [Water.]        [Carbonic        [Acid  sodium  urate  J  [Sodium 

urate.]  acid.]  carbonate.] 


This  deposit  may  be  recognised  as  follows : — 

(1)  It  has  a  pinkish  colour;  the  pigment  called  uro-erythrin  is  one 
of  the  pigments  of  the  urine,  but  its  relationship  to  the  other  urinary 
pigments  is  not  known. 

(2)  It  dissolves  upon  warming  the  urine. 

(3)  Microscopically  it  is  usually  amorphous,  but  crystalline  forms 
similar  to  those  depicted  in  fig.  431  may  occur.  Crystals  of  calcium 
oxalate  may  be  mixed  with  this  deposit  (see  fig.  433). 


Fig.  433.— Crystals  of  calcium  oxalate. 


434.— Crystals  of  cy.stin. 


Deposit  of  Calcium  Oxalate. — This  occurs  in  envelope  crystals 
(octahedra)  or  dumb-bells.  It  is  insoluble  in  ammonia,  and  in  acetic 
acid.     It  is  soluble  with  difficulty  in  hydrochloric  acid. 

Deposit  of  Cystin. — Cystin  (CgHioNoS.pj  is  recognised  by  its 
colourless  six-sided  crystals  (fig.  434).  These  are  rare:  they  occur 
only  in  acid  urine,  and  they  may  form  concretions  or  calculi. 
Cystinuria  (cystin  in  the  urine)  is  hereditary. 

Deposit  of  Phosphates. — These  occur  in  alkaline  urine.  The 
urine  may  be  alkaline  when  passed,  due  to  fermentative  changes 
occurring  in  the  bladder.  All  urine,  however,  if  exposed  to  the  air 
(unless  the  air  is  perfectly  pure,  as  on  the  top  of  a  snow  mountain), 


580  THE   URINE  [CH.  XXXVII. 

will  ill  time  become  alkaline,  owing  to  the  growth  of  the  micrococcus 
urece.     This  forms  ammonium  carbonate  from  the  urea. 

CONoH,   +    2HoO    =   (NHJoCOg. 

[Urea.]  [Water.]  [Ammonium 

carbonate.] 

The  ammonia  renders  the  urine  alkaline  and  precipitates  the 
earthy  phosphates.  The  chief  forms  of  phosphates  that  occur  in 
urinary  deposits  are — 

(1)  Calcium  phosphate,  Oa,^(VO^., ;  amorphous. 

(2)  Triple  or  ammonio-magnesium  phosphate,  MgNH4P04 ;  cofhn- 
lids  and  feathery  stars  (fig.  431). 

(3)  Crystalline  phosphate  of  calcium,  CaHPO^,  in  rosettes  of 
prisms,  in  spherules,  or  in  dumb-bells. 

(4)  Magnesium  phosphate,  Mg3(P04)2  +  22H._,0,  occurs  occasion- 
ally, and  crystallises  in  long  plates. 

All  these  phosphates  are  dissolved  by  acids,  such  as  acetic  acid, 
without  effervescence. 

A  solution  of  ammonium  carbonate  (1  in  5)  eats  magnesium 
phosphate  away  at  the  edges ;  it  has  no  effect  on  the  triple  phosphate. 
A  phosphate  of  calcium  (CaHP04  +  2HoO)  may  occasionally  be 
deposited  in  acid  urine.  Pus  in  urine  is  apt  to  be  mistaken  for 
phosphates,  but  can  be  distinguished  by  the  microscope. 

Deposit  of  calcium  carbonate,  CaCOg,  appears  but  rarely  as 
whitish  balls  or  biscuit-shaped  bodies.  It  is  commoner  in  the  urine 
of  herbivora.  It  dissolves  in  acetic  or  hydrochloric  acid,  with 
effervescence. 

The  following  is  a  summary  of  the  chemical  sediments  that  may 
occur  in  urine : — 

CHEMICAL  SEDIMENTS   IN   URINE. 
Ik  Acid  Urine.  I  In  Alkaline  Urine. 


Uric  Acid. — Whetstone,  dumb-bell, 
or  sheaf-like  aggregations  of  crystals 
deeply  tinged  by  pigment. 

Uratfs. — Generally  amorphous.  The 
acid  urate  of  sodium  and  of  ammonium 
may  sometimes  occur  in  star-shaped 
clusters  of  needles  or  spheroidal  clumps 
with  projecting  spines.  Tinged  brick- 
red.     Soluble  on  warming. 

Calcium    Oxalate.  —  Octahedra,    so- 


Fhosphates.  —  Calcium      phosphate, 
Ca.XP04)o.     Amorphous. 

Triple  phosphate, 
MgNH.POj  +   6H,0.       Coffin-lids     or 
feathery  stars. 

Calcium   hydrogen   phosphate, 
CaHPOj.    Rosettes,  spherules,  or  dumb- 
bells. 

Magnesium  phosphate, 
Mg3(P04)o   +   22H2O.     Long  plates. 


called  envelope  crystals.     Insoluble  in  All  the  preceding  are  soluble  in  acetic 

acetic  acid.  acid  without  effervescence. 

Cystin. — Hexagonal  plates.     Rare.  Calcium   Carbonate,  CaCOo. — Biscuit- 

Leucine  and  Tyrosine.— Rare.  shaped  crystals.     Soluble  in  acetic  acid 

Calcium  Phosphate,  with  effervescence. 

CaHPO,    +   2H.,0. — Rare.  Ammonium  Crate, 

C5H,,(NHJ,,.NA-    —  "Thorn-apple" 
spherules. 
i       Leucine  and  Tyrosine. — Very  rare. 


CH.  XXXVII.] 


PATHOLOGICAL   URINE 


581 


Pathological  Urine. 

Under  this  head  we  shall  briefly  consider  only  those  abnormal 
constituents  which  are  most  frequently  met  with. 

Proteins. — There  is  no  protein  in  normal  urine,*  and  the  most 
common  cause  of  the  appearance  of  albumin  in  the  urine  is  disease 
of  the  kidney  (Bright's  disease).  The  term  "al- 
bumin" is  the  one  used  by  clinical  observers. 
Properly  speaking,  it  is  a  mixture  of  serum  albumin 
and  serum  globulin.  Of  these,  serum  albumin  is 
usually  the  more  abundant.  Globulins,  and  especi- 
ally englobulins,  have  probably  larger  molecules,  so 
escape  of  globulin  indicates  more  serious  damage  to 
the  renal  cells.  The  best  methods  of  testing  for 
and  estimating  the  protein  are  the  following: — 

(«)  Boil  the  top  of  a  long  column  of  urine  in  a  test-tube. 
If  the  urine  is  acid,  the  albumin  is  coagulated.  If  the  quantity 
of  albumin  is  small,  the  cloudiness  produced  is  readily  seen, 
as  the  unboiled  urine  below  it  is  clear.  This  is  insoluble  in-  a 
few  drops  of  acetic  acid,  and  so  may  be  distinguished  from 
phosphates.  If  the  urine  is  alkaline,  it  should  be  first  rendered 
acid  with  a  little  dilute  acetic  acid. 

(h)  Heller''s  Nitrir-aeid  Test. — Pour  some  of  the  urine  gently 
on  to  the  surface  of  some  nitric  acid  in  a  test-tube.  A  ring  of 
white  precipitate  occurs  at  the  junction  of  the  two  liquids.  This 
test  is  used  for  small  quantities  of  albumin. 


Esba< 


{<•)  Estimation  of  Albwmln   l>i/  Eshnrlis  AUmm'inometei 
en's   reagent   for  precipitating  the  albumin   is  made   by 


Fio.  435.— Esbach's 
Albuminometer. 

dissolving  10  grammes  of  picric  acid  and  20  grammes  of  citric 

acid  in  800  or  900  c.c.  of  boiling  water,  and  then  adding  sufficient  water  to  make  up 

to  a  litre  (1000  c.c). 

The  albuminometer  is  a  test-tube  graduated  as  shown  in  fig.  435. 

Pour  the  urine  into  the  tube  up  to  the  mark  U  ;  then  the  reagent  up  to  the 
mark  R.  Close  the  tube  with  a  cork,  and  to  ensure  complete  mixture,  tilt  it  to  and 
fro  a  dozen  times  without  shaking.  Allow  the  corked  tube  to  stand  upright  twenty- 
four  hours  ;  then  read  off  on  the  scale  the  height  of  the  coagulum.  The  figures  indi- 
cate grammes  of  dried  albumin  in  a  litre  of  urine.  The  percentage  is  obtained  by 
dividing  by  10.  Thus,  if  the  coagulum  stands  at  3,  the  amount  of  albumin  is  3 
grammes  per  litre,  or  0"3  gr.  in  100  c.c.  If  the  sediment  falls  between  any  two 
figures,  the  distance  |,  {,,  or  j^'  from  the  upper  or  lower  figure  can  be  read  olf  with 
sufficient  accuracy.  Thus,  the  surface  of  the  sediment  being  midway  between  3  and 
4  would  be  read  as  3o.  When  the  albumin  is  so  abundant  that  the  sediment  is 
above  4,  a  more  accurate  result  is  obtained  by  first  diluting  the  urine  with  one  or 
two  volumes  of  water,  and  then  multiplying  the  resulting  figure  by  2  or  3,  as  the 
case  may  be.  If  the  amount  of  albumin  is  less  than  '05  per  cent.,  it  cannot  be 
accurately  estimated  by  this  method. 

A  condition  called  "  peptonuria,"  or  peptone  in  the  urine,  is 
observed  in  certain  pathological  states,  especially  in  diseases  where 

*  This  absolute  statement  is  true  for  all  practical  purposes.  Morner,  however, 
has  stated  that  a  trace  of  protein  (serum  albumin  plus  the  protein  constituent  of 
mucin)  does  occur  in  normal  urine  ;  but  the  trace  is  negligible,  many  hundreds  of 
litres  of  urine  having  to  be  used  to  obtain  an  appreciable  quantity. 


582  THE   URINE  [CII.  XXXVII. 

there  is  a  formation  of  pus,  and  particularly  if  the  pus  is  decomposed 
owing  to  the  action  of  a  bacterial  growth  called  staphylococcus ;  one 
of  the  products  of  disintegration  of  pus  cells  appears  to  be  peptone ; 
and  this  leaves  the  body  by  the  urine.  The  term  "  peptone,"  how- 
ever, is  in  the  strict  sense  of  the  word  incorrect ;  the  proteid  present 
is  deutero-proteose.  In  the  disease  of  bone  called  "  osteomalacia  "  a 
proteose  is  also  usually  found  in  the  urine.  This  more  nearly 
resembles  hetero-proteose  in  its  properties. 

Sugar. — Normal  urine  contains  no  sugar,  or  so  little  that  for 
cHnical  purposes  it  may  be  considered  absent.  It  occurs  in  the 
disease  called  diabetes  mellitus,  which  can  be  artificially  produced  by 
puncture  of  the  medulla  oblongata,  or  by  extirpation  of  the  pancreas. 
The  disease  as  it  occurs  in  man  may  be  due  to  disordered  metabolism 
of  the  liver,  to  disease  of  the  pancreas,  and  to  other  causes  (see  p.  526). 

The  sugar  present  is  dextrose.  Lactose  may  occur  in  the  urine 
of  nursing  mothers.  Levulose,  pentoses,  and  other  sugars  are  found 
but  rarely.  Diabetic  urine  also  contains  hydroxybutyric  acid,  and 
may  contain  or  yield  on  distillation  acetone,  and  ethyl-diacetic  acid. 
The  methods  usually  adopted  for  detecting  and  estimating  the  sugar 
are  as  follows: — 

(a)  The  urine  has  generally  a  high  specific  gravity. 

(^>)  The  presence  of  sugar  is  shown  by  the  reduction  (yellow  precipitate  of 
cuprous  oxide)  that  occurs  on  boiling  with  Fehling's  solution.  Fehling's  solution  is 
an  alkaline  solution  of  copper  sulphate  to  which  Rociielle  salt  has  been  added.  The 
Rochelle  salt  (double  tartrate  of  potash  and  soda)  holds  the  cupric  hydrate  in 
solution,  Fehling's  solution  should  always  be  freshly  prepared,  as,  on  standing,  an 
isomeride  is  formed  from  the  tartaric  acid,  which  reduces  the  cupric  to  cuprous 
oxide.  Fehhng's  solution  should,  therefore,  always  be  tested  by  boiling  before  it  is 
used.     If  it  remains  clear  on  boiling,  it  is  in  good  condition. 

(c)  Picric  Acid  Test. — Take  a  drachm  (about  4  c.c.)  of  diabetic  urine;  add  to  it 
an  equal  volume  of  satiu-ated  aqueous  solution  of  picric  acid,  and  half  the  volume 
{i.e.,  2  c.c.)  of  the  liquor  potiissas  of  the  British  Pharmacopoeia.  Boil  the  mixture 
for  about  a  minute,  and  it  becomes  so  intensely  dark  red  as  to  be  opaque.  Now  do 
the  same  experiment  with  normal  urine.  An  orange-red  colour  appears  even  in  the 
cold,  and  is  deepened  by  boiling,  but  it  never  becomes  opaque,  and  so  the  urine  for 
clinical  purposes  may  be  considered  free  from  sugar.  This  reduction  of  picric  acid 
by  normal  urine  is  due  to  creatinine. 

(f/)  QiKintitatii'P  Determination  of  Stu/ar  in  Urine. — Fehling's  solution  is  pre- 
pared as  follows: — 31  "639  grammes  of  copper  sulphate  are  dissolved  in  about  200 
c.c.  of  distilled  water;  173  grammes  of  Rochelle  salt  are  dissolved  in  600  c.c.  of  a 
14  per  cent,  solution  of  caustic  soda.  The  two  solutions  are  mixed  and  diluted  to  a 
litre.  Ten  c.c.  of  this  solution  are  equivalent  to  0*05  gramme  of  dextrose.  DiUite 
10  c.c.  of  this  solution  with  about  40  c.c.  of  water,  and  boil  it  in  a  porcelain  basin. 
Run  into  this  from  a  burette  the  urine  (which  should  be  previously  diluted  with  nine 
times  its  volume  of  distilled  water)  until  the  blue  colour  of  the  copper  solution 
disappears — that  is,  till  all  the  cupric  hydrate  is  reduced.  The  mixture  in  the  basin 
should  be  boiled  after  every  addition.  The  quantity  of  diluted  urine  used  from  the 
burette  contains  0'05  gramme  of  sugar.  Calculate  the  percentage  from  this, 
remembering  that  the  urine  has  been  diluted  to  ten  times  its  original  volume. 

Pavy's  modification  of  Fehhng's  solution  is  often  used.  Here  ammonia 
holds  the  copper  in  solution,  and  no  precipitate  forms  on  boiling  with  sugar,  as 
ammonia  holds  the  cuprous  oxide  In  solution.     The  reduction  is  complete  when  the 


cii.  XXXVII.]  PATHOLorriCAL  ttrine  583 

blue  colour  disappears;  10  r.c.  of  Pavy's  solution -1  c.o.  of  Fehling's  solution  = 
0  00;")  gramme  of  dextrose . 

In  some  cases  of  diabetic  urine  where  there  is  excess  of  ammonio-magnesic 
phosphate,  the  full  reduction  is  not  obtained  with  Fehling's  solution,  and  when  the 
quantity  of  sugar  is  small  it  may  be  missed.  In  such  a  case  excess  of  soda  or 
potash  should  be  first  added,  the  precipitated  phos])hates  filtered  off,  and  the  filtrate 
after  it  has  been  well  boiled  may  then  be  titrated  with  Fehling's  solution. 

Fehling's  test  is  not  absolutely  trustworthy.  Often  a  normal  urine  will 
decolorise  Fehling's  solution,  though  seldom  a  red  precipitate  is  formed.  This  is 
due  to  excess  of  urates  and  creatinine.  Another  substance  called  glycuronic  acid 
(C.jHiijO;)  is,  however,  very  likely  to  be  confused  with  sugar  by  Fehling's  test ;  the 
cause  of  its  appearance  is  sometimes  the  administration  of  drugs  (chloral,  camphor, 
etc.) ;  but  sometimes  it  appears  independently  of  drug  treatment.     (See  p.  527.) 

In  the  rare  and  hereditary  condition  caUed  alcaptonuria,  confusion  may  also 
arise.  Alcapton  is  a  substance  which  originates  from  tyrosine  by  an  unusual 
form  of  metabolism.  It  gives  the  urine  a  brown  tint,  which  darkens  on  exposure 
to  the  air.  It  is  an  aromatic  substance,  which  Baumann  and  Wolkow  and  later 
Garrod  identified  with  homogentisinic  acid  (C,,H.,.(OH).rH.j.COOH). 

{f)  A  good  confirmatory  test  for  sugar  is  the  fernwntation  test,  which  is  per- 
formed as  follows  : — 

Half  fill  a  test-tube  with  the  urine  and  add  a  little  German  yeast.  Fill  up  the 
tube  with  mercury ;  invert  it  in  a  basin  of  mercury,  and  leave  it  in  a  warm  place 
for  twenty-four  hours.  The  sugar  will  undergo  fermentation :  carbonic  acid  gas 
accumulates  in  the  tube,  and  the  liquid  no  longer  gives  the  tests  for  sugar,  or  only 
faintly,  but  gives  those  for  alcohol  instead.  The  specific  gravity  falls.  A  control 
experiment  should  be  made  with  yeast  and  water  in  another  test-tube,  as  a  small 
yield  of  carbonic  acid  is  sometimes  obtained  from  impurities  in  the  yeast. 

if)  The  phf.nj/lhydrazine  test  (p.  395)  may  also  be  applied. 

Bile. — This  occurs  in  jaundice.  The  urine  is  dark-brown, 
greenish,  or  in  extreme  cases  almost  black  in  colour.  The  most 
readily  applied  test  is  Gmelin's  test  for  the  bile  pigments.  Excess 
of  urobilin  should  not  be  mistaken  for  bile  pigment.  Pettenkofer's 
test  for  the  bile  acids  seldom  succeeds  in  urine  if  the  test  is  done  in 
the  ordinary  way.  The  best  method  is  to  warm  a  thin  film  of  urine 
and  cane  sugar  solution  in  a  flat  porcelain  dish.  Then  dip  a  glass  rod 
in  strong  sulphuric  acid,  and  draw  it  across  the  film.  Its  track  is 
marked  by  a  purplish  line.  Hay's  sulphur  test  is  a  good  one  for  bile 
salts.  If  some  flowers  of  sulphur  are  sprinkled  on  the  surface  of 
normal  urine,  it  remains  floating  on  the  top.  If  bile  salts  are  present 
even  in  small  quantities,  the  fine  sulphur  particles  fall  down  to  the 
bottom  of  the  vessel  in  which  the  urine  is  contained ;  this  is  due  to 
an  alteration  of  surface  tension  which  bile  salts  produce. 

Blood. — When  htemorrhage  occurs  in  any  part  of  the  urinary 
tract,  blood  appears  in  the  urine.  It  is  found  in  the  acute  stage  of 
Bright's  disease.  If  a  large  quantity  is  present,  the  urine  is  deep 
red.  Microscopic  examination  then  reveals  the  presence  of  blood 
corpuscles,  and  on  spectroscopic  examination  the  bands  of  oxyhoemo- 
globin  are  seen. 

If  only  a  small  quantity  of  blood  is  present,  the  secretion — 
especially  if  acid — has  a  characteristic  reddish-brown  colour,  which 
physicians  term  "  smoky." 


684  THE  URINE  [CH.  XXXVII. 

The  blood  pigment  may,  under  certain  circumstances,  appear  in 
the  urine  without  the  presence  of  any  blood  corpuscles  at  all.  This 
is  produced  by  a  disintegration  of  the  corpuscles  occurring  in  the 
circulation.  The  condition  so  produced  is  called  hcemoglohinuria ; 
it  occurs  in  several  pathological  states,  as  for  instance  in  the  tropical 
disease  called  "Black-water  fever."  The  pigment  is  in  the  condi- 
tion of  methaemoglobin  mixed  with  more  or  less  oxyhaemoglobin, 
and  the  spectroscope  is  the  means  used  for  identifying  these 
substances. 

Pus  occurs  in  the  urine  as  the  result  of  suppuration  in  any  part 
of  the  urinary  tract.  It  forms  a  white  sediment  resembling  that  of 
phosphates,  and,  indeed,  is  always  mixed  with  phosphates.  The  pus 
corpuscles  may,  however,  be  seen  with  the  microscope ;  their  nuclei 
are  rendered  evident  by  treatment  with  1  per  cent,  acetic  acid,  and 
the  pus  corpuscles  are  seen  to  resemble  white  blood-corpuscles,  which, 
in  fact,  they  are  in  origin.     They  dissolve  in  glacial  acetic  acid. 

Some  of  the  protein  constituents  of  the  pus  cells — and  the  same 
is  true  for  blood — pass  into  solution  in  the  urine,  so  that  the  urine 
pipetted  off  from  the  surface  of  the  deposit  gives  the  tests  for 
albumin. 

On  the  addition  of  liquor  potassse  to  the  deposit  of  pus  cells,  a 
ropy  gelatinous  mass  is  obtained.  This  is  distinctive.  Mucus  treated 
in  the  same  way  is  dissolved. 


CHAPTER  XXXVIIl 

THE  SKIN   AND   ITS   APPENDAGES 

The  skill  is  composed  of  two  parts,  epidermis  or  cuticle,  and  dermis 
or  cutis  vera. 

The  Epidermis  is  composed  of  a  large  number  of  layers  of  cells ; 
it  is  a  very  thick  stratified  epithelium.     The  deeper  layers  are  proto- 


FiG.  436. — Vertical  section  of  the  epidermis  of  the  prepuce,  a,  stratum  corneum,  of  very  few  layers 
the  stratum  lucidum  and  stratum  granulosum  not  being  distinctly  represented  ;  b,  c,  d,  and  e,  the 
layers  of  the  stratum  Malpighii,  a  certain  number  of  the  cells  in  layers  d  and  e  showing  signs  of 
division ;  it  consists  chiefly  of  prickle  cells  ;  g,  connective-tissue  cells  in  cutis  vera.    (Cadiat.) 

plasmic,  and  form  the  rete  mucosum,  or  Malpighian  layer ;  the  surface 
layers  are  hard  and  horny ;  this  horny  layer  is  the  thickest  part  of 
the  epidermis,  and  is  specially  thick  on  the  palms  and  soles,  where 


58G 


THE   SKIN    AND    ITS    APPENDAGES 


[CII.  XXXVIII. 


it  is  subjected  to  most  friction.  The  cells  of  the  deepest  layers  of 
the  Malpighian  layer  are  columnar  in  shape;  the  layers  next  to  these 
are  composed  of  polyhedral  cells,  which  become  flatter  as  they 
approach  the  horny  layers.     Between  these  cells  are  fine  intercellular 


C 


passages,  bridged  across  by  fine 
protoplasmic    processes,   which 
pass  from  cell  to  cell ;  the  spaces 
between  the  cells  serve  for  the 
passage  of  lymph.     It  is  in  the 
cells  of  the  Malpighian  layer  that  pig- 
ment  granules   are   deposited    in    the 
coloured  races. 

Between  the  horny  layer  and  the 
Malpighian  layer  are  two  intermediate 
strata,  in  which  the  transformation  of 
protoplasm  into  horny  material  {kera- 
tin) is  taking  jDlace.  In  the  first  of 
these — that  is,  the  one  next  to  the 
Malpighian  layer,  the  cells  are  flat- 
tened, and  filled  with  large  granules  of  eleidin,  an  intermediate  sub- 
stance in  the  formation  of  horn.  This  layer  is  called  the  stratum 
granulosum. 

Above  this  are  several  layers  of  clear,  more  rounded  cells,  which 
constitute  the  stratum   lucidum;   and  above  this  the  horny  layer 


Fig.  437. — Vertical  section  of  skin. 
A.  Sebaceous  gland  opening 
into  hair  follicle.  B.  Muscu- 
lar fibres.  C.  Sudoriferous  or 
sweat-gland.  D.  Subcutaneous 
fat.  B.  Fundus  of  hair  follicle, 
with  hair  papilla.    (Klein.) 


CII.  XXXVIII.] 


THE    DKIIMIS    AND    El'IDERMIS 


587 


proper,  many  strata  deep,  begins.  The  colls  become  more  and  more 
scaly  as  they  approach  the  surface,  where  they  lose  their  nuclei  and 
eventually  become  detached. 

The  epidermis  grows  by  a  multiplication  of  the  deepest  layer  of 


'.ic  d 


Fro,  438.— Surface  of  a  white  hair,  maguitied  160  diameters.    Tlie  wavy  lines  mark  the  ujjper  or  free 
edges  of  the  cortical  scales,     i?,  separated  scales,  magnified  350  diameters.    (K/illiker.) 

cells  (fig.  436  6);  the  newly-formed  cells  push  towards  the  surface 
those  previously  formed,  in  their  progress  undergoing  the  transfor- 
mation into  keratin. 

The  epidermis  has  no  blood-vessels;   nerve-fibrils  pass  into  its 
deepest  layers,  and  ramify  between  the 
cells. 

The  Dermis  is  composed  of  dense 
fibrous  tissue,  which  becomes  looser  and 
more  reticular  in  its  deeper  part,  where 
it  passes  by  insensible  degrees  into  the 
areolar  and  adipose  tissue  of  the  sub- 
cutaneous region.  The  denser  superficial 
layer  is  very  vascular,  and  is  covered 
with  minute  papillce ;  the  epidermis  is 
moulded  over  these,  and  in  the  palms 
and  soles,  where  the  papillae  are  largest 
and  are  disposed  in  rows,  their  presence 
is  indicated  by  the  well-known  ridges 
on  the  surface. 

The  papillae  contain  loops  of  capil- 
laries, and  in  some  cases,  especially  in 
the  palm  of  the  hand  and  fingers,  they 
contain  tactile  corpuscles  (which  will  be 
more  fully  described  in  connection  with 
the  sense  of  touch).  Special  capillary 
networks  are  distributed  to  the  sweat-glands,  sebaceous  glands,  and 
hair  follicles. 

The  deeper  portions  of  the  dermis  in  the  scrotum,  penis,  and 
nipple,  contain  involuntary  muscular  tissue;  there  is  also  a  bundle  of 
muscular  tissue  attached  to  each  hair  follicle. 


Fig.  439. — Longitudinal  section  of  a 
hair  follicle,  a  and  h,  external  root- 
sheath  ;  c,  internal  root-sheath ; 
d,  fibrous  layer  of  the  hair  ;  e,  me- 
dulla ;  /,  hair  papilla ;  g,  blood- 
vessels of  the  hair  papilla ;  h, 
dermic  coat.    (Cadiat.) 


588 


THE   SKIN    AND    ITS    APPENDAGES 


[CH.  XXXVIII. 


The  Nails  are  thickenings  of  the  stratum  lucidum.  Each  lies  in 
a  depression  called  the  hed  of  the  nail,  the  posterior  part  of  which  is 
overlapped  by  epidermis,  and  called  the  nail-groove.  The  dermis 
beneath  is  beset  with  longitudinal  ridges  instead  of  papillae;  these 
are  very  vascular ;  but  in  the  lunula,  the  crescent  at  the  base  of  the 
nail,  there  are  papillae,  and  this  part  is  not  so  vascular. 

The  Hairs  are  epidermal  growths,  contained  in  pits  called  hair 
follicles.     The  part  within  the  follicle  is  called  the  root  of  the  hair. 

The  main  substance  of  the  hair  is  composed  of  pigmented  horny 
fibrous  material,  in  reality  long  fibrillated  cells.     It  is  covered  by  a 


Fig.  440. — Transverse  section  of  a  liair  and  hair  follicle  made  below  the  opening  of  the  sebaceous  gland. 
a,  medulla,  or  pith  of  the  hair  ;  h,  tibrous  layer  ;  c,  cuticle ;  d,  Huxley's  layer  ;  c,  Henle's  layer  of 
internal  root-sheath  ;  /and  g,  layers  of  external  root-sheath,  outside  of  q  is  the  basement  membrane 
or  hyaline  layer;  h,  dermic  (fibrous)  coat  of  hair  follicle;  t,  vessels.     (Cadiat.) 

layer  of  scales  imbricated  upwards  {hair  cuticle).  In  many  hairs  the 
centre  is  occupied  by  a  medulla,  formed  of  rounded  cells  containing 
eleidin  granules.  Minute  air-bubbles  may  be  present  in  both  medulla 
and  fibrous  layer,  and  cause  the  hair  to  look  white  by  reflected  light. 
The  grey  hair  of  old  age,  however,  is  produced  by  a  loss  of  pigment. 

The  root  is  enlarged  at  its  extremity  into  a  hnoh,  into  which  pro- 
jects a  vascular  papilla  from  the  true  skin. 

The  hair  follicle  consists  of  two  parts,  one  continuous  with  the 
epidermis,  called  the  root-sheath,  the  other  continuous  with  the  dermis, 
called  the  dermic  coat.  The  two  are  separated  by  a  basement  mem- 
brane called  the  hyaline  layer  of  the  follicle.     The  root-sheath  con- 


CH.  XXXVIII.] 


THE    IIAUtS 


589 


sists  of  an  outer  layer  of  cells  like  the  Malpighian  layer  of  the 
epidermis,  with  which  it  is  directly  continuous  {outer  root-sheath),  and 
of  an  inner  horny  layer  {inner  root-sheath),  continuous  with  the  horny 
layer  of  the  epidermis.  The  inner  root-sheath  consists  of  three  layers, 
the  outermost  being  composed  of  long,  non-nucleated  cells  {Henle's 
layer),  the  next  of  squarish  nucleated  cells  {Huxley's  layer),  and  the 
third  is  a  cuticle  of  scales,  imbri- 
cated downwards,  which  lit  over 
the  scales  of  the  cuticle  of  the  hair 
itself. 

A  small  bundle  of  plain  mus- 
cular fibres  is  attached  to  each 
follicle  (fig.  437).  When  it  con- 
tracts, as  under  the  influence  of 
cold,  or  of  certain  emotions  such  as 
fear,  the  hair  is  erected  and  the 
whole  skin  is  roughened  ("goose 
skin ").  The  nerves  supplying 
these  muscles  are  called  pilo-motor 
nerves.  The  distribution  of  these 
nerves  closely  follows  those  of  the 
vaso-constrictor  nerves  of  the  skin  ; 


Fig.  441. — Sebaceous  gland  from  Imman  skin. 
(Klein  and  Noble  Smith.) 


their  cell  stations  are  in  the  lateral 
sympathetic  chain. 

The  sebaceous   glands  (figs. 
437  and  441)  are  small  saccular 

Fio.  442.— Terminal    tubules    of   sudoriferous  or    glands,    witll     duCtS    Opening    intO 
sweat-glands,  cut  in  various  directions  from    ^.i       m^,-,p^  r^rirtinn   nt    tViA  Vinir   fnl 
the  skin  of  the  pig's  ear.    (V.D.Harris.)  tnc  Upper  pOlUOll  01    me  nail    101- 

licles.  The  secreting  cells  become 
charged  with  fatty  matter,  which  is  discharged  into  the  lumen  of  the 
saccules  owing  to  the  disintegration  of  the  cells.  The  secretion,  sehum, 
contains  isocholesterin  (see  p.  522)  in  addition  to  fatty  matter.  It 
acts  as  a  lubricant  to  the  hairs. 

The  s-weat-glands  are  abundant  over  the  whole  human  skin,  but 
are  most  numerous  where  hairs  are  absent,  on  the  palms  and  soles. 
Each  consists  of  a  coiled  tube  in  the  deepest  part  of  the  dermis,  the 


590  THE   SKIN    AND    ITS    APPENDAGES  [Cll.  XXXVIIl 

duct  from  which  passes  up  through  the  dermis,  and  by  a  corkscrew- 
like canal  through  the  epidermis  to  the  surface. 

The  secreting  tube  is  lined  by  one  or  two  layers  of  cubical  or 
columnar  cells;  outside  this  is  a  layer  of  longitudinally  arranged 
muscular  fibres,  and  then  a  basement  membrane. 

The  duct  is  of  similar  structure,  except  that  there  is  usually  but 
one  layer  of  cubical  cells,  and  muscular  fibres  are  absent ;  the  passage 
through  the  epidermis  has  no  proper  wall ;  it  is  merely  a  channel 
excavated  between  the  epidermal  cells. 

The  ceruminous  glands  of  the  ear  are  modified  sweat-glands. 

The  Functions  of  the  Skin 

Protection. — The  skin  acts  as  a  protective  organ,  not  only  by 
mechanically  covering  and  so  defending  internal  structures  from 
external  violence,  but  more  particularly  in  virtue  of  its  being  an  organ 
of  sensation  (see  later  in  the  chapter  on  Touch). 

Heat  Regulation. — See  Chapter  XL. 

Respiration. — A  small  amount  of  respiratory  interchange  of  gases 
occurs  through  the  skin,  but  in  thick-skinned  animals  this  is  very 
small.  In  man,  the  carbonic  acid  exhaled  by  the  skin  is  about  yA-g- 
to  o-^  of  that  which  passes  from  the  lungs.  But  in  thin-skinned 
animals,  such  as  frogs,  cutaneous  respiration  is  very  important ;  after 
the  removal  of  the  lungs  of  a  frog,  the  respiratory  interchange  through 
the  skin  is  sufficient  to  keep  the  animal  alive,  the  amount  of  carbonic 
acid  formed  being  about  half  as  much  as  when  the  lungs  are  present 
(Bischoff). 

Absorption. — This  also  is  an  unimportant  function ;  but  the  skin 
will  in  a  small  measure  absorb  oily  materials  placed  in  contact  with 
it ;  thus  in  some  cases  infants  who  will  not  take  cod-liver  oil  by  the 
mouth,  can  yet  be  dosed  with  it  by  rubbing  it  into  the  skin.  Many 
ointments  also  are  absorbed,  and  thus  general  effects  produced  by 
local  inunction. 

Secretion. — The  secretions  of  the  skin  are  two  in  number.  The 
sebum  is  the  natural  lubricant  of  the  hairs.  The  secretion  of  sweat  is 
an  important  function  of  the  skin,  and  we  will  therefore  discuss  it  at 
greater  length. 

The  Sweat 

Physiology  of  the  Secretion  of  Sweat. — We  have  seen  that  the 
sweat-glands  are  most  abundant  in  man  on  the  palms  and  soles,  and 
here  the  greatest  amount  of  perspiration  occurs.  Different  animals 
vary  a  good  deal  in  the  amount  of  sweat  they  secrete,  and  in  the 
place  where  the  secretion  is  most  abundant.  Thus  the  ox  perspires 
less  than  the  horse  and  sheep;   perspiration   is   absent   from   rats, 


CH.  XXXVIII.]  THE   SWEAT  591 

rabbits,  and  goats ;  pigs  perspire  mostly  on  the  snout ;  dogs  and  cats 
on  the  pads  of  the  feet. 

As  long  as  the  secretion  is  small  in  amount,  it  is  evaporated  from 
the  surface  at  once ;  this  is  called  insensible  perspiration.  As  soon  as 
the  secretion  is  increased  or  evaporation  prevented,  drops  appear  on 
the  surface  of  the  skin.  This  is  known  as  sensible  perspiration.  The 
relation  of  these  two  varies  with  the  temperature  of  the  air;  the 
drier  and  hotter  the  air,  the  greater  is  the  proportion  of  insensible 
to  sensible  perspiration.  In  round  numbers  the  total  amount  of 
sweat  secreted  by  a  man  is  two  pounds  in  the  twenty-four  hours. 

The  amount  of  secretion  is  influenced  by  the  vaso-motor  nerves  ; 
an  increase  in  the  size  of  the  skin-vessels  leads  to  increased,  a  con- 
striction of  the  vessels  to  diminished,  perspiration.  There  are  also 
special  secretory  fibres,  stimulation  of  which  causes  a  secretion  even 
when  the  circulation  is  suspended,  as  in  a  recently  amputated  limb. 
These  fibres  are  paralysed  by  atropine.  They  are  contained  in  the 
same  nerve-trunks  as  the  vaso-motor  nerves,  as  are  also  the  nerve- 
fibres  which  supply  the  plain  muscular  fibres  of  the  sweat-glands 
which  act  during  the  expulsion  of  the  secretion.  The  secretory 
nerves  for  the  lower  limbs  issue  from  the  spinal  cord  by  the  last  two 
or  three  dorsal  and  first  two  or  four  lumbar  nerves  (in  the  cat) ;  they 
have  cell  stations  in  the  lower  ganglia  of  the  lateral  chain,  and  pass 
to  the  abdominal  sympathetic  and  thence  to  the  sciatic  nerve.  They 
are  controlled  by  a  centre  in  the  upper  lumbar  region  of  the  cord ; 
those  for  the  upper  limbs  leave  the  cord  by  the  sixth,  seventh,  and 
eighth  anterior  thoracic  roots,  have  cell  stations  in  the  ganglion 
stellatum,  and  ultimately  pass  to  the  ulnar  and  median  nerves ;  they 
are  controlled  by  a  centre  in  the  cervical  enlargement  of  the  cord. 
The  secretory  fibres  for  the  head  pass  in  the  cervical  sympathetic, 
and  in  some  branches  of  the  fifth  cranial  nerves.  These  subsidiary 
centres  are  dominated  by  one  in  the  medulla  oblongata  (Adam- 
kiewicz).  These  facts  have  been  obtained  by  experiments  on  animals 
(cat,  horse). 

The  sweat-centres  may  be  excited  directly  by  venous  blood,  as  in 
asphyxia ;  or  by  over-heated  blood  (over  45°  C.) ;  or  by  certain  drugs 
(see  further) ;  or  reflexly  by  stimulation  of  afferent  nerves  such  as 
the  crural  and  peroneal. 

Nervous  diseases  are  often  accompanied  with  disordered  sweat- 
ing; thus  unilateral  perspiration  is  seen  in  some  cases  of  hemi- 
plegia; degeneration  of  the  anterior  nerve-cells  of  the  cord  may 
cause  stoppage  of  the  secretion.  It  is  sometimes  increased  in 
paralysed  lunbs. 

The  changes  that  occur  in  the  secreting  cells  have  been  investi- 
gated by  Eenaut  in  the  horse.  When  charged  they  are  clear 
and  swollen,  the  nucleus  being  situated  near  their  attached  ends; 


592  THE   SKIN   AND    ITS    APPENDAGES  [CH.  XXXVIII. 

when  discharged  they  are  smaller,  granular,  and  their  nucleus  is 
more  central. 

The  sweat,  like  the  urine,  must  be  regarded  as  an  excretion,  the 
secreting  cells  eliminating  substances  formed  elsewhere. 

Composition  of  the  Sweat. — Sweat  may  be  obtained  in  abundant 
quantities  by  placing  the  animal  or  man  in  a  closed  hot-air  bath,  or 
from  a  limb  by  enclosing  it  in  a  vessel  made  air-tight  with  an  elastic 
bandage.  Thus  obtained,  it  is  mixed  with  epidermal  scales  and  a 
small  quantity  of  fatty  matter  from  the  sebaceous  glands.  The  con- 
tinual shedding  of  epidermal  scales  is  in  reahty  an  excretion. 
Keratin,  of  which  they  are  chiefly  composed,  is  rich  in  sulphur,  and, 
consequently,  this  is  one  means  by  which  sulphur  is  removed  from 
the  body. 

The  reaction  of  sweat  is  acid,  and  the  acidity,  as  in  the  ui'ine,  is 
due  to  acid  sodium  phosphate.  In  profuse  sweating,  however,  the 
secretion  usually  becomes  alkaline  or  neutral.  It  has  a  peculiar 
and  characteristic  odour,  which  varies  in  different  parts  of  the  body, 
and  is  due  to  volatile  fatty  acids ;  its  taste  is  saltish,  its  specific 
gravity  about  1005. 

In  round  numbers  the  percentage  of  soMs  is  1'2,  of  which  0"8 
is  inorganic  matter.  The  following  table  is  a  compilation  from 
several  analyses : — 


Water     . 

.     98-88 

per 

cent 

Solids 

.        1-12 

Salts 

.       0-57 

NaCl       . 

.       0-22  to  0 

•33       . 

^^ 

Other  salts 

.       0-18 

" 

(alkaline  sulphates,  phosphates, 
lac-tates,  and  potassium 
chloride) 

Fats 

.       0-41 

" 

(including  fatty  acids  and 
isocholesterin) 

Epithelium 

.       0-17 

Urea 

.       0-08 

The  salts  are  in  kind  and  relative  quantity  very  like  those  of  the 
urine.  Funke  was  unable  to  find  any  urea,  but  most  other  observers 
agree  on  the  presence  of  a  minute  quantity.  It  appears  to  become 
quickly  transformed  into  ammonium  carbonate.  The  protein  which 
is  present  is  probably  derived  from  the  epithelial  cells  of  the 
epidermis,  sweat-glands,  and  sebaceous  glands,  which  are  suspended 
"in  the  excretion;  but  in  the  horse  there  is  albumin  actually  in 
solution  in  the  sweat. 

Abnormal,  Unusual,  or  Pathological  Conditions  of  the  Sweat. 
— Drugs. — Certain  drugs  (sudorifics)  favour  sweating,  e.g.,  pilocarpine. 
Calabar  bean,  strychnine,  picrotoxine,  muscarine,  nicotine,  camphor, 
ammonia.  Others  diminish  the  secretion,  e.g.,  atropine  and  morphine 
in  large  doses. 


CH.  XXXVIII.]  THE   SKIN    IN    DISEASE  593 

Large  quantities  of  water,  by  raising  the  blood-pressure,  increase 
the  perspiration. 

Some  substances  introduced  into  the  body  reappear  in  the  sweat, 
e.g.,  benzoic,  tartaric,  and  succinic  acids  readily,  quinine  and  iodine 
with  more  difficulty.  Compounds  of  arsenic  and  mercury  behave 
similarly. 

Diseases. — Cystin  has  been  found  in  some  cases  of  cystinuria ; 
dextrose  in  diabetic  patients ;  bile-pigment  in  those  with  jaundice 
(as  evidenced  by  the  staining  of  the  clothes) ;  indigo  in  a  pecuHar 
condition  known  as  chromidrosis ;  blood  or  hsematin  deriva- 
tives in  red  sweat;  albumin  in  the  sweat  of  acute  rheumatism, 
which  is  often  very  acid ;  urates  and  calcium  oxalate  in  gout ; 
lactic  acid  in  puerperal  fever,  and  occasionally  in  rickets  and 
scrofula. 

Kidney  Diseases. — The  relation  of  the  secretion  of  the  skin  to  that 
of  the  kidneys  is  a  very  close  one.  Thus  copious  secretions  of  urine, 
or  watery  evacuations  from  the  aUmentary  canal,  coincide  with  dry- 
ness of  the  skin ;  abundant  perspiration  and  scanty  urine  generally 
go  together.  In  the  condition  known  as  urcemia  (see  p.  569),  when 
the  kidneys  secrete  Httle  or  no  urine,  the  percentage  of  urea  rises 
in  the  sweat;  the  sputum  and  the  saliva  also  contain  urea  under 
those  circumstances.  The  clear  indication  for  the  physician  in 
such  cases  is  to  stimulate  the  skin  to  action  by  hot-air  baths  and 
pilocarpine,  and  the  alimentary  canal  by  means  of  purgatives.  In 
some  of  these  cases  the  skin  secretes  urea  so  abundantly  that  when 
the  sweat  dries  on  the  body,  the  patient  is  covered  with  a  coating  of 
urea  crystals. 

Varnishing  the  Skin. — By  covering  the  skin  of  such  an  animal  as 
a  rabbit  with  an  impermeable  varnish,  the  temperature  is  reduced,  a 
peculiar  train  of  sjTnptoms  set  up,  and  ultimately  the  animal  dies. 
If,  however,  cooling  is  prevented  by  keeping  such  an  animal  in  warm 
cotton-wool,  it  Hves  longer.  Varnishing  the  human  skin  does  not 
seem  to  be  dangerous.  Many  explanations  have  been  offered  to 
explain  the  peculiar  condition  observed  in  animals ;  retention  of  the 
sweat  would  hardly  do  it ;  the  blood  is  not  found  post-mortem  to 
contain  any  abnormal  substance,  nor  is  it  poisonous  when  transfused 
into  another  animal.  Cutaneous  respiration  is  so  sHght  in  mammals 
that  stoppage  of  this  function  cannot  be  supposed  to  cause  death. 
The  animal,  in  fact,  dies  of  cold ;  the  normal  function  of  the  skin  in 
regulating  temperature  is  interfered  with,  and  it  is  animals  with 
dehcate  skins  which  are  most  readily  affected. 


2   P 


CHAPTEE    XXXIX 

GENERAL  METABOLISM 

The  word  metabolism  has  been  often  employed  in  the  preceding 
chapters,  and,  as  there  explained,  it  is  used  to  express  the  sum  total 
of  the  chemical  exchanges  that  occur  in  living  tissues.  The  chemical 
changes  have  been  considered  separately  under  the  headings 
Alimentation,  Excretion,  Eespiration,  etc.  We  have  now  to  put  our 
knowledge  together,  and  consider  these  subjects  in  their  relation  to 
one  another. 

The  living  body  is  always  giving  off  by  the  lungs,  kidneys,  and 
skin  the  products  of  its  combustion,  and  is  thus  always  tending  to 
lose  weight.  This  loss  is  compensated  for  by  the  intake  of  food  and 
of  oxygen.  For  the  material  it  loses,  it  receives  in  exchange  fresh 
substances.  If,  as  in  a  normal  adult,  the  income  is  exactly  equal  to 
the  expenditure,  the  body-weight  remains  constant.  If,  as  in  a 
growing  child,  the  income  exceeds  the  expenditure,  the  body  gains 
weight;  and  if,  as  in  febrile  conditions,  or  during  starvation,  the 
expenditure  exceeds  the  income,  the  body  wastes. 

The  different  parts  of  the  body  have  very  different  compositions ; 
still,  speaking  of  the  body  as  a  whole,  Volkmann  and  Bischoff  state 
that  it  contains  64  per  cent,  of  water,  16  of  proteins,  14  of  fat,  5  of 
salt,  and  1  of  carbohydrates.  The  carbohydrates  are  thus  the  smallest 
constituent  of  the  body;  they  are  the  glycogen  of  the  liver  and 
muscles,  and  small  quantities  of  dextrose  in  various  parts. 

The  most  important,  because  the  most  abundant  of  the  tissues  of 
the  body,  is  the  muscular  tissue.  Muscle  forms  about  42  per  cent, 
of  the  body-weight,*  and  contains,  in  round  numbers,  75  per  cent,  of 
water  and  21  per  cent,  of  proteins;  thus  about  half  the  protein 
material  and  of  the  water  of  the  body  exist  in  its  muscles. 

The  body,  however,  does  not  remain  in  a  stable  condition ;  even 
while  nutrition  is  occurring,  destructive  changes  are  taking  place 
simultaneously;  each  cell  may  be  considered  to  be  in  a  state  of 
unstable  equilibrium,  undergoing  anabolic,  or  constructive  processes, 
on  the  one  hand,  and  destructive,  or  katabolic,  processes  on  the  other. 

*  The  following  is  in  round  numbers  the  percentage  proportion  of  the  different 
structural  elements  of  the  body:  skeleton,  16;  muscles,  42;  fat,  18;  viscera,  9; 
skin,  S  ;  brain,  2  ;  blood,  5. 

594 


CH.  XXXIX.] 


METABOLIC    EQUILIBRIUM 


595 


The  two  sides  of  metabolism  may  be  compared  by  means  of  a 
balance-sheet,  and  the  necessary  data  for  the  construction  of  such  a 
comparison  are: — 

(1)  The  weight  of  the  animal  before,  during,  and  after  the 
experiment. 

(2)  The  quantity  and  composition  of  its  food. 

(3)  The  amount  of  oxygen  absorbed  during  respiration. 

(4)  The  quantity  and  composition  of  urine,  faeces,  sweat,  and 
expired  air. 

(5)  The  amount  of  work  done,  and  the  amount  of  heat  developed. 
(The  subject  of  animal  heat  will  be  considered  in  the  next  chapter.) 

Water  is  determined  by  subtracting  the  amount  of  water  ingested 
as  food  from  the  quantity  lost  by  bowels,  urine,  lungs,  and  skin. 
The  difference  is  a  measure  of  the  kataboHsm  of  hydrogen. 

Nitrogen. — The  nitrogen  is  derived  from  proteins,  and  appears 
chiefly  in  the  urine.  Smaller  quantities  are  eliminated  in  sweat  and 
faeces,  from  the  amount  of  nitrogen  so  found,  the  amount  of 
proteins  which  have  undergone  katabolism  is  calculated.  Proteins 
contain,  roughly,  16  per  cent,  of  nitrogen;  so  1  part  of  nitrogen  is 
equivalent  to  6 '3  parts  of  protein ;  or  1  gramme  of  nitrogen  to  30 
grammes  of  flesh. 

Fat  and  carhohydrate. — Subtract  the  carbon  in  the  katabolised  pro- 
tein (protein  contains  54  per  cent,  of  carbon)  from  the  total  carbon 
eliminated  by  lungs,  skin,  bowels,  and  kidneys,  and  the  difference 
represents  fat  and  carbohydrate  that  have  undergone  katabolism. 

Balance  of  Income  and  Discharge  in  Health. 

In  Chapter  XXVIII.  tables  are  given  of  adequate  diets;  these 
will  in  our  balance-sheet  represent  the  source  of  income ;  the  other 
side  of  the  balance-sheet,  the  expenditure,  consists  of  the  excretions. 

We  may  select  as  our  example  a  typical  table  of  this  daily 
exchange  of  material  on  an  ordinary  diet  from  the  work  of  Petten- 
kofer  and  Voit.     In  the  first  experiment  the  man  did  no  work. 


Income. 

Expenditure. 

Food. 

Nitrogen. 

Carbon. 

Excretions, 

Nitrogen. 

Carbon. 

Water. 

Protein    .     1 37  gr. 
Fat,         .     117   „ 
Carbohy- 
drate.    352  „ 
Water      .  2016   „ 

-19-5 

315-5 

Urine    . 

Faeces   . 

Expired 

air      . 

17-4 
2-1 

12-7 
14-5 

248-6 

1279 
83 

828 

19-5 

275-8          2190 

Nitrogen. 

Carbon. 

Water. 

17-4 

12-6 

1194 

2-1 

14-5 

94 

309-2 

1412 

596  GENERAL  METABOLISM  [CH.  XXXIX. 

Here  the  body  was  in  nitrogenous  equilibrium,  and  it  eliminated 
more  water  than  it  took  in  by  174  grammes,  this  being  derived  from 
oxidation  of  hydrogen.  It  stored  39 "7  grammes  of  carbon,  which  is 
equivalent  to  52  grammes  of  fat. 

The  next  table  gives  the  results  of  an  experiment  on  the  same  man 
on  the  same  diet,  but  who  did  active  muscular  work  during  the  day : — 

Expenditure. 
Urine    ..... 
Faeces  ..... 
Expired  air   . 

19-5  336-3  2700 

It  is  important  to  notice  that  the  discharge  of  nitrogen  was 
unaltered,  while  that  of  both  carbon  and  hydrogen  was  increased. 
At  one  time  protein  was  considered  to  be  the  great  source  of 
muscular  energy ;  this  was  first  disproved  by  an  historical  experiment 
made  by  Pick  and  Wislicenus  on  themselves  in  their  ascent  of  the 
Faulhorn.  Nature  works  in  a  most  economical  way  in  reference  to 
protein  waste,  and  any  increase  in  nitrogenous  katabolism  which 
occurs  during  muscular  work  is  insignificant. 

The  balance-sheet  method  of  investigation,  though  one  of  great 
usefulness,  tells  us  very  little  of  the  details  which  lead  to  the  end 
results.  We  must  therefore  now  proceed  to  study  the  details,  and 
although  there  is  a  good  deal  of  guess  work,  and  even  ignorance  upon 
some  essential  points,  we  may  most  conveniently  consider  the 
question  under  the  three  headings  of  our  principal  food  materials, 
namely,  carbohydrates,  fats,  and  proteins. 

Metabolism  of  Carbohydrates. 

In  plants,  carbohydrates  are  synthesised  by  the  agency  of  chloro- 
phyll from  the  simple  materials  carbonic  acid  and  water,  which  form 
their  chief  foods.  The  first  substance  formed  is  probably  formic 
aldehyde,  H.COH,  and  this  by  condensation  is  converted  into  sugar, 
and  finally,  into  starch.  We  have  no  evidence  that  a  synthesis  of 
this  kind  ever  takes  place  in  animals,  but  the  main  source  of  animal 
carbohydrate  is  vegetable  carbohydrate.  This  is  taken  in  the  food  and 
converted  into  glucose ;  the  glucose  is  taken  to  the  liver  and  stored 
as  glycogen,  and  in  the  liver  is  once  more  liberated  as  glucose,  and 
distributed  to  the  body  in  this  form.  The  change  from  glycogen  to 
sugar  is  the  work  of  a  ferment.  Is  the  change  from  sugar  to 
glycogen  also  a  ferment  action?  And  if  so,  is  another  ferment 
responsible  for  it,  or  have  we  to  deal  with  a  case  of  reversible 
zymolysis  ?  This  is  one  of  many  unanswered  questions.  The  other 
important  animal  carbohydrate  is  lactose,  a  compound  of  dextrose 
and  galactose.     If  the  food  contains  galactose  as  well  as  dextrose,  the 


CH.  XXXIX.]  METABOLISM    OF    CAIIBOHYDKATES  597 

condensation  of  these  two  sugars  to  form  lactose  is  a  comparatively 
simple  problem ;  there  is  no  doubt  that  galactose  is  present  in  certain 
foods,  for  instance  it  is  contained  in  some  vegetables,  and  it  also 
comes  from  the  sugar  of  milk.  Lactose  in  the  mammary  gland  is, 
however,  not  the  only  place  where  galactose  is  necessary,  for  the 
cerebrosides  of  nervous  tissue  (see  p.  176)  also  contain  it.  But  it  is  not 
necessary  to  assume  that  all  the  galactose  necessary  for  the  formation 
of  milk  sugar  and  of  the  cerebrosides  comes  direct  from  the  galactose 
of  the  food.  Dextrose,  galactose,  and  levulose  are  all  isomeric,  and 
the  intramolecular  rearrangements  that  would  be  necessary  to 
convert  one  into  another  member  of  this  group  do  not  seem  to  be 
beyond  the  power  of  the  tissue  cells,  and  there  is  a  good  deal  of 
evidence  that  such  transformations  actually  occur  in  the  body.  The 
other  carbohydrate  constituents  of  the  body  are  pentoses  found  in 
some  nucleo-proteins,  and  glucosamine  in  the  gluco-proteins,  but 
in  relation  to  these  our  knowledge  of  their  formation  is  highly 
speculative. 

It  is  further  known  that  the  hepatic  glycogen  may,  under  certain 
circumstances,  originate  from  proteins,  and  that  many  proteins  con- 
tain a  carbohydrate  radical ;  some,  such  as  mucin,  yield  a  considerable 
amount,  but  in  the  commoner  proteins,  the  amount  is  in  the  neigh- 
bourhood of  1  per  cent,  or  less.  The  mucins  do  not  participate  to  any 
great  degree  in  metabolism,  and  so  the  question  arises  whether  the 
small  amount  of  carbohydrates  in  the  ordinary  proteins  is  sufficient 
to  account  for  the  amount  of  glycogen  formed.  Arithmetic  shows  it 
will  not;  moreover,  a  protein  (such  as  casein)  which  contains  no 
carbohydrate  radical  at  all,  is  equally  eflficacious  as  the  others  in 
yielding  sugar  when  administered  to  animals  suffering  from  glycosuria 
produced  by  phloridzin.  We  must  therefore  search  for  something 
in  the  protein  molecule,  as  the  source  of  the  carbohydrate,  and 
leucine,  having  like  sugar  6  atoms  of  carbon,  was  naturally  the  first 
substance  to  be  examined.  But  all  experiments  on  the  admini- 
stration of  leucine  led  to  negative  or  nearly  negative  results.  Another 
amino-acid,  alanine  (with  its  compounds  tyrosine,  phenyl-alanine,  and 
tryptophane),  was  found  to  be  the  much  more  probable  source  of 
the  carbohydrate.  The  relationship  of  alanine  to  the  carbohydrates 
is  a  near  one,  for  if  HO  is  substituted  in  its  molecule  for  NH._,,  we 
get  lactic  acid,  and  it  was  found  that  the  administration  of  alanine 
to  rabbits  led  to  glycogen  formation  in  their  livers,  and  to  the 
passage  of  lactic  acid  into  their  urine.  Another  cleavage  product  of 
protein,  namely,  aspartic  acid,  may  act  in  a  similar  way,  and  this  also 
is  intelligible  on  chemical  lines,  for  if  aspartic  acid  loses  carbon 
dioxide,  it  is  converted  into  lactic  acid,  and  it  is  no  great  step  from 
this  to  sugar.  Similar  experiments  have  been  performed  with 
glycine  and  other  amino-acids,  but  the  results,  though  in  part  positive, 


598  GENERAL    METABOLISM  [CIL  XXXIX. 

are  by  no  means  so  clear,  nor  is  the  chemical  relationship  between 
them  and  carbohydrate  so  easy  to  understand.  The  only  other  sub- 
stance not  a  carbohydrate,  but  which  appears  to  be  converted  into 
carbohydrate  in  the  body,  which  we  will  mention  is  glycerin  ;  glyceric 
aldehyde  is  isomeric  with  lactic  acid,  so  here  again  we  have  a 
feasible  explanation. 

Turning  now  to  the  other  side  of  the  picture,  what  information 
have  we  about  carbohydrate  katabolism  ?  Tlie  final  products  of  com- 
bustion are  carbonic  acid  and  water,  but  what  are  the  intermediate 
steps  ?  Just  as  lactic  acid  has  been  assumed  to  be  sometimes  a 
stage  in  the  formation  of  sugar,  so  also  there  is  evidence  that 
it  is  a  stage  in  its  breakdown.  We  know  that  certain  micro- 
organisms possess  the  power  of  transforming  sugar  into  lactic  acid, 
and  even  still  further  into  butyric  acid  (see  formulae,  p.  395),  and 
Buchner  has  recently  asserted  that  lactic  acid  is  a  stage  in  the 
formation  of  alcohol  and  carbonic  acid  from  sugar  by  means  of  yeast. 
The  atoms  in  lactic  acid  (CyH^O.^)  are  in  the  same  proportion  as  in 
sugar  (C^.H^^Oq),  but  of  course  they  are  very  differently  arranged, 
and  the  rearrangement  involved  in  the  conversion  of  the  one  into  the 
other,  or  vice  versd,  is  differently  explained  by  different  chemists. 
Lactic  acid  undoubtedly  occurs  in  the  body,  but  whether  it  all  comes 
from  sugar  is  extremely  doubtful.  The  principal  lactic  acid  foimed 
is  the  dextro-rotatory  variety  (sarco-lactic  acid),  whereas  that  formed 
in  fermentative  processes,  as  in  milk,  is  the  optically  inactive  variety. 
Now,  there  is  a  good  deal  of  evidence  that  sarco-lactic  acid  originates 
from  proteins;  for  instance,  in  the  birds  from  which  Minkowski 
removed  the  liver,  the  giving  of  protein  food  increased  the  lactic  acid 
(which  was  not  synthesised  in  the  absence  of  the  liver  into  uric  acid) 
of  their  urine,  and  we  have  further  seen  that  alanine  and  other 
protein  cleavage  products  are  possible  parent  sulistances  of  lactic 
acid.  Still,  if  we  admit  that  some  of  the  lactic  acid  is  of  carbohydrate 
origin,  and  the  admission  is  quite  justifiable,  we  must  remember  that 
such  a  breakdown  of  sugar  yields  no  heat;  the  calorific  value  of 
sugar  and  lactic  acid  being  equal.  The  formation  of  lactic  acid 
involves  no  transformation  of  energy ;  there  is  no  formation  of  animal 
heat,  or  of  its  equivalent  in  work,  and  so  the  change  is  merely  pre- 
liminary to  a  further  change  into  carbonic  acid  and  water,  in  which 
there  will  be  that  liberation  of  energy  which  it  is  the  main  object  of 
carbohydrate  breakdown  to  accomplish.  (Glycolysis  in  the  blood 
and  tissues,  and  the  importance  of  glycuronic  acid  as  an  intermediate 
substance  on  carbohydrate  cleavage,  are  discussed  on  p.  527). 

Metabolism  of  Fat. 

Just  as  the  carbohydrate  of  the  food  is  the  usual  source  of  the 
carbohydrate  of  the  body,  so  the  fat  of  the  food  is  the  usual  source  of 


CH.  XXXIX.]  METABOLISM    OF   FATS  599 

the  fat  of  the  body.  But,  again,  fat  may  arise  from  something  which 
is  not  fat  in  the  food. 

During  absorption,  the  fatty  acid  and  glycerin  components  of  the 
fat  undergo  a  temporary  separation,  but  they  soon  reunite,  and  the 
fat  which  is  not  needed  for  immediate  use,  passes  via  the  chyle  and 
blood  to  the  cells  of  adipose  tissue  where  it  is  stored,  and  where  it 
has  the  same  composition  as  it  had  in  the  food.  The  proportion  of 
the  olein,  stearin,  and  palniitin  in  the  fat  of  an  animal  can  therefore 
be  varied  by  variations  in  their  proportion  in  the  food,  and  even  if 
unusual  glycerides  or  unusual  fatty  acids  (such  as  linolein  from  linseed 
oil,  erucic  acid  from  rape-seed  oil,  or  iodised  fats)  are  administered, 
they  will  be  discoverable  in  the  storage  fat  of  the  body.  When  the 
fat  leaves  the  cells  of  adipose  tissue  for  utilisation,  that  is  combustion, 
it  is  apparently  again  split  into  its  constituents,  and  so  it  is  rendered 
soluble  in  the  blood  for  transportation;  the  ferment  which  brings 
this  about,  acts  just  like  steapsin  does  in  the  intestine,  and  it  is 
called  lijmsc.  Lipase  is  very  widely  distributed  in  the  tissues,  and 
its  action  is  a  reversible  one ;  it  can  tie  the  knot  or  untie  it  equally 
easily.  But  there  is  no  loss  of  energy  in  the  process  of  untying,  any 
more  than  there  is  in  the  formation  of  lactic  acid  from  sugar,  or  to 
use  the  technical  phrase,  the  reaction  is  an  isothermic  one. 

But  the  fat  of  the  body  may  also  arise  from  carbohydrate  food. 
This  is  a  physiological  fact  which  was  first  firmly  established  by 
Lawes  and  Gilbert  in  their  classical  experiments  on  the  fattening  of 
cattle  and  sheep,  fifty  years  ago.  The  transformation  is  a  monopoly 
of  the  living  body :  chemists  were  inclined  to  regard  the  fact  as 
fiction,  and  they  have  never  been  able  to  repeat  it  in  the  laboratory. 
How  the  long  carbon  chains  of  the  fat  are  linked  together  from  the 
shorter  carbohydrate  chains  of  sugar  is  at  present  a  riddle.  Micro- 
organisms can  accomplish  the  change  of  lactic  acid  into  such  fatty  acids 
as  acetic,  butyric,  and  caproic  ;  boiling  with  alkali  brings  about  a  similar 
reaction ;  and  the  same  sort  of  change  must  occur  in  the  body  with 
the  formation  of  higher  fatty  acids.*  The  liver  appears  to  be  the 
place  where  the  change  occurs. 

May  fats  also  arise  from  proteins  ?  This  is  a  controversial 
question.  A^oit  and  Pettenkofer  said  yes,  because  they  were  able  to 
fatten  dogs  on  lean  meat,  but  as  the  amount  of  fat  left  in  the  meat, 
and  the  glycogen  also  present,  were  not  taken  into  account,  their 
proof  can  hardly  be  considered  satisfactory.  The  majority  of  physio- 
logists to-day  either  answer  the  question  in  the  negative,  or  regard  it 
as  unproven  one  way  or  the  other.  They  adopt  this  attitude  because 
the  main  proof  adduced  by  those  who  believed  in  the  transformation 
of  protein  into  fat  has  been  shown  to  be  fallacious.     It  was  stated 

*  Those  interested  in  speculations  in  this  and  other  metabolic  puzzles  should 
consult  Leathes'  Problems  in  Animal  Metabolism,  published  by  John  ^lurray,  1906. 


600  GENERAL    METABOLISM  [CH.  XXXIX, 

that  in  certain  pathological  conditions,  for  instance  in  phosphorus 
poisoning,  a  fatty  degeneration  of  cells  of  certain  organs  takes  place, 
and  the  fat  which  appeared  was  believed  to  originate  from  the  protein 
constituents  of  the  cell-protoplasm.  This  has  been  shown  to  be 
incorrect ;  every  case  of  so-called  fatty  degeneration  has  been  shown 
to  be  either  due  to  an  infiltration  of  fat  transported  from  elsewhere,  or 
to  a  transformation  of  the  fat  previously  present  in  the  protoplasm, 
although  not  in  the  form  of  droplets,  and  probably  also  not  in  the 
form  of  the  usual  glycerides.  In  many  cases,  the  total  fat  present  in 
this  concealed  form  in  the  cells  of  the  heart,  kidney,  and  liver,  may 
be  greater  than  when  with  disease  it  takes  the  form  of  droplets. 

With  regard  to  the  origin  of  glycerin,  there  is  no  doubt  that  the 
cells  are  able  to  produce  it,  as  was  shown  by  Munk's  experiments 
on  chyle,  which  are  referred  to  on  p.  533.  There  is  no  necessity  to 
suppose  that  it  originates  from  protein,  for  if  glycerin  can  be  con- 
verted into  sugar,  there  is  no  good  ground  for  beheving  that  the 
converse  does  not  also  take  place. 

On  katabolism,  the  fats  yield  the  same  ultimate  products  as  the 
carbohydrates,  namely,  carbonic  acid  and  water.  A  great  deal  of 
the  oxygen  we  breathe  in  is  used  up  in  the  burning  of  fats,  and  the 
simultaneous  liberation  of  heat  and  work.  It  is  quite  certain  that 
sugar  is  an  important  source  of  muscular  energy,  but  the  fats  also 
play  the  same  role,  and  muscles  which  are  perpetually  at  work  like 
the  heart  antl  the  diaphragm  are  particularly  rich  in  fats.  No 
actual  lessening  of  the  fat  has  yet  been  demonstrated  to  occur  in  excised 
muscles  subjected  to  stimulation,  but  we  have  other  and  more  trust- 
worthy evidence  that  it  does  take  place.  During  muscular  work,  the 
output  of  carbonic  acid  is  increased,  but  the  respiratory  quotient 
(see  pp.  375,  388)  is  almost  unaltered ;  if  sugar  alone  was  undergoing 
combustion,  this  quotient  would  rise.  Again,  if  the  carbohydrate 
stores  of  the  body  are  depleted  by  inanition,  or  by  giving  phloridzin 
to  an  animal,  still  muscular  work  has  but  little  influence  on  protein 
katabolism,  and  therefore  the  necessary  increased  combustion  must 
fall  on  the  fat.  But  how  the  long  carbon  chains  of  the  fats  are  taken 
to  pieces  and  burnt  up  is  entirely  a  matter  of  guess-work.  There  is 
just  the  same  fundamental  piece  of  blank  ignorance  staring  us  in  the 
face  in  the  case  of  the  proteins ;  we  know  something  of  the  way  the 
protein-nitrogen  is  disposed  of,  but  the  non-nitrogenous  residue 
(which  is  chiefly  fatty  acid  *  and  which,  hke  a  fat,  is  used  for  com- 
bustion, and  as  a  source  of  heat  and  energy),  presents  exactly  the 
same  problem  as  the  fats  do  as  to  the  way  in  which  the  final  carbonic 
acid  and  water  are  formed  from  it. 

*  The  existence  of  this  non-nitrogenous  and  fat-like  residue  of  protein  should 
make  physiologists  hesitate  before  thsy  finally  deny  the  possible  conversion  of  the 
food-protein  and  tissue-protein  into  fat. 


CH.  XXXIX.]  METABOLISM    OF    FATS  601 

One  glimmer  of  light  in  the  darkness  has  entered  from  an  unex- 
pected quarter,  namely,  from  a  study  of  acetonasmia  (see  also  p.  528). 
i8-oxybutyric  acid  arises  in  the  body  in  diabetes ;  this  by  oxidation 
in  the  body  is  partly  converted  into  aceto-acetic  acid,  and  this  in 
the  urine  loses  carbonic  acid,  and  so  is  partly  converted  into  acetone. 
This  group  of  products  were  at  one  time  believed  to  originate 
from  proteins;  but  if  that  were  so,  there  ought  to  be  a  corresponding 
excess  of  other  protein  katabolites  in  the  urine,  which  there  is  not. 
Acetonaemia  can  also  be  brought  on  in  healthy  people  by  cutting  off 
their  carbohydrate  food ;  if  sugar  is  again  added  to  the  diet,  the 
acetonsemia  ceases ;  but  if  fat  is  added  instead,  the  acetonaemia 
increases ;  fat  also  increases  acetonaemia  in  diabetes.  If  butyric  acid 
and  /3-oxybutyric  acid  are  normal  intermediate  products  in  fat  kata- 
bolism  (and  they  probably  are),  a  healthy  man  under  normal 
conditions  of  diet  is  able  still  further  to  oxidise  them  into  carbonic 
acid  and  water.  The  diabetic  patient  or  the  man  on  an  abnormal 
diet,  breaks  down  at  this  very  point. 

There  is  one  other  interesting  question  of  fat  metabolism  which 
we  must  mention.  We  have  considered  the  evidence  that  sugar 
given  in  the  food  will  become  transformed  into  fat  in  the  body.  Is 
there  any  evidence  that  fat  may  be  converted  into  carbohydrate  ? 
In  vegetable  life  there  is ;  certain  seeds  rich  in  oil,  on  germination, 
lose  a  good  deal  of  their  fat,  and  what  is  lost  reappears  as  starch. 
There  is  also  evidence  of  the  same  sort  of  change  in  animal  life.  In 
animals,  glycosuria,  produced  by  phloridzin  or  extirpation  of  the 
pancreas,  is  intensified  if  fats  are  administered ;  the  sugar  cannot  be 
derived  from  protein  in  such  cases,  because  the  ratio  of  dextrose  to 
nitrogen  in  the  urine  is  much  too  high.  Pflilger  fed  diabetic  dogs 
exclusively  on  boiled  cod,  which  in  the  winter  months  contains  no 
glycogen  and  only  a  trace  of  fat;  they  continued  to  pass  sugar 
in  their  urine,  and  in  the  course  of  a  month  one  of  these  dogs,  which 
may  be  taken  as  a  sample  of  the  others,  passed  more  than  five 
pounds  of  sugar  over  and  above  that  which  could  be  accounted  for 
by  any  carbohydrate  of  the  animal's  body.  This  sugar  must  there- 
fore have  been  derived  either  from  fat  or  from  protein.  Pfliiger 
holds  that  it  all  came  from  fat,  and  certainly  the  dog  when  it  was 
killed  had  no  visible  fat  in  its  connective  tissues ;  and  the  dextrose- 
nitrogen  ratio  was  so  variable  that  it  is  difficult  to  ascribe  the  sugar 
formation  to  protein  cleavage.  The  seat  of  the  conversion  of  fat 
into  sugar  is  the  liver ;  in  diabetic  patients  the  liver  is  always  the 
richest  in  fat;  so  it  was  with  Pfliiger's  diabetic  dogs.  In  these 
animals  the  increased  work  thrown  upon  the  liver  led  to  a  great 
enlargement  of  that  organ,  and  in  one  case  it  had  enlarged  to  five 
times  the  size  it  has  in  cases  of  ordinary  starvation.  The  fact  that 
ammonium   carbonate   increases   the   sugar   formed   in   diabetes    is 


602  GENERAL   METABOLISM  [CH.  XXXIX. 

ascribed  by  Pfliiger  to  the  stimulating  effect  this  salt  has  on  the 
functions  of  the  liver,  not  only  in  relation  to  urea  formation,  but 
also  in  connection  with  the  transformation  of  fat  into  sugar.  Pfliiger 
has  always  strenuously  resisted  the  notion  that  protein  is  a  source 
of  carbohydrate,  although  the  fact  that  his  dogs  received  only 
protein  food  would  appear  to  support  this  view.  That  such  a 
keen  observer  as  Pfliiger  has  come  to  the  opposite  conclusion,  that 
even  in  this  case  fat  is  the  real  source  of  the  sugar,  will  indicate  to 
the  student  how  difficult  the  problems  of  metabolism  are,  and  how 
impossible  it  is  at  present  to  make  definite  assertions  one  way  or 
the  other.  We  must,  therefore,  keep  an  open  mind  on  this  subject; 
we  have  already  seen  some  positive  evidence  that  protein  does  yield 
carbohydrate,  and  Pfliiger's  work  shows  us  that  sugar  may  also 
originate  from  fat.  There  is  no  reason  for  absolutely  rejecting  either 
set  of  proofs,  and  we  may  for  the  present  conclude  that  sugar  may 
arise  in  both  ways.  We  have  already  seen  the  chemical  difficulties 
of  explaining  how  sugar  can  be  converted  into  fat;  the  difficulty  of 
explaining  the  converse  change  is  equally  great 

Metabolism  of  Protein. 

In  our  discussion  of  the  origin  of  urea  in  the  urine,  we  have 
mentioned  some  of  the  main  facts  in  relation  to  the  metabolism 
of  proteins,  and  it  would  be  well  if  the  student  again  reads  these 
pages  (pp.  567  to  569)  before  studying  the  paragraphs  which  now 
follow;  for  the  laws  which  govern  the  composition  of  urine  are 
the  effect  of  more  fundamental  laws  governing  protein  katabohsni. 

Liebig  was  the  first  to  divide  foods  into  flesh-forming  and  heat- 
forming,  that  is,  into  those  which  repair  the  tissue  waste,  and  those 
which  are  not  so  intimately  assimilated  into  the  protoplasm,  but  are 
utilised  as  sources  of  energy.  The  latter  function  is  the  one  per- 
formed by  the  fats  and  carbohydrates,  and  the  former  is  more 
particularly  the  duty  of  the  proteins.  This  idea  is  reflected  in  the 
popular  use  of  the  term  nutritious ;  it  is  used  almost  synonymously 
with  nitrogenous,  and  the  notion  that  the  non-nitrogenous  foods, 
although  they  form  the  greater  part  of  our  daily  diet,  are  not 
nutritious  and  next  door  to  useless,  is  a  most  mischievous  one, 
though  it  is  carefully  fostered  by  the  advertisers  of  patent  foods. 
Both  kinds  of  food  are  equally  necessary,  and  equally  though 
dififerently  nutritious. 

It  is  now  known  that  the  proteins  are  not  only  flesh-formers, 
but  also  that  they  play  the  other  role  in  nutrition  and  act  as  a  source 
of  energy.  The  complete  breakdown  into  amino-acids  which  occurs 
in  the  gastro-intestinal  tract,  has  in  fact  a  double  signification.  It 
enables  the  cells  of  the  body  to  construct  from  the  cleavage  products 


CH.  XXXIX.]  METABOLISM    OF    PROTEIN  603 

the  proteins  peculiar  to  themselves,  and  it  further  enables  the  body 
to  easily  rid  itself  of  the  nitrogenous  portions  of  the  food-proteins 
which  are  not  wanted  for  the  repair  of  tissue  waste.  This  portion  is 
never  really  assimilated  in  the  sense  that  it  is  built  into  protoplasm, 
but  it  is  taken  in  by  the  liver  cells,  which  rapidly  convert  it  into 
urea  and  so  render  it  harmless.  The  non -nitrogenous  moiety  is 
then  utilisable  for  energy  and  heat  production. 

In  starvation,  the  income  of  the  body  is  limited  to  oxygen,  but 
if  water  is  given  also,  an  animal  will  generally  live  a  little  over  four 
weeks.  During  this  time  the  excretion  of  nitrogenous  and  carbona- 
ceous waste  continues  and  the  body  loses  weight  day  by  day.  The 
excretion  of  carbon  dioxide  continuously  falls  until  death  supervenes. 
The  nitrogen  of  the  urine  falls  also  within  the  first  few  days,  and 
then  remains  at  a  low  but  constant  level  to  the  end  of  the  fourth 
week.  Then  for  the  few  days  preceding  death,  its  amount  again 
increases.  By  this  date  nearly  every  trace  of  the  fat  of  the  body 
has  disappeared,  and  so  the  cells  fall  back  on  their  more  precious 
protein  material  and  consume  it  in  greater  quantity  than  before. 
The  nitrogen  elimination  during  the  weeks  when  it  remains  constant 
is  also  derived  from  the  proteins  of  the  body,  for  there  is  none 
coming  in,  in  the  way  of  food.  It  might  be  thought  if  at  this  time 
an  amount  of  protein  food  containing  the  same  quantity  of  nitrogen 
as  was  being  lost  by  the  body,  was  administered,  that  the  loss  of 
nitrogen  from  the  body  would  be  checked,  and  that  the  tissues  would 
seize  the  opportunity  of  repairing  their  waste.  But  this  is  not  the 
case ;  what  happens  is  that  the  amount  of  nitrogen  lost  in  the  dog  is 
almost  doubled ;  and  this  is  an  undoubted  proof  that  nearly  all  the 
protein  in  the  food  is  disintegrated  and  its  nitrogen  discharged 
within  the  twenty-four  hours.  In  order  to  get  nitrogenous  equili- 
brium, it  is  necessary  to  give  in  the  day  two  and  a  half  times  as 
much  protein  as  is  lost  during  starvation  in  that  period  of  time. 
This  was  one  of  the  earliest  proofs  adduced  that  all  the  food  protein 
is  not  used  in  tissue  repair,  and  it  led  Voit  to  formulate  his  cele- 
brated theory  of  the  distinction  between  ''  tissue  protein  "  and  what 
he  termed  "circulating  protein."  The  latter  expression  was  coined 
because  Yoit  believed  that  the  katabolism  of  this  variety  of  protein 
occurred  in  the  blood,  or  at  any  rate  in  the  tissue  juices.  In  fact, 
he  considered  that  katabolism  occurred  only  in  the  "circulating 
protein,"  the  small  amount  of  "living  protein"  which  dies  being 
dissolved  and  so  added  to  the  "  circulating  protein  "  before  katabolism 
occurs.  Voit's  great  opponent  was  Pfliiger,  and  for  many  years 
Pfliiger's  theory  replaced  Voit's ;  this  theory  states  that  all  protein 
must  first  become  assimilated ;  that  is,  must  be  built  into  and  become 
part  and  parcel  of  hving  protoplasm  before  it  undergoes  katabolism. 
Pfliiger  did  good  service  in  emphasising  the  importance  of  the  cells 


604  GENERAL   METABOLISM  [CH.  XXXIX. 

in  metabolic  processes,  and  we  certainly  do  not  now  believe  that 
respiration  or  any  other  metabolic  process  has  its  seat  in  the  circula- 
ting fluids.  But  at  the  same  time  Voit's  theory  possesses  the  correct 
underlying  idea  which  forms  the  basis  of  our  present  doctrine  of 
metabolism.  In  every  living  tissue  there  exists  a  framework  of 
what  we  may  call  more  distinctly  living  substance,  the  metabolism 
of  which  is  constant  and  does  not  give  rise  to  massive  discharges  of 
energy ;  in  the  interstices  of  this,  are  various  kinds  of  material 
related  in  different  degrees  to  this  framework ;  these  materials  are 
less  eminently  living,  and  the  chief  part  of  the  energy  set  free  comes 
directly  from  the  metabolism  of  some  or  other  of  this  material. 
Both  the  framework  and  the  intercalated  material  undergo  meta- 
bolism, and  have  in  different  degrees  their  anabolic  and  katabolic 
changes ;  both  are  concerned  in  the  life  of  the  organism ;  but  one 
more  directly  than  the  other.  When  we  now  speak  of  endogenous 
protein  metabolism  we  refer  to  that  in  the  material  highly  endowed 
with  life;  when  we  apply  the  term  exogenous  protein  metabolism  to 
the  changes  by  which  the  liver  brings  about  the  conversion  of  amino- 
acids  from  the  food  into  urea,  we  refer  to  its  action  on  intercalated 
material,  and  no  longer  use  the  phrase  ''  circulating  protein." 

We  have  already  discovered  in  our  study  of  the  urine,  that 
exogenous  protein  katabolism  is  mainly  represented  in  the  urine  by 
urea  and  inorganic  sulphates ;  while  the  final  katabolites  of  endo- 
genous metabolism  are  substances  like  creatinine  and  "  neutral 
sulphur";  but  there  is  no  doubt  that  some  urea  is  formed  also:  this 
is  seen,  for  instance,  during  starvation. 

Let  us  consider  a  man  taking  the  customary  Yoit  dietary  of 
16  or  17  grammes  of  nitrogen  in  his  daily  food;  probably  only  a 
quarter  or  even  less  of  this  is  destined  for  endogenous  use,  and  the 
protein  sufficient  to  maintain  this  is  indispensable.  Would  it  be 
possible  to  dispense  entirely  with  the  amount  which  is  exogenously 
metabolised,  and  reduce  our  protein  intake  to  the  low  level  of  say 
4  grammes  of  nitrogen  per  diem.  The  old  observations  on  starving 
animals  we  have  just  referred  to  shows  that  this  would  not  be 
possible ;  the  minimum  is  not  the  optimum ;  and  even  Chittenden 
(see  p.  471)  does  not  recommend  a  reduction  lower  than  7  or  8  daily 
grammes  of  nitrogen.  If  an  animal  cell  is  presented  only  with 
protein  food,  it  takes  and  uses  it  eagerly,  even  although  it  may  not 
ultimately  build  much  of  it  into  protoplasm.  If  substances  like  fat, 
carbohydrate,  or  the  incomplete  protein  we  call  gelatin,  is  presented 
to  it  also,  the  amount  of  protein  necessary  is  reduced,  and  so  we 
speak  of  such  foods  as  being  "protein-sparing." 

The  important  character  of  Chittenden's  work  has  given  the 
faddists  on  matters  of  diet  an  important  opportunity  of  being 
listened  to.      There  is,  for  instance,  a   group  of   these   to   whom 


CH.  XXXIX.]  THE   NECESSARY   DIET  605 

the  very  necessary  act  of  chewing  has  assumed  almost  the  nature 
of  a  religious  ceremony,  and  they  have  sought  to  convince  mankind 
of  its  superlative  importance.  These,  however,  need  not  concern 
us,  but  there  are  some  even  in  the  scientific  world  who  seem  almost 
to  believe  that  the  law  of  conservation  of  energy  does  not  apply  to 
the  chemical  changes  in  a  living  animal.  They  cite  instances  of 
people  who  do  a  large  amount  of  work,  and  do  it  upon  what  most 
would  regard  as  an  insufficient  diet,  without  detriment  or  loss  of 
body-weight.  If  a  man  only  receives  food  in  the  day  of  the  energy 
value  say  of  1500  large  calories,  and  the  heat  he  produces  and  the 
work  he  does  are  equivalent  to  2000 ;  then  the  additional  500 
must  have  come  from  his  internal  resources,  and  he  must  have  used 
up  some  of  the  material  formerly  stored  in  his  body.  This  is  as 
certain  as  the  fact  that  one  and  one  make  two.  It  is  quite  conceiv- 
able that  his  body  may  not  have  lost  weight,  but  nevertheless  fat 
may  have  disappeared,  and  been  replaced  by  an  equivalent  weight 
of  water,  and  excess  of  carbohydrate  food  which  usually  is  a  char- 
acter of  the  diets  of  such  people  is  just  the  sort  of  diet  likely  to 
cause  retention  of  water  in  the  body. 

We  have  in  our  mention  of  the  Chittenden  diet  alluded  to  several 
circumstances  that  should  make  us  hesitate  before  we  accept  his 
conclusions  to  the  full.  Many  people  eat  too  much ;  would  it  be 
advisable  for  us  all  to  eat  too  little,  and  is  Chittenden's  diet  too 
scanty  ? 

No  doubt  the  over-eaters  would  benefit  by  eating  too  little  for  a 
time.  They  would  give  their  overtaxed  digestive  and  secretory 
organs  a  necessary  rest,  and  have  time  to  consume  some  of  their 
accumulated  stores  of  material.  It  is  quite  possible  that  the  benefit 
noticed  in  some  of  the  subjects  of  Chittenden's  experiments  might 
have  been  due  to  such  a  circumstance  as  this,  or  to  the  regular  life 
they  were  compelled  to  live,  quite  apart  from  diet  altogether.  But 
to  eat  too  little  as  an  ordinary  and  permanent  thing  is  quite  another 
matter ;  and  it  is  interesting  to  be  able  to  record  that  most  of  the 
subjects  of  Chittenden's  experiments  have  now  returned  to  their 
previous  dietetic  habits. 

So  far  as  it  is  possible  to  read  history  correctly,  man  has  always 
where  he  can  taken  instinctively  more  protein  than  Chittenden 
would  allow  him,  and  with  few  exceptions,  the  meat  eating  nations 
are  those  which  have  risen  to  the  front. 

So  far  as  it  is  possible  to  draw  correct  deductions  on  questions  of 
diet  from  animals  to  man,  a  restricted  diet  over  a  long  period  has 
proved  detrimental.  Moreover,  a  careful  study  of  Chittenden's  own 
analytical  figures,  such  as  Benedict  has  made,  shows  there  was  in 
some  cases  distinct  impairment  of  absorptive  power. 

But  still  the  question  remains,  why  an  apparently  large  excess  of 


606  GENERAL   METABOLISM  [CH.  XXXIX. 

nitrogen  which  the  body  casts  out  within  a  few  hours  should  be 
advisable  ?  The  answer  to  this  appears  to  be,  that  though  most  of 
the  cleavage  products  are  dealt  with  in  this  way,  there  are  probably 
some  which  are  especially  precious  for  tissue  reconstruction,  and  it 
is  for  these  that  wo  put  up  with  the  excess  of  waste.  The  large  size 
and  activity  of  the  normal  liver  seem  to  be  for  the  express  purpose 
of  dealing  with  this  waste  rapidly. 

Nature  does  not  work  in  minimums :  Leathes  puts  it  very  well 
when  he  says  it  is  not  considered  unphysiological  to  take  more  food 
than  will  yield  the  minimum  of  fsecal  refuse ;  and  he  also  points  out 
that  in  the  infant,  even  allowing  for  its  growth,  the  normal  amount 
of  milk  provided  for  it  by  nature  is  ten  times  greater  than  would 
appear  to  l^e  the  necessary  minimum ;  and  this  is  probably  a  safer 
argument  than  the  one  so  often  used  when  the  instinctive  habits  of 
past  centuries  of  adults  are  appealed  to. 

;.  We  may  also  draw  a  useful  lesson  from  disease.  In  the  modern 
treatment  of  consumption,  the  open  air  cure  is  combined  with  a  steady 
process  of  generous  feeding ;  in  certain  cases  of  nervous  breakdown, 
an  important  part  of  the  "  rest  cure "  is  the  providing  of  abundant 
and  appetising  meals.  One  can  hardly  doubt  that  much  of  the 
benefit  noticeable  in  both  classes  is  due  to  the  "reserve  energy" 
provided,  enabling  the  body  more  fully  to  grapple  with  the  malady. 
"  Eeserve  energy "  may  be  objected  to  as  a  vague  phrase  which, 
though  comforting  to  those  who  use  it,  is  nevertheless  very  difficult 
to  explain.  There  is  a  good  deal  of  reason  in  such  an  objection,  for 
"  reserve  force  "  is  difficult  to  define  clearly.  We  have,  for  instance, 
no  knowledge  of  any  storage  places  for  protein,  in  the  same  way  in 
which  the  liver  and  adipose  tissue  act  as  storehouses  for  carbohydrate 
and  fat  respectively.  But  it  is  an  undoubted  factor  all  the  same ; 
many  people  have  more  of  it  than  others ;  and  this  "  stamina,"  as  it 
is  sometimes  called,  is  a  lucky  possession  for  those  who  have  it. 
Eesearch  on  immunity  has,  however,  shown  us  that  this  is  in  part  due 
to  the  condition  of  our  leucocytes,  and  the  opsonic  power  of  the 
blood-plasma  (see  p.  455).  It  may  be  that  it  is  in  this  direction, 
among  others,  that  the  abundance  of  protein  food  may  assist  us  in 
repelling  disease.  Each  leucocyte  may  not  require  much  in  the 
way  of  repair  every  day,  but  it  is  more  likely  to  get  this  "  stitch  in 
time "  if  there  is  an  abundant  supply  of  repairing  material 
available. 

Eubner  has  called  attention  to  what  he  terms  the  specific  dynamic 
action  of  food-stuffs.  Weight  for  weight,  fat  yields  more  heat  when 
burnt  than  protein  does,  and  outside  the  body  it  is  more  easily 
combustible  than  either  protein  or  carbohydrate.  Inside  the  body 
it  is  just  the  reverse;  proteins  are  the  most  readily  burnt  of  any 
food  material,  and  fats  the  least.     In  other  Words,  proteins  have  a 


CH.  XXXrX.]  INANITION  607 

specific  value  in  stimulating  metabolism,  and  so  leading  to  an 
increase  of  oxidation  in  the  body.  Some  of  the  subjects  of 
Chittenden's  experiments  suffered  intensely  from  the  cold  in  the 
winter,  and  this  use  of  protein  must  not  be  lust  sight  of  in  settling 
the  right  amount  which  we  should  take  in  our  daily  food. 

Some  attempt  has  been  made  to  determine  which  of  the  protein  cleavage 
products,  or  Bausteine,  to  use  the  German  term,  are  specially  valuable  in  the  body, 
either  for  the  synthesis  of  tissue  protein,  or,  as  Hopkins  has  suggested,  for  the 
formation  of  the  special  hormones  or  chemical  messenjrers  of  the  body,  such  as 
adrenaline.  Vegetable  proteins  are  not  so  nutritious  as  those  of  animal  origin,  and 
this  does  not  seem  to  be  wholly  due  to  the  fact  that  they  are  not  so  readily 
digestible.  Research  on  their  Bausteine  seems  to  show  that  they  are  not  really 
the  same  as  the  animal  proteins  ;  this  is  exemplified  by  their  high  yield  (often  over 
30  per  cent.j  of  glutamic  acid.  Barker  and  Cohoe  have  pointed  out  that  some 
articles  of  diet  will  "agree"  and  others  "disagree"  with  people.  On  the  supposi- 
tion that  this  may  be  due  to  the  distribution  of  the  nitrogen,  they  made  determina- 
tion of  the  mono-amino-nitrogen,  di-aniino-nitrogen,  etc.,  in  various  foods  (veal, 
pork,  sirloin,  chicken,  fish,  etc.),  and  have  found  very  striking  differences  between 
them.  The  ultimate  valuation  of  these  results  is  for  the  future,  but  this  is  the  sort  of 
work  which  must  be  done  before  our  knowledge  can  be  based  on  the  bed-rock  of 
experiment. 

At  present  we  can  only  make  a  rough  guess  as  to  which  of  the  Bausteine  are 
the  more  precious  building  stones  ;  but  it  does  appear  that  phenyl-alanine  and  its 
near  relative  tyrosine  are  such  ;  for  when  they  are  injected  into  the  blood-stream 
they  do  not  reappear  as  urea  in  the  urine.  We  also  know  that  proteins  which 
jield  no  tyrosine,  such  as  gelatin,  are  of  inferior  value  as  food.  Gelatin  is  also 
destitute  of  the  tryptophane  radical,  and  probably  tryptophane  is  specially  useful 
too.  Zein,  the  protein  of  maize,  lacks  tryptophane,  and  if  tryptophane  is  added  to 
a  zein  diet,  animals  fed  on  the  mixture  thrive  better  than  those  whose  sole 
nitrogenous  food  is  zein.  Histidine  and  pyrrolidine  have  been  suggested  as  being 
in  the  same  category,  but  here  again  we  must  await  further  information. 


Inanition  or  Starvation. 

During  starvation  the  body  gradually  loses  weight;  the  tempera- 
ture, after  a  preliminary  rise,  sinks ;  the  functions  get  weaker  by 
degrees,  and  ultimately  death  ensues  when  the  body  has  lost  about 
50  per  cent,  of  its  original  weight.  Death  may  be  delayed  somewhat 
by  artificial  warmth,  so  that  the  strain  on  the  internal  production  of 
heat  is  not  so  great.  If  water  is  given,  life  may  continue  for  rather 
more  than  a  month.  The  age  of  the  animal  influences  the  time  at 
which  death  occurs.  This  statement  was  originally  made  by 
Hippocrates,  and  has  been  borne  out  by  the  experiments  of  Martigny 
and  Chossat.  Young  animals  lose  weight  more  quickly,  and  die 
after  a  smaller  loss  of  weight  than  old  ones. 

The  following  table  from  Ranke's  experiment  on  himself  repre- 
sents by  the  balance-sheet  method  the  exchange  for  a  period  of 
twenty-four  hours,  the  same  time  having  elapsed  since  the  last 
meal. 


608 


GENERAL   METABOLISM 


[CH.  XXXIX. 


Income,  dae  to  Disintegration  of  Tissues. 

Expenditure,  obtained  by  analysing  the 
excretions. 

1 
Nitrogen.        Carbon.     I 

i 

Nitrogen. 

Carbon. 

Protein  .        50  gr. 

Fat         .      200   „ 

i 

7-8              26-5 
0-0             157-5 

Urine    . 
Respiration  (CO.2) 

7-8 
0-0 

3-4 
180-6 

7-8             184-0 

7-8       1      184-0 

The  excretion  of  nitrogen  falls  quickly  at  the  commencement  of 
starvation,  and  even  on  the  first  day  the  above  table  shows  us  it  has 
sunk  to  half  the  normal.  This  lessening  goes  on  for  a  few  days, 
after  which  it  remains  constant;  about  the  end  of  the  fourth  week  it 
rises  again  when  the  fat  of  the  animal  has  been  used  up,  and  the 
body  makes  an  increased  call  on  the  protein  constituents  of  its 
protoplasm.  With  the  onset  of  symptoms  of  approaching  death, 
which  is  sometimes  accompanied  by  convulsions,  the  excretion  of 
nitrogen  rapidly  falls  again.  The  sulphates  and  phosphates  of  the 
urine  show  much  the  same  series  of  changes.  The  discharge  of 
carbonic  acid  and  the  intake  of  oxygen  fall  continuously  over  the 
whole  period. 

It  is  important  to  note,  that  wasting  does  not  occur  to  an  equal 
extent  in  all  the  tissues  and  organs.  Those  which  are  most  essential 
to  life  are  fed  at  the  expense  of  the  others ;  thus  the  heart  loses  little 
or  none,  and  the  central  nervous  system  loses  at  most  3  per  cent,  of  its 
weight.  The  fat  nearly  all  disappears,  at  least  97  per  cent,  of  it 
being  used  up ;  muscles  lose  30  per  cent,  of  their  original  weight, 
and  most  of  the  other  organs  suffer  also  but  in  varying  degrees. 
Taking  the  total  loss  as  100,  Yoit  gives  the  loss  due  to  that  of 
individual  organs  as  follows : — 


Bone  . 

.      5-4 

Pancreas  . 

0-1 

Brain  and  cord  . 

0-1 

Muscle 

.    42-2 

Lungs 

0-3 

Skin  and  hair     . 

8-8 

Liver 

.      4-S 

Heart 

0-0 

Fat     . 

26-2 

Kidneys     . 

.      0-6 

Testes 

0-1 

Blood 

3-7 

Spleen 

.      0-6 

Intestines 

2-0 

Other  parts 

5-0 

CHAPTEK    XL 

ANIMAL  HEAT 

Among  the  most  important  results  of  the  chemical  processes  we  sum 
up  under  the  term  metabolism,  is  the  production  of  heat.  Heat,  like 
mechanical  motion,  is  the  result  of  the  kataboUc  side  of  metabolic 
processes ;  the  result,  or  accompaniment,  that  is  to  say,  of  the  forma- 
tion of  carbonic  acid,  water,  and  other  simple  products. 
Animals  may  be  divided  into  two  great  classes  : — 

(1)  Warm-blooded  or  homoiothermal  animals,  or  those  which  have 
an  almost  constant  temperature.     (Mammals  and  birds.) 

(2)  Cold-blooded  or  poihilothermal  animals,  or  those  whose 
temperature  varies  with  that  of  the  surrounding  medium,  being 
always,  however,  a  degree,  or  a  fraction  of  a  degree,  above  that  of  the 
medium.  This  class  includes  reptiles,  amphibians,  fish,  embryonic 
birds  and  mammals,  and  probably  most  invertebrates. 

The  temperature  of  a  man  in  health  varies  but  slightly,  being 
between  36-5"  and  37-5"  C.  (98'  to  99°  F.).  Most  mammals  have 
approximately  the  same  temperature  :  horse,  donkey,  ox,  37"5°  to  38° ; 
dog,  cat,  38-5"  to  39° ;  sheep,  rabbit,  38°  to  39-5° ;  mouse,  37-5° ;  rat, 
37'9\  Birds  have  a  higher  temperature,  about  42°  C.  The  tempera- 
ture varies  a  Httle  in  different  parts  of  the  body,  that  of  the  interior 
being  greater  than  that  of  the  surface ;  the  blood  coming  from  the 
liver  where  chemical  changes  are  very  active  is  warmer  than  that  of 
the  general  circulation ;  the  blood  becomes  rather  cooler  in  its  passage 
through  the  lungs. 

The  temperature  also  shows  slight  diurnal  variations,  reaching  a 
maximum  about  4  or  5  P.M.  (37"5'^  C.)  and  a  minimum  about  3  a.m. 
(36  "8°  C.) ;  that  is,  at  a  time  when  the  functions  of  the  body  are  least 
active.  If,  however,  the  habits  of  a  man  are  altered,  and  he  sleeps  in 
the  day,  working  during  the  night,  the  times  of  the  maximum  and 
minimum  temperatures  are  also  inverted.  Inanition  causes  the 
temperature  to  fall,  and  just  at  the  onset  of  death  it  may  be  below 
30    C.     Active  muscular  exercise  raises  the  temperature  temporarily 

(50'J  2    O 


610  ANIMAL   HEAT  [CH.  XL. 

by  about  0"5'  to  1    C.     Diseases  may  cause  the  temperature  to  vary 
considerably,  especially  those  which  we  term  febrile. 

A  mere  increase  in  the  production  of  heat  does  not  necessarily  cause  fever.  The 
administration  of  food  causes  increased  combustion  in  the  body,  but  there  is  no 
rise  of  temperature  in  health  because  jjcn-i  j)assu  with  the  increased  production 
there  is  increased  loss  of  heat.  Similarly,  diminution  in  the  loss  of  heat  such  as 
occurs  on  a  hot  as  compared  with  a  cold  day  does  not  produce  fever  because  the 
production  of  heat  within  the  body  is  correspondingly  diminished.  A  febrile 
condition  may  however  occur,  if  tight-fitting  and  otherwise  unsuitable  clothing 
which  interferes  w'ith  the  proper  action  of  the  skin  is  worn  in  hot  weather ;  this  is 
the  frequent  cause  of  "  heat-stroke"  among  soldiers  in  the  tropics. 

In  fever  there  is  increased  production  of  heat,  as  is  shown  by  metabolic  balance- 
sheets  ;  the  intake  of  food  is  usually  small,  and  the  discharge  of  carbon,  nitrogen, 
etc.,  results  mainly  from  tissue  disintegration  ;  this  is  even  greater  than  in  ordinary 
inanition  ;  the  tissues  are  said  to  be  in  a  "  labile  "  condition,  that  is,  they  are  easily 
broken  down.  Usually  the  skin  is  dry,  the  sweat  glands  like  most  of  the  secretory 
glands  being  comparatively  inactive,  and  so  the  discharge  of  heat  is  lessened.  The 
skin,  however,  may  sometimes  be  bathed  in  perspiration  and  yet  high  fever  be 
present.  The  essential  cause  of  the  high  temperature  in  fever  is  neither  increased 
formation  nor  diminished  discharge  of  heat,  but  an  interference  with  the  reflex 
mechanism  which  in  health  operates  so  as  to  equalise  the  two. 

Although  certain  mechanical  actions,  such  as  friction,  due  to 
movements  of  various  kinds,  may  contribute  a  minute  share  in  the 
production  of  heat  in  the  body,  yet  we  have  no  knowledge  as  to  the 
actual  amount  thus  generated.  The  great  source  of  heat  is,  as 
already  stated,  chemical  action,  especially  oxidation.  Any  given 
oxidation  will  always  produce  the  same  amount  of  heat.  Thus,  if  we 
oxidise  a  gramme  of  carbon,  a  known  amount  of  heat  is  produced, 
whether  the  element  be  free  or  in  a  chemical  compound.  The  follow- 
ing figures  show  the  approximate  number  of  heat-units  produced  by 
the  combustion  of  one  gramme  of  the  following  substances.  A  heat- 
unit,  or  calorie,  is  the  amount  of  heat  necessary  to  raise  the  tempera- 
ture of  one  gramme  of  water  1°  C. : — 

Hydrogen  ....  34662       Fat 9400 

Carbon        ....  8100  Cane  sugar          .         .         .  3950 

Urea 2530  Starch         ....  4160 

Albumin     ....  5600 

It  is,  however,  most  important  to  remember  that  the  "  physiologi- 
cal heat- value "  of  a  food  may  be  different  from  the  "  physical  heat- 
value,"  i.e.,  the  amount  of  heat  produced  by  combustion  in  the  body 
may  be  different  from  that  produced  when  the  same  amount  of  the 
same  food  is  burnt  in  a  calorimeter.  This  is  the  case  with  the  pro- 
teins, because  they  do  not  undergo  complete  combustion  in  the  body, 
for  each  gramme  of  protein  yields  a  third  of  a  gramme  of  urea,  which 
has  a  considerable  heat-value  of  its  own.  Thus  albumin,  which,  by 
complete  combustion,  yields  5600  heat-units,  has  a  physiological 
heat-value  =  5600  7MmMS  one-third  of  the  heat-value  of  urea  (2530) 
=  5600  —  846  =  4754.  Eubner  has  shown  that  this  figure  must  be 
reduced  to  nearly  4000,  as  some  of  the  imperfectly  burnt  products 


CH.  XL.] 


PKODUCTION    AND    DISCHARGE   OF    HEAT 


611 


of  decomposition  of  proteins  escape  as  uric  acid,  creatinine,  etc.,  in 
the  urine,  and  there  is  a  small  quantity  of  similar  substances  in  the 
ffBces.  Any  difference  between  the  physical  and  physiological  heat- 
values  of  fats  and  carbohydrates  may  be  neglected,  provided  all  the 
fat  and  carbohydrate  in  the  food  is  absorbed. 

Of  the  heat  produced  in  the  body,  it  is  estimated  by  Helmholtz 
that  about  7  per  cent,  is  represented  by  external  mechanical  work, 
and  that  of  the  remainder  about  four-fifths  are  discharged  by  radia- 
tion, conduction,  and  evaporation  from  the  skin,  and  the  remaining 
fifth  by  the  lungs  and  excreta.  This  is  only  an  average  estimate, 
subject  to  much  variation,  especially  in  the  amount  of  work  done. 

The  following  table  exhibits  the  relation  between  the  production 
and  discharge  of  energy  in  twenty-four  hours  in  the  human  organism 
at  rest,  estimated  in  calories.*  The  table  conveniently  takes  the  form 
of  a  balance-sheet  in  which  production  and  discharge  of  heat  are  com- 
pared ;  to  keep  the  body-temperature  normal  these  must  be  equal. 
The  basis  of  the  table  in  the  left-hand  (income)  side  is  the  same  as 
Eanke's  diet  (see  p.  471)  : — 


l'ro(liictio7i  of  heat. 


Metabolism  of 

Protein  (100  gr.)  .  100 

Fat  (100  gr.)  .  100: 

Carbohydrates        \.-)'f\ 

(  =  250  gr.  starch) j-^^^ 


Calories. 
4000=  400,000 
9400=     940,000 

4160  =  1,040,000 


Dhtrharife  of  heal. 

Warming  water  in  food, 

2-6  kilos.     25  C.  = 
Warming  air  in  respiration, 

16  kilos.  X  25   X  0-24  = 
Evaporation  in  lungs, 

630  gr.  X  582  = 
Radiation,  evaporation,  etc., 
at  surface,  plus  the  thermal 
equivalent  of  mechanical 
work  done  accounts  for  the 
remainder  . 


65,000 

96,000 

366,660 


1,852,340 


2,380,000 


2,380,000 


The  figures  under  the  heading  Production  are  obtained  by  multi- 
plying the  weight  of  food  by  its  physiological  heat-value.  The 
figures  on  the  other  side  of  the  balance-sheet  are  obtained  as  follows  : 
The  water  in  the  food  is  reckoned  as  weighing  2 '6  kilos.  This  is 
supposed  to  be  at  the  temperature  of  the  air  taken  as  12^  C. ;  it  has 
to  be  raised  to  the  temperature  of  the  body,  37°  C,  that  is,  through 
25°  0.  Hence  the  weight  of  water  multiplied  by  25  gives  the  number 
of  calories  expended  in  heating  it.  The  weight  of  air  is  taken  as 
weighing  16  kilos. ;  this  also  has  to  be  raised  25°  C,  and  so  to  be 
multiplied  by  25 ;  it  has  further  to  be  multiplied  by  the  relative  heat 
of  air  (0'24).     The  630  grammes  of  water  evaporated  in  the  lungs 

*  The  calorie  we  are  taking  is  sometimes  called  the  small  calorie  ;  by  some  the 
word  calorie  is  used  to  denote  the  amount  of  heat  necessary  to  raise  one  kilogramme 
of  water  1°  C.     This  is  called  the  large  caloric. 


612 


ANIMAL   HEAT 


[CH.  XL. 


must  be  multiplied  by  the  potential  or  latent  heat  of  steam  at  37°  C. 
(582) ;  the  portion  of  heat  lost  by  radiation,  conduction,  and  evapora- 
tion from  the  skin  constitutes  about  four-fifths  of  the  whole,  and  is 
obtained  by  deducting  the  three  previous  amounts  from  the  total. 
This  table  does  not  take  into  account  the  small  quantities  of  heat  lost 
with  urine  and  faeces.  "We  are  further  supposing  that  the  man 
remains  of  constant  weight,  so  that  there  is  no  storage  or  loss  of 
material,  and,  therefore,  of  energy  in  the  body.  He  is  also  supposed 
to  be  at  rest,  and  therefore  the  amount  of  work  done  is  only  what  is 
called  internal  work,  i.e.,  maintaining  the  circulation,  respiration,  etc. 

It  need  hardly  be  remarked  that  the  above  is  a  mere  average 
illustrative  experiment.  Changes  in  the  diet,  in  the  atmospheric 
temperature,  in  the  temperature  of  the  food  taken,  in  the  activity  of 
the  sweat-glands,  in  the  amount  of  moisture  in  the  atmosphere,  and 
in  the  amount  of  work  done,  would  considerably  alter  the  above 
figures. 

Calorimetry. — Calorimeters  employed  in  chemical  operations  are 
not  suitable  for  experiments  on  animals.  An  animal  surrounded  by 
ice  or  mercury,  the  melting  and  expansion  of  which  respectively  are 


Fio.  443. — Dulong's  Calorimeter :  C,  calorimeter,  consistin>,'  of  a  vessel  of  cold  water  in  wliich  the 
chamber  holding  the  animal  is  placed ;  G',  gasometer  from  which  air  is  expelled  by  a  stream  of 
water.  The  air  enters  the  respiratory  chamber.  G,  gasometer  receiving  tlie  gases  of  expiration 
and  the  excess  of  air.  t,  f,  thermometers  ;  a,  a  wheel  for  agitating  the  water.  Observe  the 
delivery-tube  on  the  left  is  mucli  twisted  in  tlie  water-chamber,  so  as  to  give  off  its  heat  to  the 
surronnding  water.    (From  McKendrick's  "Physiology.") 

measures  of  the  amount  of  heat  evolved,  would  be  under  such  ab- 
normal conditions  that  the  results  would  be  valueless.  Lavoisier, 
however,  used  an  ice  calorimeter  in  his  experiments  on  animals. 

The  apparatus  often  employed  is  the  water  calorimeter.  This 
was  first  used  by  Crawford  (1788).  Dulong's  instrument  is  shown  in 
fig.  443.  The  animal  is  placed  in  a  metal  chamber,  surrounded  by  a 
water-jacket.  There  are  also  tubes  for  the  entrance  and  exit  of  the 
inspired  and  expired  gases  respectively.     The  heat  given  out  by  the 


CII.  XL.] 


CALORIMETRY 


613 


animal  warms  the  water  in  the  jacket,  and  is  measured  by  the  rise 
of  temperature  of  the  water,  of  which  the  volume  is  also  known. 

Air  Calorimeters  are  now,  however,  generally  used.  Fig.  444 
is  an  outline  sketch  of  the  one  which  has  been  most  used  in  this 
country. 

It  consists  of  two  precisely  similar  chambers  made  of  thin  sheet 
copper.  Each  chamber  has  two  walls  between  which  is  an  air  space ; 
and  the  outer  is  covered  by  a  thick  casing  of  felt  (F)  to  prevent 
fluctuations  in  the  temperature  of  the  surroundings  from  affecting 
the  air  in  the  air-space.  The  chambers  are  made  perfectly  air-tight, 
except  for  the  ventilating  tubes  AA,  A'A'.  By  means  of  these,  the 
chambers  are  filled  with  perfectly  dry  air  before  the  experiment  is 
commenced.     Leading  from  each  air-space  is  a  tube ;  the  two  tubes 


Fig.  444.— Air  Calorimeter  of  Hakiane,  Hale  Wliite,  and  Waslibourn.  C,  cage  for  animal.  In  order  to 
make  the  conditions  in  both  chambers  as  much  alike  as  possible,  an  empty  cage  should  be  placed  in 
the  other  chambf  r. 

are  connected  to  the  two  limbs  of  a  manometer  (M)  shaped  as  in  the 
figure,  and  containing  oil  of  erigeron. 

The  action  of  the  calorimeter  is  as  follows : — In  one  chamber  the 
animal,  the  heat  production  of  which  is  to  be  ascertained,  is  placed 
within  the  cage  C.  In  the  other,  hydrogen  is  burnt  (H).  Both 
chambers  are  shut,  the  tubes  AA,  AA'  being  clamped.  The  heat 
given  off  from  the  animal  warms  its  chamber,  and  thus  increases  the 
pressure  of  the  air  in  the  air-space  between  the  two  copper  walls  of 
the  chamber.  This  would  lead  to  movement  of  the  fluid  in  the 
manometer,  but  that  the  heat  given  off  by  the  burning  of  the  hydrogen 
increases  at  the  same  time  the  pressure  in  the  air-space  between  the 
walls  of  its  chamber.  This  latter  increase  of  pressure  tends  to  make 
the  fluid  in  the  manometer  move  in  the  other  direction.  If  the  fluid 
in  the  manometer  remains  stationary,  the  amount  of  heat  given  off 
by  the  animal  is  equal  to  that  produced  by  the  burning  hydrogen ; 
and  during  an  experiment  the  fluid  in  the  manometer  is  kept  station- 
ary by  turning  the  hydrogen  flame  up  and  down.  The  amount  of 
hydrogen  burnt  is  estimated  by  the  amount  of  water  formed,  and  the 


614  ANIMAL    HEAT  [CII    XL 

heat  of  combustion  of  hydrogen  being  known,  it  is  easy  to  calcu- 
late the  calories  produced,  which  equal  those  given  off  by  the 
animal. 

The  applicability  of  the  law  of  the  conservation  of  energy  to  diverse  chemical 
reactions  has  been  amply  demonstrated.  In  view  of  the  chemical  nature  of  meta- 
bolism, we  might  assume  that  the  same  law  applies  to  the  reactions  taking  place  in 
tiie  body,  that  it  is  in  fact  one  of  the  fundamental  laws  of  the  universe.  We  have, 
however,  no  scientific  right  to  assume  in  advance  that  no  special  laws  are  operative 
in  living  matter.  The  law  therefore  here  requires  experimental  verification,  and 
much  labour  has  accordingly  been  devoted  to  this  problem.  The  early  work  of 
Lavoisier,  Crawford,  Dulong,  and  others  showed  great  discrepancies  between  the 
heat  actually  found  and  that  calculated,  but  with  the  advance  of  knowledge  and 
improvements  of  chemical  methods  and  calorimetry,  these  have  disappeared.  It  is 
to  Rubner  in  particular  that  we  owe  the  experimental  demonstration  of  the  law  of 
the  conservation  of  energy  in  the  living  organism. 

The  various  tissues  of  the  living  body  in  the  performance  of  their  several 
functions  break  down  and  oxidise  the  proteins,  fats,  carbohydrates,  and  other 
materials  of  which  they  are  composed,  and  seize  upon  the  energy  previously  stored 
and  thus  liberated,  converting  it  here  into  the  invisible  molecular  motion  of  heat, 
there  into  the  motion  of  visible  masses  of  matter  in  the  performance  of  work,  and 
again  into  the  energy  of  chemical  change  as  the  needs  of  the  organism  demand. 
Of  these  the  liberation  of  heat  is  by  far  the  greatest  in  amount,  and  for  this  reason, 
as  well  as  to  simplify  calculations,  it  has  become  customary  to  express  the  available 
energy  in  terms  of  "units  of  heat.  The  energy  expended  as  work  may  be  divided 
into  (1)  external  work,  i.<'. ,  the  work  done  on  masses  outside  the  body  ;  and  (2)  internal 
work,  i.e.,  the  physical  and  chemical  changes  produced  within  the  body  in  the 
processes  of  breathing,  digestion,  circulation,  and  the  like. 

If  the  law  of  the  conservation  of  energy  applies  to  the  animal  organism,  the 
following  are  its  necessary  consequences  : — 

1.  If  an  animal  is  doing  no  external  work,  and  is  neither  gaining  nor  losing 
substance,  the  potential  energy  of  the  food  (expressed  as  its  heat  of  combustion) 
will  be  equal  to  that  of  the  excreta,  plus  that  given  off  as  heat,  plus  that  of  internal 
work. 

2.  If  an  animal  is  doing  external  work,  and  is  neither  gaining  nor  losing 
substance,  the  potential  energy  of  the  food  will  be  equal  to  the  potential  energy  of 
the  excreta,  plus  that  given  off  as  heat,  plus  that  of  the  internal  work,  plus  that  of 
tiie  external  work. 

3.  If  an  animal  is  doing  no  external  work,  but  gaining  or  losing  body  substance, 
the  potential  energy  of  the  food  will  equal  the  potential  energy  of  the  excreta,  ])lus 
that  given  off  as  heat,  plus  that  of  the  internal  work,  plus  that  of  the  gain  by  the 
body-substance  (a  loss  by  the  body  being  regarded  as  a  negative  gain). 

'4.  In  an  animal  doing  external  work,  and  gaining  or  losing  body-substance, 
the  potential  energy  of  the  food  will  equal  the  potential  energy  of  the  excreta,  plus 
that  given  off  as  heat,  plus  that  of  the  internal  and  external  work,  jjIus  that  of  the 
gain  (positive  or  negative)  of  the  body-substance. 

In  actual  experimentation  it  is  practically  impossible  to  adjust  the  food  so  that 
there  is  no  gain  or  loss  of  body-substance,  hence  experiments  necessarily  fall  under 
(3)  or  (4) ;  and  the  majority  under  (3). 

The  quantities  to  be  determined,  then,  are  : — 

i.   Potential  energy  of  the  food. 

ii.   Potential  energy  of  excreta  (faeces,  urine,  etc.). 

iii.  The  heat  produced  (including  that  into  which  any  mechanical  work  is 
convertible). 

iv.  The  potential  energy  of  the  gain  or  loss  of  body-substance. 

If,  then,  the  equality  stated  under  (3)  and  (4)  is  found  to  exist,  we  shall  be 
justified  in  the  conclusion  that  the  law  of  the  conservation  of  energy  appHes  to  the 
animal  body.  This  is  what  the  painstaking  work  of  Rubner,  Laulanie,  Atwater, 
Benedict,  and  others  has  succeeded  in  showing  is  actually  the  case. 


CII.  XL.]  REGULATION  OF  TEMPERATURE  615 

Regulation  of  the  Temperature  of  Warm-blooded  Animals. 

The  equalisation  of  the  two  sides  of  the  balance-sheet  in  the 
maintenance  of  a  normal  temperature  may  be  accomplished  by  the 
production  of  heat  adapting  itself  to  variations  in  discharge,  or  by 
the  discharge  of  heat  adapting  itself  to  variations  in  production,  or 
lastly,  and  more  probably,  both  sets  of  processes  may  adapt  them- 
selves mutually  to  one  another.  We  have,  therefore,  to  consider 
regulation  (1)  by  variations  in  loss,  and  (2)  by  variations  in  pro- 
duction. 

Regulation  hy  Variations  in  Loss. — The  two  channels  of  loss  sus- 
ceptible of  any  amount  of  variation  are  the  lungs  and  the  skin.  The 
more  air  that  passes  in  and  out  of  the  lungs,  the  greater  will  be  the 
loss  in  warming  the  expired  air  and  in  evaporating  the  water  of  respira- 
tion. In  such  animals  as  the  dog,  which  perspire  but  little,  respiration 
is  a  most  important  means  of  regulating  the  temperature ;  and  in 
these  animals  a  close  connection  is  observed  between  the  production 
of  heat  and  the  respiratory  activity.  The  panting  of  a  dog  when 
overheated  is  a  familiar  instance  of  this.  A  dog  also,  under  the  same 
circumstances,  puts  out  its  tongue,  and  loses  heat  from  the  evapora- 
tion that  occurs  from  its  surface.  The  great  regulator,  however,  is 
undoubtedly  the  skin,  and  this  has  a  double  action.  In  the  first 
place,  it  regulates  the  loss  of  heat  by  its  vaso-motor  mechanism ;  the 
more  blood  passing  through  the  skin,  the  greater  will  be  the  loss  of 
heat  by  conduction,  radiation,  and  evaporation.  Conversely,  the  loss 
of  heat  is  diminished  by  anything  that  lessens  the  amount  of  blood 
in  the  skin,  such  as  constriction  of  the  cutaneous  vessels,  or  dilatation 
of  the  splanchnic  vascular  area.  In  the  second  place,  the  special 
nerves  of  the  sweat-glands  are  called  into  action.  Familiar  instances 
of  the  action  of  these  two  sets  of  nerves  are  the  reddening  of  the 
skin  and  sweating  that  occurs  after  exercise,  on  a  hot  day,  or  in  a 
hot-air  or  vapour  bath,  and  the  pallor  of  the  skin  and  absence  of 
sensible  perspiration  on  the  application  of  cold  to  the  body. 

Regulation  ly  Variations  in  Production. — The  rate  of  production 
of  heat  in  a  living  body,  as  determined  by  calorimetry,  depends  on 
a  variety  of  circumstances.  It  varies  in  different  kinds  of  animals. 
The  general  rate  of  katabolism  of  a  man  is  greater  than  that  of  a 
dog,  and  of  a  dog  greater  than  that  of  a  rabbit.  Probably  every 
species  has  a  specific  coefficient,  and  every  individual  a  personal 
coefficient  of  heat  production,  which  is  the  expression  of  the  inborn 
qualities  proper  to  the  living  substance  of  the  species  and  individual. 
Another  factor  is  the  proportion  of  the  bulk  of  the  animal  to  its 
surface  area,  the  struggle  for  existence  raising  the  specific  coefficient 
of  the  animals  in  which  the  ratio  is  high.  Other  important  con- 
siderations are  the  relation  of  the  intake  of  food  to  metabolic  processes. 


616  ANIMAL  HEAT  [CH.  XL. 

and  the  amount  of  muscular  work  which  is  performed.  These  various 
influences  are  themselves  regulated  by  the  nervous  system,  and 
physiologists  have  long  suspected  that  afferent  impulses  arising  in 
the  skin  or  elsewhere  may,  through  the  central  nervous  system, 
originate  efferent  impulses,  the  effect  of  which  would  be  to  increase 
or  diminish  the  metabolism  of  the  muscles  and  other  organs,  and  by 
that  means  increase  or  diminish  respectively  the  amount  of  heat 
there  generated.  That  such  a  metabohc  or  thermogenic  nervous 
mechanism  does  exist  in  warm-blooded  animals  is  supported  by  the 
following  experimental  e\T.dence : — 

(1)  Though  in  cold-blooded  animals  a  rise  or  fall  of  the  surround- 
ing temperature  causes  respectively  a  rise  and  fall  of  their  metabolic 
activity,  in  a  warm-blooded  animal  the  effect  is  just  the  reverse. 
Warmth  from  the  exterior  demands  a  diminished  production  of  heat 
in  the  interior,  and  vice  versd. 

If  the  changes  of  the  external  temperature  are  so  great  as  to  cause  a  rise  (as  in 
steam  baths)  or  a  fall  (as  in  hibernation)  of  body  temperature,  the  metabolic 
changes  are  increased  or  decreased  respectively  as  in  cold-blooded  animals. 
Perabrey  has  also  shown  that  warm-blooded  animals  in  an  embryonic  condition 
are  practically  cold-blooded,  the  regulatory  mechanism  not  being  fully  developed 
at  this  stage. 

(2)  That  this  is  due  to  a  reflex  nervous  impulse  is  supported  by 
the  fact  that  a  warm-blooded  animal,  when  poisoned  by  curare,  no 
longer  manifests  its  normal  behaviour  to  external  heat  and  cold,  but 
is  affected  in  the  same  way  as  a  cold-blooded  animal.  Section  of 
the  medulla  produces  the  same  effects,  as  the  nerve-channels,  by 
which  the  impulses  travel,  are  severed.  When  curare  is  given,  the 
reflex  chain  is  broken  at  its  muscular  end,  the  poison  exerting  its 
influence  on  the  end-plates,  and  causing  a  diminution  of  the  chemical 
tonus  of  the  muscles.  The  centre  of  this  thermotaxic  reflex  mechanism 
must  be  situated  somewhere  above  the  spinal  cord ;  according  to  some 
observers,  in  the  optic  thalamus. 

(3)  The  reflex  mechanism  is  well  exemplified  in  shivering ;  here 
the  muscles  are  thrown  into  involuntary  contraction,  and  so  produce 
more  heat,  as  the  result  of  the  stimulation  of  the  skin  by  cold. 

(4)  Various  injuries  caused  by  accident,  or  purposely  pro- 
duced by  puncture,  or  cautery,  or  electrical  stimulation  of  limited 
portions  of  the  more  central  portions  of  the  brain,  may  give  rise 
to  great  increase  of  temperature,  not  accompanied  by  other  marked 
symptoms. 

We  thus  see  that  the  nervous  system  is  intimately  associated 
with  the  regulation  of  the  temperature  of  the  body.  There  is  at 
least  one — there  may  be  several  centres  associated  in  this  action. 
The  centres  receive  afferent  impulses  from  without ;  they  send  out 
efferent  impulses  by  at  least  three  sets  of  nerves :  (1)  the  vaso-motor 


CH.  XL.]  REGULATION  OF  TEMPERATURE  617 

nerves,  (2)  the  secretory  nerves  of  the  sweat-glands,  (3)  trophic  or 
nutritional  nerves.  The  first  two  sets  of  nerves,  the  vaso-motor  and 
the  secretory,  affect  the  regulation  of  temperature  on  the  side  of 
discharge ;  the  third  set  on  the  side  of  production. 

The  foregoing  account  of  heat  regulation  does  not  take  into  account  what  after 
all  is,  at  any  rate  in  man,  a  very  important  factor,  namely,  the  voluntary  and  arti- 
ficial means  which  he  employs,  such  as  various  kinds  of  clothing  suitable  to  the 
climate,  lieating  of  rooms,  and  voluntary  nmscular  exercise. 


CHAPTEK  XLI 

THE  CENTRAL  NERVOUS  SYSTEM 

We  already  know  sufficient  from  our  preliminary  study  of  nerve- 
centres  to  be  aware  that  the  central  nervous  system  is  di\'ided  into 
the  two  main  parts  called  the  brain  and  spinal  cord. 

Fig.  445  shows  the  general  arrangement  of  the  cerebro-spinal 
axis,  and  some  anatomical  details  concerning  the  membranes  that 
envelop  the  brain  and  cord  may  here  conveniently  be  added. 

Membranes  of  the  Brain  and  Spinal  Cord. — The  Brain  and  Spinal  Cord  are 
enveloped  in  three  membranes — (1)  the  Dura  Mater,  (2)  the  Arachnoid,  (3)  the  Pia 
Mater. 

(Ij  The  Dura  Maffr,  or  external  covering,  is  a  tough  membrane  composed  of 
bundles  of  connective  tissue  which  cross  at  various  angles,  and  in  whose  interstices 
branched  connective-tissue  corpuscles  lie  :  it  is  lined  by  a  thin  elastic  membrane, 
on  the  inner  surface  of  which  is  a  layer  of  endothelial  cells. 

(2)  The  Ararlino'id  is  a  much  more  delicate  membrane,  very  similar  in  structure 
to  the  dura  mater,  and  lined  on  its  outer  or  free  surface  by  an  endothelial  mem- 
brane. 

(3)  The  Pia  Maii-r  of  the  cord  consists  of  two  layers  between  which  numerous 
blood-vessels  ramify.  In  that  of  the  brain  only  the  inner  of  the  two  layers  is  repre- 
sented. Between  the  arachnoid  and  pia  mater  is  a  network  of  fibrous  tissue 
trabeculae  sheathed  with  endothelial  cells  :  these  sub-arachnoid  trabeculae  divide  up 
the  sub-arachnoid  space  int^)  a  number  of  irregular  sinuses.  There  are  some  similar 
trabeculse,  but  much  fewer  in  number,  traversing  the  sub-dural  space,  i.e.,  the  space 
between  the  dura  mater  and  arachnoid. 

Pacchionian  bodies  are  growths  from  the  sub-arachnoid  network  of  connective- 
tissue  trabeculae  which  project  through  small  holes  in  the  inner  layers  of  the  dura 
mater  into  the  venous  sinuses  of  that  membrane.  The  venous  sinuses  of  the  dura 
mater  have  been  injected  from  the  sub-arachnoidal  space  through  the  intermediation 
of  these  villous  outgrowths. 

In  the  chapters  preceding  this  one  we  have  seen  how  all-per- 
vading nervous  action  is ;  in  connection  with  circulation,  respiration, 
secretion,  peristalsis,  etc.,  the  way  in  which  such  functions  are 
regulated  by  nervous  activity  has  taken  up  a  considerable  amount  of 
space.  Some  of  the  facts  there  described  will  be  better  understood, 
or  be  seen  in  a  clearer  light,  if  the  student  turns  back  to  them  and 
studies  them  once  more  after  he  has  grasped  what  we  are  going  to 
consider  in  the  chapters  that  follow  this  on  the  physiology  of  the 
central  nervous  system. 

It  would  also  be  ad\4sable,  before  he  begins  this  subject,  that  ho 


CH    XU.]  CENTRAL   NERVOUS   SYSTEM  019 

should  once  more  read  Chap.  XVTT.  on  norvo-oentroP,  in  order    to 


nf-  S/'.eivxl  CorU        1     [\.r 


"0\    Veitebrc, 


LowavExtremitu  -  -l-^-/-, 
of  S/itnal  Coiyi         \    (L^ 


mUl--SacnA7u 


Vio  440  -View  of  the  cerebro-.spi.al  axis  of  the  nervous  system.  The  ri:4ht  half  of  tl>e  cra'>mm  and 
trunk  of  the  body  has  been  removed  by  a  vertical  section  ;  the  membranes  of  the  brai  i  and  spina 
cord  baeaLoteen  removed,  and  the  roots  and  first  part  of  the  fifth  and  n.n  h  cranial  and  of  all 
the  sninal  nerves  of  the  right  side,  have  been  dissected  out  and  laid  separately  on  the  wall  of  the 
skull  and  on  the  several  veJtebrM-  opposite  to  the  place  of  their  natural  exit  from  the  cran.o-sp.nal 
cavity.     (After  Bourgery.) 

refresh  his  memory  concerning   the   elementary  and   fundamental 
problems  in  relation  to  nervous  activity  in  these  regions. 


CHAPTER  XLII 

STRUCTURE   OF   THE   SPINAL  CORD 

The  spinal  cord  is  a  column  of  nerve-substance  connected  above  with 
the  brain  through  the  medium  of  the  bulb,  and  situated  in  the  spinal 
canal.  In  transverse  section  it  is  approximately  circular,  but  the 
cord  is  not  of  the  same  size  throughout  its  course.  It  exhibits  two 
enlargements,  one  in  the  cervical,  the  other  in  the  lumbar  region. 
These  are  the  situations  whence  the  large  nerves  for  the  supply  of 
the  limbs  issue.  The  cord  terminates  below,  about  the  lower  border 
of  the  first  lumbar  vertebra,  in  a  slender  filament  of  grey  substance, 
the  filum  terminale,  which  lies  in  the  midst  of  the  roots  of  many 
nerves  forming  the  cauda  equina. 

It  is  composed  of  grey  and  white  matter ;  the  white  matter  is 
situated  externally,  and  constitutes  its  chief  portion ;  the  grey  matter 
is  in  the  interior,  and  is  so  arranged  that  in  a  transverse  section  of 
the  cord  it  appears  like  two  crescentic  masses  (the  horns  of  each  of 
which  are  called  respectively  the  anterior  and  posterior  cornua)  con- 
nected together  by  a  narrower  portion  or  isthmus,  caUed  the  posterior 
commissure  (fig.  446).  Passing  through  the  centre  of  this  isthmus 
in  a  longitudinal  direction  is  a  minute  canal ;  in  a  transverse  section 
it  appears  as  a  hole ;  this  central  canal  of  the  spinal  cord  is  continued 
throughout  its  entire  length,  and  opens  above  into  the  space  at  the 
back  of  the  medulla  oblongata  and  pons  Varolii,  called  the  fourth 
ventricle.  It  is  lined  by  a  layer  of  columnar  ciliated  epithelium,  and 
contains  a  fluid  called  cerelro-spinal  fiuid. 

The  spinal  cord  consists  of  two  symmetrical  halves,  separated 
anteriorly  and  posteriorly  by  vertical  fissures  (the  posterior  fissure 
being  deeper,  but  less  wide  and  distinct  than  the  anterior),  and 
united  in  the  middle  by  nervous  matter  which  is  usually  described 
as  forming  two  commissures — an  anterior  commissure  (consisting  of 
medullated  nerve-fibres)  in  front  of  the  posterior  commissure,  which 
is  the  isthmus  of  grey  matter  pierced  by  the  central  canal,  to  which 


WHITE   MATTEIl   OF   THE   SPINAL   COIIU 


621 


CH.  XLII.] 

we  referred  in  the  last  paragraph  (fig.  446,  u).  Each  half  of  the  spinal 
cord  is  marked  on  the  sides  (obscurely  at  the  lower  part,  but  dis- 
tinctly above)  ])y  two  longitudinal  furrows,  which  divide  it  into  three 


;.  446.— Different  views  of  a  portion  of  the  spinal  cord  from  the  cervical  region,  with  the  roots  of  the 
nerves  (slightly  enlarged).  In  a,  the  anterior  surface  of  the  specimen  is  shown  ;  the  anterior  nerve- 
root  of  its  right  side  is  divided ;  in  b,  a  view  of  the  right  side  is  given  ;  in  c,  the  upper  surface  is 
shown  ;  in  d,  the  ner\'e-roots  and  ganglion  are  shown  from  below.  1,  the  anterior  median  fissure ; 
2,  posterior  median  fissure  ;  8,  anterior  lateral  depression,  from  which  the  anterior  nen'e-roots  are 
seen  to  issue  ;  4,  posterior  lateral  groove,  into  which  the  posterior  roots  are  seen  to  sink ;  5, 
anterior  roots  passing  the  ganglion ;  5',  in  a,  the  anterior  root  divided  ;  6,  the  posterior  roots,  the 
fibres  of  which  pass  into  the  ganglion  6' ;  7,  the  united  or  compound  nerve  ;  7',  the  posterior  primary 
branch,  seen  in  a  and  d  to  be  derived  in  part  from  the  anterior  and  in  part  from  the  posterior  root. 
(Allen  Thomson.) 


portions,  columns,  or  tracts,  an  anterior,  lateral,  and  posterior.  From 
the  groove  between  the  anterior  and  lateral  columns  spring  the 
anterior  roots  of  the  spinal  nerves  (fig.  446,  B  and  c,  5) ;  and  just 
in  front  of  the  groove  between  the  lateral  and  posterior  column  the 
posterior  roofs  enter  (b,  6)  :  a  pair  of  roots  on  each  side  corresponds 
to  each  vertebra. 

White  matter. — The  white  matter  of  the  cord  is  made  up  of 
medullated  nerve-fibres,  of  different  sizes,  running  mainly  in  a 
longitudinal  direction,  and  of  a  supporting  material  of  two  kinds, 
viz. : — (a)  ordinary  fibrous  connective-tissue  with  elastic  fibres,  which 
is  connected  with  septa  from  the  pia  mater  which  pass  into  the  cord 
to  carry  the  blood-vessels,  (h)  Neuroglia;  the  processes  of  the: 
neui'oglia-cells  are  arranged  so  as  to  support  the  nerve-fibres  which 
arc  without  the  usual  neurilemmal  nerve-sheaths. 


622  STRUCTURE   OF   THE   SPINAL   CORD  [CH.  XLII. 

The  general  rule  respecting  the  size  of  different  parts  of  the  cord 
is,  that  each  part  is  in  direct  proportion  to  the  size  and  number  of 
nerve-roots  given  off  from  it.  Thus  the  cord  is  very  large  in  the 
middle  and  lower  part  of  its  cervical  portion,  whence  arise  the  large 
nerve-roots  for  the  formation  of  the  brachial  plexuses  and  the  supply 
of  the  upper  extremities ;  it  again  enlarges  at  the  lowest  part  of  its 
dorsal  portion  and  the  upper  part  of  its  lumbar,  at  the  origins  of  the 
large  nerves  which,  after  forming  the  lumbar  and  sacral  plexuses,  are 
distributed  to  the  lower  extremities.  The  chief  cause  of  the  greater 
size  at  these  parts  of  the  spinal  cord  is  increase  in  the  quantity  of 
grey  matter;  the  white  part  of  the  cord  (especially  the  lateral 
columns)  becomes  gradually  and  progressively  smaller  from  above 
downwards,  because  a  certain  number  of  fibres  coming  down  from  the 
brain  pass  into  the  spinal  grey  matter  at  different  levels. 

Grey  matter. — The  grey  matter  of  the  cord  consists  of  nerve- 
fibres,  most  of  which  are  very  fine  and  delicate,  of  nerve-cells  with 
branching  processes,  and  of  an  extremely  delicate  network  of  the 
primitive  fibrilliB  of  axis-cylinders  and  of  dendrites.  This  fine  plexus 
is  called  Gerlach's  network,  and  is  mingled  with  the  meshes  of 
neuroglia.  The  neuroglia  of  the  grey  matter  resembles  that  of  the 
white,  but  instead  of  everywhere  forming  a  close  network  to  support 
the  nerve-fibres,  here  and  there  it  is  in  the  form  of  a  more  open 
sponge- work  to  support  the  nerve-cells.  It  is  especially  developed 
around  the  central  canal,  which  is  lined  with  columnar  ciliated 
epithelium,  the  cells  of  which  at  their  outer  end  terminate  in  fine 
processes,  which  join  the  neuroglia  network  surrounding  the  canal, 
and  form  the  substantia  gelatinosa  centralis.  It  is  also  developed  at 
the  tip  of  the  posterior  cornu  of  grey  matter,  forming  what  is  known 
as  the  substantia  gelatinosa  lateralis  of  Eolando,  which  is  much 
enlarged  in  the  upper  cervical  region. 

Groups  of  cells  in  the  grey  matter. — The  multipolar  cells  of  the 
grey  matter  are  either  scattered  singly  or  arranged  in  definite 
groups. 

(1)  Anterior  horn  cells. — In  the  cervical  and  lumbar  enlargements 
there  are  several  groups  of  large  multipolar  cells  in  the  anterior 
horn ;  in  the  thoracic  region  these  are  reduced  to  two,  a  mesial  and  a 
lateral  group.  The  larger  groups  correspond  with  segments  of  the 
limbs,  and  in  the  cervical  cord  there  is  one  special  group  from  which 
the  phrenic  nerve  arises  for  the  supply  of  the  diaphragm.  The  axons 
pass  out  by  the  anterior  nerve-roots  of  the  same  side,  but  a  few  axons 
pass  to  the  antero-lateral  column  of  the  same  side,  and  by  the  white 
commissure  to  that  of  the  opposite  side.  In  birds,  a  few  axons  are 
stated  to  pass  to  the  posterior  roots. 

(2)  Posterior  vesicular  column  of  Lochhart  Clarke ;  generally  known 
as  Clarke  s  column. — This  is  a  group  of  large  nerve-ceUs  with  their  long 


CII.  XLII.] 


(iREY    MATTER   OF   THE   CORD 


623 


axis  vertical.  It  lies  at  the  base  of  the  posterior  horn,  and  is  best 
marked  in  the  thoracic  region.  Their  axons  pass  into  the  direct 
cerebellar  tract. 

(3)  Interniedio-lateral  group. — This  is  seen  in  the  outer  part  of 
the  grey  matter  of  the  lateral  horn,  and  is  most  distinct  in  the  upper 
thoracic  and  lower  cervical  regions. 

(4)  llie  middle  cell  column  lies  in  the  middle  of  the  crescent. 

(5)  The  cells  of  the  posterior  horn  are  usually  small;  they  are 
numerous,  but  are  not  disposed  in  special  groups. 

Columns  and  tracts  in  the  lohite  matter  of  the  spinal  cord. — Tlie 
columns  of  the  white  matter  which  are  marked 
out  by  the  points  from  which  the  nerve-roots 
issue,  are  called  the  anterior,  the  lateral,  and 
the  posterior  columns ;  the  posterior  is  further 
divided  by  a  septum  of  the  pia  mater  into 
two  almost  equal  parts,  constituting  the  postero- 
external column,  or  column  of  Burdach,  and  the 
poster o-median,  or  column  of  Goll  (fig.  449). 
In  addition  to  these  columns,  however,  it  has 
been  shown  that  the  white  matter  can  be  still 
further  subdivided.  These  tracts  in  the  white 
matter  perform  different  functions  in  the  con- 
duction of  impulses. 

The  methods  of  observation  are  the  follow- 


incr: 


Fio.  447.— Section  of  half  tho 
spinal  cord  to  show  the 
principal  groups  of  cells  in 
the  grey  matter ;  a,  groups 
of  cells  in  the  anterior 
horn  ;  c,  Clarke's  column  ; 
i,  intermedio-lateral  group ; 
m,  middle  cell  column  ;  p, 
scattered  cells  of  the  pos- 
terior horn.  (Diagrammatic 
after  Schiifer.) 


(a)  The  embryological  method.  It  has  been 
found  by  examining  the  spinal  cord  at  different 
stages  of  its  development  that  certain  groups 
of  the  nerve-fibres  put  on  their  myelin  sheath 
at  earlier  periods  than  others,  and  that  the  different  groups  of  fibres 
can  therefore  be  traced  in  various  directions.  This  is  also  known 
as  the  method  of  Flechsig. 

{h)  Wallerian  or  degeneration  method. — This  method  depends  upon 
the  fact  that  if  a  nerve-fibre  is  separated  from  its  nerve-cell,  it  wastes 
or  degenerates.  It  consists  in  tracing  the  course  of  tracts  of 
degenerated  fibres,  which  result  from  an  injury  to  any  part  of  the 
central  nervous  system.  When  fibres  degenerate  below  a  lesion,  the 
tract  is  said  to  be  of  descending  degeneration,  and  when  the  fibres 
degenerate  in  the  opposite  direction,  the  tract  is  one  of  ascending 
degeneration.  By  the  modern  methods  employed  in  staining  the 
central  nervous  system,  it  has  proved  comparatively  easy  to  distinguish 
degenerated  parts  in  sections  of  the  cord  and  of  other  portions  of  the 
central  nervous  system.  Degenerated  fibres  have  a  different  staining 
reaction  when  the  sections  are  stained  by  what  are  called  Weigert's 
and  Pal's  methods ;    this  consists  in   subjecting  them   to  a  special 


624  STRUCTURE   OF   THE   SPINAL   CORD  [CH.  XLIL 

solution  of  haematoxylin,  and  then  to  certain  dififerentiating  solutions. 
The  degenerated  fibres  appear  light  yellow,  whereas  the  healthy  fibres 
are  a  deep  blue.  Marchi's  method  is  even  better.  After  hardening 
in  Miiller's  fluid,  Marchi's  solution  (a  mixture  of  MiiUer's  fluid  and 
osmic  acid)  stains  degenerated  fibres  black,  and  leaves  the  rest  of  the 
tissue  unstained.  Accidents  to  the  central  nervous  system  in  man 
have  given  us  much  information  upon  this  subject,  but  this  has  of 
late  years  been  supplemented  and  largely  extended  by  experiments 
on  animals,  particularly  upon  monkeys ;  and  considerable  Hght  has 
been  shed  upon  the  conduction  of  impulses  to  and  from  the  nervous 
system  by  the  study  of  the  results  of  section  of  different  parts  of 
the  central  nervous  system,  and  of  the  spinal  nerve-roots. 

By  these  methods  the  tracts  in  the  white  matter  have  now  been 
mapped  out,  and  the  principal  ones  are  shown  in  the  succeeding 
diagrams. 

It  will  be  convenient  to  begin  by  considering  the  result  of  cutting 
through  the  roots  of  the  spinal  nerves. 

Gutting  the  anterior  roots  produces  chromatolysis  of  the  cells  of 
the  anterior  horn  from  which  they  originate  ;  this  slow  atrophy  is  the 
result  of  disuse  of  the  axons  which  are  cut  and  still  remain  attached  to 
the  cell-bodies.  "Wallerian  degeneration  is  limited  to  the  motor  nerve- 
fibres  on  the  distal  side  of  the  point  of  section.  The  fact  that  chro- 
matolysis (see  p.  202)  occurs  when  the  axon  of  a  nerve-cell  is  cut 
through,  furnishes  us  with  a  valuable  method  of  ascertaining  what 
nerve-cells  various  tracts  originate  from. 

Cutting  the  posterior  roots  between  the  spinal  ganglia  and  the 
cord  leaves  the  peripheral  part  of  the  nerve  healthy,  and  degeneration 
occurs  in  the  portion  of  the  root  which  runs  into  the  cord,  because 
the  fibres  are  cut  off  from  the  cells  of  the  spinal  ganglion  from  which 
they  grew.  These  degenerated  nerve-fibres  may  be  traced  up  the 
cord  for  a  considerable  distance.  Each  posterior  root-fibre  when  it 
enters  the  cord  bifurcates,  the  main  branch  passing  upwards,  and  the 
shorter  branch  downwards,  so  that  the  degeneration  is  seen  in  a 
small  tract  called  the  comma  tract  (fig.  450)  immediately  below  the 
point  of  entrance  of  the  cut  posterior  root.  The  upgoing  fibre  is 
contained  in  the  posterior  colimm  of  white  matter,  and  it  terminates 
in  the  grey  matter  either  in  the  cord  itself  at  a  higher  level,  or  in 
the  medulla  oblongata. 

Eig.  448  represents  in  a  schematic  way  the  manner  in  which  the 
fibres  of  the  two  roots  of  a  spinal  nerve  are  connected  to  the  grey 
matter  in  the  cord. 

1,  2,  3,  4  represent  four  cells  of  the  anterior  horn.  Each  gives 
rise  to  an  axis-cyhnder  process  A,  one  of  which  is  shown  terminating 
in  its  final  ramification  in  the  end -plate  of  a  muscular  fibre  M.  Each 
of  these  four  cells  is  further  surrounded  by  an  arborisation  (synapse) 


CH.  XLII.] 


ROOTS   OF  THE   SPINAL   NERVES 


62{ 


derived  from  the  fibres  of  the  pyramidal  tract  P,  which  comes  down 
from  the  brain. 

According  to  Schafer's  recent  work,  the  pyramidal  fibres  really 
terminate  around  the  cells  at  the  base  of  the  posterior  horn ;  these 
cells  therefore  act  as  intermediate  cell-stations  on  the  way  to  those 
in  the  anterior  horn.     This  is  not  shown  in  the  diagram. 

A  fibre  of  the  posterior  root  is  also  shown ;  this  originates  from 
the  cell  G  of  the  spinal  ganglion ;  the  process  of  this  cell  bifurcates, 
one  branch  (B)  passing  to  the  periphery,  where  it  ends  in  an  arbor- 


Fin.  448. — Course  of  iiprve-fibres  in  spinal  cord.     (After  Schiifer.) 

escence  in  the  skin  (S) ;  the  arrow  by  the  side  of  this  branch 
represents  the  direction  of  conduction  of  the  sensory  impulses  from 
the  skin.  An  arrow  in  the  opposite  direction  would  indicate  the 
direction  of  its  growth.  The  other  branch  C  passes  into  the  spinal 
cord,  where  it  again  bifurcates;  the  branch  E,  a  short  one,  passes 
downwards  and  ends  in  an  arborisation  around  one  of  the  small  cells 
Pj  of  the  posterior  cornu;  from  which  a  new  axis-cylinder  arises, 
and  terminates  around  one  of  the  multipolar  cells  (4)  of  the  anterior 
horn. 

The  main  division  D  travels  up  in  the  posterior  column  of  the 
cord,  and  ends  in  grey  matter  at  various  levels.     Some  collaterals  (5) 

2  R 


626 


STRUCTURE   OF   THE   SPINAL   CORD 


[CH.  XLII. 


Goll 


terminate  by  arborising  directly  around  the  anterior  cornual  cells, 
principally  of  the  same  side ;  others  (6)  do  so  with  an  intermediate 
cell  station  in  a  posterior  cornual  cell  P^ ;  others  (7)  arborise  around 
the  cells  of  Clarke's  column  (C)  in  the  thoracic  region  of  the  cord, 
and  from  these  cells  fresh  axis-cylinders  carry  up  the  impulse  to  the 
cerebellum  in  what  is  called  the  direct  cerebellar  tract,  while  the 
main  fibre  (8)  may  terminate  in  any  of  these  ways  at  a  higher  level 
in  the  cord,  or  above  the  cord  in  the  medulla  oblongata.  When  we 
become  acquainted  with  the  structure  of  the  medulla  oblongata,  we 
shall  be  able  to  trace  these  fibres  further. 

In  general  terms  the  anterior  root-fibres  pass  out  of  the  grey 
matter  of  the  anterior  horns,  and  after  a  short  course  leave  the  spinal 
cord  in  the  anterior  spinal  nerve-roots.  The  posterior  roots,  on  the 
other  hand,  do  not  pass  to  any  great  extent  into  the  grey  matter 

immediately,  but  into  the  white 
matter  on  the  inner  side  of  the 
posterior  horn ;  in  other  words, 
they  go  into  the  column  of 
Burdach  (fig.  449);  they  pass 
up  in  this  column,  but  gradu- 
ally approach  the  middle  hne, 
and  are  continued  upwards  to 
the  medulla  in  the  column  of 
Goll;  but  as  they  go  up  they 
become  less  numerous,  as  some 
terminate  in  the  grey  matter  of 
the  cord  on  the  way  in  the 
manner  described.  A  few  fibres 
of  the  posterior  root,  however, 
travel  for  a  short  distance  in  a 
smaU  tract  on  the  outer  side  of  the  posterior  horn ;  this  is  called  the 
tract  of  Lissauer  (fig.  451);  the  comma  tract  (fig.  450)  has  been 
already  explained. 

Suppose  now  one  cuts  through  several  posterior  roots  between  the 
spinal  gangha  and  the  cord,  so  that  the  course  of  degeneration  may 
be  more  readily  traced.  Immediately  below  the  points  of  entrance  of 
these  nerve-roots,  the  comma  tract  will  be  found  degenerated ;  imme- 
diately above,  the  degenerated  fibres  will  be  found  in  the  column  of 
Burdach ;  higher  up  in  the  cord  they  will  be  less  numerous,  and  have 
approached  the  middle  line ;  the  fibres  which  enter  the  cord  lowT.st 
get  ultimately  nearest  the  middle  line,  so  that  the  greater  part  of  the 
column  of  Goll  is  made  up  of  sensory  fibres  from  the  legs ;  the  fibres 
which  enter  the  cord  last,  for  instance  those  from  the  upper  limbs 
and  neck,  pursue  their  course  in  the  inner  part  of  the  column  of 
Burdach. 


Fig.  449. — Degeneration  in  column  of  Goll  after 
section  of  posterior  nerve-roots. 


CH.  XLII.]  DEGENERATION   TRACTS  G27 

The  preceding  figure  (fig.  449)  shows  the  degeneration  in  a  section 
of  the  spinal  cord,  after  the  division  of  a  number  of  nerve-roots  on 
one  side.  The  microscopic  section  is  taken  high  up,  so  that  all  the 
degenerated  fibres  have  passed  into  the  column  of  Goll  on  the  same 
side ;  the  inner  set  (1)  are  shaded  differently  from  the  outer  set  (2), 
indicating  that  those  nearest  the  middle  line  come  from  the  lowest 
nerve-roots. 

We  may  pass  from  this  to  consider  the  tracts  of  degeneration 
that  occur  when  the  spinal  cord  is  cut  right  across  in  the  thoracic 
region.  Some  tracts  will  be  found  degenerated  in  the  piece  of  cord 
below  the  lesion ;  these  consist  of  nerve-fibres  that  are  connected 
with  the  nerve-cells  in  the  brain ;  the  principal  ones  are  the  pyramidal 
tracts.  Other  tracts  are  found  degenerated  in  the  piece  of  cord 
above  the  lesion ;  these  consist  of  nerve-fibres  that  are  connected 
with  the  nerve-cells  of  the  spinal  ganglia,  or  with  the  cells  of  the 
spinal  cord  itself  below  the  lesion  and  are  passing  upwards. 

In  general  terms  we  may  say  that  the  tracts  which  degenerate 
downwards  are  the  motor  tracts,  and  those  which  degenerate  upwards 
are  the  afferent  or  sensory  channels.  We  must  also  take  into 
account  groups  of  association  fibres  which  unite  together  different 
regions  of  the  cord ;  these  are  generally  short  tracts  in  which,  there- 
fore, degeneration  can  only  be  traced  a  short  distance  up  or  down. 
The  long  tracts  are  those  which  connect  cord  or  spinal  nerves  with 
brain,  like  those  of  Goll  and  Burdach  just  mentioned,  or  the  pyramidal 
tracts  the  main  efferent  pathways. 

Tracts  of  Descending  Degeneration  (fig.  450). 

(1.)  The  crossed  pyramidal  tract. — This  is  situated  in  the  lateral 
column  on  the  outer  side  of  the  posterior  cornu  of  grey  matter.  At 
the  lower  part  of  the  spinal  cord  it  extends  to  the  margin,  but  higher 
up  it  becomes  displaced  from  this  position  by  the  interpolation  of 
another  tract  of  fibres,  to  be  presently  described,  viz.,  the  direct 
cerebellar  tract.  The  crossed  pyramidal  tract  is  large,  and  may 
touch  the  grey  matter  at  the  tip  of  the  posterior  cornu,  but  is 
separated  from  it  elsewhere.  Its  shape  on  cross  section  is  somewhat 
like  a  lens,  but  varies  in  different  regions  of  the  cord,  and  diminishes 
in  size  from  the  cervical  region  downwards,  its  fibres  passing  off  as 
they  descend,  to  arborise  around  the  nerve-cells  and  their  branchings 
in  the  grey  matter  of  the  cord.  The  fibres  of  which  this  tract  is  com- 
posed are  moderately  large,  but  are  mixed  with  some  that  are  smaller. 

(2.)  TJie  direct  or  uncrossed  pyramidal  tract,  or  column  of  Tilrck. — 
This  tract  is  situated  in  the  anterior  column  by  the  side  of  the 
anterior  fissure.  It  ends  in  the  mid  or  lower  thoracic  region  of  the 
cord. 


628  STRUCTURE   OF   THE   SPINAL   CORD  [CH.  XLII. 

The  two  pjTrainidal  tracts  come  down  from  the  brain  ;  in  the 
medulla  oblongata,  the  greater  number  of  the  pyramidal  fibres  cross 
over  to  the  other  side  of  the  cord  which  they  descend ;  hence  the 
term  crossed  pyramidal  tract ;  a  smaller  collection  of  the  pyramidal 
fibres  goes  straight  on,  on  the  same  side  of  the  cord,  and  these  cross 
at  different  levels  in  the  anterior  commissure  of  the  cord  lower  down  ; 
hence  the  disappearance  of  the  direct  pyramidal  tract  in  the  lower 
part  of  the  cord.  The  fact  that  the  crossed  pyramidal  tract  of  one 
side  is  the  feUow  of  the  direct  pyramidal  tract  of  the  other  side,  is 
indicated  in  the  diagram  by  the  direction  of  shading  (see  fig.  450). 

Comma  tract SeptO;mar^inal 

^Oval  bundle 

Crossed 
pyramidal 
"^^  tract 

Prepyramidal 
tract 

Bundle  of 
Antero-lateral '^^.^i!  ^  Jls  "^     ' — ^^  Helwe^ 


descending 
tract 


Direct  pyramidal 

tract 


Fio.  450.— Tracts  of  rlescending  degeneration.    For  the  sake  of  clearness  each  is  shown  on  only  one 

side.    (After  Schiifer.) 

Mingled  with  the  fibres  of  the  crossed  pyramidal  tract  are  a  few 
fibres  of  the  pyramid  which  have  not  crossed  in  the  medulla 
oblongata,  and  are  therefore  derived  from  the  same  side  of  the 
cerebrum  {uncrossed  lateral  pyramidal  fibres). 

The  pyramidal  fibres  are  not  found  at  all  in  vertebrates  below  the  mammals. 
In  the  lower  mammals  they  are  very  few,  and  in  some  rodents  (rat,  mouse, 
^inea-pig)  they  are  placed  in  the  posterior  columns.  The  direct  pyramidal  tract  is 
found  only  in  man  and  the  higher  apes. 

The  paralysis  that  results  from  the  section  of  the  pyramidal 
tracts  passes  off  very  soon  in  many  animals,  whereas  that  which 
results  from  section  of  the  anterior  column  and  the  adjacent  part  of 
the  lateral  column  is  more  permanent.  It  is  probable  that  the  two 
tracts  next  to  be  described  may  be  the  second  path  for  volitional 
impulses,  and  perhaps  derive  their  importance  from  the  fact  that  the 
impulses  which  travel  down  them  are  necessary  in  the  maintenance 
of  the  tone  of  the  anterior  horn  cells. 

(3.)  Antero-lateral  descending  tract,  or  tract  of  Loewenthal,  lies  by 
the  side  of  the  anterior  median  fissure,  and  extends  along  the  margin 


CH.  XLII.] 


DEGENERATION   TRACTS 


629 


of  the  cord  towards  the  lateral  column.  These  originate  from  the 
posterior  longitudinal  bundle  of  the  medulla  oblongata,  and  from 
other  sources  to  be  described  later.  They  end  by  synapses  in  the 
anterior  horn. 

(4.)  The  prepyramidal  tract  (Monakow's  bundle). — This  is  situated 
just  in  front  of  the  crossed  pyramidal  tract.  Its  origin  is  in  the  cells 
of  the  red  nucleus  in  the  raid-brain.  Its  fibres  end  by  arborisations 
in  the  grey  matter  about  the  middle  of  the  crescent. 

(5.)  Bundle  of  Helweg. — The  exact  origin  and  destination  of  these 
fibres  are  not  known :  they  can  be  traced  from  the  neighbourhood  of 
the  olivary  body  in  the  medulla  oblongata,  and  pass  down  in  the 
anterior  part  of  the  lateral  column  in  the  cervical  region. 

(6.)  Short  tracts  in  the  posterior  column. — These  are  {a)  the  Comma 
tract ;  though  this  degenerates  downwards,  it  is  in  reality  a  sensory 
tract,  being  composed,  as  we  have  already  seen,  of  the  branches  of 
the  entering  posterior  root-fibres  which  pass  downwards  on  entering 
the  cord.  It  is  only  found  for  a  comparatively  short  distance  below 
the  actual  lesion.  (&)  Septo-marginal  fibres;  these  are  few  in 
number,  and  are  mainly  found  near  the  median  fissure,  where  they 
constitute  the  oval  bundle,  and  near  the  posterior  surface,  where  they 
form  the  median  triangle  bundle.  These  are  doubtless  short  associa- 
tion tracts,  and  are  mixed  with  others,  especially  in  the  ventral  part 
of  the  posterior  column,  which  have  an  "  ascending  "  course. 


Tracts  of  Ascending  Degeneration  (fig.  451). 

(1.)  Postero-medial  column,  or  column  ofGoll. — This  consists  of  fibres 
derived  from  the  posterior  roots  of  the  sacral,  lumbar,  and  lower 

Co//', 

ler's  tract 


Direct  cerebellar 
tract 


Kio.  451.— Tracts  of  ascending  degeneration,  shown  on  one  side  of  the  cord  only.     (After  Schiifer.) 

thoracic  nerves.     These  fibres  enter  the  postero-lateral  column,  and 
gradually  pass  towards  the  mid-line,  as  already  explained.     They 


630  STRUCTURE  OF  THE   SPINAL  CORD  [CH.  XLIl. 

end  in  the  grey  matter  of  the  nucleus  gracilis  of  the  meduUa 
oblongata, 

(2.)  Postero-lateral  column,  or  column  of  Burdach. — Many  of  the 
fibres  of  this  tract,  which  is  also  composed  of  the  entering  posterior 
nerve-roots,  pass  into  the  grey  matter  of  the  cord  either  immediately  on 
entrance,  or  in  their  course  upwards.  The  rest  continue  upwards  to  the 
medulla  oblongata,  but  those  from  the  lower  roots  pass  into  the  column 
of  Goll,  as  just  stated ;  those  from  the  upper  roots  continue  to  travel 
upwards  in  the  column  of  Burdach,  and  end  in  the  grey  matter  of  the 
nucleus  cuneatus  in  the  medulla  oblongata. 

(3.)  Dorsal  or  direct  cerebellar  tract,  or  tract  of  Flechsig. — This  is 
found  in  the  cervical  and  thoracic  regions  of  the  cord,  and  is  situated 
between  the  crossed  pyramidal  tract  and  the  margin.  It  degenerates 
on  injury  or  section  of  the  cord  itself,  but  not  on  section  of  the 
posterior  nerve-roots.  In  other  words,  its  fibres  are  endogenous,  i.e., 
arise  from  cells  within  the  grey  matter  of  the  cord ;  these  cells  are 
those  of  Clarke's  column  of  the  same  side ;  the  fibres  are  large  ones. 

(4.)  Ventral  cerebellar  or  antero-lateral  ascending  tract,  or  tract  of 
Gowers. — This  is  situated  in  front  of  the  crossed  pyramidal  and  direct 
cerebellar  tracts  in  the  lumbar  region,  while  in  the  thoracic  and 
cervical  regions  it  forms  a  narrow  band  at  the  margin  of  the  cord, 
curving  round  even  into  the  anterior  column.  Its  fibres  intermingle 
with  those  of  the  antero-lateral  descending  tract.  They  originate 
probably  from  cells  in  the  middle  and  posterior  parts  of  the  grey 
crescent,  partly  on  the  same,  but  mainly  on  the  opposite  side  of  the 
cord. 

Both  of  these  tracts,  as  their  names  indicate,  go  to  the  cerebellum ; 
the  dorsal  cerebellar  enters  the  cerebellum  by  its  lower  peduncle, 
while  the  ventral  cerebellar  entf  rs  by  its  superior  peduncle.  The 
fibres  terminate  by  arborising  around  the  cells  of  that  part  of  the 
cerebellum  known  as  the  vermis  or  middle  lobe.  V.  Gehuchten  states 
that  the  ventral  tract  gives  off  a  few  fibres  that  enter  the  opposite 
cerebellar  hemisphere  by  its  middle  peduncle. 

(5.)  Tract  of  Lissauer,  or  posterior  marginal  zone. — This  is  a  small 
tract  of  ascending  fibres  situated  at  the  outer  side  of  the  tip  of  the 
posterior  horn.  These  are  fine  fibres  from  the  posterior  roots ;  they 
subsequently  pass  into  the  posterior  column. 

(6.)  A  number  of  association  tracts  have  been  differentiated  by 
Flechsig's  and  Sherrington's  method  (see  next  paragraph). 

Association  fibres  in  the  Spinal  Cord, 

The  numerous  short  tracts  already  mentioned  as  demonstrable  in  the  spinal 
cord  are  doubtless  bundles  of  association  fibres  which  connect  its  different  levels 
together.  The  main  difficulty  of  investigating  them  by  the  degeneration  method 
has  arisen  from  the  fact  that  they  are  largely  intermingled  with,  and  so  are  hard  to 
distinguish  from  the  long  tracts  which  connect  brain  and  cord  together.     In  1853 


CII.  XLir.]  RESULTS   OF   CUTTING   THE   CORD  631 

Pfliiger  stated  that  reflex  irradiation  within  the  spinal  eord  always  took  place  in  an 
upward  direction,  but  Sherrington  in  his  work  found  many  exceptions  to  this  rule, 
and  he  sought  for  the  paths  which  are  capable  of  carrying  the  impulses  down  the 
cord  by  a  very  ingenious  method.  The  spinal  cord  of  a  dog  was  completely 
divided  across,  and  the  animal  was  ke])t  alive  for  a  considerable  time  afterwards  ; 
sufficient  time  was  allowed  to  elapse  (roughly  about  a  year)  for  all  traces  of  the 
degeneration  due  to  this  lesion  to  have  disappeared.  The  cord  is  then  left,  as  it 
were,  like  a  cleaned  slate,  on  which  once  more  a  new  degeneration  can  be  written 
without  fear  of  confusion  with  a  previous  one.  The  second  degeneration  produced 
by  such  an  operation  as  hemisection  would  then  affect  the  intra-spinal  fibres  only, 
all  the  long  tracts  from  brain  to  cord  having  been  wiped  out  by  the  first  operation. 
The  complete  topography  of  all  these  fibres,  which  are  very  numerous,  has  not  yet 
been  worked  out.  The  degenerated  fibres  are  scattered  throughout  the  white 
matter,  but  are  most  numerous  at  the  margins  of  the  cord.  This  is  especially  true 
for  the  longer  fibres,  and  some  of  them  appear  to  be  very  long  indeed.  In  the  case 
of  the  longer  fibres  there  is  no  evidence  of  decussation  ;  in  the  case  of  the  shorter 
fibres  there  is  some  evidence  that  they  in  part  cross  to  the  other  side. 

Complete  transverse  section  of  the  spinal  cord  leads  to : — 

1.  Loss  of  motion  of  the  parts  supplied  by  the  nerves  below  the 
section  on  both  sides  of  the  body.  The  paralysis  is  not  confined  to 
the  voluntary  muscles,  but  includes  the  muscular  fibres  of  the 
blood-vessels  and  viscera.  Hence  there  is  fall  of  blood-pressure, 
paralysis  of  sphincters,  etc. 

2.  Loss  of  sensation  in  the  same  regions. 

3.  Degeneration,  ascending  and  descending,  on  both  sides  of  the 
cord. 

Hemisection. — If  the  operation  performed  is  not  a  complete  cut- 
ting of  the  spinal  cord  across  transversely,  but  a  cutting  of  half  the 
cord  across,  it  is  termed  hemisection,  or  semi-section. 

This  operation  leads  to : — 

1.  Loss  of  motion  of  the  parts  supplied  by  the  nerves  below  the 
section  on  the  same  side  of  the  body  as  the  injury. 

2.  Loss  of  sensation  in  the  same  region.  The  loss  of  sensation  is 
not  a  very  prominent  symptom,  and  is  limited  to  the  sense  of  locaUsa- 
tion  and  the  muscular  sense.  The  animal  can  still  feel  sensations  of 
pain  and  of  heat  and  cold. 

3.  Degeneration,  ascending  and  descending,  nearly  entirely  con- 
fined to  the  same  side  of  the  cord  as  the  injury.  The  most  important 
of  these  are  shown  in  the  photo-micrographs  (fig.  452)  on  the  next 
page,  the  small  text  beneath  which  should  be  carefully  studied. 

Differences  in  different  rer/ions  of  the  spinal  cord. — The  white  matter  decreases 
in  amount  from  above  downwards.  The  amount  of  grey  matter  varies ;  it  is 
greatest  in  the  cervical  and  lumbar  enlargements,  viz. ,  at  and  about  the  5th  lumbar 
and  6th  cervical  nerve,  and  least  in  the  thoracic  region.  The  greatest  development 
of  grey  matter  corresponds  with  greatest  number  of  nerve-fibres  passing  from  the 
cord. 

In  the  reri'ical  enlargement  the  grey  matter  occupies  a  large  proportion  of  the 
section,  the  grey  commissure  is  short  and  thick,  the  anterior  horn  is  blunt,  whilst 
the  posterior  is  somewhat  tapering.  The  anterior  and  posterior  roots  run  some 
distance  through  the  white  matter  before  they  reach  the  periphery.     At  the  extreme 


632 


STRUCTURE   OF   THE   SPINAL   CORD 


[CH.  XLII 


upper  part  of  the  cervical  region,  the  end  of  the  posterior  horn  is  swollen  out  by 
excess  of  neuroglia  into  a  rounded  mass  called  the  substantia  (/elatinosa  of  Rolando. 
The  cervical  cord  is  wider  from  side  to  side  than  from  before  back ;  this  is  owing 
to  the  great  width  of  the  lateral  columns. 

In  the  dorsal  region  the  grey  matter  bears  only  a  small  proportion  to  the  white, 
and  the  posterior  roots  in  particular  run  a  long  course  through  the  white  matter  after 
they  enter  the  cord  ;  the  grey  commissure  is  thinner  and  narrower  than  in  the 


c 


Fio.  452. — The  above  diagrams  are  reproductions  of  photo-micrographs  from  the  spinal  cord  of  a  monkey, 
in  which  the  operation  of  left  hemisection  had  been  performed  some  weeks  previously  (Mott).  The 
sections  were  stained  by  Weigert's  method,  by  which  the  grey  matter  is  bleached,  while  the  healthy 
white  matter  remains  dark  blue.  The  degenerated  tracts  are  also  bleached.  A  is  a  section  of  the 
cord  in  the  thoracic  region  below  the  lesion ;  the  crossed  pyramidal  tract  is  degenerated.  B  is  a 
section  lower  down  in  the  lumbar  enlargement :  the  ilegenerated  pyramidal  tract  is  now  smaller. 
C  is  a  section  in  the  thoracic  region  some  little  distance  above  the  lesion.  The  degenerated  tracts 
seen  are  in  the  outer  part  of  Goll's  column,  and  in  the  direct  cerebellar  tract.  D  is  a  section  higher 
up  in  the  cendcal  region  ;  the  degeneration  in  Goll's  column  now  occupies  a  median  position;  the 
degenerations  in  the  direct  cerebellar  tract,  and  in  the  tract  of  Gowers,  are  also  well  shown.  Notice 
that  in  all  cases  the  degenerated  traces  are  on  the  same  side  as  the  injury. 


cervical  region.  The  intermedio-lateral  tract  is  here  most  marked,  and  forms  a 
prominence  often  called  the  lateral  horn.  This  is  shown  in  fig.  4,52  C.  Clarke's 
column  is  also  confined  to  this  region  of  the  cord. 

In  the  lumbar  enlargement  the  grey  matter  again  bears  a  very  large  proportion 
to  the  whole  size  of  the  transverse  section,  but  its  posterior  cornua  are  shorter  and 
blunter  than  they  are  in  the  cervical  region.  The  grey  commissure  is  short  and 
extremely  narrow.     The  cord  is  circular  on  transverse  section. 

At  the  upper  part  of  the  conns  medallaris,  which  is  the  portion  of  the  cord  im- 
mediately below  the  lumbar  enlargement,  the  grey  substance  occupies  nearly  the 


CH.  XLII.]  REGIONAL   DIFFEUENCES    IN    CORD  633 

whole  of  the  transverse  section,  as  it  is  only  invested  by  a  thin  layer  of  white  sub- 
stance. This  thin  layer  is  wanting  in  the  neighbourhood  of  the  posterior  mrve-roots. 
The  grey  commissure  is  extremely  thick. 

^It  the  level  of  the  fifth  sacral  nerve  the  grey  matter  is  also  in  excess,  and 
the  central  canal  is  enlarged,  appearing  T-shaped  in  section  ;  whilst  in  the  upper 
portion  of  the  filum  ierminale  tiie  grey  matter  is  uniform  in  shape  without  any 
canal. 


CHAPTEE   XLIU 


THE  BRAIN 


A  student's  first  glance  at  a  brain,  or  at  such  a  drawing  of  it  as  is 
given  in  fig.  453,  will  be  sufficient  to  convince  him  of  its  compUcated 


Fio.  453.— Base  of  the  brain.  1,  supurior  longitudinal  fissure  ;  i,  2',  2",  anterior  cerebral  lobe  ;  3,  fissurn 
of  Sylvius,  between  anterior  and  4,  4',  4",  middle  cerebral  lobe  ;  5,  5',  posterior  lobe  ;  6,  medulla 
oblonRata  ;  the  figure  is  in  the  right  anterior  pyramid  ;  7,  s,  ii,  10,  the  cerebellum;  +,  the  inferior 
vermiform  process.  The  figures  from  I.  to  IX.  are  placed  against  the  corresponding  cerebral  nerves ; 
III.  is  placed  on  the  right  crus  cerebri.  VI.  and  VII.  on  the  pons  Varolii ;  X.  the  first  cervical  or 
suboccipital  nerve.    (Allen  Thomson.)    i. 

structure.  We  shall  devote  this  and  a  few  succeeding  chapters  to 
anatomical  considerations,  before  passing  on  to  the  study  of  its 
physiology. 


en.  xuii.] 


THE   BRAIN 


635 


At  the  lowest  part  of  the  brain  (fig.  454),  continuing  the  spinal 
cord  upwards,  is  the  medulla  oblongata  or  hulb  (D).  Next  comes  the 
pons  Varolii  (C),  very  appropriately  called  the  bridge,  because  in  it 
are  the  connections  between  the  bulb  and  the  upper  regions  of  the 
brain,  and  between  the  cerebellum  or  small  brain  (B)  and  the  rest  of 
the  nervous  system. 

The  mid-brain  comes  next  {a,  b),  and  this  leads  into  the  peduncles 
or  crura  of  the  cerebrum  (A),  the  largest  section  of  the  brain. 

Through  the  brain  runs  a  cavity  filled  with  cerebro-spinal  fluid 
(see  p.  178),  and  lined  by  ciliated  epithelium  ;  this  is  continuous  with 
the  central  canal  of  the  spinal  cord.     In  the  brain,  however,  it  does 


Fig.  454. — Plan  in  outline  of  the  brain,  as  seen  from  the  right  side.  A.  The  parts  are  represented  as 
separated  from  one  another  somewhat  more  than  natural,  so  as  to  show  their  connections.  A, 
cerebrum ;  /,  g,  h,  its  anterior,  middle,  and  posterior  lobes ;  e,  fissure  of  Sylvius ;  B,  cerebellum  ; 
C,  pons  Varolii ;  D,  medulla  oblongata ;  a,  peduncles  of  the  cerebrum  ;  b,  c,  d,  superior,  middle,  and 
inferior  peduncles  of  the  cerebellum.    (From  Quain.) 

not  remain  a  simple  canal,  but  is  enlarged  at  intervals  into  what  are 
called  the  ventricles.  There  is  one  ventricle  in  each  half  or 
hemisphere  of  the  cerebrum ;  these  are  called  the  lateral  ventricles, 
they  open  into  the  third  ventricle,  which  is  in  the  middle  line ;  and 
then  a  narrow  canal  {aqueduct  of  Sylvius)  leads  from  this  to  thQ  fourth 
ventricle,  which  is  placed  on  the  back  of  the  bulb  and  pons,  which 
form  its  floor;  its  roof  is  formed  partly  by  the  overhanging  cere- 
bellum, partly  by  pia  mater.  This  piece  of  pia  mater  is  pierced  by  a 
hole  {Foramen  of  Magendie),  and  so  the  cerebro-spinal  fluid  in  the 
interior  of  the  cerebro-spinal  cavity  is  continuous  with  that  which 
bathes  the  external  surface  of  brain  and  cord  in  the  sub-arachnoid 
space.     The  fourth  ventricle  leads  into  the  central  canal  of  the  spinal 


636 


THE   BRAm 


[CH.  XLIII. 


PM 


cord.     The  fifth  ventricle  in  the  central  structures  of  the  brain  does 

not  communicate  with  the  others. 

Speaking  generally,  there  are  two  main  collections  of  grey 
matter — that  on  the  surface,  and  that  in 
the  interior  bordering  on  the  cerebro-spinal 
cavity,  and  subdi^-ided  into  various  masses 
(floor  of  fourth  ventricle,  corpora  striata, 
optic  thalami,  etc.),  whose  closer  acquaint- 
ance we  shall  make  presently. 

In  the  foetus  the  central  nervous  system 
is  formed  by  an  infolding  of  a  portion  of  the 
surface  epiblast.  This  becomes  a  tube  of 
nervous  matter,  which  loses  all  connection 
with  the  surface  of  the  body,  though  later 
in  hfe  this  is  in  a  sense  re-estabhshed  by  the 
nerves  that  grow  from  the  brain  and  cord  to 
the  surface.  The  anterior  end  of  this  tube 
becomes  greatly  thickened,  to  form  the 
brain,  its  caLvitj  becoming  the  cerebral  ven- 
tricles ;  the  rest  of  the  tube  becomes  the 
spinal  cord.  The  primitive  brain  is  at  first 
subdivided  into  three  parts,  the  primary 
cerebral  vesicles;  the  first  and  third  of  these 
again  subdi^^.de,  so  that  there  are  ultimately 
five  divisions,  which  have  received  the 
following  names : — 

1.  Pros-enceplialon,  telencephalon  or  fore 
train.  This  is  developed  into  the  cerebrum 
with  the  corpora  striata.  It  encloses  the 
lateral  ventricles. 

2.  Thalam-encephalon,  diencephalon  or 
twixt  hrain.  This  is  developed  into  the  parts 
including  the  optic  thalami,  which  enclose 
the  third  ventricle. 

3.  Mes-encephalon,  or  viid  hrain,  con- 
sists of  the  parts  which  enclose  the  aque- 
duct of  Sylvius  —  namely,  the  corpora 
quadrigemina,  which  form  its  dorsal,  and 
the  crura  cerebri,  which  form  its  ventral 
aspect. 

4.  Met-encephalon,  or  hind  hrain,  which  forms  the  cerebellum 
and  pons. 

5.  Myel-encephalon,  or  after  hrain,  which  forms  the  bulb  or 
medulla  oblongata. 


Fig.  455. — Diagrammatic  hori- 
zontal section  of  a  vertebrate 
brain.  The  figures  serve  both 
for  this  and  the  next  diagram. 
Mb,  mid-brain :  what  lies  in 
front  of  this  is  the  fore-,  and 
vrhat  lies  behind,  the  hind- 
brain  ;  Lt,  lamina  terminalis  ; 
Olf,  olfactory  lobes ;  Hmp, 
hemispheres ;  Th.  E,  thala- 
mencephalon ;  Pn ,  pineal 
gland  ;  Py,  pituitary  body  ; 
F.M.,  foramen  of  Munro;  cj, 
corpus  striatum ;  Tk,  optic 
thalamus  ;  CC,  crura  cerebri : 
the  mass  lying  above  the  canal 
represents  the  corpora  quad- 
rigemina ;  Cb,  cerebellum ; 
M.O.,  medulla  oblongata : 
7 — IX,  nine  pairs  of  cranial 
nerves ;  1,  olfactory  ventri- 
cle ;  2,  lateral  ventricle ; 
3,  third  ventricle ;  4,  fonrth 
ventricle;  — ,  iter  a  tertio 
ad  qnartum  ventriculum,  or 
aqaedact  of  Sylvius. 

(Huxley.) 


CH.  XLIII.] 


PRIMARY   DIVISIONS    OF   BRAIN 


637 


Figs.  455  and  456  represent  a  diagrammatic  view  of  a  vertebrate 
brain ;  the  attachment  of  the  pineal  gland,  pituitary  body,  and 
olfactory  (I)  and  optic  (II)  nerves  is  also  shown. 


Fio.  456. — Longitudinal  and  vertical  diagrammatic  section  of  a  vertebrate  brain.  Letters  as  before. 
PV,  pons  Varolii.  Lamina  terminalis  is  represented  by  the  .strong  black  line  joining  Pa  and  Py. 
(Huxley.) 


CHAPTEE  XLIV 

STRUCTUKE  OF   THE  BULB,   PONS,   AND   MID-BRAIN 

We  may  study  the  bulb  and  pons  by  examining  first  the  anterior 
or  ventral,  then  the  posterior  or  dorsal  aspect,  and  last  of  all  the 
interior. 

Anterior  Aspect. 

The  bulb  is  seen  to  be  shaped,  like  an  inverted  truncated 
cone,  larger  than  the  spinal  cord,  and  enlarging  as  it  goes  up  until 
it  terminates  in  the  still  larger  pons  (fig.  457,  p).  In  the  middle  hne 
is  a  groove,  which  is  a  continuation  upwards  of  the  anterior  median 
fissure  of  the  spinal  cord;  the  columns  of  the  bulb  are,  speaking 
roughly,  continuations  upwards  of  those  of  the  cord,  but  there  is  a 
considerable  rearrangement  of  the  fibres  in  each.  Thus  the  prominent 
columns  in  the  middle  hne,  called  the  pyramids  {a  a),  are  composed 
of  the  pyramidal  fibres,  which  in  the  spinal  cord  are  situated  princi- 
pally in  the  lateral  columns  of  the  opposite  side  (crossed  pyramidal 
tracts).  The  decussation  or  crossing  of  the  pyramids  (b)  occurs  at 
their  lower  part:  a  small  collection  of  the  pyramidal  fibres  is, 
however,  continued  down  the  cord  in  the  anterior  column  of  the  same 
side  of  the  cord  (direct  pyramidal  tract):  these  cross  at  different 
levels  in  the  cord. 

On  the  outer  side  of  each  pyramid  is  an  oval  prominence  (c  c), 
which  is  not  represented  in  the  spinal  cord  at  all.  These  are  called 
the  olivary  todies  or  olives;  they  consist  of  white  matter  outside, 
with  grey  and  white  matter  in  their  interior. 

The  restiform  todies  at  the  sides  {d  d)  are  the  continuation  upwards 
of  those  fibres  from  cord  and  bulb  which  enter  the  cerebellum,  and 
the  upper  part  of  each  restiform  body  is  called  the  inferior  peduncle 
of  the  cerehelkcm* 

*  Each  half  of  the  cerebellum  has  three  peduncles  :  inferior,  middle,  and 
superior. 


CH.  XLIV.] 


STRUCTURE   OF   BULB   AND   PONS 


639 


Posterior  Aspect. 

Fig.  458  sliows  a  surface  view  of  the  back  of  the  bulb,  pons,  and 
mid-brain.  Again  we  recognise  some  of  the  parts  of  the  spinal  cord 
continued  upwards,  though  generally  with  new  names,  and  again  we 
see  certain  new  structures. 

The  posterior  median  fissure  is  continued  upwards,  and  on  each 
side  of  it  is  the  prolongation  upwards  of  the  posterior  column  of 


Fio.  457. — Ventral  or  anterior  surface  of 
the  pons  Varolii,  and  medulla  oblon- 
gata, a,  a,  pyramids ;  h,  their  decus- 
sation ;  c,  c,  olivary  bodies ;  d,  d, 
restiform  bodies ;  e,  arcuate  fibres ; 
/,  fibres  passing  from  the  anterior 
column  of  the  cord  to  the  cere- 
bellum ;  (/,  anterior  column  of  the 
spinal  cord  ;  k,  lateral  column  ;  p, 
pons  Varolii;  /,  its  upper  fibres; 
5,  5,  roots  of  the  fifth  pair  of  nerves. 


Fig.  458.— Dorsal  or  posterior  surface 
of  the  pons  Varolii,  corpora  quad- 
rigemina,  and  medulla  oblongata. 
The  peduncles  of  the  cerebellum 
are  cut  short  at  the  sides,  a,  a,  the 
upper  pair  of  corpora  quadri- 
gemina  ;  b,  b,  the  lower ;  /,  /,  supe- 
rior peduncles  of  the  cerebellum ; 
c,  eminence  connected  with  the 
nucleus  of  the  hypoglossal  nerve  : 
«,  that  of  the  glosso-pharyngeal 
nerve ;  i,  that  of  the  vagus  nerve ; 
rf,  d,  restiform  bodies ;  p,  p,  poste- 
rior columns ;  v,  v,  groove  in  the 
middle  of  the  fourth  ventricle, 
ending  below  in  the  calamus  scrip, 
torius  ;  7,  7,  roots  of  the  auditory 
nerves. 


the  cord.     The  column  of  Goll  is  now  called  the  Funiculus  gracilis, 
and  the  column  of  Burdach  the  Funiculus  cuneatus. 

The  two  funiculi  graciles  lie  at  first  side  by  side,  but  soon 
diverge  and  form  the  two  lower  boundaries  of  a  diamond-shaped  space 
called  the  ^oor  of  the  fourth  ventricle ;  this  is  made  of  grey  matter; 
the  central  canal  of  the  cord  gets  nearer  and  nearer  to  the  dorsal 
surface  of  the  bulb,  till  at  last  it  opens  out  on  the  back  of  the  bulb, 
and  its  surrounding  grey  matter  is  spread  out  to  form  the  floor  of 
the  fourth  ventricle.    The  two  upper  boundaries  of  the  diamond-shaped 


640  STRUCTURE  OF  THE  BULB,   PONS,   AND   MID-BRAIN        [CH.  XLIV. 

space  are  made  by  the  superior  peduncles  of  the  cerebellum,  which 
contain  fibres  going  up  through  the  mid-brain  to  the  cerebrum. 
The  middle  peduncles  of  the  cerebellum  are  principally  made  up  of 
fibres  running  from  one  cerebellar  hemisphere  towards  the  other 
through  the  pons. 

Running  down  the  centre  of  the  floor  of  the  fourth  ventricle  is 
a  shallow  groove;  on  each  side  of  this  is  a  rounded  longitudinal 
eminence  called  the  eminentia  teres ;  running  across  the  middle  of 
the  floor  are  a  number  of  fibres  (the  stri(£  acousticce),  which  join  the 
auditory  nerve. 

In  the  upper  part  of  the  diagram,  the  mid-brain,  with  the  corpora 
quadrigemina  {a  a,  h  h),  is  shown.  Here  there  is  once  more  a  canal 
which  penetrates  the  substance  of  the  mid-brain,  and  is  called  the 
aqueduct  of  Sylvius,  or  the  iter  a  tertio  ad  quartum  ventriculum ;  it 
leads,  as  its  name  indicates,  from  the  third  to  the  fourth  ventricle. 

The  Internal  Structure  of  the  Bulb,  Pons,  and  Mid-Brain. 

The  structure  of  the  interior  of  these  parts  is  complex,  and  the 
complexity  arises  from  the  circumstance  that  here  we  have  to  deal 
not  only  with  parts  running  upwards  from  cord  to  brain,  or  down 
from  brain  to  cord,  but  also  with  a  considerable  amount  of  grey 
matter  in  which  some  of  the  white  tracts  terminate,  or  from  which 
new  tracts  issue.  The  most  important  stretch  of  grey  matter  is  that 
which  appears  on  the  floor  of  the  fourth  ventricle,  and  which  is 
continued  upwards  around  the  Sylvian  aqueduct,  and  downwards 
into  the  spinal  cord ;  here  are  situated  groups  of  nerve-cells,  which 
are  spoken  of  as  centres,  or  nuclei.  The  most  important  of  these  are 
those  which  are  connected  with  the  cranial  nerves.  There  are 
twelve  pairs  of  cranial  nerves,  and  of  these  the  last  ten  pairs  originate 
from  the  floor  of  the  fourth  ventricle  or  the  neighbouring  grey 
matter. 

The  following  is  a  list  of  the  cranial  nerves : — 

1.  Olfactory. — This  is  the  nerve  of  smell. 

2.  Optic. — This  is  the  nerve  of  sight. 

/   yr     7  7         I  These  three   nerves   supply   the  muscles   of   the 

a     A-Lj  I  eyeball. 

D.  Aoducens    )  '' 

5.  Trigeminal. — This  is  the  great  sensory  nerve  of  the  face  and 

head.     Its  smaller  motor  division  supplies  the  muscles  of  mastication 

and  a  few  other  muscles  also. 

7.  Facial. — This  is  mainly  the  motor  nerve  of  the  face  muscles. 

8.  Auditory. — This  is  divided  into  two  parts,  one  of  which,  called 
the  cochlear  nerve,  is  the  true  nerve  of  hearing,  and  is  distributed  to 
the  cochlea  of  the  internal  ear ;  the  other  division,  called  the  vestibular 


CH.  XLIV.]  CRANIAL  NERVES  641 

nerve,  is  distributed  to  the  vestibule  and  semicircular  canals  of  the 
internal  ear. 

9.  Glosso -pharyngeal. — This  is  a  mixed  nerve ;  its  motor  fibres  pass 
to  certain  of  the  pharyngeal  muscles ;  its  sensory  fibres  are  mainly 
concerned  in  the  sense  of  taste. 

10.  Vagus  or  pneumogastric. — This  is  a  nerve  with  varied  efferent 
and  afferent  functions ;  its  branches  pass  to  pharynx,  larynx, 
oesophagus,  stomach,  lungs,  heart,  intestines,  liver  and  spleen. 
These  functions  we  have  already  studied  in  connection  with  those 
organs. 

11.  Spinal  accessory. — The  internal  branch  of  this  nerve  blends 
with  the  vagus,  and  its  larger  external  division  supplies  the  trapezius 
and  the  sterno-mastoid  muscles. 

12.  Hypoglossal. — This  is  the  motor  nerve  to  the  tongue  muscles. 
A  mere  enumeration  of  the  nerves  connected  to  the  bulb  shows 

how  supremely  important  this  small  area  of  the  brain  is  for  carrying 
on  the  organic  functions  of  life.  It  contains  centres  which  regulate 
deglutition,  vomiting,  the  secretion  of  saliva,  etc.,  respiration,  the 
heart's  movements,  and  the  vaso-motor  nerves. 

When  we  further  consider  that  the  various  centres  are  connected 
by  groups  of  association  fibres,  we  at  once  reahse  the  reason  for 
the  complexity  of  the  structures  where  all  this  busy  trafi&c  takes 
place. 

In  the  enumeration  of  the  cranial  nerves,  it  will  be  noticed  that 
many  of  them  are  either  wholly  motor  or  wholly  sensory,  and  that 
some  of  them,  like  the  spinal  nerves,  have  a  double  function.  The 
motor  nerve  fibres  start  as  axons  from  the  groups  of  nerve-ceUs  in 
the  grey  matter  of  this  region,  just  as  the  motor  fibres  in  the  spinal 
nerves  originate  from  the  cells  of  the  spinal  grey  matter.  There  is 
a  corresiDonding  resemblance  in  the  origin  of  the  sensory  fibres  of 
the  cranial  and  spinal  nerves.  In  the  latter,  it  will  be  remembered, 
they  originate  as  outgrowths  from  the  cells  of  the  spinal  ganglia,  one 
branch  growing  to  the  periphery,  and  the  other  to  the  spinal  cord, 
where  it  terminates  after  a  more  or  less  extended  course  by  forming 
synapses  with  the  cells  of  the  grey  matter.  In  the  cranial  nerves 
they  have  a  corresponding  origin  in  peripheral  ganglia,  and  those 
branches  which  grow  towards  the  bulb  terminate  by  arborising  around 
special  groups  of  cells  spoken  of  as  the  sensory  nuclei. 

The  following  diagram  (fig.  459)  roughly  indicates  the  position 
of  these  nuclei ;  the  motor  nuclei  are  coloured  blue,  and  the  sensory 
red.  It  must,  however,  be  clearly  recognised  that  while  the  motor 
nuclei  are  true  centres  of  origin,  that  the  so-called  sensory  nuclei  are 
groups  of  cells  around  which  the  entering  sensory  fibres  arborise ;  these 
cells  do  not  give  origin  to  the  axons  of  the  sensory  nerves.  After  we 
have  studied  the  internal  structure  of  the  bulb  we  shall  be  able  to 

2  S 


642 


STRUCTURE   OF   THE   BULB,    PONS,    AND    MID-BRAIN        [CH.  XLIV. 


return  once  more  to  the  cranial  nerves,  in  order  that  we  consider  their 
origin  and  function  in  greater  detail. 

But  this  diagram  will  give  a  general  idea  of  the  positions  of  the 


3rcl.  Ventricle 


Sir.  A 


Lateral  column 
Funiculus   cuneatus 
Funiculus   gracilis 


Pio.  459. — Diagram  to  show  the  iiositiim  of  the  nuclei  of  the  cranial  nerves  (after  Sherriugtou).  The 
medulla  and  pons  are  \-iewed  from  the  dorsal  aspect,  the  cerebrum  and  cerebellum  having  been  cut 
away.  The  nuclei  (sensory  coloured  red,  and  motor  blue)  are  represented  as  being  seen  through 
transparent  material.  C.Q.  a.,  anterior  corpus  quadrigeminum  ;  C.Q.  y.,  posterior  corpus  quadri- 
gemlnum  ;  G.G.,  corpus  genicidatum  ;  I'.r.,  value  of  Vieussens  ;  Lc,  locus  cceruleus;  c.f.,  eminentia 
teres;  str.  A.,  stria;  acoustica?.  S.P.,  M.P.,  and  I. P.,  superior  middle  and  inferior  cerebsllum 
peduncles  respectively  cut  through.  The  numerals  III.  to  XII.  indicate  the  nuclei  of  the  respec- 
tive  cranial  nerves,  all  shown  on  the  left  side  except  the  accessory-vago-glossopharyngeal  IX.,  X.,  XI., 
■which  to  avoid  confusion  is  placed  on  the  right  side.  V»!.  is  the  motor  nucleus  of  the  fifth  nerve  ; 
Yd.,  the  sensory  nucleus  of  the  same  nerve  with  its  long  descending  root;  Xlllin.,  the  median 
nucleus  of  the  auditory  nerve;  N.D.  Nucleus  of  Deiters  ;  n.  amh.  imcleus  ambiguus.  The  position 
of  the  descending  root  of  the  ninth  and  tenth  (fasciculus  solitarius)  is  also  indicated  (/.  s.). 

nuclei.  It  will  be  noticed  that  the  so-called  sensory  nuclei  (coloured 
red)  are  in  the  minority ;  they  comprise  the  sensory  nucleus  of  the 
fifth  nerve  with  its  long  descending  (formerly  called  ascending)  root, 


CII.  xuv.] 


CRANIAL   NERVES 


643 


the  nuclei  of  the  eighth  nerve  (only  one  of  which,  Vlllm.,  is  seen  in  the 
diagram),  and  the  glossopharyngeal  and  vagal  portions  of  a  long 
strand  of  nerve-cells  called  the  combined  nucleus  of  the  ninth,  tenth, 
and  eleventh  nerves.  The  remaining  nuclei  (coloured  blue)  are 
efferent,  and  may  be  principally  arranged  into  two  groups : — (1)  the 
nuclei  of  the  third,  fourth,  sixth,  and  twelfth  nerves,  which  are  close 
to  the  middle  line ;  and  (2)  the  motor  nucleus  of  the  fifth,  the  nucleus 
of  the  seventh,  and  the  nucleus  ambiguus  (motor  nucleus  of  the  ninth 
and  tenth  nerves)  which  form  a  line  more  lateral  in  position. 

It  should  be  added  that  van  Gehuchten  has  shown  that,  except 
a  few  fibres  of  the  third,  and  the  whole  of  the  fourth  nerves,  none 
of  the  fibres  of  the  cranial  nerves  cross  to  the  opposite  side. 


CEREBELLAR   ^te3' 


HEMISPHERE 


Fig.  460.— Diagmmnialic  represeutatiou  of  dorsal  aspect  of  medulla,  f^ns,  and  mid-brain. 


The  first  two  pairs  of  cranial  nerves,  the  olfactory  and  the  optic, 
will  be  studied  in  connection  with  smell  and  vision  later  on. 

We  can  now  pass  to  the  consideration  of  transverse  sections  of 
this  part  of  the  central  nervous  system.  We  will  limit  ourselves  to 
seven,  the  level  of  which  is  indicated  in  the  above  diagram  (fig.  460). 
The  cerebellum  has  been  bisected  into  two  halves  and  turned  out- 
wards, its  upper  peduncles  having  been  cut  through  to  render  the 


644  STRUCTURE   OF   THE   BULB,   PONS,    AND    MID-BRAIN         [CH.  XLIV. 


parts  more  evident.     The  position  of  our  seven  sections  is  indicated 
by  the  transverse  lines  numbered  1  to  7. 

First  section. — Thio  is  taken  at  the  lowest 

through  the  region 

of  the    p}Taniids. 

the    cervical    cord 


level  of  the  bulb, 

of  the  decussation 

The  similarity  to 

will    be    at    once 


p       P 

Fig.  461.— Section  through  the  bulb  at 
the  level  of  the  decussation  of  the 
pyramids.  «,  funiculus  gracilis,  con- 
tinuation of  column  of  GoU  ;  c,  funiculus 
cuneatus,  continuation  of  column  of 
Burdach ;  r,  substantia  gelarinosa  of 
Bolando,  continuation  of  posterior  horn 
of  spinal  cord  ;  l,  continuation  of  lat- 
eral column  of  cord  ;  a,  remains  of  part 
of  the  anterior  horn,  separated  from 
the  rest  of  the  grey  matter  by  the 
pjTamidal  fibres  p,  which  are  crossing 
from  the  p>Tamid  of  the  medulla  to  the 
posterior  part  of  the  lateral  column  of 
the  opposite  side  of  the  cord. 

(After  L.  Clarke.) 


recognised ;  the  passage  of  the  pyra- 
midal fibres  (P)  from  the  anterior  part 
of  the  bulb  to  the  crossed  pyramidal 
tract  of  the  opposite  side  of  the  cord 
cuts  off  the  tip  of  anterior  horn  (A), 
which  in  sections  higher  up  appears  as 
an  isolated  mass  of  grey  matter,  called 
the  lateral  nucleus  (fig.  462,  nl).  The 
V  formed  by  the  two  posterior  horns 
is  opened  out,  and  thus  the  grey 
matter  with  the  central  canal  is  brought 
nearer  to  the  dorsal  aspect  of  the  bulb ; 
the  tip  of  the  cornu  swells  out  to 
form  the  substantia  gelatinosa  of  Bo- 
lando (Pi),  which  causes  a  prominence 
on  the  sui'face  called  the  tubercle  of 
Bolando;  G-  and  G  are  the  funiculi 
gracilis  and  cuyieatus  respectively,  the 
continuations  upwards  of  the  columns 
of  Goll  and  Burdach. 

Many  of  the  fibres  of  the  pyramidal  tract  terminate  in  the  mid-brain  and 
pons,  hence  this  tract  is  reduced  in  size  when  it  reaches  the  bulb.  The  pyramidal 
fibres  on  their  long  journey  give  off  collaterals  to  the  cortex  cerebri,  the  basal 
ganglia  of  the  cerebrum,  the  substantia  nigra  of  the  raid-brain,  the  nuclei  pontis  of 
the  pons,  and  lower  down  in  the  cord  to  the  base  of  its  posterior  horn.  They, 
however,  do  not  give  off  collaterals  to  the  motor  nuclei  of  the  cranial  nerves  on  their 
passage  through  the  bulb  (Schafer).  The  only  collaterals  given  off  in  this  region 
are  a  few  to  the  olivary  nuclei. 

Second  section  (fig.  462). — This  is  taken  through  the  upper 
part  of  the  decussation.  Beginning  in  the  middle  line  at  the  top  of 
the  diagram,  we  see  first  the  posterior  median  fissure  (jj.mf),  below 
which  is  the  grey  matter  enclosing  the  central  canal  (c.c),  and  con- 
taining the  nuclei  of  the  eleventh  and  twelfth  nerves ;  the  funiculus 
gracilis  (fg.)  comes  next,  and  then  the  funiculus  cuneatus  (f.c.)  ;  these 
two  funiculi  have  now  grey  matter  in  their  interior :  these  masses 
of  grey  matter  are  called  respectively  nucleus  gracilis  (n.g.)  and 
nucleu^s  cuneatu^s  (n.c.) ;  the  fibres  which  have  ascended  the  posterior 
columns  of  the  cord  terminate  by  arborising  around  the  cells  of  this 
grey  matter ;  the  fibres  from  the  lower  part  of  the  body  end  in  the 
nucleus  gracilis,  and  those  from  the  upper  part  of  the  body  in  the 


CH.  XLIV.] 


INTERNAL   STItUCTURE   OF   T5ULB 


64f 


nucleus  cuneatus.  These  nuclei  form  a  most  important  position  of 
relay  in  the  course  of  the  afferent  fibres  from  cord  to  brain.  The 
new  fibres  (the  second  relay  of  the  sensory  spinal  path)  arising  from 
the  cells  of  these  nuclei  pass  in  a  number  of  different  directions,  and 


p.m.f.    M    y      f.c.  ^ 


a.m.f.        f.n.  '"^- 


Fig.  462. — Transverse  section  of  the  medulla  oblongata  in  tbe  region  of  the  superior  decussation,  a.m.f., 
anterior  median  fissure ; /.a.,  superficial  arcuate  fibres ;  py.,  pyramid;  n.a.r.,  nuclei  of  arcuate 
fibres ;  /.ai,  deep  arcuate  filjres  becoming  superficial ;  o,  o',  lower  end  of  olivary  nucleus ;  n.l., 
nucleus  lateralis;  f.r.,  formatio  reticularis;  f.cfl,  arcuate  fibres  proceeding  from  the  formatio 
reticularis;  g,  substantia  gelatinosa  of  Rolando;  d.V.,  descending  root  of  fifth  nerve;  f.c, 
funiculus  cuneatus;  n.c,  nucleus  cuneatus;  n.c.',  external  cuneate  nucleus;  n.g.,  nucleus 
gracilis ; /.(/.,  funiculus  gracilis;  p.m,.f.,  posterior  median  fissure;  c.c,  central  canal  surrounded 
by  grey  matter,  in  which  are  n.XL,  nucleus  of  the  eleventh  and  n.XIL,  nucleus  of  the  twelftli 
nerve ;  s.d.,  superior  decussation  (decussation  of  fillet).    (Modified  from  Schwalbe.) 


break  up  the  rest  of  the  grey  matter  into  what  is  called  t\iQ  forw.atio 
reticularis. 

The  nucleus  gracilis  and  nucleus  cuneatus  are  often  spoken  of  as 
the  posterior  column  nuclei ;  they  do  not  receive  all  the  ascending 
branches  of  the  posterior  root  fibres,  for  a  number  of  these  branches 
have  already  entered  the  grey  matter  and  arborised  amongst  its  cells 
in  the  spinal  cord  itself.  The  cells  of  the  posterior  column  nuclei 
are  of  moderate  size,  and  their  axons  pass  as  internal  arcuate  fibres 
into  the  reticular  formation  between  the  two  olivary  bodies,  which 
is  known  as  the  inter-olivary  layer.  They  cross  the  median  raphe 
dorsal  to  the  pyramids,  and  then  turn  upwards  towards  the  upper 
parts  of  the  brain,  and  so  constitute  what  is  known  as  the  fillet.  In 
the  higher  parts  of  the  bulb  and  pons,  this  tract  is  reinforced  by 
fibres  from  the  cells  of  the  sensory  nuclei  of  the  cranial  nerves. 
The  fillet  becomes  a  longitudinal  bundle,  which  passes  upwards  to 


646 


STRUCTURE   OF   THE   BULB,    PONS,    AND    MID-BRAIN      [CH.  XLIV. 


various  parts  of  the  cerebrum,  but  the  sensory  impulses  go  through 
one  or  more  cell-stations  (positions  of  relay)  before  they  ultimately 
arrive  at  the  cortex.  We  now  see  that  the  brain  has  a  crossed 
relationship  to  the  body,  the  left  half  of  the  brain  governing  the 
right  half  of  the  body,  and  vice  versd,  both  as  regards  motion  and 
sensation;  the  motor  fibres  mostly  cross  at  the  decussation  of  the 
pyramids,  some  few  (those  in  the  direct  pyramidal  tract)  crossing  at 
lower  levels  in  the  cord ;  the  sensory  fibres  mostly  cross  at  the 
decussation  of  the  fillet,  though  some  few  cross  at  lower  levels  in  the 

n.M.    -nX.      \_j<y 


n.ar. 


Fig.  463. — Section  of  the  medulla  oblongata  at  about  the  middle  of  the  olivary  body,  f.l.a.,  anterior 
median  fissure;  n.ar.,  nucleus  arcuatus;  p,  pyramid;  XII.,  bundle  of  hypoglossal  nerve  emerging 
from  tlie  surface;  at  &,  it  is  seen  coursing  between  the  pyramid  and  the  olivary  nucleus,  c  ;  f.a.e., 
external  arcuate  fibres  ;  n.l.,  nucleus  lateralis ;  a.,  arcuate  fibres  passing  towards  restiform  body, 
partly  through  the  substantia  gelatinosa,  g.,  partly  superficial  to  the  descending  root  of  the  fifth 
nerve,  d.V. ;  A'.,  bundle  of  vagus  root  emerging;  f.r.,  formatio  reticularis;  C.r.,  corpus  restiforme, 
beginning  to  be  formed,  chiefly  by  arcuate  fibres,  superficial  and  deep  ;  n.c,  nucleus  cuneatus  ;  n.g., 
nucleus  gracilis;  /,  attachment  of  the  ligula ;  f.s.,  funiculus  solitarius  ;  7i.X.,  n.X.',  two  parts  of 
the  vagus  nucleus;  n.XII.,  hypoglossal  nucleus;  n.t.,  nucleus  of  the  funiculus  teres;  n.am., 
nucleus  ambiguus ;  r.,  raphe;  A.,  continuation  of  the  anterior  column  of  cord;  o',  o",  accessory 
olivary  nucleus;  p.o.l.,  pedunculus  olivae.    (Modified  from  Schwalbe.) 

cord,  soon  after  their  entrance  into  the  cord  by  the  posterior  nerve- 
roots. 

Other  points  to  be  noticed  in  the  section  are  the  substantia 
gelatinosa  of  Eolando  (g)  (representing  the  tip  of  the  posterior  cornu 
of  the  cord),  now  separated  from  the  surface  by  the  descending  root 
of  the  fifth  nerve  (d.  V.) ;  the  lateral  nucleus  (n  T)  (remains  of  the 
anterior  cornu  of  the  cord) ;  the  lower  part  of  the  grey  matter  of  the 
olivary  body  (o,  o'),  and  most  anteriorly  the  pyramid  (py). 

Third  section. — This  (fig.  463)  is  taken  at  about  the  middle  of 
the  olivary  body,  and  passes  also  through  the  lower  part  of  the  floor 


CH.  XLIV.]  TRANSVERSE   SECTIONS    OF   BULB  647 

of  the  fourth  ventricle.  The  central  canal  has  now  opened  out  into 
the  fourth  ventricle,  and  the  grey  matter  on  its  floor  contains  the 
nuclei  of  the  twelfth  and  tenth  nerves ;  bundles  of  the  fibres  of  these 
nerves  course  through  the  substance  of  the  bulb,  leaving  it  at  the 
places  indicated  in  the  diagram. 

The  nucleus  gracilis,  nucleus  cuneatus,  are  pushed  into  a  more 
lateral  position,  and  higher  up  are  replaced  by  small  masses  of  grey 
matter  mingled  with  nerve-fibres  {nucleus  posterior) ;  the  restiform 
lady  (C.r.)  now  forms  a  well-marked  prominence,  and  the  olivary 
body  is  well  seen  with  its  dentate  nucleus ;  from  the  open  mouth  of 
this  corrugated  layer  of  grey  matter  a  large  number  of  fibres  issue, 
and  passing  through  the  raphe,  course  as  internal  arcuate  fibres  to 
the  opposite  restiform  body,  and  thus  to  the  cerebellum ;  some  pass 
to  the  restiform  body  of  the  same  side;  the  continuation  of  the 
direct  cerebellar  tract  of  the  cord  also  passes  into  the  restiform  body. 
Its  fibres  terminate  by  arborisations  round  Purkinje's  cells  in  the 
vermis  of  the  cerebellum.  The  continuation  of  the  tract  of  Gowers 
lies  just  dorsal  to  the  olivary  body.  The  funiculus  solitarius  and 
nucleus  amhiguus,  also  seen  in  this  section,  will  be  considered  in 
our  account  of  the  origin  of  the  ninth  and  tenth  cranial  nerves. 

Fourth  section  (fig.  4G4). — This  is  taken  through  the  middle  of 
the  pons,  and  shows  much  the  same  kind  of  arrangement  as  in  the 
upper  part  of  the  bulb.  The  general  appearance  of  the  section  is, 
however,  modified  by  a  number  of  transversely  coursing  bundles  of 
fibres,  most  of  which  are  passing  from  the  cerebellar  hemispheres 
to  the  raphe,  and  form  the  middle  cerebellar  peduncles.  Intermingled 
with  these  is  a  considerable  amount  of  grey  matter  {nuclei  pontis). 

From  the  cells  of  the  nuclei  pontis,  many  of  the  fibres  of  the  middle 
peduncle  take  origin,  and  many  fibres  and  collaterals  of  the  pyramidal 
tract  arborise  around  them.  The  continuation  of  the  pyramids  {py)  is 
embedded  between  these  transverse  bundles.  The  pyramidal  fibres 
which  terminate  in  the  pons  are  situated  postero-laterally,  and  are 
spoken  of  as  cortico-pontine  in  contradistinction  with  those  of  the 
pyramidal  tract  proper  {cor tico -spinal)  which  pass  down  through  the 
bulb  to  the  cord. 

The  pyramidal  bundles  are  separated  from  the  reticular  formation 
by  deeper  transverse  fibres,  which  constitute  what  is  known  as  the 
trapezium  {t).  These  fibres  belong  to  a  different  system,  and  form 
part  of  the  central  auditory  path ;  some  of  them  connect  the  auditory 
nuclei  of  the  two  sides  together.  The  larger  olivary  nucleus  is  no 
longer  seen,  but  one  or  two  small  collections  of  grey  matter  {o.s.)  repre- 
sent it  and  constitute  the  superior-  olivary  nucleus.  These  as  well  as  a 
collection  of  nerve-cells  in  the  trapezium  {nucleus  of  the  trapezium) 
are  connected  with  fibres  of  the  trapezium,  while  some  of  their  axons 
pass  into  the  adjacent  lateral  part  of  the  fillet. 


648 


STRUCTURE   OF   THE   BULB,   PONS,   AND   MID-BRAIN      [CH.  XLIV. 


The  nucleus  of  Deiters  (n.  VIII,  fig.  464)  begins  to  appear  in  the 
upper  part  of  the  bulb,  and  extends  into  the  pons ;  it  lies  near  the 
floor  of  the  ventricle,  a  little  mesial  to  the  restiform  body.  The 
nerve-fibres  connected  with  its  cells  pass  towards  the  middle  line, 
and  enter  the  ^posterior  longitudinal  bundle,  which  is  more  clearly  seen 


J^^AI    \  VIlixVL  Vila.  Ytta      VII 

^^Nr^v•    J— i  '■    ■         '■' 


Fio.  464.— Section  across  the  pons,  about  the  middle  of  the  fourth  ventricle,  pij.,  pyramidal  bundles; 
po.,  transverse  libres  passing  po,  behind,  and  po.^,  in  front  of  py  ;  r.,  raphe  ;  o.s.,  superior  olive ; 
a.V.,  bundles  of  motor  root  of  V.  nerve  enclosed  In  a  prolongation  of  the  substance  of  Rolando;  t, 
trapezium  ;  VI.,  the  sixth  nerve,  n.VI.,  its  nucleus  ;  VII.,  facial  nerve;  VH.  a.,  intermediate  por- 
tion, n.VII.,  its  nucleus;  VIII.,  auditory  nerve,  n.VIII.,  Deiters'  nucleus  formerly  called  the 
lateral  nucleus  of  the  auditory.    (After  Quain.) 

in  the  two  next  sections  (fig.  465).  This  bundle  of  fibres  connects 
Deiters'  nucleus,  the  nucleus  of  the  third  and  sixth  nerves,  and  the 
anterior  horn  cells  of  the  spinal  cord.  The  fibres  which  pass  into  it 
from  Deiters'  nucleus  bifurcate,  one  branch  passing  upwards  to 
arborise  around  the  cells  mainly  of  the  oculo-motor  nucleus  of  the 
opposite  side ;  the  other  extends  downwards  through  the  bulb  into 
the  cord,  where  they  are  found  in  the  antero-lateral  descending  tract 
of  each  side.     They  end  by  synapses  around  the  anterior  horn  cells. 

This  bundle  receives  in  addition  to  the  fibres  from  Deiters'  nucleus,  other  fibres 
from  the  sensory  nucleus  of  the  fifth  nerve,  and  from  large  cells  in  the  reticular  for- 
mation of  mid-brain,  pons,  and  bulb. 

The  nerves  which  are  connected  with  the  grey  matter  of  this 
region  of  the  pons  are  the  sixth,  seventh,  and  eighth,  as  shown  in  the 
diagram.  The  nuclei  in  connection  with  the  fifth  nerve  are  higher 
up,  where  the  floor  of  the  ventricle  is  again  narrowing.  At  last,  in 
the  region  of  the  mid-brain,  we  once  more  get  a  canal  (Sylvian 
aqueduct)  which  corresponds  to  the  central  canal  of  the  spinal  cord. 


CH.  XLIV.]  TRANSVERSE   SECTIONS    OF   MID-BRAIN  649 

Fifth  and  Sixth  sections  are  taken  through  the  mid -brain,  and 
are  drawn  on  a  smaller  scale  than  the  others  we  have  been  examin- 
ing ;  they  represent  the  actual  size  of  the  sections  obtained  from  the 
human  subject. 

Near  the  middle  is  the  Sylvian  aqueduct,  with  its  lining  of  ciliated 
epithelium.  In  the  grey  matter  which  surrounds  it  are  large  nerve- 
cells  from  which  the  fourth  nerve,  and  higher  up  the  third  nerve, 
originate ;  the  fibres  of  the  third  nerve  are  seen  issuing  from  these  in 
fig.  465,  B.,  Ill,  The  reticular  formation  of  the  pons  is  continued  up 
into  the  mid-brain,  and  is  called  the  tegmentum.  It  is  composed  of 
both  longitudinal  and  transverse  bundles  of  fibres  intermingled  with 


Fio.  465. — Outline  of  two  sections  across  the  mid-brain :  A,  through  the  middle  of  the  inferior ;  B, 
through  the  middle  of  the  superior  corpora  quadrigemina,  C.Q.  Cr.,  crusta;  S.N.,  substantia  nigra 
— shown  only  on  one  side  ;  T,  tegmentum ;  S,  Sylvian  aqueduct,  with  its  surrounding  grey  matter ; 
L.G.,  lateral  groove;  p.l.,  posterior  longitudinal  bundle;  d.V.,  descending  root  of  the  fifth  nerve; 
S.C.P.,  superior  cerebellar  peduncle;  F,  fillet ;  III.,  third  nerve.  The  dotted  circle  in  B  represents 
the  situation  of  the  tegmental  nucleus.  In  B  the  three  divisions  of  the  crusta  are  indicated  on  one 
side.  The  pyramidal  fibres  {Py)  are  in  the  middle,  and  the  fronto-cerebellar  (F.C.)  and  temporo- 
occipital  cerebellar  (T.O.C.)  at  the  sides.    (After  Schiifer.) 

grey  matter.  Its  transverse  fibres  include  those  of  the  superior 
peduncles  of  the  cerebellum  which  decussate  in  the  middle  line  (fig. 
465,  A.,  S.C.P.).  These  originate  from  the  cells  of  the  dentate  nucleus 
of  the  cerebellum;  after  decussation  they  bifurcate,  the  ascending 
branches  being  lost  in  the  collection  of  nerve-ceUs  in  the  tegmentum 
known  as  the  tegmental  or  red  nucleus,  while  the  descending  branches 
turn  downwards  in  the  reticular  formation.  The  axons  from  the  cells 
of  the  red  nucleus  run  downwards  and  form  Monakow's  bundle,  or 
the  prepyramidal  tract  which  we  have  already  seen  in  the  spinal  cord. 
Another  important  longitudinal  bundle  in  the  tegmentum  is  the 
fillet.  This,  we  have  seen,  is  the  longitudinal  continuation  of  the 
internal  arcuate  fibres,  which,  starting  from  the  cells  of  the  posterior 
column  nuclei  of  the  opposite  side,  form  the  second  relay  on  the 
sensory  path ;  to  these  fibres  others  are  added  which  originate  from 
other  masses  of  grey  matter  in  bulb  and  pons.  In  the  mid-brain  the 
fillet  splits  into  three  bundles,  termed  the  lateral,  the  upper,  and  the 
mesial  fillet. 

(1)  Tlie  lateral  fillet  is  chiefly  formed  by  fibres  derived  from  the  accessory  audi- 
tory, the  inferior  olivary,  and  trapezoid  nuclei  of  the  opposite  side.  Some  of  its 
fibres  terminate   by  synapses   around  a  new  collection  of  cells  (the  lateral  fillet 


650  STEUCTURE   OF   THE   BULB,    PONS,    AND    MID-BRAIN       [CH.  XLIV. 

nucleus) ;  their  axons  pass  inwards  towards  the  raphe.  The  rest  of  its  fibres  can  be 
traced  to  the  grey  matter  of  the  inferior  corpora  quadrigeraina. 

(2)  The  ujiper  fillet  consists  of  fibres  which  go  to  the  superior  corpora  qiiadri- 
gemina  and  partly  to  the  tegmental  region  of  the  mid-brain  and  optic  thalamus. 

(8)  The  menial  fillet  goes  on  through  the  tegmentum  of  the  crus  cerebri,  and  its 
fibres  terminate  around  the  cells  of  the  optic  thalamus,  and  the  subthalamic  region. 
From  here  fresh  axons  forming  a  new  relay  continue  the  afferent  impulses  to  the 
cortex  of  the  cerebrum. 

The  mesial  fillet  is  the  important  link  in  this  region  between 
the  sensory  spinal  nerves  and  the  part  of  the  brain  which  is  the  seat 
of  those  processes  we  call  sensations.  But  most  of  the  fibres  which 
continue  the  sensory  path  of  the  cranial  nerves  form  another  less 
well-defined  tract  (the  central  tract  of  the  sensory  cranial  nerves)  which 
lies  dorsal  to  the  fillet,  but  terminates  like  it  in  the  subthalamic 
region  and  optic  thalamus,  whence  a  new  relay  carries  on  the 
impulses  to  the  cortex. 

Ventral  to  the  tegmentum  is  a  layer  of  grey  matter,  of  which 
the  cells  are  deeply  pigmented ;  hence  it  is  called  the  substantia 
nigra  (S.N.).  This  receives  many  collaterals  from  the  pyramidal 
bundles. 

The  white  matter  on  the  ventral  side  of  this  is  known  as  the 
critsta  (Cr)  ox  pes.  It  is  here  that  the  pyramidal  bundles  are  situated  ; 
these  occupy  its  middle  three-fifths  {Py).  The  mesial  fifth  is  occupied 
by  fibres  passing  from  the  frontal  region  of  the  cerebrum  to  the  pons, 
and  thence,  it  is  believed,  to  the  cerebellum ;  hence  they  are  called 
fronto-cerehellar  fibres.  The  fibres  occupying  the  lateral  fifth  are 
usually  spoken  of  as  temporo-occipital  cerebellar  fibres,  but  there  is  no 
certainty  as  yet  regarding  their  origin  or  functions. 

The  corpora  quaclrigemina  are  formed  mainly  of  grey  matter ; 
from  each  superior  corpus  a  bundle  of  white  fibres  passes  upwards 
and  forwards  to  the  geniculate  bodies,  eventually  joining  the  optic 
tract  of  the  same  side.  The  white  layer  on  the  surface  of  the  grey 
matter  of  the  C.  quadrigemina  is  derived  from  the  optic  tract ;  these 
fibres  come  from  the  retina,  and  terminate  by  arborising  around  the 
cells  of  the  grey  matter  of  the  C.  quadrigemina. 

The  cells  of  the  grey  matter  of  the  corpora  quadrigemina  differ 
greatly  in  form  and  size ;  the  destination  of  their  axons  is  not  pre- 
cisely known,  but  some  pass  ventralwards,  cross  at  the  raphe,  and 
constitute  the  fountain  decussation  of  Meynert ;  after  decussation 
they  form  the  main  mass  of  the  ventral  longitudinal  bundle ;  this 
gives  off  collaterals  to  the  nuclei  of  the  three  nerves  that  supply  the 
eye  muscles,  and  then  runs  ventro-laterally  to  the  posterior  longi- 
tudinal bundle,  with  which  its  fibres  ultimately  mix  in  the  antero- 
lateral descending  tract  of  the  spinal  cord. 

Seventh  section. — This  is  through  the  crus.  It  is  made  up  of 
crusta  (which  contains  the  motor  fibres),  tegmentum  (which  contains 


CII.  XLIV.]  MAIN   TRACTS  651 

the  sensory  fibres,  especially  the  bundle  called  the  mesial  fillet),  and 
the  substantia  nigra,  the  grey  matter  which  separates  them. 

The  destination  of  one  of  the  spinal  cord 
tracts   we   have   not   yet   mentioned;   this  is  /'     \    S.N, 

the  tract  of  Gowers.  This  is  continued  up 
through  the  ventral  part  of  the  pons  lateral 
to  the  pyramidal  bundles ;  when  it  reaches 
the    superior    cerebellar    peduncles    the   main 

part   of    the   tract    takes   a    sharp    backward      ^..^^   4.io.-section  through 
turn   and   enters   the   middle   lobe   or   vermis       cius   of  cerebrum,    cr, 

p     ,,  in  1,1  •  11  crusta ;     S.N.,    substantia 

of   the   cerebellum   by  the  superior  peduncle        nigra;  t, tegmentum. 
and  superior  medullary  velum.     Some  of  the 
fibres  of  the  tract  are  continued,  however,  into  the  corpora  quadri- 
gemina,  and  some  to  the  optic  thalamus. 

The  Tracts  of  the  Bulb,  Pons,  and  Mid-Brain. 

In  the  preceding  description  we  have  had  occasion  to  mention 
the  main  tracts  which  are  seen  in  transverse  section.  It  will  now 
be  convenient  to  summarise  matters  by  enumerating  them  again  as 
weU  as  certain  others  which  are  of  less  importance,  or  concerning 
which  we  know  less.  The  tracts  may  be  divided  into  two  main 
groups,  those  which  are  descending  and  those  which  are  ascending. 

Descending  tracts. — The  principal  descending  tract  is  (a)  the 
pyramidal  tract.  This  has  already  been  sufficiently  described,  so  also 
have  (b)  the  posterior  and  (c)  the  ventral  longitudinal  bundles.  The 
remaining  tracts  are : — 

{(I)  Monahno's  hundh. — These  fibres  start  from  the  cells  of  the  red  nucleus, 
cross  the  raphe  in  Forel's  fountain  decussation  ;  they  eventually  pass  into  the  lateral 
column  of  the  cord  as  the  prepyramidal  tract. 

{e)  The  ponto-spinal  hUcml  tracA  starts  from  the  large  cells  of  the  forraatio 
reticularis,  and  runs  down  the  lateral  portion  of  this  formation  through  the  pons  and 
bulb.  In  tiie  spinal  cord  the  fibres,  mixed  with  many  others  of  different  origin.  He  in 
the  lateral  column  between  the  grey  matter  and  the  tracts  of  Gowers  and  Monakow. 
They  pass  like  the  fibres  of  the  posterior  and  ventral  longitudinal  bundles  into  the 
grey  matter  of  the  anterior  cornu. 

(/)  Thi-  rfistihulo-sphud  tract  fibres  are  similar  in  origin  to  those  of  the  posterior 
longitudinal  bundle  ;  its  fibres  He  mixed  with  those  of  the  two  last-mentioned  tracts, 
and  their  destination  is  the  grey  matter  of  the  anterior  horn. 

(//)  T/if  ontral  tract  of  the  tfijmi'ntuin:  this  is  a  distinct  bundle  which  Hes  in  the 
middle  of  the  reticular  formation,  but  its  origin  and  destination  are  both  unknown. 

(A)  Other  longitudinal  fibres  of  the  tegmentum  are  (1)  the  fasciculus  rftrofle.viis, 
which  passes  obHquely  from  the  ganghon  of  the  habenula  (a  collection  of  cells 
near  the  middle  of  the  optic  thalamus  j  to  the  interpeduncular  ganghon  of  the  opposite 
side  (a  collection  of  cells  just  where  the  peduncles  diverge  from  the  transverse  fibres 
of  the  pon.*);  (2)  Von  Guddens  tiundU,  which  runs  from  the  corpora  mammillaria 
to  end  in  the  tegmentum  ;  these  fibres  decussate,  and  their  intercrossing  together 
with  that  of  Monakow's  bundle  constitutes  the  fountain  decussation  of  Forel. 

Ascending  Tracts. — The  most  important  of  these  are — (a)  the 
tract  of  the,  fillet,  and  (&),  the  central  tract  of  the  cranial  sensory  nerves. 


652  STRUCTURE   OF   THE   BULB,    PONS,   AND    MID-BRAIN       [CH.  XLIV. 

We  must  also  remember  the  fibres  that  connect  the  cord  to  the 
cerebellum  ( (c)  dorsal  and  (d)  ventral  cerebellar  tracts),  and  (e)  the 
fibres  that  pass  into  the  restiform  lody  (inferior  cerebellar  peduncle) 
from  the  olivary  body. 

The  superior  cerehellar  peduncles  originate  from  the  dentate  nucleus  of  the 
cerebellum  ;  we  have  already  seen  them  converging  to  the  middle  line  as  they  pass 
upwards,  and  decussating  in  the  mid-brain  at  the  level  of  the  posterior  C.  quadri- 
gemina ;  they  terminate  in  the  red  nucleus  of  the  tegmentum  and  in  the  optic 
thalamus.  Before  they  cross  they  give  off  branches  which  Cajal  describes  as  form- 
ing a  descendinc/  cerebellar  bundle,  which  gives  off  collaterals  to  the  motor  nuclei 
of  cranial  and  spinal  nerves. 

Origins  and  Functions  of  the  Cranial  Nerves. 

Having  now  studied  the  internal  construction  of  these  parts,  we 
can  take  up  more  fully  the  origins  and  functions  of  the  cranial  nerves 
which  originate  there.  The  olfactory  nerve  is  connected  to  the 
cerebrum,  and  will  be  considered  with  the  sense  of  smell.  The 
optic  nerve  will  be  studied  with  vision,  though  it  is,  as  we  have  seen, 
immediately  connected  with  the  mid-brain. 

The  third,  fourth,  and  sixth  nerves  are  wholly  motor,  and  supply 
the  muscles  of  the  eye.  Gaskell  discovered  among  the  rootlets  of 
the  third  and  fourth  nerves  the  vestiges  of  a  degenerated  and  function- 
less  ganglion,  which  indicates  the  previous  existence  of  a  sensory  por- 
tion of  these  nerves. 

The  third  nerve  {motor  oculi)  arises  in  a  group  of  nerve-cells  in 
the  grey  matter  on  the  side  of  the  Sylvian  aqueduct  underneath  the 
superior  corpus  quadrigeminum,  and  close  to  the  middle  line.  The 
anterior  part  of  this  nucleus  is  composed  of  small  cells  from  which 
small  nerve-fibres  originate  for  the  ciliary  muscle  and  sphincter  of 
the  iris  (intrinsic  muscles  of  the  eyeball).  These  fibres  correspond 
to  the  visceral  fibres  of  a  spinal  nerve,  and,  like  them,  have  a  cell 
station,  namely,  in  the  ciKary  ganglion.  The  posterior  part  of  the 
nucleus  is  composed  of  larger  cells,  and  these  give  rise  to  larger  fibres 
which  supply  the  following  extrinsic  eye-muscles : — superior  rectus, 
inferior  rectus,  internal  rectus,  inferior  oblique  and  levator  palpebrse. 

The  fourth  nerve  (trochlear)  takes  origin  from  the  grey  matter 
immediately  below  the  centre  of  the  third,  but  slightly  more  lateral 
in  position.  It  is  underneath  the  inferior  corpus  quadrigeminum. 
It  supplies  the  superior  oblique  muscle  of  the  opposite  eyeball. 

The  sixth  nerve  (abducens)  arises  from  a  centre  beneath  the 
eminentia  teres  in  the  upper  part  of  the  floor  of  the  fourth  ventricle 
near  the  middle  line.     It  supplies  the  external  rectus. 

It  is  obviously  necessary  that  the  eye-muscles  should  work 
together  harmoniously,  that  the  two  eyeballs  should  also  be  moved 
simultaneously  and  in  corresponding  directions,  and  that  such  move- 
ments should  take  place  in  accordance  with  the  necessities  of  vision. 


CH.  XLIV.]  THE    FIFTH    AND   SEVENTH   NERVES  653 

This  is  provided  for  in  the  shape  of  association  fibres  which  link  the 
centres  of  the  eye-muscles  together.  The  principal  association  tracts 
are  the  posterior  longitudinal  bundle,  which  connects  the  nuclei  of 
the  third  and  sixth  nerves,  and  the  ventral  longitudinal  bundle 
which  unites  the  optic  nerves  through  the  intermediation  of  the  cells 
of  the  C.  quadrigemina,  with  the  nuclei  of  all  these  nerves.  It  should 
also  be  remembered  that  all  the  fibres  of  the  fourth,  and  some  of 
those  of  the  third  nerve  decussate,  in  the  middle  line. 

The  fifth  nerve  {trigeminal)  is  a  mixed  nerve  ;  it  leaves  the  side  of 
the  pons  in  a  smaller  motor,  and  a  larger  sensory  division.  The 
former  supplies  the  muscles  of  mastication,  the  tensors  of  the  palate 
and  tympanum,  the  mylo-hyoid,  and  the  anterior  belly  of  the 
digastric ;  the  sensory  division  has  upon  it  a  ganglion  called  the 
Gasserian  ganglion;  it  is  the  great  sensory  nerve  of  the  face  and 
head.  The  motor  fibres  arise  from  the  motor  nucleus  (Vm,  fig.  459), 
which  Hes  at  the  lateral  edge  of  the  upper  part  of  the  floor  of  the 
fourth  ventricle,  but  a  certain  number  of  its  fibres  arise  from  cells 
in  the  lower  part  of  the  mid-brain  and  upper  part  of  the  pons ; 
this  long  stretch  of  nerve-cells,  indicated  by  the  long  blue  tail  in  the 
diagram,  is  called  the  accessory  or  superior  motor  nucleus  of  the  fifth. 
The  sensory  fibres  arise  from  the  cells  of  the  Gasserian  ganglion, 
which  resemble  in  structure  those  of  a  spinal  ganglion ;  one  branch 
of  each  passes  to  the  periphery  in  the  skin  of  the  head  and  face,  and 
the  other  grows  centralwards ;  on  reaching  the  pons  these  bifurcate, 
the  ascending  branches  arborise  around  the  principal  sensory  nucleus 
of  the  fifth  (Yd,  fig.  459),  which  lies  just  lateral  to  the  motor  nucleus, 
while  the  descending  branches  pass  down  into  the  bulb,  where  they 
form  the  descending  root  of  the  fifth,  and  some  reach  as  far  do\\  n 
in  the  spinal  cord  as  the  second  cervical  nerve.  Mingled  with  these 
descending  fibres  are  numerous  nerve-cells,  many  of  which  are  grouped 
in  clusters  (islands  of  Calleja),  and  the  descending  fibres  form  synapses 
around  them.  The  new  axons  arising  from  the  cells  of  the  sensory 
nuclei  pass  upwards  in  three  principal  tracts : — (1)  The  greater 
number  cross  the  raphe  and  join  the  mesial  fillet ;  (2)  some  ascend 
the  fillet  of  the  same  side ;  and  (3)  others  pass  into  a  special  ascending 
bundle  which  lies  near  the  ventricular  floor  (the  central  tract  of  the 
cranial  sensory  nerves). 

The  seventh  nerve  {facial)  is  the  great  motor  nerve  of  the  face 
muscles.  It  also  supplies  the  platysma,  the  stapedius,  stylo-hyoid.. 
and  posterior  belly  of  the  digastric.  When  it  is  paralysed,  the 
muscles  of  the  face  being  all  powerless,  the  countenance  acquires  on 
the  paralysed  side  a  characteristic,  vacant  look,  from  the  absence  of  all 
expression :  the  angle  of  the  mouth  is  lower,  and  the  paralysed  half 
of  the  mouth  looks  longer  than  that  on  the  other  side ;  the  eye  has 
an  unmeaning  stare,  owing  to  the  paralysis  of  the  orbicularis  palpe- 


654  STRUCTURE   OF   THE    BULB,    PONS,    AND    MID-BRAIN        [CH.  XLIV, 

brarum.  All  these  peculiarities  are  exaggerated  when  at  any  time 
the  muscles  of  the  opposite  side  of  the  face  are  made  active  in  any 
expression,  or  in  any  of  their  ordinary  functions.  In  an  attempt  to 
blow  or  whistle,  one  side  of  the  mouth  and  cheeks  acts  properly,  but 
the  other  side  is  motionless,  or  flaps  loosely  at  the  impulse  of  the 
expired  air ;  so,  in  trying  to  suck,  one  side  only  of  the  mouth  acts  ; 
in  feeding,  on  account  of  paralysis  of  the  buccinator  muscle,  food 
lodges  between  the  cheek  and  gums. 

The  motor  fibres  originate  from  a  nucleus  in  the  ventricular  floor 
below  that  of  the  fifth  and  to  the  outer  side  of  that  of  the  sixth 
nerve.  As  they  curve  over  the  nucleus  of  the  sixth,  they  give  off  a 
bundle  of  fine  fibres  which  cross  the  raphe,  but  their  destination  is 
unknown.  The  facial  nucleus  receives  collaterals  from  the  sensory 
tracts  in  the  reticular  formation. 

The  seventh  nerve,  however,  is  not  whoUy  motor.  The  geniculate 
ganglion  on  it  is  of  spinal  type ;  the  fibres  which  arise  from  it  pass 
centrally  into  the  pars  intermedia  of  Wrisberg,  which  enters  the  pons 
between  the  seventh  and  eighth  nerves ;  these,  like  other  sensory  fibres, 
divide  into  ascending  and  descending  branches ;  the  latter  have  been 
traced  down  to  the  sensory  nucleus  of  the  glosso-pharyngeal  nerve. 
The  peripheral  branches  of  the  geniculate  ganglion  cells  pass  into  the 
large  superficial  petrosal  and  chorda  tympani,  the  gustatory  fibres  of 
which  they  probably  furnish.  The  secretory  fibres  of  the  chorda 
tympani  are  efferent  fibres  which  reach  it  from  the  facial  nucleus 
viO.  the  pars  intermedia. 

The  eighth  nerve  {auditory)  runs  into  the  hinder  margin  of  the 
pons  by  two  roots.  One  winds  round  the  restiform  body  dorsal  to 
it,  and  is  known  as  the  dorsal  or  cochlear  division ;  the  other  passes 
ventro-mesiaUy  on  the  other  side  of  the  restiform  body,  and  is  known 
as  the  ventral  or  vestibular  division. 

We  will  take  these  two  parts  separately.  The  fibres  of  the 
cochlear  nerve  take  origin  from  the  bipolar  nerve-ceUs  of  the  spiral 
ganglion  of  the  cochlea;  the  peripheral  axons  ramify  among  the 
hair  cells  of  the  organ  of  Corti,  and  the  central  axons  pass  towards 
the  pons ;  as  they  enter  they  bifurcate,  and  some  pass  to  and  arborise 
around  a  collection  of  nerve-cells  situated  between  the  two  roots  and 
the  restiform  body,  called  the  accessory  auditory  nucleus ;  the  remain- 
ing fibres  terminate  similarly  in  a  collection  of  cells  in  the  grey  matter 
overlying  the  restiform  body,  and  extending  into  the  ventricular 
floor  in  its  widest  part.  This  is  called  the  ganglion  of  the  root,  and 
the  mass  of  grey  matter  is  termed  the  acoustic  tubercle.  The  auditory 
path  is  continued  by  new  axons  that  arise  from  these  cells.  Those 
from  the  accessory  nucleus  enter  the  trapezium,  and  pass  in  it  partly 
to  the  superior  olive  and  trapezoid  nucleus  of  the  same  side,  but 
mainly  to  the  corresponding  nuclei  of  the  opposite  side ;  some  fibres 


Cll,  XLIV.] 


THE    AUDITORY    NEllVE 


655 


end  here,  others  traverse  the  nuclei,  and  merely  give  off  collaterals  to 
them ;  they  then  turn  upwards  in  the  lateral  fillet,  and  so  reach  the 
inferior  C.  ({uadrigemina.  The  fibres  which  arise  in  the  acoustic 
tubercle  pass  superficially  over  the  floor  of  the  ventricle,  forming  the 
stri<ie  acousticcc;  having  crossed  the  raphe,  they  join  the  fibres  from  the 
accessory  nucleus  in  their  course  to  the  superior  olive  and  fillet. 
Here  again,  however,  a  few  fibres  pass  to  the  fillet  of  the  same  side. 


tub.ac^ 


FIBRES  TO  NUCL  LEMNISCI 
&CORPORA  QUAORIGEMINA 


PYRAMID 


NERVE-ENDINGS 

IN  ORGAN  OF  CORTI 

Fig.  467. — Cochlear  root  of  the  auditory  nerve,  r,  restiforiji  body ;  V,  descending  root  of  the  fifth 
nerve;  tub.  oc,  acoustic  tubercle;  n.  ace,  accessory  nucleus  ;  s.o.,  superior  olive;  n.tr.,  trapezoid 
nucleus;  ?t.ri'.,  nucleus  of  the  sixth  nerve;  F/.,  issuing  fibre  of  sixth  nerve.    (Schafer.) 


The  vestibular  nerve  arises  from  the  bipolar  cells  of  the  ganglion 
of  Scarpa  in  the  internal  ear.  The  peripheral  axons  ramify  among 
the  hair  cells  of  the  epithelium  in  the  utricle,  saccule,  and  semi- 
circular canals.  The  central  axons  enter  a  collection  of  small  nerve- 
cells  between  the  restiform  body  and  the  descending  root  of  the  fifth ; 
this  is  termed  the  principal  nucleus;  here  they  bifurcate;  the 
descending  branches  run  towards  the  lower  part  of  the  bulb,  and 
arborise  around  the  cells  of  the  neighbouring  grey  matter  (descending 
vestibular  nucleus).  The  ascending  branches  pass  upwards  in  the 
restiform  body  to  the  cerebellum,  in  their  course  giving  off  many 
collaterals  which  form  synapses  with  the  large  cells  of  two  nuclei 
near  the  outer  angle  of  the  ventricular  floor,  and  known  as 
the  nucleus  of  Deiters  and  nucleus  of  Bechterew  respectively.  The 
fibres  which  arise  from  Deiters'  nucleus  pass  into  the  posterior 
longitudinal  bimdles  of  both  sides  (see  p.  648) ;  those  which  start 
in  Bechterew's  nucleus  become  longitudinal,  but  their  destination  is 
uncertain. 


656  STRUCTUKE   OF   THE   BULB,    PONS,    AND    MID-BRAIN         [CH.  XLIV. 

The  accompanying  diagrams  (figs.  467  and  468)  will  serve  to  render 
these  complex  relationships  clearer. 


:::^T0  VERMIS 


TO  HEMISPHERE 


FIBRES    O 

VESTIBULA 

ROOT 


NERVE      -Vy/f^GANGLION   OF 
ENDINGS      'V/^  SCARPA 
IN  MACULAE 
&  AMPULL/E 


Fio.  468. — Vestibular  root  of  the  auditory  nerve ;  r,  restiform  body ;  V,  descending  root  of  the  fifth 
nerve ;  d,  fibres  of  descending  vestibular  root ;  n.  d.,  cell  of  descending  vestibularnucleus  ;  D,  nucleus 
of  Deiters  ;  B,  nucleus  of  Bechterew:  n.  t.,  nucleus  tecti  of  cerebellum  :  p.  I.  b.,  posterior  longitudinal 
bundle.    (Schafer.) 

The  ninth  nerve  (glosso-pharyngeal)  gives  filaments  through  its 
tympanic  branch  (Jacobsen's  nerve)  to  the  fenestra  ovalis  and 
fenestra  rotunda,  and  the  Eustachian  tube,  parts  of  the  middle  ear ; 
also,  to  the  carotid  plexus,  and  through  the  great  superficial  petrosal 
nerve,  to  the  spheno-palatine  (Meckel's)  ganglion.  The  small 
superficial  petrosal  (Jacobsen's  nerve)  passes  to  the  otic  ganghon, 
and  thus  controls  the  parotid  secretion.  The  carotid  plexus  may 
also  connect  the  nerve  with  the  spheno-palatine  ganglion.  Connections 
are  also  made  with  the  sympathetic  plexus  on  the  great  meningeal 
artery  by  the  external  superficial  petrosal.  This  is  important,  as 
another  possible  connecting  link  between  the  glosso-pharyngeal  and 
the  otic  ganghon  is  thus  provided.  After  communicating,  either 
within  or  without  the  cranium,  with  the  vagus,  it  leaves  the  cranium, 
divides  into  the  two  principal  divisions  indicated  by  its  name,  and 
supplies  the  mucous  membrane  of  the  posterior  and  lateral  walls  of 
the  upper  part  of  the  pharynx,  the  Eustachian  tube,  the  arches  of 
the  palate,  the  tonsils  and  their  mucous  membrane,  and  the  tongue 
as  far  forwards  as  the  foramen  caecum  in  the  middle  line,  and  to  near 
the  tip  at  the  sides  and  inferior  part. 

It  contains  motor  fibres  to  the  stylo-pharyngeus,  middle  con- 
strictor of  pharynx,  and  crico-thyroid  muscles,  and  probably  to  the 


CH.  XLIV.]  THE   TENTH    AND    ELEVENTH   NERVES  657 

levator  palati  and  other  muscles  of  the  palate,  except  the  tensor, 
which  is  supplied  by  the  fifth  nerve,  and  the  other  constrictors  of 
the  pharynx,  which  are  supplied  from  the  nucleus  ambiguus  l)y  cranial 
rootlets  of  both  ninth  and  tenth  nerves.  The  nerve  also  contains 
fibres  concerned  in  common  sensation,  and  the  sense  of  taste,  and 
secretory  fibres  for  the  parotid  gland. 

The  cells  from  which  the  motor  fibres  originate  are  situated  in  a 
special  nucleus,  which  is  a  continuation  upwards  of  the  nucleus 
ambiguus  (the  chief  motor  nucleus  of  the  tenth  or  vagus  nerve).  The 
sensory  fibres  arise  in  the  jugular  and  petrosal  gangHa  from  cells  of 
the  spinal  ganglion  type.  When  the  central  axons  reach  the  bulb 
they  bifurcate  as  usual;  the  descending  branches  pass  down  the 
funiculus  solitarius  and  terminate  in  synapses  around  the  cells 
scattered  among  its  fibres.  The  ascending  branches  pass  almost 
horizontally  to  arborise  around  the  cells  of  the  principal  nucleus 
(IX  in  fig.  459).  The  arrangement,  in  fact,  is  very  like  that  of  the 
tenth  nerve  now  to  be  described. 

The  tenth  nerve  {vagus  or  pneumo-gastric)  has  so  many  and 
important  functions  that  I  shall  not  attempt  to  describe  them  here ; 
it  would  mean  rewriting  a  great  deal  of  what  we  have  already  learnt 
in  connection  with  heart,  respiration,  digestion,  etc.  It  is  sufficient 
to  say  that  it  contains  both  efferent  and  afferent  fibres.  The  efferent 
fibres  arise  partly  from  the  upper  part  of  the  combined  nucleus,  which 
lower  down  gives  origin  to  the  spinal  accessory  nerve  (fig.  459,  X) 
but  mainly  from  the  nucleus  ambiguus,  the  position  of  which  is 
shown  in  fig.  459,  coloured  blue,  and  also  in  transverse  section  in  fig. 
463.  The  afferent  fibres  originate  from  the  ceUs  of  the  ganglion  of 
the  trunk  and  of  the  root ;  they  enter  the  bulb  and  bifurcate ;  the 
ascending  branches  are  short  and  arborise  around  the  cells  of  the 
principal  nucleus  (X  in  fig.  459) ;  the  descending  fibres,  together  with 
similar  ones  derived  from  the  glosso-pharyngeal  nerve,  and  pars 
intermedia,  pass  down  in  the  descending  root  of  vagus  and  glosso- 
pharyngeal, which  is  also  known  as  the  funiculus  solitarius.  These 
fibres  terminate  by  arborising  around  the  cells  of  the  grey  matter 
that  lies  along  its  mesial  border  {descending  nucleus  of  vagus  and 
glosso-pharyngeal).  This  approaches  the  middle  line  as  it  descends, 
and  finally  joins  that  of  the  opposite  side  over  the  central  canal 
{commissural  nucleus). 

The  eleventh  nerve  {spinal  accessory)  is  wholly  efferent :  it  arises 
by  two  distinct  origins — one  from  a  centre  in  the  floor  of  the  fourth 
ventricle,  and  connected  with  the  glosso-pharyngeal-vagus-nucleus ; 
the  other,  from  the  outer  side  of  the  anterior  cornu  of  the  spinal  cord 
as  low  down  as  the  fourth  cervical  nerve.  The  fibres  from  the  two 
origins  come  together  at  the  jugular  foramen,  but  separate  again  into 
two   branches,   outer   and   inner.      The   outer,   consisting   of    large 

2   T 


658  STRUCTURE   OF   THE   BULB,    PONS,    AND    MID-BRAIN        [CH.  XLIY. 

medullated  fibres  from  the  spinal  origin,  supplies  the  trapezius  and 
sterno-mastoid  muscles.  The  inner  branch,  consisting  of  small 
medullated  fibres  from  the  medulla,  suppKes  chiefly  viscero-motor 
filaments  to  the  vagus.  The  muscles  of  the  larynx,  all  of  which  are 
supplied  by  branches  of  the  vagus,  derive  their  motor  nerves  from  the 
accessory ;  and  (which  is  a  very  significant  fact)  Vrolik  states  that  in 
the  chimpanzee  the  internal  branch  of  the  accessory  does  not  join  the 


c/.n.x  x/. 


Fig.  469. — The  tenth  and  twelfth  nerves,  pyr,  pyramid  ;  n.XIL,  nucleus  of  hypoglossal ;  XII.,  fihre  of 
hypoglossal;  d.n.X.XI.,  combined  nucleus  of  vagus  and  spinal  accessory;  n.amb.,  nucleus 
ambiguus; /.s.,  fasciculus  solitarius,  descending  fibres  of  vagus  and  glosso-pharyngeal;  f.s.n.,  its 
nucleus;  A'.,  motor  fibre  of  vagus ;  g,  ganglion  cell  in  vagus  trunk  giving  rise  to  a  sensory  fibre; 
d.V.,  descending  root  of  the  fifth  nerve  ;  r,  restiform  body.    (Schafer.) 

vagus  at  all,  but  goes  direct  to  the  larynx.  The  crico-thyroid,  how- 
ever, receives  fibres  which  leave  the  bulb  by  glosso-pharyngeal 
rootlets. 

The  twelfth  nerve  (hypoglossal)  is  also  entirely  efiferent.  It  arises 
from  a  large  celled  and  long  nucleus  in  the  bulb,  close  to  the  middle 
line,  inside  the  combined  nucleus  of  the  ninth,  tenth,  and  eleventh 
nerves.  It  receives  numerous  collaterals  from  adjacent  sensory 
tracts,  and  from  the  descending  nuclei  of  the  fifth,  ninth,  and  tenth 
nerves,  and  from  the  posterior  longitudinal  bundle.  Fibres  from  this 
nucleus  run  from  the  ventral  surface  through  the  reticular  formation 
in  a  series  of  bundles,  and  emerge  from  a  groove  between  the  anterior 
pyramid  and  olivary  body.  It  is  the  motor  nerve  to  the  muscles  of 
the  tongue  (stylo-glossus,  hyo-glossus,  genio-hyo-glossus,  and  lingu- 
ales).  The  branches  of  this  nerve  to  the  genio-hyoid,  thyro-hyoid, 
sterno-thyroid,  sterno-hyoid,  and  omo-hyoid  are  branches  of  the  first, 
second,  and  third  cervical  nerves  carried  down  in  its  sheath  and 
slipped  off  at  various  points  as  descendens  (hypoglossi)  cervicis. 


CHAPTER  XLV 

STRUCTURE   OF   THE   CEREBELLUM 

The  cerebellum  is  composed  of  an  elongated  central  portion  or  lobe, 
called  the  vermis  or  vermiform  process,  and  two  hemispheres.  Each 
hemisphere  is  connected  with  its  feUow,  by  means  of  the  vermiform 
process. 

The  cerebellum  is  composed  of  white  and  grey  matter,  the  latter 


FiQ.  470. — Cerebellum  in  section  and  fourth  ventricle,  with  the  neighbouring  parts.  1,  median  groove 
of  fourth  ventricle,  ending  below  in  the  calamus  scriptoriiis,  with  the  longitudinal  eminences  formed 
by  the  fasciculi  terctes,  one  on  each  side ;  2,  the  same  groove,  at  the  place  where  the  white  streaks 
of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ventricle  ;  3,  inferior  peduncle  of  the 
cerebellum,  formed  by  the  restiform  body  ;  4,  funiculus  gracilis  ;  above  this  is  the  calamus  scrip- 
torius  ;  5,  superior  peduncle  of  cerebellum  ;  0,  6,  fillet  to  the  side  of  the  crura  cerebri ;  7,  7,  lateral 
grooves  of  the  crura  cerebri ;  8,  corpora  quadrigemiua.  (From  Sappey  after  Hirschfeld  and 
LeveiUe.) 

being  external,  like  that  of  the  cerebrum,  and  like  it,  infolded,  so 
that  a  larger  area  may  be  contained  in  a  given  space.  The  convolu- 
tions of  the  grey  matter,  however,  are  arranged  after  a  dififerent 
pattern,  as  shown  in  fig.  470.     The  tree-like  arrangement  of  the  white 


660  STKUCTURE   OF   THE   CEREBELLUM  [CH.  XLV. 

matter  has  given  rise  to  the  name  arbor  vitce.  Besides  the  grey 
substance  on  the  surface,  there  are,  in  the  centre  of  the  white  sub- 
stance of  each  hemisphere,  small  masses  of  grey  matter,  the  largest  of 
which,  called  the  corpus  dentatum  (fig.  471,  cd),  resembles  very  closely 


Fig.  471. — Outline  sketch  of  a  section  of  the  cerebellum,  showing  the  corpus  dentatum.  The  section 
has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the  superior  peduncle  and 
pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body  has  also  been 
divided  longitudinally  so  as  to  expose  in  section  its  corpus  (hntatum.  cr,  crus  cerebri  ;  /,  fillet ;  q, 
corpora  quadrigemina ;  sp,  superior  peduncle  of  the  cerebellum  divideil ;  mp,  middle  peduncle  or 
lateral  part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  tlie  white  stem  ;  av,  continuation 
of  the  white  stem  radiating  towards  the  arbor  vike  of  the  folia  ;  cd,  corpus  dentatum  ;  o,  olivary 
body  with  its  corpus  dentatum  ;  p,  pyramid.    (Allen  Thomson.)     ^• 

the  corpubs  dentatum  of  the  olivary  body  of  the  medulla  oblongata  in 
appearance. 

If  a  section  is  taken  through  the  cortical  portion  of  the  cere- 
bellum, the  following  distinct  layers  can  be  seen  (fig.  472)  by  micro- 
scopic examination. 

Underneath  the  pia  mater  is  the  external  layer  of  grey  matter;  it 
is  formed  chiefly  of  fine  nerve-fibres  with  small  nerve-cells  scattered 
through  it.  Into  its  outer  part,  processes  of  pia  mater  pass  verti- 
cally; these  convey  blood-vessels.  There  are  also  here  numerous 
long  tapering  neuroglia-cells.  The  internal  or  granular  layer  of  grey 
matter  is  made  up  of  a  large  number  of  smaU  nerve-ceUs  mixed  with 
a  few  larger  ones,  and  some  neuroglia-cells.  Between  the  two  layers 
is  an  incomplete  stratum  of  large  flask-shaped  cells,  called  the  cells  of 
Purkinje.  Each  of  these  gives  ofl*  from  its  base  a  fine  process  which 
becomes  the  axis-cylinder  of  one  of  the  medullated  fibres  of  the  white 
matter ;  the  neck  of  the  flask  passing  in  the  opposite  direction  breaks 
up  into  dendrites  which  pass  into  the  external  layer  of  grey  matter. 
By  Golgi's  method  (fig.  473)  these  dendrons  have  been  shown  to 
spread  out  in  planes  transverse  to  the  direction  of  the  lameUse  of  the 
organ. 

Each  cell  of  Purkinje  is  fui-ther  invested  by  arborisations  of  two 
sets  of  nerve-fibres.  One  of  these  (originating  from  the  fibres  of  the 
white  matter  which  are  not  continuous  as  axis-cylinders  from  the 
cells  of  Purkinje)  forms  a  basket-work  round  the  dendrons ;  the  other 
(originating  as  axis-cylinder  processes  from  the  nerve-cells  of  the 


CH.  XLV.] 


STRUCTURE  OF  THE  CEREBELLUM 


661 


external  layer)  forms  a  felt-work  of  fibrils  round  the  body  of  the 
cell. 


lavn^ 


^'^o"5^--r;\.  .'^  -''- '■'-.^'-c?-o'--v- 


/ 


Fig.  472.— Vertical  section  of  'lug's  cerelielluiii ;  vm,  pia  inater;  p,  cells  of  Purkinje,  which  are 
branched  nerve-cells  lying  in  a  single  layer  and  sending  single  processes  downwards  and  more 
numerous  ones  upwards,  which  branch  continuously  and  extend  through  the  external  "molecular 
layer  "  towards  the  free  surface;  3,  dense  (granular)  layer  of  small  nerve-cells  ;/,  layer  of  nerve- 
tibres,  with  a  few  scattered  nerve-cells.  This  last  layer  (//)  constitutes  part  of  the  u-)dtt:  matter  of 
the  cerebellum,  while  the  layers  between  it  and  the  free  surface  are  grey  matter.  (Klein  and  Noble 
Smith.) 

The  cells  of  the  internal  layer  of  grey  matter  are  small ;  their 
dendrites  intermingle  with  those  of  neighbouring  cells ;  their  axons 
penetrate  into  the  external  layer,  but  their  final  destination  is 
uncertain.     Ramifying  among  these  cells  are  fibres  characterised  by 


662 


STRUCTURE    OF   THE   CEREBELLUM 


[CH.  XLV. 


possessing  bunches  of   short  branches  at  intervals   (moss-fibres  of 
Cajal). 

The  peduncles  of  the  cerebelhira  are  three  in  number — superior,  middle,  and 
inferior  ;  we  have  already  had  occasion  to  mention  them  in  our  study  of  the  bulb, 
pons,  and  mid-brain.  The  course  of  the  fibres  has  been  studied  by  the  degenera- 
tion method.  The  superior  peduncle  consists  mainly  of  fibres  which  originate  in 
the  corpus  dentatum  ;  some  fibres  are  said  to  arise  in  the  cerebellar  hemisphere, 
and  to  pass  throujjh  the  corpus  dentatum  without  communicating  with  its  cells. 
These  fibres  cross  the  raphe  in  the  mid-brain,  and  terminate  in  the  red  or  tegmental 
nucleus.  The  direction  of  the  impulses  in  these  fibres  is  from  cerebellum  to 
cerebrum,  the  red  nucleus  being  a  cell  station  on  the  road.  There  appear,  however, 
to  be  some  fibres  starting  from  the  optic  thalamus  which  convey  impulses  in  the 
opposite  direction.     In  addition  to  these  there  is  Cajal's  descending  cerebellar  bundle. 

I. 


Fig.  473. — Section  of|cerebellar  cortex,  stained  by  Golgi's  method  ;  I.  taken  across  the  lamina  ;  II.  in 
the  direction  of  the  lamina;  a,  outer  or  molecular  layer;  e,  inner  or  granular  layer ;  c,  white 
matter,  a,  Cell  of  Purkinje  ;  5,  small  cells  of  inner  layer ;  c,  dendrons  of  these  cells  ;  d,  axis- 
cylinder  process  of  one  of  these  cells  becoming  longitudinal  in  the  outer  layer  ;  c,  bifurcation  of  one 
of  these  ;  g,  a  similar  cell  lying  in  the  white  matter.     (Ramon  y  Cajal.) 

This  consists  of  branches  which  are  given  off  by  the  fibres  before  they  cross  at  the 
raphe  ;  they  pass  towards  the  bulb,  giving  off  collaterals  to  the  motor  nucleus  of  the 
fifth  nerve,  to  the  facial  nucleus,  to  the  nucleus  ambiguus,  and  others.  One  must 
not  forget  that  besides  all  these  fibres  the  tract  of  Gowers  joins  the  superior 
peduncle,  and  runs  back  along  its  mesial  border  to  the  vermis. 

The  middle  peduncle  consists  of  fibres  which  form  the  anterior  transverse  fibres 
of  the  pons.  They  pass  from  the  nuclei  pontis  to  the  opposite  cerebellar  hemi- 
sphere. Others  convey  impulses  in  the  opposite  direction  from  the  hemisphere  to 
the  pons  ;  on  section,  these  fibres  degenerate  as  far  as  the  raphe,  where  they  inter- 
mingle with  those  from  the  opposite  side. 

The  inferior  peduncle  or  restiforra  body  is  composed  of  ascending  fibres,  which 
pass  into  it  from  the  direct  cerebellar  tract,  from  both  olivary  nuclei,  but  mainly 
from  that  of  the  opposite  side,  from  the  nucleus  gracilis  and  nucleus  cuneatus,  and 
from  the  nuclei  of  the  sensory  roots  of  the  cranial  nerves.  The  fibres  pass  mostly 
to  the  vermis,  crossing  to  the  opposite  side  over  the  fourth  ventricle,  but  giving  off 
strong  collaterals  to  the  cerebellar  hemisphere  of  the  same  side  ;  these  account  for 
the  fact  that  each  cerebellar  hemisphere  is  in  principal  physiological  connection  with 
the  same  side  of  the  spinal  cord- 


CHAPTEE  XLVI 


STKUCTURB  OF  THE  CEEEBRUM 


The  cerebrum  consists   of   two   halves   called   cerebral  hemispheres, 
separated  by  a  deep  longitudinal  fissure  and  connected  by  a  large 


Fio.  474. — View  of  the  Corpus  Callosum  froui  aU.A  e.  A. — The  upper  surface  of  the  corjius  callosum  has 
been  fully  exposed  by  separating  the  cerebral  hemispheres  and  throwing  them  to  the  side ;  the  gyrus 
fomicatus  has  been  detached,  and  the  transverse  fibres  of  the  corpus  callosum  traced  for  some 
distance  into  the  cerebral  medullary  substance.  1,  the  upper  surface  of  the  corpus  callosum;  2, 
median  furrow  or  raphe ;  3,  longitudinal  strite  bounding  ilie  furrow ;  4,  swelling  formed  by  the 
transverse  bands  as  they  pass  into  the  cerebrum ;  5,  anterior  extremity  or  knee  of  the  corpus  cal- 
losum ;  6,  posterior  extremity ;  7,  anterior,  and  S,  posterior  part  of  the  mass  of  fibres  proceeding 
from  the  corpus  callosum ;  ;i,  margin  of  the  swelling ;  10,  anterior  part  of  the  convolution  of  the 
corjjus  callosum;  U,  hem  or  band  of  union  of  this  convolution;  lii,  internal  convolutions  of  the 
parietal  lobe  ;  13,  upper  surface  of  the  cerebellum.    (Sappey  after  Foville.) 

band  of  transverse  commissural  fibres  known  as  the  corpus  callosum 
(fig.  474).     The  interior  of  each  hemisphere  contains  a  cavity  of  com- 


664 


STRUCTURE  OF  THE  CEREBRUM 


fCH.  XLVI 


plicated  shape  called  the  lateral  ventricle ;  the  lateral  ventricles  open 
into  the  third  ventricle.  Fig.  475  represents  a  dissected  brain  in  which 
the  corpus  callosum  has  been  removed;  the  ventricles  are  thus 
exposed. 

Each  hemisphere  is  covered  with  grey  matter,  which  passes  down 


Fig.  1475. — Dissection  of  brain,  from  above,  exposing  the  lateral,  fourth,  and  fifth  ventricles  with  the 
surrounding  parts.  A. — o,  anterior  part,  or  gcnv  of  corpus  callosum  ;  b,  corpus  striatum  ;  b',  the 
corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  grey  substance  ;  c,  points  by  a  line  to  the 
tKnia  semicircularis  ;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided  ;  below  they  are  seen 
descending  in  front  of  the  third  ventricle,  and  between  them  is  seen  part  of  the  anterior  commis- 
sure ;  in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between  the  two  lamina  of  the 
septum  lucidum  ;  /,  soft  or  middle  commissure  ;  a  is  placed  in  the  posterior  part  of  the  third 
ventricle  ;  immediately  behind  the  latter  are  the  posterior  commissure  (just  visible)  and  the  pineal 
gland,  the  two  crura  of  which  extend  forwards  along  the  inner  and  upper  margins  of  the  optic 
thalami ;  h  and  i,  the  corpora  quadrigemina ;  k,  superior  crus  of  cerebellum  ;  close  to  k  is  the  valve 
of  Vieussens,  which  has  been  divided  so  as  to  expose  the  fourth  ventricle ;  I,  hippocampus  major 
and  corpus  fimbriatum,  or  t»nia  hippocampi;  m,  hippocampus  minor;  n,  eminentia  collateralis  ; 
0,  fourth  ventricle;  p,  posterior  surface  of  medulla  oblongata  ;  ;•,  section  of  cerebellum  ;  s,  upper  part 
of  left  hemisphere  of  cerebellum  exposed  by  the  removal  of  part  of  the  posterior  cerebral  lobe. 
(Hirschfeld  and  Leveillf.) 

into  the  fissures.  This  surface  grey  matter  is  called  the  cerebral 
cortex.  The  amount  of  this  grey  matter  varies  directly  with  the 
amount  of  convolution  of  the  surface.  Under  it  white  matter  is 
situated ;  and  at  the  base  there  are  masses  of  grey  matter ;  part  of 
these  basal  ganglia  are  seen  forming  part  of  the  wall  of  the  ventricles. 
The  anterior   basal   ganglion    is   called    the   corpus   striatum ;  it  is 


CII.  XLVI.] 


INTERIOR   OF   THE   CEREBRUM 


665 


divided  into  two  parts  called  the  lenticular  or  extraventricular  nucleics, 
and  the  caudate  or  intraventricular  nucleus.  It  has  received  the 
latter  name  because  it  is  seen  in  the  interior  of  the  ventricle.  The 
posterior  basal  ganglion  is  called  the  02)tic  thalamus. 

Passing  up  between  the  basal  gangha  are  the  white  fibres  which 
enter  the  cerebral  hemisphere  from  the  crus ;  these  constitute  the 
internal  capsule.  This  passes  in  front  between  the  two  subdivisions 
of  the  corpus  striatum,  and  behind  between  the  optic  thalamus  and 
the  lenticular  nucleus  of  the  corpus  striatum. 

The  relationship  of  these  parts  is  best  seen  in  a  vertical  section ; 
such  as  is  represented  in  the  next  diagram  (fig.  476). 


Fig.  476. — Vertical  section  through  the  cerebrum  and  basal  ganglia  to  show  the  relations  of  the  latter. 
CO.,  cerebral  convolutions;  c.c,  corpus  caUosum  ;  v. I.,  lateral  ventricle;  /,  fornix;  vIII.,  third 
ventricle;  «.c.,  caudate  nucleus;  <A,  ojjtic  thalamus ;  n.i.,  lenticular  nucleus  ;  c.i.,  internal  capsule  ; 
e^.,  claustrum  ;  c.e.,  external  capsule  ;  m,  corpus  mammillare ;  t.o.,  optic  tract ;  s.t.t.,  stria  termin- 
alis  ;  n.a.,  nucleus  amygdalae  ;  cm,  soft  commissure  ;  eo.i.,  Island  of  Rail.    (Schwalbe.) 

One  hemisphere  is  seen,  with  portions  of  the  other.  The  surface 
darkly  shaded  indicates  the  grey  matter  of  the  cortex,  which  passes 
down  into  the  fissures ;  one  very  extensive  set  of  convolutions  (co.i.), 
passes  deeply  into  the  substance  of  the  hemisphere;  this  is  called 
the  Island  of  Eeil ;  the  lowest  stratum  of  grey  matter  is  separated 
from  tliis  to  form  a  narrow  isolated  strip  of  grey  matter  called  the 
claustrum  {cl.).  In  the  middle  line  the  great  longitudinal  fissure 
is  seen  extending  as  far  as  (c.c.)  the  corpus  callosimi,  the  band  of 
white  matter  that  forms  the  great  commissure  between  the  two 
hemispheres ;  beneath  this  are  the  lateral  ventricles  which  com- 
municate by  the  foramen  of  Munro  with  the  third  ventricle :  the 
fornix  is  indicated  by  the  letter  /.  Contributing  to  the  floor  of  the 
lateral  ventricle,  one  next  sees  the  optic  thalamus  {th.),  and  the  tail 


666  STRUCTUEE  OF  THE  CEREBRUM  [CH.  XLVI. 

end  of  the  nucleus  caudatus  (n.c.) ;  the  section  being  taken  somewhat 
posteriorly.  The  nucleus  lenticularis  is  marked  nl. ;  and  the  band  of 
white  fibres  passing  up  between  it  and  the  thalamus  is  called  the 
internal  capsule  (c.i.) ;  the  narrow  piece  of  white  matter  between  the 
claustrum  and  the  lenticular  nucleus  is  called  the  external  capsule. 

For  the  student  of  medicine  the  internal  capsule  is  one  of  the 
most  important  parts  of  the  brain.  Into  it  are  continued  up  the 
fibres  which  we  have  previously  traced  as  far  as  the  crus  cerebri ; 
the  motor-fibres  of  the  crusta  are  continued  into  the  anterior  two- 
thirds  of  its  posterior  limb  {i.e.  behind  the  genu  *  in  fig.  477) ;  the 
sensory  fibres  of  the  tegmentum  into  the  posterior  third  of  this  limb. 
When  these  fibres  get  beyond  the  narrow  pass  between  the  basal 
ganglia,  they  spread  out  in  a  fan-like  manner  and  are  distributed  to 
the  grey  cortex ;  the  motor-fibres  coming  down  from  the  motor  con- 
volutions around  the  fissure  of  Eolando ;  the  sensory  fibres  going  to 
the  same  convolutions  and  also  to  others  behind  these  which  are 
associated  with  special  sensations.  The  name  corona  radiata  is 
appKed  to  the  fan-like  spreading  of  the  fibres;  the  fibres  as  they 
pass  through  the  handle  of  the  fan,  or  internal  capsule,  communicate 
with  the  nerve-cells  of  the  grey  matter  of  the  basal  ganglia;  the 
pyramidal  fibres  on  their  way  down  to  the  medulla  and  cord  from 
the  motor  areas  of  the  brain  send  off  collaterals  or  side  branches 
which  arborise  around  the  cells  of  the  corpus  striatum,  and  to  a 
lesser  degree  around  those  of  the  optic  thalamus ;  the  axis-cylinder 
processes  of  these  cells  pass  out  to  join  the  pyramidal  tract  on  its 
downward  course.  The  sensory  fibres  on  their  way  up  may  pass 
straight  on  to  the  cortex,  but  the  majority,  especially  those  in  the 
fillet,  terminate  by  arborising  round  the  cells  of  the  optic  thalamus, 
and  in  the  subthalamic  area.  This,  in  fact,  is  another  cell-station  or 
position  of  relay  :  the  fibres  passing  out  from  the  cells  of  the  thalamus 
continue  the  impulse  on  to  the  cortex. 

The  importance  of  the  internal  capsule  is  rendered  evident  when 
one  considers  the  blood  supply  of  these  parts ;  at  the  anterior  and 
posterior  perforated  spots,  numerous  small  blood-vessels  enter  for  the 
supply  of  the  basal  ganglia,  and  these  are  liable  to  become  diseased, 
and  if  they  rupture,  a  condition  called  apoplexy  is  the  result ;  if  the 
haemorrhage  is  excessive,  death  may  occur  almost  immediately ;  but 
if  the  patient  recovers,  a  condition  of  more  or  less  permanent  paralysis 
remains  behind ;  and  a  very  large  amount  of  paralysis  results  from  a 
comparatively  limited  lesion,  because  so  many  fibres  are  congregated 
together  in  this  narrow  isthmus  of  white  matter.  If  the  haemorrhage 
is  in  the  anterior  part  of  the  posterior  limb,  motor  paralysis  of  the 
opposite  side  of  the  body  (hemiplegia)  will  be  the  most  marked 
symptom.  If  the  haemorrhage  occurs  in  the  posterior  part,  sensory 
paralysis  of  the  opposite  side  of  the  body  will  be  the  most  marked 


CII.  XLVI.] 


INTERIOR   OF  THE   CEREBRUM 


667 


symptom.  If  the  motor-fibres  are  affected,  degeneration  will  occur 
in  the  pyramidal  tract,  and  can  be  traced  through  the  pes  of  the  crus 
and  mid-brain  to  the  pyramid  of  the  pons  and  bulb,  and  then  in  the 
crossed  pjTamidal  tract  of  the  opposite  side  and  in  the  direct  pyra- 
midal tract  of  the  same  side  of  the  cord. 

Fig.  477  represents  a  horizontal  view  through  the  hemisphere. 
The  internal  capsule  (c)  at  the  point  *  makes  a  bend  called  the  genu 


Fig.  477. — Diagram  to  show  the  connection  of  the  Frontal  and  Occipital  Lobes  with  the  Cerebellum,  etc. 
The  dotted  lines  passing  in  the  crusta  (t.oc),  outside  the  motor  fibres,  indicate  the  connection 
between  the  temporo-occipital  lobe  and  the  cerebellum,  f.c,  the  fronto-cerebellar  fibres,  which 
pass  anteriorly  to  the  motor  tract  in  the  crusta;  i.f.,  fibres  from  the  caudate  nucleus  to  the  pons. 
Fc. ,  frontal  lobe ;  Oc,  occipital  lobe  ;  af.,  ascending  frontal;  ap.,  ascending  parietal  convolutions; 
PCF.,  precentral  fissure  in  front  of  the  ascending  frontal  convolution;  fr.,  fissure  of  Rolando;  ipf., 
intraparietal  fissure.  A  section  of  the  crus  is  lettered  on  the  left  side,  s.k.,  substantia  nigra  ;  pv., 
pyramidal  motor  fibres,  which  on  the  right  are  shown  as  continuous  lines  converging  to  pass  through 
the  posterior  limb  of  i.e.,  internal  capsule  (the  knee  or  elbow  of  which  is  shown  thus  '')  upwards  inio 
the  hemisphere  and  downwards  through  the  pons  to  cross  at  the  medulla  in  the  pyramidal  decussa- 
tion.   Ipt,  crossed  pyramidal  tract;  apt,  direct  pyramidal  tract.    (Gowers.) 

or  knee,  behind  which  the  motor-fibres,  and  more  posteriorly  still 
sensory-fibres,  pass.  The  connection  between  cerebrum  and  the 
cerebellum  is  also  indicated ;  one  cerebral  hemisphere  is  connected 
with  the  opposite  cerebellar  hemisphere  by  fronto-cerebellar  and 
temporo-occipito-cerebellar  fibres  which  pass  respectively  in  front 
of  and  behind  the  pjTamidal  fibres  in  the  internal  capsule. 


Histological  Structure  of  the  Cerebral  Cortex. 

The  grey  matter  of  the  cortex  is  composed  of  a  number  of  layers 
which  are,  however,  not  well  marked  off  from  one  another.  The 
number  of  these  layers  is  variously  given    by  different   authorities 


668 


STEUCTURE   OF   THE   CEREBRUM 


[ClI.  XLVI. 


from  three  up  to  nine.     The  most  satisfactory  division  appears  to 
me  to  be  that  into  three. 

1.  The  molecular  layer. — Most  superficially  is  a  thin  stratum  of 


\\A\\M  Hi  1 1^ 


Fig.  478.— The  layers  of  the  cortical  grey 
matter  of  the  cerebrum.    (Meynert.) 


Fig.  479. — Principal  types  of  cells  in  the 
cerebral  cortex. 

A,  medium-sized   pyramidal   cell    of    the 
second  layer. 

B,  large  pyramidal  cell. 

C,  polymorphous  cell. 

D,  cell  of  which  the  axis-cylinder  process  is 

ascending. 

E,  neuroglia  cell. 

F,  cell  of  the  first,  or  molecular,   layer, 

forming  an  intermediate  cell-station 
between  sensory  fibres  and  motor  cells. 
Notice  the  tangential  direction  of  the 
nerve-fibres. 

G,  sensory  fibre  from  the  white  matter. 
H,  white  matter. 

I,  collateral  of  the  white  matter.     (Ramon 
y  Cajal.) 


medullated  nerve-fibres  largely  derived  from  the  dendrons  of  the 
cells  of  the  next  layer.  The  nerve-cells  (F  in  fig.  479)  intermingled 
with  these  are  branched,  and  have  several  processes  which  lie 
horizontally  beneath  the  surface  (tangential  fibres).  Neuroglia  cells 
are  also  present. 


CH.  XLVI.] 


THE  CEREBRAL  CORTEX 


669 


2.  The  layer  of  pyramids. — There  are  several  deep,  and  the  largest 
cells  are  situated  most  deeply.  Each  of  these  has  an  apical  process 
running  to  the  surface,  where  the  branches  run  tangentially.  The 
lateral  processes  are  also  branched  dendrons.  The  axon  originates 
from  the  base.  The  largest  pyramids  (Betz  cells)  are  found  in  the 
so-called  motor  cortex  (Eolandic  area)  and  give  origin  to  the  fibres 
of  the  pyramidal  tract.     The  smaller  pyramids  are  association  units. 

3.  Tlie  layer  of  polymorphous  cells. — There  are  small  scattered 
cells,  many  of  a  fusiform  shape.  In  the  Island  of  Eeil  this  layer  is 
hypertrophied,  and  is  separated  from  the  rest  of  the  grey  matter  by 
a  stratum  of  white  fibres ;  it  is  known  then  as  the  claustrum. 

Variations  in  different  regions  of  the  cortex  will  be  found  described 


Fifi.  480.— Human  cerebral  cortex  :  Golgi's  method.    Low  power.    (Mott.) 


in  histological  works,  but  the  physiological  meaning  of  these  is  not 
clear  in  many  cases.  The  Golgi  method  has  proved  conspicuously 
useful  in  the  study  of  the  shapes  and  dispositions  of  the  cells  (see 
figs.  479, 480, 481).  Bundles  of  medullated  nerve-fibres  pass  in  vertical 
streaks  fhrough  the  deeper  layers  of  the  grey  matter ;  some  of  these 
are  axis  cylinder  processes  of  the  pyramidal  and  polymorphous  cells, 
and  are  conveying  impulses  downwards ;  others  conveying  impulses 
upwards  pass  from  the  white  matter  into  the  cortex  to  arborise  among 
its  various  cells.  In  addition  to  these  fibres,  other  strands  lie  parallel 
to  the  surface  of  the  cortex,  and  have  received  various  names,  such  as 
the  outer  line  of  Baillarger  in  the  layer  of  medium-sized  pyramids, 
the  inner  Kne  of  Baillarger  in  the  layer  of  large  pyramids,  and  the 


670  STRUCTURE  OF  THE  CEREBRUM  [CH.  XLVI. 

line  of  Gennari  in  the  occipital  region.    There  can  be  little  or  no  doubt 
that  these  are  association  tracts  linking  the  convolutions  together. 

The  cells  of  the  cortex  thus  give  rise  to  the  motor  or  efferent 
fibres ;  these  pass  into  the  white  matter  of  the  interior  of  the  brain. 
Some  go  either  directly  or  by  collaterals,  (1)  to  the  cortex  of  more 
or  less  distant  convolutions.  These  are  called  Association  fibres.  (2) 
Others  pass  to  the  corpus  callosum,  and  so  reach  the  cortex  of  the 
opposite  hemisphere.  These  are  called  Commissural  fibres.  In  each 
case  they  terminate  by  arborisations  (synapses)  around  the  cells  of 
the  grey  matter  of  the  cortex ;  while  others  again,  especially  those 
of  the  largest  pyramidal  cells,  extend  downward  through  the  corona 
radiata  and  inte  nal  capsule,  and  become,  (3)  fibres  of  the  pyramidal 


Fio.  481. — Human  cerebral  cortex :  Golgi's  method.    High  power.    (Mott.) 

tract.  These  are  called  Projection  fibres.  As  they  pass  down  they 
give  ofif  collaterals  to  the  adjacent  grey  matter,  to  the  opposite 
hemisphere  vid  the  corpus  callosum,  to  the  corpus  striatum  and  the 
optic  thalamus,  which  terminate  there  by  arborisations;  the  main 
fibres  terminate  in  synapses  round  the  multipolar  cells  of  the  grey 
matter  of  the  opposite  side  of  the  spinal  cord.  These  are  termed  the 
cortico-spinal  fibres ;  von  Monakow  has  shown  that  some  of  the 
pyramidal  fibres  terminate  in  the  mid-brain  and  pons  (cortico-pontine 
fibres),  and  a  fresh  relay  of  fibres  thence  continues  the  impulse 
downwards. 

The  cells  of  the  cortex  are,  in  addition  to  all  this,  surrounded  by 
the  arborising  terminations  of  the  sensory  nerve-fibres,  which,  after 
relays  at  various  cell-stations,  ultimately  reach  the  cortex. 


CH.  XLVI.] 


MAIN   TRACTS 


671 


We  are  now  in  a  position  to  complete  diagram  448  (p.  625),  and 
obtain  an  idea  of  the  relations  of  the  principal  cells  and  fibres  of  the 
cerebro-spinal  nervous  system  to  one  another. 

Pyr.  (fig.  482)  is  a  cell  of  the  Rolandic  area  of  the  cerebral  cortex  ;  ax  is  its 
axis-cylinder  process  which  passes  down  in  the  pyramidal  tract,  and  crosses  the 

A.C.N 


Uultipolai 

Cello/ Ant 

Horn 


Fig.  482. 


-Scheme  of  relationship  of  cells  and  fibres  of  brain  and  cord.    (In  the  preparation  of  this 
diagram  I  have  received  considerable  assistance  from  Dr  Mott.) 


middle  line  ab  at  the  pyramidal  decussation.  It  gives  off  collaterals,  one  of  which 
{call)  is  shown  passing  in  the  corpus  callosura  to  terminate  in  an  arborisation  in  the 
cortex  of  the  opposite  hemisphere ;  another  (str)  passes  into  the  corpus  striatum. 
In  the  cord  collaterals  pass  off  and  end  in  arborisations  around  cells  of  the  anterior 
horn  of  the  spinal  cord  (see  also  fig.  448) ;  the  main  fibre  has  a  similar  termination.  * 


*  The  intermediate  cell-station  in  the  posterior  horn  between  the  pyramidal  fibre 
and  the  anterior  cornual  cell  (Schafer)  is  act  shown  in  the  diagram  (see  also  p.  625). 


672  STRUCTURE  OF  THE  CEREBRUM  [CH.  XLVl. 

The  motor  nerve-fibre  passes  fi-om  the  anterior  cornual  cell  to  muscular  fibres,  where 
it  ends  in  the  terminal  arborisations  called  end-plates. 

Coming  now  to  the  sensory  fibres,  a  cell  of  one  of  the  spinal  ganglia  is  shown. 
Its  axis-cylinder  process  bifurcates,  and  one  branch  passes  to  the  periphery,  ending 
in  arborisations  in  skin  and  tendon.  The  other  (central)  branch  bifurcates  on  entering 
the  cord,  and  its  divisions  pass  upwards  and  downwards,  the  latter  for  a  short 
distance  only  :  the  terminations  of  this  descending  branch  and  of  collaterals  of  the 
ascending  branch  round  the  cells  of  the  spinal  cord  are  more  fully  shown  in  fig.  448. 
The  main  ascending  branch  arborises  around  a  cell  of  the  nucleus  gracihs  (x.g.)  or 
nucleus  cuneatus  in  the  posterior  columns  of  the  bulb  ;  the  axis-cyhnder  process  of 
this  cell  passes  over  to  the  other  side  as  an  internal  arcuate  fibre  (i.a.),  and  becomes 
longitudinal  as  one  of  the  fibres  of  the  mesial  fillet  (k),  which  terminates  round  a  cell 
of  the  optic  thalamus  (o.t.),  from  which  a  new  axis-cylinder  process  passes  to  form 
an  arborisation  around  the  dendrons  of  one  of  the  cerebral  cells  (Cajal's  nerve-unit 
of  association  a. ex.)  in  the  surface  layer  of  the  cortical  grey  matter  (shown  on  a 
larger  scale  in  fig.  479  r) :  the  axis-cylinder  process  of  a.c.x.  arborises  round  the 
dendrons  of  the  pyramidal  cell  from  which  we  started. 

In  this  way  one  gets  a  complete  physiological  circle  of  nerve-units  ;  the  segments 
of  the  circle  are,  however,  anatomically  distinct,  and  the  impulses  travel  Uirough 
contiguous,  not  through  continuous,  structures.  The  simple  arrows  indicate  the 
direction  of  the  impulies  in  the  eiTerent  projection  system  ;  the  feathered  arrows  in 
the  afferent  projection  system. 

Next  we  come  to  the  connections  of  the  cerebellum.  One  of  the  collaterals  of 
the  sensory  nerve-fibre  arborises  round  a  cell  of  Clarke's  column,  from  which  a  fibre 
of  the  direct  cerebellar  tract  passes  to  end  in  an  arborisation  around  a  cell  in  the 
vermis  of  the  cerebellum,  p  is  one  of  the  cells  of  Purkinje,  the  axis-cylinder  process 
of  which  p. ax  passes  to  the  cerebro-spinal  axis;  it  is  depicted  as  passing  down  to 
envelop  one  of  the  cells  of  the  anterior  horn  ;  but  this  has  never  been  satisfactorily 
demonstrated :  so  a  dotted  line  has  been  used  to  indicate  this  uncertainty.  Most 
of  its  collaterals  pass  up  to  the  cerebrum  through  intermediate  cell-stations. 

The  origin  and  destination  of  the  tract  of  Gowers  are  not  shown  in  the  diagram  ; 
the  fibres  of  communication  from  the  cerebellar  to  the  opposite  cerebral  hemisphere, 
which  pass  through  the  superior  cerebellar  peduncle,  are  also  omitted.  The 
sympathetic  system,  with  its  numerous  cell-stations  in  the  sympathetic  gangha,  we 
have  studied  in  connection  with  the  blood-vessels  and  viscera  to  which  the  sympa- 
thetic fibres  are  distributed  (see  especially  pp.  299  to  303). 

G.M.  is  the  grey  matter  which  is  continuous  from  spinal  cord  to  the  optic 
thalamus,  and  through  this  certain  afferent  impulses,  such  as  those  of  pain,  travel 
upwards. 

Particular  attention  should  be  paid  to  the  following  point :  when 
an  afferent  fibre  enters  the  spinal  cord,  it  di^ddes  into  three  main 
sets  of  branches.  The  first  set,  the  shortest,  forms  synapses  with 
the  motor  cells  of  the  anterior  horn ;  here  we  have  the  anatomical 
basis  of  spinal  reflex  action.  The  second  set  passes  through  an 
intermediate  cell-station  in  Clarke's  column  to  the  cerebellum,  the 
emerging  fibres  from  which  also  influence  the  motor  discharge  of 
the  anterior  horn  cells.  The  third  set,  the  longest,  passes  through 
three  intermediate  cell-stations  (the  first  in  the  nucleus  gracilis  or 
cuneatus,  the  second  in  the  optic  thalamus,  the  third  in  the  associa- 
tion units  in  the  cortex),  and  ultimately  reaches  the  pyramidal  nerve- 
cells  of  the  cerebral  cortex,  the  efferent  fibres  (pyramidal  fibres) 
of  which  pass  to  the  motor  cells  of  the  anterior  cornu  and  influence 
their  discharge.  The  motor  nerve-cells  of  the  anterior  horn  may 
thus   be   influenced   by   the   afferent   impulses   via   three   paths  or 


CH.  XLVI.] 


THE  CEREBRAL  CONVOLUTIONS 


673 


nervous  circles.  In  health,  all  these  nervous  circles  are  in  action  to 
produce  co-ordinated  muscular  impulses.  In  locomotor  ataxy,  which 
is  a  degeneration  of  the  cells  of  the  ganglia  on  the  posterior  roots 
and  their  branches,  all  these  nervous  circles  are  deranged,  and  the 
result  is  loss  of  reflex  action,  and  inco-ordination  of  muscular  move- 
ments. 

It  should  be  noted  that  the  pyramidal  cells  in  the  cortex,  though 
the  largest  in  size,  are  the  least  numerous.  Similarly  the  large 
motor  cells  of  the  cord  are  relatively  few  in  number.  The  innumer- 
able smaller  cells  in  both  situations  are  association  cells  concerned 
in  the  co-ordination  of  impulses. 


The  Convolutions  of  the  Cerebrum. 

The  surface  of  the  brain  is  marked  by  a  great  number  of  depres- 
sions which  are  called  fissures  or  sulci,  and  it  is  this  folding  of  the 
surface  that  enables  a  very  large  amount  of  the  precious  material 


A.  Cerebral  Hemisphere  of  adult  Maeacque  monkey. 

B.  Cerebral  Hemisphere  of  child  shortly  before  birth. 

The  two  brains  are  very  much  alike,  but  the  growth  forwards  of  the  frontal  lobes  even  at  this  early 
stage  of  development  of  the  human  brain  is  quite  well  seen.  S,  fissure  of  SyUius  ;  E,  fissure  of 
Rolando. 

called  the  grey  matter  of  the  cortex  to  be  packed  within  the  narrow 
compass  of  the  cranium.  In  the  lowest  vertebrates  the  surface  of 
the  brain  is  smooth,  but  going  higher  in  the  animal  scale  the  fissures 
make  their  appearance,  reaching  their  greatest  degree  of  complexity 
in  the  higher  apes  and  in  man. 

In  an  early  embryonic  stage  of  the  human  foetus  the  brain  is  also 
smooth,  but  as  development  progresses  the  sulci  appear,  until  the 
climax  is  reached  in  the  brain  of  the  adult. 

The  sulci,  which  make  their  appearance  first,  both  in  the  animal 
scale  and  in  the  development  of  the  human  foetus,  are  the  same. 
They  remain  in  the  adult  as  the  deepest  and  best  marked  sulci ;  they 
are  called  the  primary  fissures  or  sulci,  and  they  divide  the  brain  into 
lohes ;  the  remaining  sulci,  called  the  secondary  fissures  or  sulci, 
further  subdivide  each  lobe  into  convolutions  or  gyri. 

A  first  glance  at  an  adult  human  brain  reveals  what  appears  to 
be  a  hopeless  puzzle ;  this,  however,  is  reduced  to  order  when  one 

2   U 


674 


STRUCTURE  OF  THE  CEREBRUM 


[CH.  XLVI. 


studies  the  brain  in  different  stages  of  development,  or  compares  the 
brain  of  man  with  that  of  the  lower  animals.  The  monkey's  brain 
in  particular  has  given  the  key  to  the  puzzle,  because  there  the 
primary  fissures  are  not  obscured  by  the  complexity  and  contorted 
arrangement  of  secondary  fissures. 

The  preceding  figure,  comparing  the  brain  of  one  of  the  lower 
monkeys  with  that  of  the  child  shortly  before  birth,  shows  the  close 
family  likeness  in  the  two  cases. 

Fig.  484  gives  a  representation  of  the  brain  of  one  of  the  higher 
monkeys,  the  orang-outang,  where  there  is  an  intermediate  condition 
of  complexity  by  which  we  are  led  lastly  to  the  human  brain. 


Fig.  484.— Brain  of  the  Drang,  ^  natural  size,  showing  the  arrangement  of  the  convolutions.  Sy,  fissure 
of  Sylvius;  R,  fissure  of  Rolando;  EF,  external  parieto-occipital  fissure;  Olf,  olfactory  lobe;  Cb, 
cerebellum;  /t,  pons  Varolii;  il/0,  medulla  oblongata.  As  contrasted  with  the  human  brain,  the 
frontal  lobe  is  short  and  small  relatively,  the  lissure  of  Sylvius  is  oblique,  the  temporo-sphenoidal 
lobe  very  prominent,  and  the  external  parieto-occipital  fissure  very  well  marked.  Note  also  the 
bend  or  genu  in  the  Rolandic  fissure.     This  is  found  in  all  anthropoid  apes. 


Let  us  take  first  the  outer  surface  of  the  human  hemisphere ;  the 
primary  fissures  are — 

1.  The  fissure  of  Sylvius ;  this  divides  into  two  limbs,  the  posterior 
of  which  is  the  larger,  and  runs  backwards  and  upwards,  and  the 
anterior  limb,  which,  passing  into  the  substance  of  the  hemisphere, 
forms  the  Island  of  Rcil. 

2.  The  fissure  of  Rolando  runs  from  about  the  middle  of  the 
top  of  the  diagram  (fig.  485)  downwards  and  forwards. 

3.  The  external  parieto-occipital  fissure  (Par.  oc.  f.)  is  parallel  to  the 
fissure  of  Eolando  but  more  posterior  and  much  shorter ;  in  monkeys 
it  is  longer  (see  fig.  484). 


CH    XLVI.] 


THE    LOBES    OF   THE   BRAIN 


675 


the 


These  three  fissures  divide  the  brain  into  five  lohes : — 

1.  The  frontal  lobe  ;  in  front  of  the  fissure  of  Rolando. 

2.  'The  parietal  lobe ;   between   the   fissure  of  Eolando  and 
external  parieto-occipital  fissure. 

3.  Tlie  occipital  lobe ;  behind  the  external  parieto-occipital  fissure, 

4.  The  tempoi-o-sphenoidal  lobe ;  below  the  fissure  of  Sylvius. 

5.  The  Island  of  Reil. 

It  will  be  noticed  that  the  names  of  the  lobes  correspond  to  those 
the  bones  of  the  cranial  vault  which  cover  them.     There  is  no 

exact  correspondence  between  the  bones  and  the  lobes,  but  the  precise 
position  of  the  various  convolutions  in  relation  to  the  surface  of  the 
skull  is  a  matter  of  anatomy,  which,  in  these  days  of  brain -surgery, 
is  of  overwhelming  importance  to  the  surgeon.  The  position  of  a 
localised  disease  in  the  brain  can  be  determined  very  accurately,  as 
we  shall  see  later,  by  the  symptoms  exhibited  by  the  patient,  and  it 


f  B  O  N  T  A  I. 


of 


.'E/HPORAL      L0B£ 

Fio.  485. — Bight  cerebral  hemisphere,  outer  surface. 

would  be  obviously  inconvenient  to  the  patient  if  the  surgeon  was 
unable  to  trephine  over  the  exact  spot  under  which  the  diseased  con- 
volution lies,  but  had  to  make  a  number  of  exploratory  holes  to  find 
out  where  he  was. 

Each  lobe  is  divided  into  convolutions  by  secondary  fissures. 

1.  The  frontal  lobe  is  divided  by  the  central  frontal  ov  prefrontal 
sulcus,  which  runs  upwards  parallel  to  the  fissure  of  Eolando,  and  two 
transverse  frontal  sulci,  upper  and  lower,  into  four  convolutions ; 
namely,  the  ascendinfj  frontal  convolution  in  front  of  the  fissure  of 
Rolando,  and  three  transverse  frontal  convolutions,  upper,  middle,  and 
loiver,  which  run  outwards  and  forwards  from  it. 

2.  The  parietal  lobe  has  one  important  secondary  sulcus,  at  first 
running  parallel  to  the  fissure  of  Rolando  and  then  turning  back 
parallel  to  the  margin  of  the  brain.  It  is  called  the  intra-parietal 
sulcus.  The  lobe  is  thus  divided  into  the  ascending  parietal  convolu- 
tion behind  the  fissure  of  Rolando,  the  supra-marginal  convolution 
between   the   intra-parietal   sulcus,  and   the  fissure  of  Sylvius,  the 


676 


STRUCTURE  OF  THE  CEREBRUM 


[CH.  XLVI. 


angular  convolution  which  turns  round  the  end  of  the  Sylvian  fissure, 
and  the  superior  parietal  convolution,  or  parietal  lohule,  in  front  of  the 
external  parieto-occipital  fissure. 

3.  The  occipital  lobe  is  divided  into  upper,  middle,  and  lower 
occipital  convolutions  by  two  secondary  fissures  running  across  it. 

4.  The  temporal  or  temporo-sphenoidal  lobe  is  similarly 
divided  into  wj9/)er,  middle,  and  laiver  temporal  convolutions  by  two 
fissures  running  parallel  to  the  fissure  of  Sylvius ;  the  upper  of  these 
fissures  is  called  t\\Q  parallel  fissure. 

5.  The  Island  of  Reil  is  divided  into  convolutions  by  the  break- 
ing up  of  the  anterior  limb  of  the  Sylvian  fissure. 

Coming  now  to  the  mesial  surface  of  the  hemisphere  (fig.  486), 
its  subdivisions  are  made  evident  by  cutting  through  the  corpus 
callosum   which   unites    the   hemisphere    to   its  fellow.      The   sub- 


L  OBC 


Fig.  4S6.— Bight  cerebral  hemisphere,  mesial  surface. 

division  into  lobes  is  not  so  apparent  here  as  on  the  external 
surface  of  the  hemisphere,  so  we  may  pass  at  once  to  the  con- 
volutions into  which  it  is  broken  up  by  fissures. 

In  the  middle  the  corpus  callosum  is  seen  cut  across ;  above  it 
and  parallel  to  its  upper  border  is  a  fissure  called  the  calloso-marginal 
fissure,  which  turns  up  and  ends  on  the  surface  near  the  upper  end 
of  the  fissure  of  Eolando.  The  convolution  above  this  is  called  the 
TTiarginal  convolution,  and  the  one  below  it  the  callosal  convolution  or 
gyrus  fornicatus.  The  deep  fissure  below  the  corpus  callosum  running 
from  its  posterior  end  forwards  and  downwards  is  called  the  dentate 
fissure ;  this  forms  a  projection  seen  in  the  interior  of  the  lateral 
ventricle,  and  called  there  the  hippocampus  major;  the  hippocampal 
convolution,  together  with  the  gyrus  fornicatus  above  the  corpus 
callosum,  constitutes  the  limbic  lobe.  Below  the  dentate  fissure  is 
another  called  the  collateral  fissure,  above  which  is  the  uncinate 
convolution,  and  below  which  is  the  inferior  temporal  convolution 
which   we  have   previously   seen   on   the   external   surface    of    the 


CH.  XLVI.] 


THE   ARCHIPALLIUM 


677 


P.S 


Fio.  4S7.— Orbital  surface  of  frontal  lobe. 

M,  marginal  convolution. 

0,  olfactory  sulcus. 
O.S.,  orbital  sulcus. 

1,  island  of  Reil. 

iS.a.,  anterior  limb  of  Sylvian  fissure. 
S.p.,  posterior  limb  of  Sylvian  fissure. 
A.P.S.,  anterior  perforated  spot. 


hemisphere  (see  fig.  485).  In  the  occipital  region  the  internal  parieto- 
occipital fissitre,  which  is  a  continuation  of  the  external  parieto-occipital 
fissure,  passes  downwards  and  forwards  till  it  meets  the  calcarine 
fissure;  these  two  enclose  between  them  a  wedge-shaped  piece  of 
brain  called  the  cuneus  or  cuneate 
lobule;  the  square  piece  above  it  is 
called  the  precuneus  or  quadrilateral 
lobule. 

The  only  convolutions  now  left  are 
those  which  are  placed  on  the  surface 
of  the  frontal  lobe  that  rests  on  the 
orbital  plate  of  the  frontal  bone ;  they 
are  shown  in  fig.  453,  2  2'  2"  (p.  634), 
and  may  be  seen  diagrammatically  in 
fig.  487,  the  end  of  the  temporal  lobe 
being  cut  off  to  expose  the  convolutions 
of  the  central  lobe  or  Island  of  Eeil. 

Along  the  edge  is  the  continuation 
of  the  marginal  convolution  (m)  ;  next 
comes  the  olfactory  sulcus  (o)  in  which  the  olfactory  tract  and  bulb 
lie ;  then  the  triradiate  orbital  sulcus  (o.s.)  which  divides  the  rest  of 
this  surface  into  three  convolutions. 

The  Archipallium  and  the,  Neopcdlinm. — The  grey  matter  of  the  fore-brain  which 
makes  its  appearance  earliest  in  vertebrates  is  that  which  is  associated  with  the 
sense  of  smell  (rhinencephalon),  and  is  termed  the  archipallium ;  it  forms  the 
principal  part  of  the  primitive  cortex  and  even  in  some  mammals  (those  in  which 
the  olfactory  sense  is  highly  developed),  remains  large  and  important,  consisting  of 
a  large  hollow  olfactory  bulb  continuous  with  the  hippocampus,  and  separated  from 
the  rest  of  the  cortex  by  the  limbic  fissure.  In  the  higher  mammals  it  is  reduced 
to  small  proportions  in  comparison  with  the  rest  of  the  cortex,  which  is  termed 
on  account  of  its  later  appearance  in  historical  development,  the  neopallium.  In 
man  the  rhinencephalon  consists  of  the  olfactory  bulb  and  tract  (see  Chapter 
LI II.)  ;  posteriorly  the  grey  cortex  to  which  this  passes  is  doubled  in  to  form 
the  hippocampus  major  which  projects  into  the  lateral  ventricle  ;  this  is  continuous 
externally  around  the  dentate  sulcus  with  the  gyrus  hippocampi.  This  part  of  the 
cortex  is  easily  distinguishable  microscopically  from  the  neopallium,  but  without 
going  into  minute  details,  it  may  be  stated  in  general  terms  that  it  is  simpler  in 
structure  than  the  grey  matter  elsewhere ;  in  the  hippocampus,  for  instance,  the 
pyramids  are  reduced  to  a  single  layer  of  large  cells ;  in  the  lobus  pyriformis 
(anterior  part  of  the  gyrus  hippocampi)  the  cells  are  grouped  in  a  characteristic 
nest-like  way. 


CHAPTEE  XLVII 

FUNCTIONS    OF   THE   SPINAL   COED 

The  functions  of  the  spinal  cord  fall  into  two  categories  :  functions 
of  the  grey  matter,  which  consist  in  the  reflection  of  afferent  im- 
pulses, and  their  conversion  into  efferent  impulses  {reflex  action) ;  and 
functions  of  the  white  matter,  which  are  those  of  conduction. 

The  Cord  as  an  Organ  of  Conduction. 

We  have  studied  at  some  length  the  various  paths  in  the  white 
matter,  and  so  we  have  the  materials  at  hand  for  recapitulating  the 
main  facts  in  connection  with  the  physiological  aspect  of  the  problem. 

Complete  section  of  the  spinal  cord  in  animals,  and  diseases  or 
injuries  of  the  cord  or  spinal  canal  in  man,  which  practically  cut  the 
cord  in  two,  lead  to  certain  histological  changes  of  a  degenerative 
nature,  which  we  have  already  studied,  and  to  physiological  results, 
which  are  briefly — (1)  paralysis,  both  motor  and  sensory,  of  the  parts 
of  the  body  supplied  by  spinal  nerves  which  originate  below  the 
point  of  injury;  and  (2)  increased  reflex  irritability  of  the  same 
parts,  the  reason  for  which  we  shall  study  immediately. 

Heraisection  of  the  cord  leads  to  degenerative  changes  on  the 
same  side  of  the  cord,  and  loss  of  motion  and  sensation  on  the  same 
side  of  the  body  below  the  lesion  (see  p.  631). 

The  main  motor  path  in  the  cord  from  the  brain  is  the  pyramidal 
tract;  the  anatomy  of  this  tract  is  described  in  Chapters  XLI I.  to 
XLVL,  and  we  need  do  no  more  here  than  remind  the  reader  that  it 
originates  from  the  pyramidal  cells  of  the  cortex  of  the  opposite 
cerebral  hemisphere,  and  that  the  principal  decussation  occurs  at  the 
lower  part  of  the  bulb. 

The  sensory  tracts  are  more  complex,  on  account  of  the  numerous 
cell-stations  on  their  course.  The  path  for  tactile  and  muscular 
sense  impressions  is  up  the  posterior  columns  to  the  nucleus  gracilis 
and  nucleus  cuneatus ;  thence  by  the  internal  arcuate  fibres  and  fillet 
to  the  optic  thalamus  of  the  opposite  side,  and  thence  by  the  posterior 

678 


CII.  XLVII.]  CONDUCTING   PATHS   IN   SPINAL   CORD  679 

part  of  the  internal  capsule  to  the  Eolandic  area  of  the  hemisphere ; 
the  decussation  of  the  fillet  occurs  in  the  bulb. 

Schiff,  one  of  the  earliest  to  work  at  the  subject  of  conducting 
paths  in  the  cord,  arrived  at  the  conclusion  that  painful  impressions 
travelled  to  the  brain  by  the  grey  matter  of  the  cord.  This  conclu- 
sion was  regarded  as  paradoxical,  for  white  matter  is  conducting, 
grey  matter  is  central  or  reflecting.  But  the  conclusion  is  not  so 
paradoxical  as  it  appears  at  first  sight,  for  we  now  know  the  grey 
matter  is  made  up  of  nerve-units,  communicating  physiologically  by 
thoir  interlacement  of  dendrons ;  and  it  is  quite  easy  to  understand 
that  impulses  may  travel  up  grey  matter  through  a  vast  series  of 
cell-stations  or  positions  of  relay.  The  more  exact  methods  of 
modern  research  have  gone  far  to  justify  Schiff' s  conclusions,  and  it 
is  now  generally  held  that  the  impulses  due  to  painful  impressions, 
and  also  those  produced  by  heat  and  cold,  travel  up  to  the  optic 
thalamus  by  the  loopings  of  fibres  from  cell  to  cell  through  the  tract 
of  grey  matter,  which  is  continuous  from  cord  to  optic  .thalamus 
(fig.  482,  G.M.) ;  from  the  optic  thalamus  the  fibres  of  the  corona 
radiata  carry  on  the  impulse  to  the  cortex.  These  conclusions  are 
confirmed  by  recent  experiments  on  hemisection  (see  p.  631),  and  by 
the  phenomena  seen  in  certain  diseases.  One  of  the  most  instructive 
of  these  from  the  physiological  standpoint  is  known  as  locomotor 
ataxy.  This  disease  is  an  affection  of  the  afferent  neurons,  and  the 
most  marked  and  constant  change  in  the  spinal  cord  is  a  degenerative 
one  in  the  posterior  columns.  In  such  a  case  muscular  and  tactile 
sense  are  abolished,  particularly  in  the  lower  limbs,  but  painful  and 
thermal  sensations  are  felt.  On  the  other  hand,  in  the  disease  of  the 
grey  matter  of  the  cord  called  syringomyelia,  sensations  of  heat,  cold, 
and  pain  are  lost,  and  tactile  sensations  remain. 

Some  afferent  impulses  reach  the  cerebellum  viA  the  cells  of 
Clarke's  column  and  the  direct  or  dorsal  cerebellar  tract  to  the  resti- 
form  body  and  inferior  peduncle  of  the  cerebellum ;  it  terminates  in 
the  vermis  or  middle  lobe  of  the  cerebellum.  The  fibres  of  the  tract 
of  Gowers  originate  in  the  same  or  neighbouring  cells,  and  those  of 
its  fibres  which  enter  the  cerebellum  do  so  by  its  superior  peduncle, 
and  these  also  end  in  the  vermis. 

This  leaves  us  still  one  more  set  of  fibres  to  consider ;  these  are 
the  fibres  that  leave  the  cerebellum  and  travel  up  to  the  brain  and 
down  the  cord.  They,  like  most  of  the  other  tracts,  have  been  in- 
vestigated by  the  degeneration  method.  Their  exact  course  is,  how- 
ever, uncertain,  though  probably  they  ultimately  terminate  by 
arborising  round  the  multipolar  cells  of  the  cerebrum  and  of  the 
anterior  horn  of  the  cord  (see  fig.  482,  p.  671 ;  see  also  under 
Cerebellum,  Chapter  XLIX.). 


680  FUNCTIONS    OF   THE   SPINAL   CORD  [CH.  XLVII. 

Reflex  Action  of  the  Spinal  Cord. 

There  are  two  theories  of  a  speculative  nature  regarding  the 
relationship  of  reflex  and  voluntary  actions :  one  is,  that  all  actions 
are  in  essence  reflex,  and  that  the  so-called  voluntary  actions  are 
modified  reflexes,  in  which  the  afferent  impulse  to  act,  though  often 
obscure,  is  nevertheless,  by  seeking,  always  to  be  found.  Put  in 
popular  language,  this  theory  implies  that  we  have  really  no  such 
thing  as  a  will  of  our  own,  but  our  actions  are  simply  the  result  of 
external  circumstances. 

The  other  theory  is  the  exact  opposite — namely,  that  all  actions 
are  in  the  beginning  voluntary,  and  become  reflex  by  practice  in  the 
lifetime  of  the  individual,  or  the  lifetime  of  his  ancestors,  who  trans- 
mit this  character  to  their  descendants. 

This  is  not  the  place  to  discuss  a  philosophical  question  of  this 
kind,  and  still  less  the  debated  question  whether  acquired  characters 
are  transmissible  by  inheritance.  The  distinction  between  voluntary 
and  reflex  actions  is  a  useful  practical  one,  and  certainly  it  cannot 
be  doubted  that  many  practised  actions  become  reflex  in  the  lifetime 
of  every  one  of  us.  Take  walking,  skating,  or  bicycling  as  examples : 
at  first  these  acts  of  locomotion  are  those  in  which  the  brain  is  con- 
cerned ;  they  are  actions  demanding  the  concentration  of  the  atten- 
tion ;  but  later  on  the  action  is  largely  carried  out  by  the  spinal  cord, 
the  afferent  impulses  to  the  cord  from  the  lower  limbs  directing  the 
efferent  impulses  to  the  muscles  concerned. 

The  reflex  actions  of  the  spinal  cord  may  first  be  studied  in  a 
brainless  frog,  as  in  this  animal  the  spinal  cord  possesses  a  great 
power  of  controlling  very  complex  reflex  actions. 

Reflexes  in  a  Brainless  Frog. 

After  destruction  of  the  cerebrum  the  shock  of  the  operation 
renders  the  animal  for  a  short  time  motionless  and  irresponsive  to 
stimuli,  but  in  a  few  minutes  it  gradually  assumes  a  position  which 
differs  but  little  from  that  of  a  living  conscious  frog.  If  thrown  into 
water  it  will  swim ;  if  placed  on  a  slanting  board  it  will  crawl  up  it 
(Goltz) ;  if  stroked  on  the  flanks  it  will  croak  (Goltz) ;  if  it  is  laid  on 
its  back,  and  a  small  piece  of  blotting-paper  moistened  with  acid  be 
placed  on  the  skin,  it  will  generally  succeed  in  kicking  it  off;  if  a 
foot  is  pinched  it  will  draw  the  foot  away ;  if  left  perfectly  quiet  it 
remains  motionless.  Even  when  the  optic  thalami  are  destroyed 
also,  it  still  executes  complex  reflex  actions,  but  all  power  of  balancing 
and  all  spontaneity  are  lost. 

The  muscular  response  that  follows  an  excitation  of  the  surface 
is  purposive  and  constant,  the  path  along  which  the  impulse  is  pro- 
pagated being  definite. 


CH.  XLVII.]  REFLEX  ACTION  681 

Under  certain  abnormal  conditions,  however,  the  pro])agation  of 
the  impulse  in  the  cord  is  widespread,  the  normal  paths  being,  as  it 
were,  broken  down.  This  is  seen  in  the  convulsions  that  occur  on 
slight  excitation  in  animals  or  men  who  have  suffered  from  profuse 
haemorrhage,  or  in  the  disease  called  lockjaw  or  tetanus.  Such  a 
condition  is  easily  demonstrable  in  a  brainless  frog  under  the  influence 
of  strychnine:  after  the  injection  of  a  few  drops  of  a  1  per  cent, 
solution  under  the  skin,  cutaneous  excitation  no  longer  produces  co- 
ordinated responses,  but  paroxysms  of  convulsions,  in  which  the  frog 
assumes  a  characteristic  attitude,  with  arms  flexed  and  legs  extended. 

Spreading  of  reflexes. — If  one  lower  limb  is  excited,  it  is  that  limb 
which  responds :  if  the  excitation  is  a  strong  one  it  will  spread  to  the 
limb  of  the  opposite  side,  and  if  stronger  still  to  the  upper  limbs  also. 

Pfliiger  taught  that  the  direction  of  irradiation  within  the  spinal 
cord  was  always  upwards.  Sherrington  has  shown  that  this  is  not 
so,  and  has  discovered  many  descending  paths  (see  p.  631). 

Cumulation  of  reflexes. — This  is  well  illustrated  by  Turck's  method. 
If  a  number  of  beakers  of  water  are  prepared,  acidulated  with  1,  2, 
4,  etc.,  parts  of  sulphuric  acid  per  1000,  and  the  tips  of  the  frog's 
toes  are  immersed  in  the  weakest,  the  frog  at  first  takes  no  notice  of 
the  fact,  but  in  time  the  cumulation  or  summation  of  the  sensory 
impulses  causes  the  animal  to  withdraw  its  feet.  If  this  is  repeated 
with  the  stronger  liquids  in  succession,  the  time  that  intervenes  before 
the  muscles  respond  becomes  less  and  less.  This  method  also  serves 
to  test  reflex  irritability  when  the  frog  is  under  the  influence  of 
various  drugs. 

Inhibition  of  reflexes. — If,  instead  of  the  whole  brain,  the  cerebrum 
only  is  destroyed,  and  the  optic  lobes  are  left  intact,  response  to 
excitation  is  much  slower,  the  influence  of  the  remaining  part  of  the 
brain  inhibiting  the  reflex  action  of  the  cord.  Or  if  in  doincr  the 
experiment  with  acid  just  described  the  toes  of  the  other  foot  are 
being  simultaneously  pinched,  the  response  to  the  acid  is  delayed. 

This  influence  of  the  brain  on  the  cord  is  also  illustrated  in  man, 
by  the  fact  that  a  strong  effort  of  the  will  can  control  many  reflex 
actions.  It  is,  for  instance,  possible  to  subdue  the  tendency  to 
sneeze ;  if  one  accidentally  puts  one's  hand  in  a  flame,  the  natural 
reflex  is  to  withdraw  it :  yet  it  is  well  known  that  Cranmer,  when  being 
burnt  at  the  stake,  held  his  hand  in  the  flames  till  it  was  consumed. 

After  the  spinal  cord  has  been  divided  by  injury  or  disease  in  the 
thoracic  region,  the  brain  can  no  longer  exert  this  controlling  action  ; 
hence  the  part  of  the  cord  below  the  injury  having  it,  as  it  were,  all 
its  own  way,  has  its  reflex  irritability  increased.*     The  increase  of 

*  In  some  injuries  to  the  cord  produced  by  crushing,  there  is  a  loss  of  reflexes 
below  the  injury.  These,  however,  are  not  simple  transverse  lesions  ;  the  loss  of 
reflex  action  is  due  partly  to  shock,  and  partly  to  extensive  injury  of  the  grey  matter. 


682    ■  FUNCTIONS    OF   THE   SPINAL   CORD  [CH.  XLVII. 

reflex  irritability  is  also  seen  in  the  disease  called  lateral  sclerosis ; 
here  the  lateral  columns,  including  the  pyramidal  tract,  become 
degenerated,  and  so  the  path  from  the  brain  to  the  cells  of  the  cord 
is  in  great  measure  destroyed.  In  these  patients  the  increase  of 
reflex  irritability  may  become  a  very  distressing  symptom,  slight 
excitations,  like  a  movement  of  the  bed-clothes,  arousing  powerful 
convulsive  spasms  of  the  legs. 

Refiex  time. — In  the  frog,  deducting  the  time  taken  in  the  trans- 
mission of  impulses  along  nerves,  the  time  consumed  in  the  cord 
(reflex  time)  varies  from  O'OOS  to  0"015  second;  if  the  reflex  crosses 
to  the  other  side  it  is  one-third  longer.  It  is  lessened  by  heat,  and 
under  the  influence  of  a  strong  stimulus  (see  also  p.  205). 

Reflex  Action  in  Man. 

The  reflexes  obtainable  in  man  form  a  most  important  factor 
in  diagnosis  of  diseases  of  the  nervous  system ;  each  action  is  effected 
through  an  afferent  sensory  nerve,  a  system  of  nerve-cells  in  the 
cord  termed  the  reflex  centre,  and  an  efferent  motor  nerve ;  the 
whole  constitutes  what  is  called  the  refiex  arc.  The  absence  of 
certain  reflexes  may  determine  the  position  in  the  spinal  cord,  which 
is  the  seat  of  disease. 

Two  forms  of  reflex  action  must  be  distinguished : — 

1.  Superficial  reflexes.  These  are  true  reflex  actions,  and  are 
excited  by  stimulation  of  the  skin. 

2.  Deep  reflexes  or  tendon  reflexes.  This  is  a  most  undesirable 
name,  as  they  are  not  true  reflex  actions. 

Superficial  Reflexes. — These  are  obtained  by  a  gentle  stimula- 
tion, such  as  a  touch  on  the  skin ;  the  muscles  beneath  are  usually 
affected,  but  muscles  at  a  distance  may  be  affected  also.  Thus  a 
prick  near  the  knee  will  cause  a  reflex  flexion  of  the  hip. 

The  most  important  of  these  reflexes  are : 

a.  Plantar  refiex:  withdrawal  of  the  feet  when  the  soles  are 
tickled. 

b.  Gluteal  refiex :  a  contraction  in  the  gluteus  when  the  skin  over 
it  is  stimulated. 

c.  Cremasteric  refiex:  a  retraction  of  the  testicle  when  the  skin  on 
the  inner  side  of  the  thigh  is  stimulated. 

d.  Abdominal  refiex :  in  the  muscles  of  the  abdominal  wall  when 
the  skin  over  the  side  of  the  abdomen  is  stroked ;  the  upper  part  of 
this  reflex  is  a  very  definite  contraction  at  the  epigastrium,  and  has 
been  termed  the  epigastric  refiex. 

e.  A  series  of  similar  reflex  actions  may  be  obtained  in  the  muscles 
of  the  back,  the  highest  being  in  the  muscles  of  the  scapula. 

f.  In  the  region  of  the  cranial  nerves  the  most  important  reflexes 


CII.  XLVII.] 


TENDON  REFLEXES 


683 


are  those  of  the  eye — (i)  the  conjunctival  reflex,  the  movement  of  the 
eyelids  when  the  front  of  the  eyeball  is  touched ;  and  (ii)  the  con- 
traction of  the  pupil  on  exposure  of  the  eye  to  light,  and  its  dilatation 
on  stiiuulation  of  the  skin  of  the  neck. 

Tendon  Reflexes. — When  the  muscles  are  in  a  state  of  slight 
tension,  a  tap  on  their  tendons  will  cause  them  to  contract.  The  two 
so-called  tendon  reflexes  which 
are  generally  examined  are  the 
patella  tendon  reflex  or  knee- 
jerk,  and  the  foot  phenomenon 
or  ankle-clonus. 

The  knee-jerk. — The  quad- 
riceps muscle  is  slightly 
stretched  by  putting  one  knee 
over  the  other ;  a  slight  blow 
on  the  patella  tendon  causes  a 
movement  of  the  foot  for- 
wards, as  indicated  in  the 
dotted  Une  of  fig.  488.  The 
phenomenon  is  present  in 
health. 

Ankle-clonus. — This  is  eli- 
cited as  depicted  in  the  next 
figure :    the   hand    is   pressed 
against  the  sole  of  the  foot,  the  calf  muscles  are  thus  put  on  the 
stretch  and  they  contract,  and  if  the  pressure  is  kept  up  a  quick 

succession  or  clonic  series  of 
contractions  is  obtained.  This, 
however,  is  not  readily  obtained 
in  health. 

These  phenomena  are  not 
true  reflexes;  the  time  that  in- 
tervenes between  the  tap  and 
the  response  is  so  short  that 
they  must  be  due  to  direct 
stimulation  of  the  muscles  by 
the  sudden  stretching  of  their 
tendons. 

Nevertheless,  the  idea  that 
they  are  reflex  is  supported  by 
the  following  facts  : — 

1.  There  are  nerves  in  tendon. 

2.  The  phenomena  depend  for  their  occurrence  on  the  integrity 

of  the  reflex  arc.     Disease  or  injury  to  the  afferent  nerve,  efferent 

nerve,  or  spinal  grey  matter,  aboKshes   them.     Thus  they  cannot 


Fig.  4S8.— The  Knee-jerk.    (Gowers.) 


Fig.  489.— Ankle-clonus.    (Gowers.) 


684  FUNCTIONS    OF   THE    SPINAL   COED  [CH.  XLVII, 

be  obtained  in  locomotor  ataxy  (damage  to  the  posterior  nerve- 
roots),  or  in  infantile  paralysis  (damage  to  the  anterior  horns  of 
grey  matter). 

3.  They  are  excessive  in  those  conditions  which  increase  true 
reflex  irritability,  such  as  severance  of  brain  from  cord,  and  in 
lateral  sclerosis. 

These  two  sets  of  facts  can  be  reconciled  in  the  following  way 
(Gowers) : — 

The  tendon  reflexes  are  not  reflexes,  but  are  due  to  direct 
stimulation  of  the  muscle  itself.  In  order  that  the  muscle  may 
respond,  it  is  necessary  that  it  be  in  an  irritable  condition;  this 
is  accomplished  by  putting  it  slightly  on  the  stretch,  and  so  calling 
forth  the  condition  called  tonus,  and  thus  a  readiness  to  contract 
on  slight  provocation.  Muscular  tonus  depends  on  the  integrity 
of  the  reflex  arc.  The  sensory  stimulus  for  this  reflex  muscular 
tone  arises  in  the  muscle  itself,  and  also  in  the  condition  of  the 
antagonistic  muscles.  Hence  injury  to  any  part  of  the  reflex  arc, 
by  abolishing  the  healthy  tone  of  a  muscle,  deprives  it  of  that 
irritable  condition  necessary  for  the  production  of  these  so-called 
reflex  actions. 

The  exact  course  of  the  reflex  arc  concerned  in  the  knee-jerk  has  been  worked 
out  by  Sherrington  in  the  monkey.  The  nerve-fibres  are  mainly  those  which  pass 
(1)  to  and  from  the  crureus  by  the  anterior  crural  nerve,  and  (2)  to  and  from  the 
hamstrings  by  the  sciatic  nerve.  The  fibres  which  supply  the  crureus  arise  from  the 
spinal  nerve-roots  which  in  man  correspond  to  the  3rd  and  4th  lumbar ;  the  ham- 
string supply  is  from  the  5th  lumbar  and  1st  and  2nd  sacral  roots. 

Reciprocal  Action  of  Antagonistic  Muscles. — This  is  an 
interesting  branch  of  muscle  physiology,  which  we  owe  to  the 
researches  of  Sherrington.  In  brief,  he  shows  that  the  inhibition 
of  the  tonus  of  a  voluntary  muscle  may  be  brought  about  by 
excitation  of  its  antagonist. 

Movement  at  a  joint  in  any  direction  involves  the  shortening 
of  one  set  of  muscles  and  the  elongation  of  another  (antagonistic) 
set.  The  stretching  of  a  muscle  produced  by  the  contraction  of 
its  antagonist  may  excite  (mechanically)  the  sensorial  organs 
(probably  the  muscle-spindles,  see  p.  86)  in  the  muscle  that  is 
under  extension  ;  in  this  way  a  reflex  of  pure  muscular  initiation  may 
be  started.  Experiments  show  that  electrical  excitation  of  the 
central  end  of  an  exclusively  muscular  nerve  produces  inhibition 
of  the  tonus  of  its  antagonist.  For  instance,  the  central  end  of  the 
severed  hamstring  nerve  is  faradised.  This  nerve  contains  in  the 
cat  4510  nerve-flbres,  and  of  these  about  1810  are  sensory  in 
function  * ;  these  come  from  the  flexor  muscles  of  the  knee,  not 

*  The  number  of  sensory  nerve-fibres  is  determined  by  counting  the  healthy 
fibres  in  the  nerve  after  section  of  the  anterior  nerve-roots. 


CH.  XLVII.]  RECIPROCAL  ACTION   OF   MUSCLES  685 

from  the  skin.  The  effect  of  the  stimulation  of  the  nerve  on  the 
tonus  of  the  extensor  muscles  of  the  knee  is  seen  (a)  in  elongation 
of  those  muscles,  (b)  in  temporary  diminution  of  the  knee-jerk. 
The  experiment  may  be  varied  as  follows :  the  exposed  flexor 
muscles  detached  from  the  knee,  and  therefore  incapable  of 
mechanically  affecting  the  position  of  the  joint,  are  stretched  or 
kneaded.  This  produces  a  reflex  elongation  of  the  extensor  muscles 
of  the  knee  and  a  temporary  diminution  of  the  knee-jerk.  The 
effects  are  in  fact  the  same  as  those  produced  by  faradisation  of  the 
central  end  of  the  nerve  supplying  them.  It  may  therefore  be  that 
reciprocal  innervation,  which  is  a  common  form  of  co-ordination  of 
antagonistic  muscles,  is  secured  by  a  simple  reflex  mechanism,  an 
important  factor  in  its  execution  being  the  tendency  for  the  action  of 
a  muscle  to  produce  its  own  inhibition  reflexly  by  mechanical  stimu- 
lation of  the  sensory  apparatus  in  its  antagonist. 

On  p.  672  we  have  drawn  attention  to  the  three  "nervous  circles" 
by  which  an  afferent  impulse  may  affect  the  motor  discharge  from 
the  anterior  horn-cells  of  the  cord ;  there  is  the  short  path  by  the 
collaterals  of  the  entering  fibre  which  pass  directly  to  these  cells,  and 
there  are  the  two  longer  paths,  vid  the  cerebellum  and  cerebrum 
respectively.  In  the  execution  of  a  voluntary  action  all  three  circles 
are  in  activity  to  produce  the  co-ordination  and  due  contraction  and 
elongation  of  antagonistic  muscles  which  characterise  an  effective 
muscular  act.  Section, of  the  posterior  roots  produces  not  only  an 
inability  to  carry  out  reflex  actions,  but  also  leads  to  an  inability  to 
carry  out  effectively  those  more  complicated  reflex  actions  which  are 
called  voluntary,  and  in  which  the  brain  participates.  Locomotor 
ataxy,  or  tabes  dorsalis,  is  a  slowly  progressive  disease,  the  anatomical 
basis  of  which  is  a  degeneration  of  the  nerve-units  of  the  spinal 
ganglia.  It  is,  therefore,  analogous  to  a  physiological  experiment  in 
which  the  posterior  roots  are  divided,  and  although  fibres  may  remain 
which  still  allow  of  the  passage  of  nervous  impulses,  the  action  of  the 
three  circles  is  greatly  interfered  with;  the  spinal  reflex  arc  is  at 
fault ;  this  is  shown  by  the  loss  of  reflex  action,  the  disappearance  of 
the  tendon  reflexes,  and  the  want  of  tonus  in  antagonistic  muscles ; 
the  main  symptom  of  the  disease  is  want  of  muscular  co-ordination, 
and  this  is  produced  not  only  by  the  lesion  in  the  spinal  cord,  but  is 
accentuated  by  the  want  of  continuity  in  the  other  two  circles,  so 
that  the  brain  is  unable  to  effectively  control  the  motor  discharge 
from  the  anterior  cornual  cells. 

The  tendon  phenomena  are  important  to  the  pathologist;  they 
furnish  him  with  a  valuable  means  of  diagnosis  in  nervous  disorders. 
Their  usefulness  in  the  normal  state  is  very  well  put  by  Starling  in 
the  following  words: — "Every  joint  is  protected  by  inextensible 
ligaments   and   by  muscles.     A   sudden   strain    on  a  ligament  will 


686  FUNCTIONS    OF   THE   SPINAL   CORD  [CH.  XLVII. 

rupture  some  of  its  fibres,  and  perhaps  injure  the  joint  surfaces.  An 
ordinary  reflex  contraction  could  not  prevent  this,  for  the  mischief 
would  be  done  before  the  reaction  could  take  place.  But  the  central 
nervous  system  keeps  the  muscles  awake,  so  that  they  themselves 
may  react  to  any  sudden  increase  in  the  tension  by  an  equally 
sudden  contraction  which  saves  the  joint,  before  the  central  nervous 
system  has  had  time  to  become  aware  of  the  strain." 

The  Principle  of  the  Common  Path  (Sherrington). — When  an 
afferent  nerve  is  stimulated,  the  impulse  enters  that  complex  network 
of  conducting  paths,  which  is  called  the  central  nervous  system.  So 
numerous  are  the  potential  connections  in  this  labyrinth  that  the 
impulse  may,  under  such  abnormal  conditions  as  strychnine  j^oison- 
ing,  radiate  in  all  directions,  and  be  discharged  so  as  to  throw  all  the 
muscles  of  the  body  into  action.  But  under  normal  circumstances 
the  irradiation  is  limited  to  certain  lines,  which  increase  in  number 
with  the  strength  of  the  entering  impulse.  The  general  pattern  of 
the  nervous  web  remains  fairly  constant,  but  its  details  are  subject 
to  great  variations,  and  a  new  stimulus  may  act  like  a  tap  on  a 
kaleidoscope,  and  throw  a  new  pattern  into  being. 

At  the  commencement  of  every  reflex  arc  is  a  receptive  neuron 
extending  from  a  sensory  surface  to  the  brain  or  cord,  and  this  is  a 
private  path  exclusively  occupied  by  impulses  from  its  own  receptive 
points  on  the  surface  of  the  body.  These  impulses  pass  along 
certain  association  tracts  or  internuncial  paths  in  the  central  nervous 
system,  and  at  the  termination  of  the  arc  we  have  a  final  neuron 
which  acts  as  the  conducting  link  between  the  central  nervous 
system  and  the  muscle  or  gland  which  it  supplies.  This  final  neuron 
does  not  subserve  exclusively  impulses  generated  at  one  receptive 
source,  but  can  be  used  in  the  conduction  of  impulses  generated  at 
many  points  of  the  body's  surface.  The  arm  muscles,  for  instance, 
can  be  thrown  into  play  in  response  to  visual,  auditory,  tactile,  and 
other  sensations.  The  final  neuron  thus  differs  from  the  initial 
neuron  in  bemg  public,  not  private,  and  may  be  spoken  of  as  the 
final  common  path.  Of  course,  in  every  reflex  action  we  are  not 
really  concerned  with  individual  neurons,  but  with  thousands  of 
them  acting  in  harmony ;  still,  for  descriptive  purposes,  it  is  well  to 
speak  of  one  set  of  neurons  only  as  a  sample  of  the  rest.  An  ordinary 
motor  nerve  is  thus  a  collection  of  many  final  common  paths. 

Now  let  us  suppose  that  two  stimuli  are  acting  on  different  parts 
of  the  body's  surface,  each  of  which  would  produce  impulses  that 
ultimately  reach  the  same  final  common  path  together,  though  they 
may  throw  it  into  action  in  rather  a  different  way.  Under  such 
circumstances,  it  is  found  that  the  occupation  of  the  public  path  by 
one  impulse  prevents  it  being  simultaneously  used  by  the  other ; 
one  reflex  or  the  otiier  takes  place,  but  not  both  of  them. 


CH.  XLVII.]  THE  SCRATCH   REFLEX  687 

For  the  investigation  of" such  a  problem,  the  "scratch  reflex"  of 
the  dog  is  one  that  lends  itself  admirably.  This  can  best  be  studied 
in  the  "  spinal "  dog,  that  is  in  a  dog  in  which  cerebral  influence  is 
shut  off  by  division  of  the  spinal  cord  in  the  cervical  region.  If 
the  skin  over  a  large  saddle-shaped  area  covering  the  shoulders  and 
back  is  gently  irritated  on  one  side,  the  hind  leg  of  the  same  side 
executes  scratching  movements,  which  involve  flexor  muscles  princi- 
pally ;  the  rate  of  scratching  is  about  4  per  second,  and  each  move- 
ment is  presumably  a  short  tetanus.  The  best  "artificial  flea"  to 
employ  is  a  weak  faradic  current,  and  it  is  the  nerves  at  the  roots 
of  the  hair  follicles  which  are  specially  susceptible  when  eliciting 
the  reflex.  The  internuncial  paths  in  the  cord  are  in  the  lateral 
part  of  the  lateral  column,  and  division  of  that  region  of  the  cord 
abolishes  the  reflex. 

But  there  is  another  form  of  stimulation  which  also  throws 
the  same  flexor  muscles  into  action,  although  in  rather  a  different 
way,  and  that  is  stimulation  of  the  sole  of  the  foot.  The  foot 
and  leg  are  withdrawn,  and  the  action  is  a  steady  one,  and  not 
a  succession  of  rhythmic  discharges  as  in  scratching.  Both  reflexes, 
however,  end  in  the  same  final  common  path  ;  and  if  while  scratch- 
ing is  being  elicited  by  stimulation  of  the  shoulder,  the  foot  is  then 
stimulated  simultaneously,  scratching  immediately  ceases,  one  set 
of  impulses  has  displaced  the  other  from  the  final  common  path. 
If  then  one  ceases  to  stimulate  the  foot,  the  scratch  reflex  returns  if 
the  irritation  of  the  shoulder  is  kept  up.  This  is  well  illustrated  by 
the  accompanying  tracing  (fig.  490). 

But  there  is  also  another  way  in  which  the  inhibition  of  reflexes 
may  be  produced.  The  contraction  of  one  set  of  muscles  is  usually 
accompanied  by  relaxation  of  its  antagonists,  and  the  contraction  of 
the  flexors  in  the  scratch  reflex  may  therefore  be  inhibited  by  making 
the  antagonistic  muscles  (the  extensors)  contract.  Further,  the 
scratch  reflex  is  unilateral,  but  this  does  not  mean  that  the  muscles 
supplying  the  other  legs  are  inactive,  for  they  must  act  in  such  a 
way  as  to  support  the  ilog  on  three  legs,  while  it  scratches  with  the 
fourth  So  if  the  right  shoulder  is  stimulated,  the  right  hind  leg 
scratches ;  if  the  lefc  shoulder  is  stimulated,  the  left  hind  leg 
scratches ;  but  if  both  shoulders  are  stimulated  together,  only  one  or 
the  other  leg  scratches,  not  the  two  at  once ;  parts  of  the  final  paths 
are  common  to  both  sides,  and  there  is  a  struggle  for  their  occupa- 
tion. Some  instances  of  reinforcing  action  were  found  ;  for  example, 
if  two  points  of  the  skin  of  one  shoulder  are  stimulated  with  a  very 
feeble  current,  neither  stimulus  alone  may  be  sufficient  to  evoke  the 
scratch  reflex,  but  the  two  together  may  elicit  it;  in  order  to  attain 
this  result  the  two  points  of  skin  must  be  fairly  close  together. 

The  afferent  neurons  (private  paths)  of  the  body  are  about  five 


688 


FUNCTIONS   OF   THE   SPINAL   CORD 


[CH.  XLVII. 


times  more  numerous  than  the  efferent  (final  common  paths),  and  in 
the  struggle  for  the  occupation  of  these  public  paths  by  the  impulses 


AJUinnjuir 


TUTrinj"JTJ'iJTJiJTnj~J'jTnjTJxaJ^ 


Fig  490  —The  Scratch  reflex.  Tracing  of  the  flexors  of  left  hip  evoked  by  stimulation  of  the  skin 
'of  the  shoulder.  The  depression  m  the  signal  line  S  indicates  the  commencement  of  the  stimulation, 
and  its  rise  the  termination.  While  this  was  going  on,  the  left  foot  was  stimulate'i,  and  the 
depression  of  the  signal  line  L  indicates  the  duration  of  this  stimulation;  during  the  stimulation 
of  the  foot  and  for  a  short  time  afterwards,  the  scratch  reflex  is  inhibited,  but  the  scratch  reflex 
returns  so  n  afterwards.  The  time  is  registered  in  fifths  of  seconds.  To  be  read  from  left  to 
right.    (Sherrington.) 

that  enter  the  central  nervous  system  by  the  more  numerous 
private  paths,  three  factors  are  specially  concerned  :— (1)  Strength  of 
stimulus ;  the  stronger  the  stimulus  the  better  chance  the  resulting 


CH.  XLYII.] 


REACTION    TIME 


689 


impulse  has  of  getting  round  to  the  motor  organ.  (2)  Character  of 
impulse ;  sensations  of  painful  nature  and  sexual  feelings  win  the 
final  path  easily ;  it  is  a  matter  of  common  experience  that  such 
sensations  dominate  and  even  exclude  other  sensations ;  a  man  with 
bad  toothache  is  not  likely  to  take  much  notice  of  anyone  who  pulls 
his  coat  tails.  (3)  Fatigue ;  at  the  end  of  a  long  stimulation,  a 
stimulus  applied  to  a  fresh  reflex  arc  has  a  better  chance  of  capturing 
the  common  path. 

Reaction  Time  in  Man. — The  term  reaction  time  is  applied  to  the  time  occu- 

Eicd  in  the  centre  in  that  complex  response  to  a  pre-arranged  stimulus  in  which  the 
rain  as  mcU  as  the  cord  comes  into  play.  It  is  sometimes  called  the  penonal 
equation.  It  may  be  most  readily  measured  by  the  electrical  method,  and  the 
accompanying  diagram  (fig.  491)  will  illustrate  one  of  the  numerous  arrangements 
which  have  been  proposed  for  the  purpose. 

In  the  primary  circuit  two  keys  A  and  B  are  included,  and  a  chronograph  (1), 
arranged  to  write  on  a  revolvmg  cylinder  (fast  rate).     Another  chronograph   (2), 


~^^^~JL^SJXSlXI    '      D  "^^ 


Fig.  491. — Reaction  time. 

marking  1-lOOths  of  a  second,  is  placed  below  this.  The  experiment  is  performed 
by  two  persons  C  and  D.  The  key  A,  under  the  control  of  C,  is  opened.  The  key 
B,  under  the  control  of  2),  is  closed.  The  electrodes  E  are  applied  to  some  part  of 
Z>'s  body.  C  closes  A.  The  primary  circuit  is  made,  and  tJie  chronograph  moves. 
As  soon  as  L  feels  the  shoc-k  he  opens  B,  the  current  is  thus  broken,  and  the 
chronograph  lever  returns  to  rest.  Measure  the  time  between  the  two  movements 
of  the  chronograph  (1),  by  means  of  the  time  tracing  written  by  chronograph  (2). 
J'rom  this,  the  time  occupied  by  transmission  along  the  nerves  has  to  be  deducted, 


Fig.  492.— The  DUemma. 

and  the  remainder  is  the  rertc^jon /«m«.     It  usually  varies  from  0"15  to  0'2  second, 
but  is  increased  in  : — 

The  Dilemma. — The  primary  circuit  is  arranged  as   before.     Lead   the   wires 

2  X 


690  FUNCTIONS    OF   THE   SPINAL   CORD  [CII.  XLVII. 

from  the  secondary  coil  to  the  middle  screws  of  a  reverser  without  cross  wires.  To 
each  pair  of  end  screws,  attach  a  pair  of  electrodes  E  and  E',  applied  to  different 
parts  of  i)'s  body  (fig.  492).  Arrange  previously  that  D  is  to  open  B,  when  one 
part  is  stimulated,  but  not  the  other,  G  adjusting  the  reverser  unknown  to  D. 
Under  these  circumstances  the  reaction  time  is  longer. 

The  reaction  time  in  response  to  various  kinds  of  stimuli,  sound,  light,  pain, 
etc.,  varies  a  good  deal;  the  condition  of  the  subject  of  the  experiment  is  also  an 
important  factor.  This,  however,  is  really  a  practical  branch  of  psychology,  and 
has  recently  been  much  worked  at  by  students  of  that  science  (see  also  p.  205). 

Spinal  Visceral  Reflexes. 

The  spinal  grey  matter  contains  centres  which  regulate  the 
operation  of  many  involuntary  muscles.   Some  of  these  centres  are  : — 

The  cilio-spinal  centre  controls  the  dilatation  of  the  pupil ;  it  is 
situated  in  the  lower  cervical  region,  reaching  as  far  down  as  the 
origin  of  the  first  to  the  third  thoracic  nerve. 

Subsidiary  vaso-motor  centres.  The  principal  vaso-motor  centre 
is  situated  in  the  bulb,  and  subsidiary  centres  are  scattered  through 
the  spinal  grey  matter  (see  p.  298). 

The  same  is  probably  true  for  all  the  muscular  viscera,  but 
particular  study  has  been  directed  to  those  in  the  pelvis,  and  centres 
for  micturition,  defcecation,  erection,  and  parturition  are  contained  in 
the  lumbo-sacral  region  of  the  cord.  If  the  spinal  cord  is  cut  through 
above  the  situation  of  these  centres,  the  result  is  in  general  terms 
that  any  influence  of  the  higher  (voluntary)  centres  over  these 
actions  is  no  longer  possible.  The  actions  in  question  are  then 
simply  reflex  ones  occurring  unconsciously  at  certain  intervals,  and 
set  in  movement  by  the  peripheral  stimulus  (fulness  of  bladder,  or  of 
rectum,  etc.).  If  the  portion  of  the  cord  where  these  centres  are 
placed  is  entirely  destroyed,  the  result  is  paralysis  of  the  muscles 
concerned,  though  in  certain  cases,  even  after  such  a  severe  injury, 
some  amount  of  recovery  has  been  noticed,  which  must  be  attributed 
to  the  peripheral  gangha  being  able  to  play  the  part  of  reflex  centres. 

The  viscera  are  supplied  not  only  by  efferent  (motor  and  inhibi- 
tory) nerves,  but  are  connected  to  the  central  nervous  system  by  certain 
afferent  channels,  namely,  (1)  the  vagus ;  (2)  the  spinal  roots  from 
the  thoracic  and  first  two  lumbar  nerves ;  and  (3)  the  second,  third, 
and  fourth  sacral  roots.  Under  normal  circumstances,  the  afferent 
impulses  do  not  rise  into  consciousness,  and  even  on  injury  pain  is 
often  absent.  In  disease  where  they  are  stirred  up  to  excessive 
action,  as  in  various  forms  of  colic,  the  pain,  however,  may  be  intense, 
A  good  deal  of  pain  is  usually  "  referred "  to  skin  areas  which  are 
"  tender,"  and  Boss's  suggestion  that  the  pain  in  such  cases  is  referred 
to  parts  supplied  by  sensory  cutaneous  fibres  ending  in  the  same 
segments  of  the  cord  as  do  the  afferent  fibres  from  the  viscera  in 
(question,  has  been  placed  beyond  doubt  by  Head's  researches. 


CII.  XLVII.]  VISCERAL   REFLEXES  691 

Bladder  Reflexes. — The  spinal  rep,ion  which  ucts  as  the  micturition  centre  is 
that  witl\  wiiicli  the  first,  si'conci,  and  lliird  lumbar,  and  the  second,  third,  and  fourtii 
sacral  roots  are  coiniected.  Transvt-rse  section  of  the  cord  about  the  level  of  the 
sixth  lumbar  segment  (in  cat  and  ral)bit)  causes  immediate  escape  of  urine  from  the 
bladcK'r.  In  the  first  days  after  the  operation  the  bladder  can  only  be  emptied 
by  artificial  stimulation,  and  especially  easily  by  a  light  quick  pressure  on  the  dis- 
tended bladder  through  the  abdominal  walls.  It  is  not  the  pressure  that  squeezes 
out  the  urine,  it  merely  sets  going  a  reHex  in  which  contraction  of  the  detrusor  and 
relaxation  of  the  sphincter  constitute  the  final  stage.  Later  on  the  urine  is  voided 
*'  spontaneously  "  at  intervals,  and  this  is  usually  accomjianied  by  defaecation. 

Goltz  and  Ewald  found  in  dogs  in  which  the  lower  part  of  the  cord  had  been 
removed,  that  the  bladder  emptied  itself  spontaneously  from  time  to  time  months 
later,  but  usually  it  had  to  be  emptied  by  artificial  means.  In  man  retention  of 
urine  is  usually  a  permanent  symjjtora  after  a  total  transverse  lesion  of  the  cord. 

Defaecation. — A  regular  expulsion  of  faecal  matter  occurs  without  difficulty  in 
animals  after  transverse  section  of  the  cord  in  the  upper  lumbar  region.  The  tone  of 
the  external  sphincter  is  generally  restored  a  few  minutes  after  the  operation  ;  and 
in  Goltz  and  Ewald's  dogs  the  tonus  returned  even  when  the  lower  part  of  the  cord 
was  entirely  removed.  After  a  total  transverse  lesion  of  the  cord  in  man,  incontin- 
ence of  faeces  is  usually  described,  but  this  is  not  the  case  in  monkeys.  Gowcrs 
describes  two  states  in  disease  which  can  be  distinguished  by  introducing  the  finger 
into  the  rectum  :  (1)  if  the  centre  is  inactive  a  momentary  contraction  caused  by  local 
irritation  of  the  sphincter  is  followed  by  permanent  relaxation ;  (2)  relaxation  is 
followed  by  gentle  tonic  contraction  :  in  such  cases  the  reflex  arc  is  intact. 

Uterine  Reflexes. — Uterine  contractions  can  be  induced  by  rectal  injections, 
the  passage  of  a  foreign  body  into  the  uterus,  the  application  of  the  child  to  the 
breast,  and  by  other  means.  In  animals  faradisation  of  the  central  end  of  the  first 
sacral  nerve  produces  the  same  result.  The  contractions  of  the  uterus  are  therefore 
reflex.  Several  cases  have  been  recorded  in  which  parturition  has  occurred  normally 
in  women  who  have  had  the  cord  divided  across  completely  in  the  thoracic  region  ; 
it  is  thus  evident  the  centre  must  be  a  lumbar  one.  In  such  cases  the  uterine  con- 
tractions technically  called  "  pains  "  are  strong,  but  pain  is,  of  course,  absent.  The 
communication  with  the  lumbar  region  appears  to  be  principally  by  the  first  three 
lumbar  nerves.  Similar  observations  have  been  made  experimentally  in  animals,  and 
in  one  of  Goltz  and  Ewald's  dogs  in  which  the  cord  had  been  removed  from  the  lower 
thoracic  region  downwards,  pregnancy  followed  coitus,  and  terminated  with  success- 
ful parturition.  The  mammary  glands  enlarge  as  usual  in  such  cases,  even  when,  as 
in  Rouths  well-known  case  (where  the  cord  was  completely  destroyed  at  the  seventh 
thoracic  segment),  there  can  be  no  spinal  communication  between  the  pelvis  and  the 
breast  (see  also  p.  476). 

Erection. — This  can  be  excited  in  man  even  immediately  after  a  transverse 
lesion  of  the  cord  ;  so  also  can  ejaculation,  but  not  so  commonly.  The  evidence 
in  favour  of  such  acts  being  spinal  reflexes  is  very  complete  in  the  case  of  animals. 


CHAPTEE  XLVIII 

FUNCTIONS    OF   THE   CEKEBKUM 

The  brain  is  the  seat  of  those  psychical  or  mental  processes  which 
are  called  volition  and  feeling ;  volition  is  the  starting-point  in  motor 
activity ;  feeling  is  the  final  phase  of  sensory  impressions. 

In  the  days  of  the  ancients  very  curious  ideas  prevailed  as  to 
the  use  of  the  brain.  It  is  true  that  Alkmiion,  as  early  as  580  B.C., 
placed  the  seat  of  consciousness  in  the  brain,  but  this  view  was  of 
the  nature  of  a  guess,  and  did  not  meet  with  general  acceptance ; 
and  two  hundred  years  later  Aristotle  considered  that  the  principal 
use  of  the  brain  was  to  cool  the  hot  vapours  rising  from  the  heart. 
At  this  time  the  seat  of  mental  processes,  especially  those  of  an 
emotional  kind,  was  supposed  to  be  in  the  heart,  an  idea  now  con- 
fined to  poets ;  or  in  the  bowels,  as  those  acquainted  with  such  ancient 
writings  as  the  Bible  will  know. 

As  time  went  on,  truer  notions  regarding  the  brain  came  to  the 
fore :  thus  Herophilus  (300  B.C.)  was  aware  of  the  danger  attending 
injury  to  the  medulla;  Aretseus  and  Cassius  (a.d.  97)  knew  that 
injury  to  one  side  of  the  brain  produced  paralysis  of  the  opposite 
side  of  the  body;  and  Galen  (a.d.  131 — 203)  was  acquainted  with  the 
main  motor  and  sensory  tracts  in  brain  and  cord.  Between  that 
time  and  this,  most  of  the  celebrated  anatomists  have  contributed 
something  to  our  knowledge,  and  one  may  particularly  mention 
Vesalius,  Sylvius,  Kolando,  G-all,  Carus,  Willis,  and  Burdach ;  many 
of  these  names  are  familiar  because  certain  structures  in  the  brain 
have  been  christened  after  them.  The  erroneous  notion  that  the 
brain  was  not  excitable  by  stimuli  lasted  even  to  the  days  of 
Flourens  and  Magendie. 

Effects  of  Removal  of  the  Cerebrum. 

When  the  brain  is  removed  in  a  frog,  it  is  deprived  of  volition 
and  of  feeling ;  it  remains  perfectly  quiescent  unless  stimulated ;  it 
is  entirely  devoid  of  initiatory  power,  but,  as  we  have  already  seen, 
it  will  execute  reflex  actions,  many  of  which  are  of  a  complex  nature 
(see  p.  680  and  also  Chapter  L.). 


CH.  XLVIII.] 


REMOVAL   OF   CEREBRUM 


693 


A  pigeon  treated  in  the  same  way  remains  perfectly  motionless 
and  nnconscions  unless  it  is  disturbed  (see  fig.  493).  When  disturbed 
in  any  way  it  will  move ;  for  instance,  when  thrown  into  the  air  it 
will  tly ;  but  these  movements  are,  as  in  the  frog,  purely  reflex  in 
character. 

In  mammals  the  operation  of  extirpation  of  the  brain  is  attended 
with  such  severe  haemorrhage  that  the  animal  dies  very  rapidly,  but 


Fio.  493.— Pigeon  after  removal  of  the  hemispheres.    (Dalton.) 

in  some  few  cases  where  the  animals  have  been  kept  alive,  the 
phenomena  they  exhibit  are  precisely  similar  to  those  shown  by  a 
frog  or  pigeon.  In  the  case  of  the  dog,  portions  of  the  cortex  have 
been  removed  piecemeal  by  Goltz  of  Strasburg,  until  at  last  the  whole 
of  the  cortex  has  been  extirpated.  Such  animals  carry  out  co- 
ordinated movements  of  a  complicated  character  very  well,  but  they 
manifest  no  intelligence,  and  have  complete  lack  of  memory.  They 
are  in  a  condition  analogous  to  that  of  the  frogs  and  pigeons  just 
mentioned. 


Localisation  of  Cerebral  Functions. 

When  the  main  function  of  the  cerebrum  was  understood,  physio- 
logists were  divided  into  two  schools ;  those  who  thought  that  the 
brain  acted  as  a  whole,  and  those  who  thought  that  different  parts 
of  the  brain  had  different  functions  to  perform.  One  of  the  most 
prominent  of  the  first  school  was  Flourens ;  and  Goltz,  whose 
work  has  been  done  chiefly  on  dogs,  is  the  only  eminent  living 
survivor  of  this  set  of  physiologists.  Gradually,  as  better  methods 
have  come  in,  and  especially  since  monkeys  have  been  used  for 
experiment,  those  who  believe  in  the  localisation  of  function  have 
multiplied ;  and  now,  localisation  of  cerebral  function  is  more  than 


69-i  FUNCTIONS    OF   THE   CEREBRUM  [CH.  XLVIII. 

a  theory,  it  is  an  accepted  fact.  Perhaps  the  best  practical  evidence 
of  this  is  the  fact  that  experiments  on  monkeys  have  been  taken  as 
the  basis  for  surgical  operations  on  the  human  brain,  and  with 
perfect  success. 

The  earliest  to  work  in  the  direction  of  localisation  were  Hitzig 
and  Fritsch.  The  subject  was  then  taken  up  by  Terrier  and  Yeo, 
and  later  by  Schafer,  Horsley,  etc.,  in  this  country,  and  by  Munk 
and  many  others  in  Germany.  In  a  ddition  to  those  who  have  studied 
the  matter  from  the  experimental  standpoint,  must  also  be  reckoned 
the  pathologists,  who  in  the  post-mortem  room  have  examined  the 
brains  of  patients  dying  from  cerebral  disease,  and  carefully  com- 
pared the  position  of  the  disease  with  the  symptoms  exhibited  by  the 
patients  during  life.  In  this*  way  two  series  of  independent  investi- 
gations have  led  to  the  same  results ;  both  methods  are  essential,  as 
many  minor  details  discovered  by  the  one  method  correct  the 
erroneous  conclusions  which  are  apt  to  be  drawn  by  those  who  devote 
their  entire  attention  to  the  other. 

The  main  point  which  these  researches  have  brought  out  is  the 
overwhelming  importance  of  the  cortex ;  it  contains  the  highest 
cerebral  centres.  Before  Hitzig  began  his  work,  the  corpus  striatum 
was  regarded  as  the  great  motor  centre,  and  the  optic  thalamus  as 
the  chief  centre  of  sensation ;  very  little  note  was  taken  of  the 
cortex ;  it  appears  to  have  been  almost  regarded  as  a  kind  of  orna- 
mental finish  to  the  brain.  The  idea  that  the  basal  ganglia  were  so 
important  arose  from  the  examination  of  the  brains  of  people  who 
had  died  from,  or  at  least  suffered  from,  cerebral  haemorrhage. 

The  most  common  situation  for  cerebral  haemorrhage  is  either  in 
the  region  of  the  corpus  striatum  or  optic  thalamus ;  it  was  noticed 
that  motor  paralysis  was  the  most  marked  symptom  if  the  corpus 
striatum  was  injured,  and  sensory  paralysis  if  the  optic  thalamus 
was  injured.  The  paralysis,  however,  is  due,  not  to  injury  of  the 
basal  ganglia,  but  of  the  neighbouring  internal  capsule.  The  internal 
capsule  consists  in  front  of  the  motor  fibres  passing  down  from  the 
cortex  to  the  cord,  and  behind  of  the  sensory  fibres  passing  up  from 
cord  to  the  cortex  (see  p.  666).  Hence,  if  these  fibres  are  ploughed 
up  by  the  escaping  blood,  paralysis  naturally  is  the  result.  If  a 
haemorrhage  or  injury  is  so  limited  as  to  affect  the  basal  ganglia  only, 
and  not  the  fibres  that  pass  between  them,  the  resulting  paralysis  is 
slight  or  absent. 

The  question  will  next  be  asked :  What,  then,  is  the  function  of 
the  basal  ganglia  ?  They  are  what  we  may  term  subsidiary  centres : 
the  corpus  striatum,  principally  in  connection  with  movement,  and 
the  optic  thalamus,  in  connection  with  sensation,  and  especially  with 
the  sense  of  vision  as  its  name  indicates. 

A  subsidiary  centre  may  be  compared  to  a  subordinate  ofi&cial  in 


CU.  XLVIII.]       STIMULATION    AND    EXTIRPATION   OF   CORTEX  695 

an  army.  The  principal  centre  may  be  compared  to  the  commander- 
in-chief.  This  highest  officer  gives  a  general  order  for  the  movement 
of  a  body  of  troops  in  a  certain  direction ;  we  may  compare  this  to 
the  principal  motor-centre  of  the  cortex  sending  out  an  impulse  for 
a  certain  movement  in  a  limb.  But  the  general  does  not  give  the 
order  himself  to  each  individual  soldier,  any  more  than  the  cerebral 
cortex  does  to  each  individual  muscle ;  but  the  order  is  first  given 
to  subordinate  officers,  who  arrange  exactly  how  the  movement  shall 
be  executed,  and  their  orders  are  in  the  end  distributed  to  the 
individual  men,  who  must  move  in  harmony  with  their  fellows  with 
regard  to  both  time  and  space.  So  the  subsidiary  nerve-centres  or 
positions  of  relay  enable  the  impulse  to  be  widely  distributed  by 
collaterals  to  numerous  muscles  which  contract  in  a  similar  orderly, 
harmonious,  and  co-ordinate  manner. 

There  is  just  the  same  sort  of  thing  in  the  reverse  direction  in 
the  matter  of  sensory  impulses.  Just  as  a  private  in  the  army, 
when  he  wishes  to  communicate  with  the  general,  does  so  through 
one  or  several  subordinate  officers,  so  the  sensory  impulse  passes 
through  many  cell-stations  or  subsidiary  centres  on  the  way  to  the 
highest  centre,  where  the  mental  process  called  sensation,  that  is, 
the  appreciation  of  the  impulse,  takes  place. 

There  are  two  great  experimental  methods  used  for  determining 
the  function  of  any  part  of  the  cerebrum.  The  first  is  stimulation ; 
the  second  is  extirpation.  These  words  almost  explain  themselves ; 
in  stimulation  a  weak  interrupted  induction  current  is  applied  by 
means  of  electrodes  to  the  convolution  under  investigation,  and  the 
resulting  movement  of  the  muscles  of  the  body,  if  any  occurs,  is 
noticed.  In  extirpation  the  piece  of  brain  is  removed,  and  the  result- 
ing paralysis,  if  any,  is  observed. 

It  is  essential,  when  the  experiment  of  stimulating  the  cortex  of  the  brain  is 
being  performed,  that  the  animal  should  be  anaesthetised  and  absolutely  uncon- 
scious, otherwise  voluntary  or  reflex  actions  will  occur  which  mask  those  produced 
by  stimulation.  If,  however,  the  animal  is  too  deeply  under  the  influence  of  a 
narcotic  the  brain  is  inexcitable. 

On  p.  378  Ehrhch's  experiments  with  methylene  blue  are  described  In  an 
anaesthetised  animal  the  brain  is  inactive,  and  if  the  pigment  is  injected  into  the 
blood,  the  brain  is  seen  to  be  of  a  blue  colour.  If,  however,  a  spot  of  the  cerebral 
surface  is  stimulated,  that  part  of  the  brain  is  thrown  into  action,  oxygen  is  used 
up,  and  the  methylene  blue  is  reduced,  and  in  consequence  that  area  of  the  brain 
loses  its  blue  tint.  If  the  animal  is  so  deeply  narcotised  that  the  brain  does  not 
discharge  an  impulse,  the  part  stimulated  remains  blue. 

By  such  means  the  cortex  has  been  mapped  out  into  what  we 
may  provisionally  term  motor  areas  and  sensory  areas. 

Motor  areas. — These  areas  are  also  termed  sensori-motor  or 
kincesthetic,  for  reasons  which  will  be  explained  more  fully  later. 
The  name  Rolandic  area  which  they  have  also  received  is  derived 
from  their  anatomical  position. 


696 


FUNCTIONS    OF   THE   CEREBRUM 


[CH.  XLVIIl. 


Stimulation  of  them  produces  movement  of  some  part  of  the 
opposite  side  of  the  body;  excitation  of  the  same  spot  is  always 
followed  by  the  same  movement  in  the  same  animal.  In  different 
animals  excitation  of  anatomically  corresponding  spots  produces 
similar  or  corresponding  results.  It  is  this  which  has  enabled  one 
to  apply  the  results  of  stimulating  areas  of  the  monkey's  brain  to 
the  elucidation  of  the  function  of  the  similar  brain  of  man. 

If  the  stimulation  used  is  too  powerful  the  result  is  a  movement 
of  other  parts,  and  a  considerable  portion  of  the  body  may  be  thrown 
into  convulsive  movements  similar  to  those  seen  in  epilepsy. 

Extirpation,  or  removal,  of  these  areas  produces  paralysis  of  the 
same  muscles  which  are  thrown  into  action  by  stimulation. 

The  degeneration  tracts  after  destruction  of  the  Rolandic  area 
are  shown  in  fig.  494.     The  shaded  area  in  each  case  represents  the 


INTERNAL     CAPSULE 

^Fillet 


MID.  BRAIN 


Fig.  494. — Degeneration  after  destruction  of  the  Rolandic  area  of  the  right  hemisphere. 
(After  Gowers.) 

injured  or  degenerated  material ;  a  in  the  cortex,  B  in  the  anterior 
part  of  the  posterior  limb  of  the  internal  capsule,  C  in  the  middle 
of  the  crusta  of  crus  and  mid-brain,  D  in  the  pyramidal  bundles 
of  the  pons,  E  in  the  pyramid  of  the  bulb,  and  F  in  the  crossed 
and  direct  pyramidal  tracts  of  the  cord. 

Sensory  areas. — Stimulation  of  these  produces  no  direct  move- 
ments, but  doubtless  sets  up  a  sensation  called  a  subjective  sensation ; 
that  is,  one  produced  in  the  animal's  own  brain,  and  this  indirectly 
leads  to  movements  which  are  reflex ;  thus  on  stimulating  the 
auditory  area  there  is  a  pricking  up  of  the  ears ;  on  stimulating  the 
visioal  area  there  is  a  turning  of  the  head  and  eyes  in  the  direction 


CH.  XLVIII.]  JACKSONIAN    EPILEPSY  697 

of  the  supposed  visual  impulse.  That  such  movements  are  reflex 
and  not  direct  is  shown  by  the  long  period  of  delay  intervening 
between  the  stimulation  and  the  movement. 

Extirpation  of  a  sensory  area  leads  to  loss  of  the  sense  in  question. 

The  rougher  experiments  performed  by  nature  in  the  shape  of 
diseases  of  the  brain  produce  corresponding  results. 

Some  diseases  are  of  the  nature  of  extirpation. 

An  instance  of  this  is  cerebral  haemorrhage.  If  the  haemorrhage 
is  in  the  region  of  the  internal  capsule,  it  cuts  through  fibres  to  the 
muscles  of  the  whole  of  the  opposite  side  of  the  body,  as  they  are 
all  collected  together  in  a  narrow  compass,  and  the  condition 
obtained  is  called  hemiplegia.  The  varieties  of  hemiplegia  are 
numerous,  according  as  motor  or  sensory  fibres  are  most  affected, 
and  in  one  variety  of  hemiplegia,  called  crossed  hemiplegia,  the  face 
is  paralysed  on  one  side  of  the  body,  the  limbs  on  the  other ;  this 
is  due  to  injury  of  the  tracts  in  the  bulb,  above  the  crossing  of  the 
pyramids. 

If  now  the  haemorrhage  occurs  on  the  surface  of  the  brain,  a  much 
more  limited  paralysis,  called  monoplegia,  is  the  result ;  if  the  arm  area 
is  affected,  there  will  be  paralysis  of  the  opposite  arm ;  if  the  leg 
area,  of  the  opposite  leg ;  if  a  sensory  area,  there  will  be  loss  of  the 
corresponding  sense. 

Some  diseases,  on  the  other  hand,  act  as  the  induction  currents 
do  in  artificial  stimulation ;  they  irritate  the  surface  of  the  brain ; 
such  a  disease  is  a  tumour  growing  in  the  membranes  of  the  brain ; 
if  the  tumour  irritates  a  piece  of  the  motor  area,  there  will  be 
involuntary  movements  in  the  corresponding  region  of  the  body; 
these  movements  may  culminate  in  the  production  of  epileptiform 
convulsions  commencing  in  the  arm,  leg,  or  other  part  of  the  body 
which  corresponds  to  the  brain  area  irritated.  It  is  these  cases  of 
"  Jacksonian  Epilepsy  "  which  have  given  the  best  results  in  surgery ; 
the  movement  produced  is  an  indication  of  the  area  of  the  brain 
which  is  being  irritated,  and  the  surgeon  after  trephining  is  able  to 
remove  the  source  of  the  mischief.  If  the  area  of  the  brain  which 
is  irritated  is  a  sensory  area,  the  result  produced  is  a  subjective 
sensation,  similar  to  what  we  imagine  is  produced  in  animals  with 
an  electric  current. 

We  may  now  proceed  from  these  general  considerations  to 
particular  points,  and  give  maps  of  the  brain  to  show  the  areas  we 
have  been  speaking  of. 

Figs.  495  and  496  are  views  of  the  dog's  brain.  It  is  convenient 
to  take  this  first  because  it  was  the  starting-point  of  the  experimental 
work  on  the  subject  in  the  hands  of  Hitzig  and  Fritsch.  If  the  text 
beneath  the  figure  is  consulted,  it  will  be  seen  that  the  motor  areas, 
mapped  out   by  the   method    of   stimulation,  are   situated   in   the 


698 


FUNCTIONS    OF   THE   CEREBRUM 


[CH.  XLVIII. 


neighbourhood  of  the  crucial  sulcus,  which  corresponds  to  the  fissure 
of  Rolando  in  man. 


FlQ.  495. 


Figs.  495  and  496.— Brain  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure,  sometimes  termed 
crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man.  .S,  fissure  of  Sylvius,  around  which 
the  four  longitudinal  convolutions  are  concentrically  arranged ;  1,  flexion  of  head  on  the  neck,  in 
the  median  line  ;  '2,  flexion  of  head  on  the  neck,  with  rotation  towards  the  side  of  the  stimulus  ;  3, 
4,  flexion  and  extension  of  anterior  limb;  5,  6,  flexion  and  extension  of  posterior  limb;  7,  S,  9, 
contraction  of  orbicularis  oculi,  and  the  facial  muscles  in  general.  The  unshaded  part  is  that 
exposed  by  opening  the  skull.    (Dalton.) 


Coming  next  to  the  brain  of  the  monkey,  figure  497  is  repro- 
duced  from   Ferrier's   book.     He   marked  out  the   surface  into  a 


CH.  XLVIII.] 


LOCALISATION   IN   MONKEY'S   BRAIN 


Fig.  407. 


number  of  circles,  stimulation  of  each  of  which  produced  movements 
of  various  sets  of  muscles,  face,  arm,  and  leg  from  below  upwards ; 
extirpation  of  these  same  areas  produced  the  corresponding  paralysis. 
It  will  be  further  noticed 
that    these   areas  are  all 
grouped  around  the  tissure 
of   Eolando,    particularly 
in  the   ascending  frontal 
and  ascending  parietal  con- 
volutions ;  hence  the  term 
Rolandic    area    which    is 
often     applied     to     this 
region  of  the  brain. 

Most  of  our  know- 
ledge concerning  the  locali- 
sation of  the  sensori-motor 
area  in  the  human  brain 
has  been  deduced  from  ex- 
periments on  the  lower  monkeys.  Valuable  as  such  knowledge  is, 
infinitely  more  useful  knowledge,  from  the  standpoint  of  the  human 
brain,  would  be  obtained  by  examining  the  brains  of  those 
monkeys  nearest  to  man,  which  are  known  as  the  anthropoid  apes. 
The  difficulty  and  expense  of  obtaining  such  animals  has  hitherto 
deterred  investigators  from  performing  such  experiments.  Horsley 
and  Beevor  examined  the  brain  of  an  orang-outang  some  years 
ago,  and  now  Sherrington  and  Griinbaum  have  made  a  number 
of  experiments ;  several  specimens  of  two  species  of  chimpanzee, 
the  orang  and  the  gorilla,  have  been  examined.  Their  conclusions 
are  of  great  importance.  The  figure  on  p.  700  (fig.  498)  of  the 
chimpanzee's  brain  shows  wdiat  has  been  found ;  the  orang  and  the 
gorilla  gave  practically  the  same  results,  and  no  doubt  the  human 
brain  would  give  identical  results  also  if  it  could  be  examined. 

The  method  used  is  to  expose  the  brain  in  an  anaesthetised  animal, 
and  thoroughly  explore  it  with  a  weak  faradic  current,  one  electrode 
being  placed  on  the  brain,  and  the  other  attached  to  an  indifferent 
part  of  the  animal's  body.  This  allows  of  finer  localisation  than  is 
possible  with  the  ordinary  double-point  electrodes. 

The  so-called  "motor"  area  includes  continuously  the  whole 
length  of  the  ascending  frontal,  or  as  it  is  sometimes  called,  the  pre- 
central  convolution.  It  never  extends  behind  the  central  sulcus,  or, 
as  it  is  sometimes  called,  the  fissure  of  Eolando.  On  the  mesial 
surface  it  extends  but  a  short  distance,  and  never  as  far  as  the 
calloso-marginal  fissure.  The  motor  area  extends  also  into  the  depth 
of  the  Eolandic  and  other  fissures;  the  part  of  the  excitable  area 
thus  hidden  equals  or  may  even  exceed  that  on  the  free  surface  of 


700 


FUNCTIONS    OF   THE   CEREBRUM 


[CH.  XLVIIl. 


the  hemisphere.  The  arrangement  of  the  various  regions  of  the 
musculature  follow  the  segmental  sequence  of  the  cranio-spinal  series 
to  a  remarkable  extent ;  in  fact,  the  excitable  area  may  be  compared 


Toes 
Ankle  "■, 


Anus  &<,va.^ina. 
,:'    SxilctLS 
,■■'     .  centralis 


Abdomen 


Wri 

Finders 
tr  thum  ' 


Vocsil 
cards 


Sulcus   ceatraMs 
Mastication 


Pig.  498. — Brain  of  Cliimpanzee.  Left  hemisphere  \iewed  from  side  and  above  so  as  to  obtain  the 
configuration  of  the  Rolandic  area.  The  figure  involves  some  foreshortening  about  both  ends  of 
the  sulcus  centralis  or  fissure  of  Rolando.  The  extent  of  the  so-called  motor  area  on  the  free 
surface  of  the  hemisjihere  is  indicated  bj-  black  stippling  which  extends  back  to  the  central  sulcus. 
Much  of  the  "  mot«r  "  area  is  hidden  in  sulci  ;  for  instance,  it  extends  into  both  the  central  and 
precentral  sulci.  The  names  printed  in  capitals  on  the  stippled  area  indicate  the  main  subdivisions 
of  the  "motor"  area;  the  names  printed  small  outside  the  brain  indicate  by  their  pointing  lines 
some  of  the  chief  subdivisions  of  the  main  areas.  But  there  is  much  overlapping  of  the  areas  which 
it  is  not  possible  to  indicate  in  a  diagram  of  this  kind.  The  shaded  regions  marked  "eyes"  in  the 
frontal  and  occipital  regions  indicate  the  areas  which  under  faradisation  jield  coi\iugate  movements 
of  the  eyeballs.  S.F.=  superior  frontal  sulcus.  s.Pr.=superior  precentral  sulcus.  I.Pr.  =iuferior 
precentral  sulcus.    (After  Sherrington  and  Griinbaum.) 


to  the  spinal  cord  upside  down.     The  accompanying  figure  indicates 
this  better  than  any  verbal  description. 

The  sulci  in  the  region  of  the  cortex  dealt  with  cannot  be  con- 
sidered to  act  as  physiological  boundaries,  and  the  variations  in  the 
sulci  in  these  higher  brains  are  so  great  that  they  prove  to  be  pre- 
carious or  even  fallacious  landmarks  to  the  details  of  the  true 
topography  of  the  cortex. 


CH.  XLVIII.] 


LOCALISATION    IN   MONKEYS   BHAIN 


701 


It  cannot  fail  to  strike  even  a  superficial  observer  how  large 
the  cortical  area  is  that  deals  with  movements  of  the  head  and  arm 
regions  when  compared  with  that  of  the  lower  limb,  and  still  more 
with  that  of  the  trunk.  The  trunk  itself  has  a  larger  mass  of 
muscular  tissue,  but  it  is  in  the  head  region  (which  includes  the 
complex  movements  of  the  tongue  and  such  structures  as  the  vocal 
cords)  and  in  the  arm  and  hand  that  the  movements  are  most  varied 
and  most  delicate.  No  doubt  this  is  the  explanation  of  the  greater 
size  of  their  cortical  representation. 

The  experiments  of  extirpation  confirm  those  of  stimulation  ;  for 
example,  extirpation  of  the  hand  area  is  followed  by  severe  paralysis 
of  the  hand,  but  in  a  few  weeks  use  and  power  return  in  a  remarkable 


Pig.  499. — Diagram  to  show  the  relative  positions  of  the  several  motor  tracts  in  their  course  from  the 
cortex  to  the  crus.  The  section  through  the  convolutions  is  vertical ;  that  through  the  internal 
capsule,  I,  C,  horizontal ;  that  through  the  crus  also  horizontal.  C.N.,  caudate  nucleus;  O.TH., 
optic  thalamus  ;  L2  and  L3,  middle  and  outer  part  of  lenticular  nucleus ;  /,  a,  I,  face,  arm,  and  leg 
fibres.  The  words  in  italics  indicate  cori'esponding  cortical  centres ;  F.S.,  fissure  of  Sylvius. 
(Gowers.) 

degree.  On  the  other  hand,  ablations  of  even  larger  portions  of  the 
parts  behind  the  Rolandic  fissure  do  not  give  rise  to  even  transient 
paralysis,  and  do  not  lead  to  degeneration  in  the  pyramidal  system 
of  fibres. 

Sherrington  and  Griinbaum  also  found  that  the  part  of  the  frontal 
region  which  yields  conjugate  movements  of  the  eyeballs  is  separated 
from  the  Rolandic  area  by  a  field  of  "  inexcitable  "  cortex.  As  to  the 
occipital  lobe,  only  from  its  extreme  posterior  apex  did  faradisation 
yield  any  movement  of  the  eyes,  and  then  not  easily.  This  becomes 
intelligible  on  histological  examination ;  the  large  cells  in  the 
deeper  layer  of  the  grey  matter  are  so  scattered  that  they  are  called 
"  solitary  cells " ;  their  axons  pass  to  the  oculo-motor  nuclei,  and  so 


702 


FUNCTIONS    OF   THE    CEREBRUM 


[CH.  XLVIII. 


the  pathway  is  provided  for  the  movements  of  the  eyes  in  accordance 
with  the  necessities  of  vision. 

The  marginal  convolution  on  the  mesial  surface  of  the  hemisphere  was  first 
investigated  by  Schafer  and  Horsley,  in  the  lower  monkeys.  They  found  in  these 
animals  that  it  contained  a  considerable  extension  of  the  "  motor  "  area,  including 
the  cortical  centres  for  the  trunk  muscles.  This,  at  any  rate,  is  not  the  case  for  the 
higher  apes,  and  therefore  probably  is  not  true  for  man. 

In  experiments  on  unilateral  extirpation  in  animals,  and  in 
destructive  lesions  of  one  side  of  the  brain  in  man,  it  is  the  muscles 
which  act  normally  unilaterally  which  are  most  paralysed.  The 
muscles  which  normally  move  bilaterally,  e.g.,  the  chest  muscles  in 
breathing,  the  trunk  muscles  in  maintaining  an  erect  position,  are 
comparatively  little  affected ;  the  spinal  centres  of  such  muscles  are  no 
doubt  connected  by  commissural  fibres,  and  therefore  can  be  affected 
from  both  sides  of  the  brain. 

The  diagram.  Fig.  499,  is  an  instructive  one  indicating  the  relative 
positions  of  the  principal  motor  fibres  in  their  course  from  cortex 
to  the  crus.     The  letterpress  beneath  it  should  be  carefully  consulted. 

The  Speech  Centre. — Fig.  500  is  an  outline  map  of  the  left 
cerebral  hemisphere  in  man.     The  speech  centre  is  surrounded  by 


VISUO-PSYCHIC    SPHERE 
VISUO-SENSORY   SPHERE 


FiQ.  500. — Left  cerebral  hemlspliere,  outer  surface.    The  lobes  and  the  principal  sulci  are  indicated  by 
their  initial  letters;  A.E.M.,  anterior  centre  for  eye  movements  ;  B.C.,  Broca's  convolution. 


a  dotted  circle.  There  are  other  centres  concerned  in  speech,  as 
we  shall  see  when  considering  the  question  of  association  fibres ; 
but  this  is  the  centre  for  the  muscular  actions  concerned  in  speech. 
The  discovery  of  this  centre  was  the  earliest  feat  in  the  direction 
of  cerebral  localisation.  It  was  discovered  by  a  French  physician 
named  Broca ;  he  noticed  that  patients  who  died  after  haemorrhage 
in  the  brain,  but  who  previous  to  death  exhibited  a  curious  disorder 
of  speech  called  aphasia,  were  found,  after  death,  to  have  the  seat  of 
the  haemorrhage  in  this  convolution.  The  convolution  is  generally 
called  Broca's  convolution.     Experiments  on  animals  are  useless  in 


CH.  XLVIII.]  SENSOKY   AREAS    OF     BRAIN  703 

discovering  the  centre  for  speech.  Sherrington  and  Griinbaum  found 
in  the  higher  apes  that  faradisation  of  the  Broca  area  does  not  evoke 
vocalisation. 

The  most  curious  fact  about  the  speech-centre  is  that  it  is  uni- 
lateral ;  it  is  situated  only  on  the  left  side  of  the  brain,  except  in 
left-handed  people,  where  it  is  on  the  right.  We  are  thus  left- 
brained  so  far  as  the  finer  movements  of  the  hand-muscles  are  con- 
cerned, as  in  writing,  and  we  are  also  loft-brained  in  regard  to  speech, 
an  action  intimately  associated  with  writing. 

The  visual  area  is  in  the  occipital  lobe.  Eemoval  of  one  occipi- 
tal lobe  in  a  monkey,  or  disease  of  that  lobe  in  man,  produces  blind- 
ness of  the  same  side  of  each  retina,  or  inability  to  see  the  opposite 
half  of  the  visual  field.  This  is  called  hemianopsia;  the  head  and 
eyes  are  turned  to  one  side  {conjugate  deviation  to  the  side  of  the 
injury).  Such  an  operation  does  not  destroy  vision  in  the  central 
portion  {macula  lutea)  of  either  retina,  because  each  macula  sends 
impulses  to  both  sides  of  the  brain.  Stimulation  of  one  visual  area 
leads  to  a  subjective  sensation  apparently  coming  from  the  same 
halves  of  both  retinae,  and  also  excites  the  solitary  cells  (see  p.  701); 
this  produces  conjvgate  deviation  of  head  and  eyes  towards  the 
opposite  side  to  that  stimulated. 

The  optic  radiations  consist  of  (1)  sensory  fibres  from  the  optic  tracts  vm  the 
external  geniculate  bodies  ;  (2)  efferent  fibres  to  the  centres  for  eye-movements  ;  and 
(3)  association  fibres  which  are  last  developed.  The  last  named  link  one  convolu- 
tion to  others,  and  the  two  hemispheres  together,  and  bring  about  association  of 
ideas  of  vision  in  both  hemispheres,  and  with  other  sensations.  A  large  collection 
of  such  fibres  runs  horizontally  through  the  grey  matter.  This  white  stripe  is  visible 
to  the  naked  eye  ;  it  is  the  anatomical  mark  of  the  visuo-sensory  cortex,  and  is  called 
the  line  of  Gennari.  The  growth  of  the  great  parietal  association  centre  pushes  the 
visuo-sensory  area  in  man  mainly  on  to  the  mesial  surface  of  the  hemisphere  (see 
area  4  in  figs.  506,  507.  The  visuo-psychic  region  (fig.  500)  has  no  line  of  Gennari, 
but  possesses  many  pyramidal  cells  in  its  outer  layers,  which  plaj"-  the  part  of 
association  units  where  memory  pictures  are  stored  and  visual  sensations  corre- 
lated with  those  from  other  sense-organs  ;  the  higher  one  ascends  the  animal  scale, 
the  greater  becomes  the  depth  of  this  layer.  The  eye  centre  in  the  frontal  lobe  is 
separated,  as  in  the  higher  apes,  by  inexcitable  grey  matter  from  the  rest  of  the 
sensori-motor  area.  In  the  lower  monkeys  the  anterior  eye  centre  is  not  insulated 
in  this  way.  No  cortical  centre  is  purely  motor  or  purely  sensory,  and  this  one, 
though  usually  called  motor,  has  its  sensory  complement  probably  from  the  eyeballs 
and  eyelids  (5th  nerve).  The  newly  developed  grey  matter  between  it  and  the 
Rolandic  region  is  an  area  probably  concerned  in  the  association  of  eye  movements 
with  equilibration  and  the  maintenance  of  the  erect  position ;  we  know  that  the 
fibres  from  the  frontal  lobe  to  the  cerebellum  are  very  numerous. 

The  auditory  area  is  in  the  posterior  part  of  the  upper  temporal 
convolution,  and  is  connected  to  the  visual  by  annectent  g}Ti.  Taste 
and  smell  are  closely  connected ;  their  cerebral  area  is  in  the  uncinate 
convolution  and  tip  of  the  temporal  lobe.  This  part  is  enlarged  in 
animals  with  a  keen  sense  of  smell. 

Munk's  view,  supported  in  this  country  by  Bastian,  Mott,  and 


704  FUNCTIONS    OF   THE   CEREBRUM  [CH.  XLVIII. 

numerous  others,  is  that  the  sensory  fibres  from  the  skin  and 
muscles  terminate  in  the  Eolandic  area ;  and  the  histological 
researches  of  Golgi  and  Ramon  y  Cajal  (see  figs.  479  and  482)  point 
to  the  same-  conclusion.  This  is,  in  fact,  what  one  would  expect ; 
volition  and  feeling  are  associated  together  so  cksely  physiologically, 
that  anatomically  we  should  expect  to  find  the  commencement  of  the 
volitional  fibres  contiguous  to  the  terminations  of  the  sensory  fibres. 
That  this  is  really  the  case  has  been  shown  by  a  careful  examination 
of  the  sensation  in  animals  in  which  the  Rolandic  area  has  been 
removed,  and  in  cases  of  hemiplegia  in  man.  A  delicate  test  is  to 
place  a  clip  on  the  fingers  or  toes,  taking  care  the  animal  does  not 
see  the  clip  put  on.  If  there  is  loss  of  tactile  sensibility  the  monkey 
either  takes  no  notice  at  all  of  the  clip  or  removes  it  after  a  long 
delay.  Whereas  if  sensation  is  perfect  the  monkey  at  once  seizes  the 
clip  and  flings  it  away.  It  is  found  that  the  intensity  of  both  the 
motor  and  sensory  paralysis  are  directly  proportional  to  each  other. 
Hence  the  term  motor  area,  which  we  have  been  provisionally 
employing  for  the  Rolandic  area,  should  be  replaced  by  the  more 
correct  term  sensori-motor  or  kinaesthetic  area.  These  new  terms 
indicate  that  what  really  occurs  in  the  Rolandic  area  is  a  sense  of 
movement,  and  this  acts  as  a  stimulus  vid  the  pyramidal  tracts  to  the 
true  motor  centres  which  are  in  the  opposite  anterior  horn  of  the 
spinal  cord.  If  the  posterior  roots  of  the  spinal  nerves  are  divided 
there  is  a  loss  of  sensation,  and  so  the  sense  of  movement  cannot 
reach  the  brain  from  the  muscles,  and  consequently  the  muscles  are 
not  called  into  action ;  when  all  the  posterior  roots  coming  from  a 
limb  in  a  monkey  are  cut,  the  muscles,  so  far  as  voluntary  move- 
ments are  concerned,  are  in  fact  as  effectually  paralysed  as  if  the 
anterior  roots  of  the  spinal  nerves  had  been  cut.  The  muscles, 
however,  do  not  degenerate  as  they  would  if  the  anterior  roots  had 
been  cut.  They  merely  undergo  a  small  amount  of  wasting  due  to 
want  of  use  ("  disuse  atrophy  "). 

Prof.  Schafer  is  one  prominent  worker  who  has  not  accepted 
Munk's  views  on  this  subject.  He  still  regards  the  Rolandic  area  as 
essentially  motor  in  function.  Naturally,  he  does  not  deny  that  it 
has  connections  with  sensory  fibres,  but  he  considers  it  incorrect  to 
speak  of  the  area  as  a  sensory  one.  He  has  produced  injuries  of  the 
area  without  obtaining  any  loss  of  sensation,  and  in  testing  the 
sensations  of  his  monkeys  employs  the  method  of  stroking  the  skin, 
which  he  regards  as  more  trustworthy  than  SchifTs  clip  test.  The 
sensory  disturbances  observed  by  others  he  regards  as  due  to  general 
disturbance  of  the  brain  produced  by  the  severity  of  the  operation. 

On  referring  once  more  to  the  maps  of  the  brain,  it  will  be  seen 
that  there  are  many  blanks ;  one  of  these  is  in  the  anterior  part  of 
the  frontal  region.     Extirpation  or  stimulation  of  this  part  of  the 


CH.  XLVIII.]  INTELLECTUAL   AKEAS   OF   BRAIN  705 

brain  in  animals  produces  but  little  result.  The  large  size  of  this 
portion  of  the  brain  is  very  distinctive  of  the  human  brain,  and  it 
has  therefore  been  supposed  that  here  is  the  seat  of  the  higher  intel- 
lectual faculties.  Such  a  question  is  obviously  very  difhcult  to 
answer  by  experiments  on  animals.  Both  experimental  physiology 
and  pathology  have  localised  the  sensory  areas  (and  sensations  are 
the  materials  for  intellect)  either  within  or  behind  the  Eolandic  area, 
but  this  does  not  necessarily  mean  that  the  frontal  convolutions  have 
nothing  to  do  with  intellectual  functions.  The  celebrated  American 
crowbar  accident  is  generally  quoted  as  a  proof  to  the  contrary ; 
owing  to  the  premature  explosion  of  a  charge  of  dynamite  in  one  of 
the  American  mines  a  crowbar  was  sent  through  the  frontal  region  of 
the  foreman's  head,  removing  the  anterior  part  of  his  brain.  He  is 
usually  stated  to  have  subsequently  returned  to  his  work,  without 
any  noteworthy  symptoms.  Eecent  examination  of  the  records  of 
the  case  has  shown  that  this  is  not  correct ;  when  he  returned  to 
work  he  was  practically  useless,  having  lost  just  those  higher 
functions  which  are  so  important  in  the  superintendence  of  other 
people.  Mott's  observations  on  lunatics  show  that  this  region  is 
important  for  intellectual  operations,  though  not  so  important  as  the 
parietal  association  area  behind  the  Eolandic  area;  the  greater  the 
intellectual  development,  the  larger  and  more  convoluted  does  this 
parietal  region  become. 

The  association  fibres  have  been  the  subject  of  special  study  by 
Flechsig,  who  has  shown  that  in  the  development  of  the  brain  these 
are  the  last  to  become  myelinated ;  white  fibres  do  not  become  fully 
functional  until  they  receive  their  medullary  sheath.  This  coincides 
with  the  well-known  fact  that  association  of  ideas  is  the  last  phase  in 
the  psychical  development  of  the  child.  It  has  been  shown  that  the 
frontal  convolutions  are  connected  by  important  association  tracts 
with  the  more  posterior  regions  of  the  brain,  and  that  there  is  there- 
fore no  difficulty  in  understanding  that  the  frontal  convolutions  play 
the  part  of  a  centre  for  the  association  of  ideas,  or  in  other  words  for 
intellectual  operations. 

Function  and  Myelination. 

Flechsig's  embryological  method  has  given  us  most  valuable  knowledge  of  the 
structure  and  functions  of  the  human  brain.  The  method  depends  on  the  fact  that 
various  tracts  of  fibres  become  myehnated,  i.e.,  acquire  their  medullary  sheath  at 
successive  periods  of  time  in  development.  The  myehn  sheath  appears  three  or  four 
months  after  the  axis  cyhnder  is  formed.  The  Weigert  method  of  staining  renders 
the  detection  of  a  medullary  sheath  an  easy  task.  Flechsig's  method  is  in  short  the 
complement  of  the  Wallerian  method.  In  the  former  method  the  tracts  are  isolated 
by  the  diiferences  in  the  origin  of  the  myelin  sheath ;  in  the  latter  method,  the  same 
object  is  obtained  by  observing  the  degeneration  which  is  most  noticeable  in  the 
same  sheath. 

In  the  central  nervous  system,  the  afferent  projection  fibres  are  myelinated  first ; 

2   Y 


706 


FUNCTIONS  OF  THE  CEREBRUM 


[CH.  XLVIII. 


the  ciTerent  projection  fibres  and  the  association  fibres  are  myehnated  later.  Thus 
in  the  human  ftr'tus  the  peripheral  nerves  and  nerve-roots  become  myelinated  in  the 
fifth  month  of  intra-uterine  life  ;  of  the  tracts  in  the  cord,  those  of  Burdach  and  Goll 
{('.rotjcnoiis  fibres  springing  from  the  cells  of  the  spinal  ganglia)  are  the  first  to  be 
myelinated  ;  next  come  the  tracts  of  Flechsig  (dorsal  cerebellar)  and   of  Gowers 


.^ 


P.V.' 


MO 


Fio.  501. — Diagram  of  vertical  section  through  brain  of  new-boni  cliild,  drawn  from  one  of  Fleclisig's 
photograplis.  The  section  was  treated  by  Weigert's  method,  by  which  myelinated  fibres  are  deeply 
stained.  Attention  is  drawn  to  the  deep  shading  indicating  myelination  around  the  central  lissnre, 
whicli  corresponds  to  the  sensori-motor  area,  and  also  around  the  calcarine  fissure  in  the  visual 
sjihere.  The  association  fibres  are  not  myelinateii.  The  fibres  of  the  pyramidal  efferent  system 
have  also  no  myelin.  M.O.,  medulla  oblongata;  P.V.,  pons  Varolii;  O.M.N.,  oculo-motor  nerve; 
O.C.,  optic  commissure;  F.  A.C.,  frontal  association  centre;  CO.,  corpus  callosum  ;  C.P.,  central 
fissure,  or  fissure  of  Rolando;  P.A.C.,  posterior  association  centre;  V.S.,  visual  sphere;  C,  cere- 
bellum ;  S.C.,  spinal  cord. 


(ventral  cerebellar) :  these  are  endof/f.nous  fibres  springing  from  cells  within  the  cord. 
All  these  tracts  are  aiferent.  The  pyramidal  tracts,  the  great  efferent  or  motor 
channels,  are  not  myelinated  until  after  birth.  The  whole  afferent  tr^ct  is  myelinated 
at  birth ;  these  fibres  have  in  ufero  been  exercised  in  conveying  impressions  to  the 
afferent  reception  centres,  the  stimuli  arising  from  contact  of  the  fct'tal  integuments 

with  the  maternal  tissues.     There 
Cf^-  is  also  early  myelination  around 

i  the  calcarine  fissure  in  the  visual 

sphere,  and  in  connection  with 
the  areas  related  to  other  special 
senses.  This  is  shown  in  figs.  .501 
and  r)02,  where  the  condition  at 
birth  and  that  some  months  later 
are  compared. 

Flechsig  considers  that  at 
least  two-thirds  of  the  cortex  con- 
sists of  neurons  of  association, 
and  further  that  these  association 
centres  possess  no  neurons  of  the 
efferent  or  afferent  projection 
systems.  The  last  part  of  this 
statement  is  probably  not  cor- 
rect, and  has  not  been  accepted 
in  its  entirety  by  the  majority  of 
neurologists. 

Ambronn  and  Held  confirm 
Flechsig  in  finding  that  the  affer- 
ent fibres  are  myelinated  before  the  efferent,  in  the  central  nervous  system,  but  in 
the  case  of  the  nerve-roots  this  is  reversed,  the  anterior  root  fibres  being  myehnated 
before  the  posterior. 

Held  has  also  demonstrated  the  important  influence  of  stimulus  on  myelination. 


FiA.C- 


Pio.  502. — Diagram  of  vertical  section  of  tlie  brain  of  a  chil(i 
5  months  of  age.  'I'lie  greater  part  of  the  white  matter 
now  shows  myelination,  thus  indicating  development  of 
the  association  centres.  The  letters  have  the  same 
meaning  as  in  Fig.  501.  (After  F'lechsig;  Weigert 
method  of  staining.) 


CII.  XLVIIl.] 


ASSOCIATION    CENTRES    AND    FIBRES 


707 


His  experiments  were  made  on  cats,  dogs,  and  rabbits,  whic;li  are  born  blind.  If 
light  is  admitted  to  one  eye  by  opening  the  lid,  more  obvious  myclination  is  siibse- 
(piently  found  in  the  correspondmg  optic  nerve  than  in  that  of  the  opposite  side. 
This  is  not  due  to  the  irritation  caused  by  forcibly  opening  the  lid,  for  if  the  lid  be 
opened  and  the  animal  kept  in  the  dark,  no  difference  in  the  myelination  of  the  two 
optic  nerves  is  observable.  Flechsig  also  showed  that  a  child  born  at  8  months  had 
more  marked  myelination  of  its  optic  nerves,  a  month  later,  than  a  child  born  in  the 
usual  way  at  the  ninth  month. 

The  richness  of  the  brain  in  myelinated  fibres  increases  for  many  years  after 
birth  with  the  progress  of  intellectual  development.  Kaes  states  this  continues 
up  to  forty  years  of  age,  and  that  in  old  age  the  number  diminishes.  Myelin 
appears  to  be  necessary  for  the  functional  activity  of  nerve  tracts,  and  its 
development  progresses  pari  passx  with  development  of  function ;  the  reverse 
change  (atrophy  and  degeneration)  correspondingly  accompanies  marked  disturb- 
ances of  function. 

Association  Fibres  and  Association  Centres. 

We  know  by  common  experience  that  any  group  of  muscles  can  be  voluntarily 
contracted  in  reply  to  any  form  of  stimulus,  cutaneous,  visual,  auditory,  etc.  If, 
for  instance,  the  wrist  is  flexed  in  response  to  an  auditory  stimulus,  the  nerve 
impulses  pass  first  to  the  auditory  area,  then  by  certain  fibres  to  the  cerebral  cells 
which  control  the  muscles  of  the  arm.  The  fibres  which  connect  the  two  areas  are 
termed   assuciation  fibrt'.s.      A   diagrammatic    view    of   the    principal    bundles    of 


Fio.  503. — Lateral  view  of  a  human  hemisphere,  showing  the  main  bundles  of  association  flbre.s  (Starr). 
A,  A,  between  ailjacent  convolutions  ;  b,  between  frontal  and  occipital  areas  ;  c,  between  frontal  and' 
temporal  areas  (ci'igulum) ;  d,  between  frontal  and  temporal  areas  (fasciculus  uncinatus)  ;.e, 
between  occipital  and  temporal  areas  (fasciculus  longitudinalis  inferior);  c.n.,  caudate  nucleus; 
O.T.,  optic  thalamus. 

association  fibres  is  given  in  fig.  .".03,     This  figure  may  be  usefully  compared  with 
the  next  (fig.  504),  which  shows  the  general  plan  of  the  projection  fibres. 

The  terra  '■^ assocudiuu  centres'"  is  given  by  Flechsig  to  those  portions  of  the 
cortex  that  lie  between  the  sensory  centres  he  has  been  able  to  demonstrate.  The 
function  of  these  centres  is  first  to  furnish  pathways  between  the  several  centies,Iand 
secondly  to  retain  as  memories  previous  sense  impressions,  so  that  in  action  they  may 
modify  the  impulses  sent  into  them,  and  by  these  modifications  adjust  to  an  almost 
infinite  degree  the  form  of  the  final  response. 


708 


FUNCTIONS    OF   THE   CEREBRUM 


[CH.  XLVin. 


The  association  centres  comprise  a  very  large  area  of  the  cortex,  and  are 
divided  into  three:— (1)  The  great  anterior  association  centre  in  the  frontal 
lobe:  (-J)  the  posterior  association  centre  in  the  parieto-temporal  region;  (•:;)  the 
middle  association  centre;  this  is  smaller  and  coincides  with  the  island  of  Reil. 
These  regions  are  in  fact  those  in  which  no  evident  response  follows  excitation  ; 


Fig.  504. — Schema  of  the  projection  fibres  within  the  brain  (Starr),  a,  tract  from  the  frontal  gyri  to  the 
pons  nuclei  and  so  to  the  cerebeUiim ;  e,  motor  pyramidal  tract ;  c,  sensory  tract  for  tonch 
(separated  from  b  for  the  sake  of  clearness  in  the  diagram);  d,  visual  tract;  e,  auditory  tract; 
F,  G,  H,  superior,  middle,  and  inferior  cerebellar  peduncles  ;  j,  fibres  between  the  auditory  nucleus 
and  the  inferior  corpus  quadrigeminum  ;  k,  motor  decussation  in  the  bulb ;  f.v.,  fourth  ventricle. 
The  numerals  refer  to  the  cranial  nerves.  The  sensory  radiations  are  seen  to  be  massed  towards  the 
occipital  end  of  the  hemisphere. 

they  are  sometimes  called  the  "  latent  or  inexcitable  cortex."  The  human  brain  is 
characterised  by  the  high  development  of  these  parts,  and  as  already  explained  they 
are  doubtless,  as  Flechsig  terms  them,  the  organs  of  thought. 

The  importance  of  the  association  of  ideas,  which  has  for  its  anatomical  basis 
the  association  of  cortical  centres,  will  be  at  once  grasped  when  one  considers  such 
complex  actions  as  reading  aloud  or  writing  from  dictation.  The  accompanying 
diagram  ffig.  ',05)  shows  the  position  of  the  main  centres  involved,  particulars  of 
which  will  be  found  in  the  small  text  beneath  the  figure. 

In  reading  aloud,  the  impressions  of  the  words  enter  by  the  eyes,  reach  that 
portion  of  the  visual  sphere  known  as  the  risual  u-ord  ci-ntrf,  travel  across  to  the 
au(Hforij  irord  c-ntr'-  by  association  fibres,  where  the  memory  of  their  sounds  is 
revived;  another  tract  of  association  fibres  connects  this  to  the  sen sori-motor  area 
in  Broca"s  convolution  called  by  Bastian  the  (jlosso-kiucesthetic  area,  whence  motor 
impulses  originate  which  finally  reach  the  muscles  concerned  in  pronouncing  the 
words  originally  seen. 

Writing  from  dictation  is  just  as  complex ;  the  course  of  the  impulses  is  by 
the  auditory  channels  to  the  'in'Iitori^  irord  cf-ntre,  then  by  association  tracts  to  the 
visual  word  centre,   where  the  shapes   of  the   letters   composing  the   words  are 


CH.  XLVIII.]  CENTRES    FOR   SPEECH    A_ND    WRITING 


709 


revived ;  another  association  tract  carries  the  iiiipulse  thence  to  the  sensori-raotor 
area  connected  with  the  inovenients  of  the  hand  {BASiian^s  clifiro-kvicBsflw/ic  area)  in 
the  middle  region  of  the  Rolaiidic  cortex,  and  finally  the  movement  of  writing  is 
accomplished.  The  diverse  symptoms  exhibited  by  patients  suffering  from  various 
forms  of  apiiasia  can  be  all  explained  by  more  or  less  extensive  damage  either  to 
the  centres  themselves  or  to  the  association  tracts  which  connect  them. 

The  association  fibres  of  the  spinal  cord  are  described  on  p.  630. 

In  the  development  of  a  neuron,  four  stages  can  be  distinguished : — (1)  Cells 
without  processes ;  (2)  the  appearance  of  simple  branches,  the  axon  developing 
most  rapidly  ;  (3)  the  formation  of  collaterals  ;  (4)  the  appearance  of  the  medullary 
sheath.  In  the  cerebral  convolutions  the  fibres  become  myelinated  in  a  strictly 
regular  sequence;  some  convolutions  have  their  fibres  medullated  three  months 
before  birth,  while  in  others  complete  myelination  has  not  occurred  six  months  later. 
Fibres  of  equally  great  importance  become  medullated  at  the  same  time;  those  of 


Fig.  505. — Lateral  view  of  the  left  cerebral  hemisphere  of  niau  (after  Donaldson),  v  i^s  the  cortical  area, 
damage  to  which  produces  "word  blindness  "  ;  it  is  situated  in  the  angular  gjTus,  and  is  called  the 
visual  word  centre,  h  is  the  area  in  the  superior  temporal  convolution,  called  the  ouditoiy  word 
centre,  damage  to  which  jjroduces  "word  deafness."  s  is  Broca's  convolution,  damage  to  which 
produces  loss  of  audible  speech  (motor  aphasia) ;  this  is  the  sensoii-motor  area  for  the  movements 
of  the  tongue,  vocal  cords,  etc.,  concerned  in  speaking;  Bastiau  terms  it  the  glosso-kina'sthetic  area. 
The  area  w,  called  by  Bastian  the  cheiro-kinoxthetic  area,  is  the  corresponding  region  concerned  in 
hand  movements,  damage  to  which  abolishes  the  power  of  writing  (agraphia). 

primary  importance  first,  and  so  on.  In  this  way,  myelogenetic  cortical  fields  can 
be  mapped  out,  which  retain  their  contours  for  some  time.  Thirty-six  of  such  fields 
were  made  out  by  Flechsig,  and  can  be  divided  chronologically  into  three  groups, 
primari/,  intermediate,  and  terminal. 

The  primary  fields  are  darkly  shaded  in  the  accompanying  diagrams  (figs.  506 
and  507). 

They  are  10  in  number,  and  are  those  provided  with  myelinated  fibres  at  birth  ; 
they  contain  the  seats  of  the  cortical  representation  of  aU  the  senses.  To  No.  1  is 
assigned  the  cutaneous  and  muscular  sense ;  to  No.  2  the  sense  of  smell ;  to  Xo.  i 
that  of  vision ;  to  No.  5  that  of  hearing.  The  functions  of  some  of  the  primary 
areas  had  not  been  determined.  The  principal  efferent  projection  tracts  originate 
from  the  primary  fields ;  thus  the  pyramidal  tract  starts  from  No.  1 ,  but  mainly 
from  the  ascending  frontal  convolution.*  The  sensory  fibres  connected  with  the 
skin  and  muscles  terminate  mainly  in  the  ascending  parietal  convolution.  The 
inferior  fornix  is  connected  with  Nos.  2  and  3.  The  inner  bundle  of  the  pes  springs 
from  1  b,  6,  12,  14  and  15;  the  origin  of  the  outer  bundle  of  the  pes  is  doubtful. 
From  the  visual  area  (No.  4)  a  tract  arises  which  passes  mainly  into  the  anterior 

*  This  coincides  well  with  the  work  of  Sherrington  and  Griinbaum  (p  699). 


710 


FUNCTIONS  OF  THE  CEREBRUM 


[CH.  XLVm. 


corpus  quadrigeminum ;  the  auditorj'  zone  (No.  5),  towards  which  a  tract  proceeds 
that  leads  from  the  internal  corpus  geniculatum.  sends  an  outgoing  tract  into  the 
column  of  Tiirck,  and  thus  motor  functions  of  the  upper  part  of  the  body  are 
possible  as  a  direct  result  of  auditory   impressions.     In   fact   in   every  case  each 


Fig.  506. —  Outer  surface  of  human  brain,  showing  Flechsig's  developmental  zones ;  primary  (1 — 10) 
darkly  shaded ;  intermediate  (11 — 31),  less  deeply  shawied  ftemunal  (32 — 3o),  not  shaded.    (Flechsig.) 

primordial  sensory  zone  is  connected  with  a  well-defined  pair  of  tracts,  one  proceed- 
ing to  it  (cortico-petal)  and  the  other  from  it  (cortico-fugal).  It  is  thus  impossible  to 
speak  of  a  purely  motor  or  a  purely  sensory  area. 

The  ttrminal  areas  (Xos.  ol  to  'iQ,  unshaded  in  the  diagrams)  do  not  begin  to 


Fig.  dOT. — Inner  surface  of  same.    (Flechsig.) 

be  myelinated  until  at  least  a  month  after  birth.  These  and  the  majority  of  the 
intTyntiUaft  areas  (Xos.  11  to  31,  lightly  shaded  in  the  diagrams)  show  few  or  no 
projection  fibres  '  even  8  months  after  birth.  They  comprise,  in  fact,  the  association 
centres,  and  are  rich  in  long  association  fibres. 

*  That  they  never  have  any  projection  fibres  at  all  is  denied  by  most  observers. 


CH.  XLVIII.]  ELECTRICAL   CHANGES   IN   SPINAL   COKD  711 

Electrical  Variation  in  Central  Nervous  System. 

Du  Bois  RejinGnd  found  that  the  spinal  cord,  like  a  nerve, 
exhibits  a  demarcation  current  between  its  longitudinal  surface  and 
a  cross-section,  and  that  a  diminution  of  this  current  occurs  on 
excitation  (negative  variation).  Gotch  and  Horsley  investigated  the 
currents  of  the  cord  very  thoroughly.  If  the  Eolandic  area  of  the 
cortex  is  stimulated,  and  a  portion  of  the  thoracic  region  of  the 
spinal  cord  is  led  off  to  a  galvanometer,  a  persistent  negative  varia- 
tion followed  by  a  series  of  intermittent  variations  is  observed ;  this 
exactly  corresponds  to  the  tonic  spasm  followed  by  clonic  con- 
tractions which  occur  in  the  muscles  excited  by  this  means. 

The  galvanometer  in  the  hands  of  these  observers  also  proved  to 
be  a  valuable  instrument  for  determining  the  paths  taken  by  nervous 
impulses  in  the  cord.  One  example  will  suffice :  If  the  central  end 
of  one  sciatic  nerve  is  stimulated,  the  chief  electrical  variation  in  the 
cord  is  noticed  to  be  obtained  when  the  same  side  of  the  cord  is  led 
off  to  the  galvanometer,  but  a  certain  amount  of  electrical  variation 
is  obtainable  from  the  opposite  side  of  the  cord.  This  coincides  with 
the  fact  ascertained  by  other  methods,  that  the  main  sensory 
channel  is  on  the  same  side  of  the  cord  as  the  entering  nerves,  but 
that  there  is  a  certain  small  amount  of  decussation  below  the  level 
of  the  bulb. 

Electromotive  changes  also  occur  during  activity  in  the  cortex 
cerebri,  but  they  have  not  been  much  studied,  and  we  do  not  know 
whether  they  have  their  seat  in  the  grey  or  in  the  underlying  \vhite 
matter. 

Sleep. 

The  conditions  that  favour  sleep  are : — 

(1)  A  diminution  of  the  impulses  entering  the  central  nervous 
system  by  the  afferent  channels.  This  is  under  our  voluntary 
control,  as,  for  instance,  in  closing  the  eyes,  or  retiring  to  a  quiet 
room. 

(2)  Fatigue.  This  diminishes  the  readiness  of  the  central 
nervous  system  to  respond  to  stimuli. 

The  first  two  hours  of  sleep  are  always  the  most  profound ;  later 
on,  relatively  weak  stimuli  will  cause  awakening.  Of  the  parts  of 
the  central  nervous  system,  the  spinal  cord  is  always  less  profoundly 
affected  than  the  brain,  but  even  the  brain  is  never  entirely  irrespon- 
sive, and  unless  slumber  is  very  profound,  dreams  are  the  subjective 
result  of  external  stimuli. 

Sleep  has  been  attributed  by  some  to  changes  in  the  blood-supply 
of  the  brain,  and  ultimately  referred  to  fatigue  of  the  vaso-motor 
centres.     The  existence  of  an  effective  vaso-motor  mechanism  in  the 


712  FUNCTIONS    OF   THE   CEREBRUM  [CH.  XLVIIl. 

cerebral  blood-vessels  themselves  is  problematical  (see  p.  311);  so 
that  if  changes  occur  in  the  cerebral  blood-pressure  or  rate  of  flow, 
they  are  mainly  secondary  to  those  which  are  produced  in  other 
parts  of  the  body.  Plethysmographic  records  from  the  arm  of  a 
sleeping  man  show  a  diminution  in  its  volume  every  time  he  is 
disturbed,  even  though  the  disturbance  may  not  be  sufficient  to 
awaken  him.  This  is  interpreted  as  meaning  a  diminution  in  the 
blood  of  the  body,  and  a  corresponding  increase  in  the  blood-flow 
through  the  brain.  It  is,  however,  quite  possible  that  the  vascular 
condition  is  rather  the  concomitant  or  consequence  of  sleep  than  its 
cause. 

Some  of  the  theories  to  account  for  sleep  have  been  chemical. 
Thus  certain  observers  have  considered  that  sleep  is  the  result  of  the 
action  of  chemical  materials  produced  during  waking  hours,  which 
have  a  soporific  effect  on  the  brain;  according  to  this  theory 
awakening  from  sleep  is  due  to  the  action  of  certain  other  materials 
produced  during  rest,  which  have  the  opposite  effect.  Obersteiner 
has  gone  so  far  as  to  consider  that  the  soporific  substances  are 
reducing  in  nature,  and  others  regard  them  as  alkaloidal.  These 
theories  all  rest  upon  the  slimsiest  foundations,  and  none  has  yet 
been  found  to  stand  experimental  tests. 

Then  there  are  what  we  may  term  histological  theories  of  sleep, 
and  these  are  equally  unsatisfactory.  The  introduction  of  the  Golgi 
method  opened  a  fresh  field  for  investigators,  and  several  have 
sought  to  find  by  this  method  a  condition  of  the  neurons  produced 
by  narcotics  such  as  opium  and  chloroform,  which  is  different  from 
that  which  obtains  in  the  waking  state. 

Demoor  and  others  found  that  in  animals  in  which  deep  anaes- 
thesia has  occurred,  that  the  dendrites  exhibit  moniliform  swellings, 
that  is,  a  series  of  minute  thickenings  or  varicosities.  On  the 
strength  of  this  observation,  he  has  formulated  what  we  may  call  a 
bio-physical  theory  of  sleep.  In  the  waking  state,  the  neighbouring 
nerve  units  are  in  contact  wdth  each  other ;  transmission  of  nerve 
impulses  from  neuron  to  neuron  is  then  possible,  and  the  result  is 
consciousness ;  during  sleep  the  dendrites  are  retracted  in  an 
amoeboid  manner ;  the  neurons  are  therefore  separated,  and  the  result 
is  unconsciousness. 

Lugaro,  on  the  other  hand,  takes  the  precisely  contrary  view. 
He  was  not  able  to  discover  moniliform  enlargements,  and  his  bio- 
physical hypothesis  is  that  the  interlacing  of  dendrites  is  much  more 
intimate  during  sleep  than  during  consciousness.  He  therefore 
explains  sleep  by  supposing  that  the  definite  and  limited  relation- 
ships between  neurons  no  longer  exists,  but  are  lost  and  rendered 
ineffective  by  the  universality  of  the  connecting  paths.  It  is  not 
very  difficult  to  explain  such  divergence  of  views,  for  they  both 


CH.  XLVIII.]  SLEEP   AND   NARCOSIS  713 

depend  mainly  on  observations  made  by  a  single  method ;  and  the 
method  itself  is  open  to  objection.  It  is  one  which  gives  even  in  the 
same  brain  most  inconstant  results,  and  is  not  calculated  to  show 
much  more  than  a  mere  outline  of  a  few  of  the  cells  and  their 
branches.  So  much  doubt  has  arisen  of  late  in  regard  to  the  trust- 
worthiness of  the  method,  that  many  neurologists  are  beginning  to 
doubt  whether  the  neuron  theory  implying  absolute  non-continuity 
of  nerve  units  has  been  satisfactorily  proved,  and  there  is  a  tendency 
to  return  to  the  idea  of  a  connecting  network  not  very  different  from 
that  originally  put  forward  by  Gerlach. 

A  more  satisfactory  investigation  of  the  effect  of  anaesthetics  on 
nerve-cells  was  carried  out  by  Hamilton  Wright. 


Fig.  50S.— Moniliform  enlargements  on  dendrites  of  nen-e-cells,  rendered  evident  bv  Cox's  modification 
of  Golgi's  method,  a,  in  a  cortical  cell  of  a  rabbit ;  b,  in  a  corresponding  cell  of  a  dog's  brain,  after 
six  hours'  ansesthetisation  with  ether  in  each  case.    (Hamilton  Wright.) 

He  used  rabbits  and  dogs,  and  subjected  them  to  ether  and 
chloroform  narcosis  for  periods  varpng  from  half  an  hour  to  nine 
hours.  In  both  animals  he  found  that  the  nerve-cells  are  affected, 
but  in  rabbits  much  more  readily.  This  accords  quite  well  with 
what  is  known  regarding  the  susceptibility  of  rabbits  as  compared  to 
dogs  towards  the  influence  of  these  narcotising  agents.  In  a  rabbit, 
the  nerve-cells,  especially  of  the  cerebrum,  show  changes  even  after 
only  half  an  hour's  anaesthesia,  but  in  dogs  at  least  four  hours'  anses- 
thesia  must  be  employed.  By  the  Golgi  method  the  moniliform 
enlargements  can  be  seen.  These  become  more  numerous,  larger, 
and  encroach  more  and  more  on  the  dendritic  stems,  the  longer  the 
angesthesia  is  kept  up.  The  accompanying  illustrations  show  the 
appearances  seen  (fig.  508). 


714  FUNCTIONS   OF  THE   CEREBRUM  [CH.  XLVIII 

Lugaro's  failure  to  find  these  appearances  is  doubtless  due  to  his 
not  having  maintained  the  ansesthesia  long  enough  in  his  dogs. 

Wright  started  his  work  with  a  bias  in  favour  of  Demoor's  bio- 
physical theory,  but  he  soon  found  that  the  theory  was  untenable ; 
the  results  of  his  observations  have  shown  him  that  the  action  of 
anaesthetics  is  bio-chemical  rather  than  bio-physical,  and  he  has  been 
led  to  this  conclusion  by  the  employment  of  other  histological 
methods,  particularly  the  most  sensitive  one  we  possess,  namely,  the 
methylene-blue  reaction. 

Owing  to  the  chemical  action  of  the  anaesthetic  on  the  cells,  the 
Nissl  bodies  have  no  longer  an  affinity  for  methylene-blue,  and  the 
cells  consequently  present  what  Wright  calls  a  rarefied  appearance ; 
when  this  becomes  marked  the  cells  appear  like  the  skeletons  of 
healthy  cells.  In  extreme  cases  the  cells  look  as  though  they  had 
undergone  a  degenerative  change,  and  after  eight  or  nine  hours' 
anaesthesia  in  dogs,  even  the  nucleus  and  nucleolus  lose  their  affinity 
for  basic  dyes.  The  change,  however,  is  not  a  real  degeneration,  and 
passes  off  when  the  drug  disappears  from  the  circulation.  Even 
after  nine  hours'  anaesthesia  the  cells  return  rapidly  to  their  normal 
condition,  stain  normally,  moniliform  enlargements  have  disappeared, 
and  no  nerve-fibres  show  a  trace  of  Wallerian  degeneration.  The 
pseudo-degenerative  change  produced  by  the  chemical  action  of  the 
anaesthetic  no  doubt  interferes  with  the  normal  metabolic  activity 
of  the  cell-body,  and  this  produces  effects  on  the  cell-branches.  In 
the  early  stages  of  Wallerian  degeneration,  the  branch  of  the  nerve- 
cell  which  we  call  the  axis-cylinder  presents  swellings  or  varicosi- 
ties, produced  by  hydration  or  some  similar  chemical  change.  The 
moniliform  enlargements  seen  during  the  temporary  pseudo-degenera- 
tive effects  produced  by  anaesthetics  are  comparable  to  this.*  These 
enlargements  are  therefore  not  the  primary  cause  of  loss  of  conscious- 
ness, but  are  merely  secondary  results  of  changes  in  the  cell-body. 
When  a  tree  begins  to  wither  the  earliest  apparent  change  is  noticed 
in  the  branches  most  remote  from  the  centre  of  nutrition,  the  root ; 
as  the  changes  in  the  centre  of  nutrition  become  more  profound,  the 
larger  branches  become  implicated,  but  the  seat  of  the  mischief  is 
not  primarily  in  the  branches.  This  illustration  may  serve  to  render 
intelligible  what  is  found  in  nerve-cells  and  their  branches. 

Whether  the  appearances  found  in  dogs  and  rabbits  are  appli- 
cable to  the  human  subject  is  another  question.  I  am  inclined  to 
think  that  we  may  safely  regard  them  as  such ;  there  is  no  reason 
why  an  anaesthetic  should  act  differently  in  different  animals.  The 
resistance  of  the  animal  is  a  variable  factor,  and  this  causes  a  varia- 

*  Some  observers  look  upon  the  varicosities  as  artifacts.  If  they  are,  they 
ought  to  have  been  found  in  all  Wright's  specimens,  for  the  method  of  preparation 
was  the  same  throughour. 


Ch.  xlviii.]  sleep  and  naUcosis  ^15 

tion  in  degree  only ;  the  effect  is  probably  the  same  in  kind  for  all 
animals,  man  included. 

But  I  feel  that  we  should  be  very  chary  in  concluding  that  the 
artificial  sleep  of  a  deeply-narcotised  animal  is  any  criterion  of  what 
occurs  during  normal  sleep.  The  sleep  of  anaesthesia  is  a  pathologi- 
cal condition  due  to  the  action  of  a  poison.  The  drug  reduces  the 
chemico-vital  activities  of  the  cells,  and  is,  in  a  sense,  dependent  on 
an  increasing  condition  of  exhaustion,  which  may  culminate  in  death. 
Normal  sleep,  on  the  other  hand,  is  not  produced  by  a  poison,  or  at 
any  rate  we  have  no  evidence  of  any  poison ;  it  is  the  normal  mani- 
festation of  one  stage  in  the  rhythmical  activity  of  nerve-cells,  and 
though  it  may  be  preceded  by  fatigue  or  exhaustion,  it  is  accom- 
panied by  repair,  the  constructive  side  of  metabolic  activity. 

Loss  of  sleep  is  more  damaging  than  starvation.  Dogs  will  recover  after  being 
starved  for  three  weeks,  but  they  die  from  loss  of  sleep  in  five  days.  The  body 
temperature  falls,  reflexes  disappear,  and  post-mortem  the  brain  is  found  to  contam 
capillary  haemorrhages,  the  cord  is  dry  and  anaemic,  and  fatty  degeneration  is  found 
in  most  of  the  tissues. 

In  man,  loss  of  sleep  curiously  enough  causes  a  slight  rise  in  weight ;  the  body 
temperature  falls  ;  the  excretion  of  nitrogen  and  still  more  so  that  of  phosphoric  acid 
increases  ;  the  reactions  of  the  muscular,  and  later  those  of  the  nervous,  system 
diminish  in  intensity,  except  that  in  all  cases  there  is  an  increase  in  acuteness  of 
vision.  These  experiments  were  made  by  Patrick  and  Gilbert  on  three  young  men, 
who  voluntarily  went  without  sleep  for  ninety  hours.  At  the  end  of  the  experiment 
a  very  small  extra  amount  of  sleep  beyond  the  normal  caused  complete  restoration, 
and  all  the  symptoms,  including  the  increase  of  weight,  disappeared. 

Action  of  aiupsthelics  — Moore  and  Roaf  point  out  that  the  cells  usually  investi- 
gated, as  in  Wright's  work,  are  the  nerve  cells,  for  the  state  of  quiescence  produced 
in  these  by  an  anaesthetic  underlies  the  state  of  unconsciousness.  All  other  cells 
are,  however,  similarly  affected,  although  in  varying  degree.  The  changes  noted 
by  Wright  form  a  signal  of  the  changes  produced  in  protoplasm  by  the  prolonged 
action  of  the  anaesthetic.  The  action  must  be  due  to  a  change  in  some  substance 
present  in  all  cells,  and  this  substance  is  protein.  They  have  shown  that  un.stable 
compounds  of  protein  and  chloroform  are  obtainable,  hence  the  great  solubility  of 
chloroform  in  blood  as  compared  to  water.  The  chloroform-protein  compound  may 
be  compared  to  oxy haemoglobin,  for  it  undergoes  dissociation  in  the  same  kind  of 
way.  Just  as  oxyhaemoglobin  parts  with  its  oxygen  to  the  tissue-cells,  so  the 
chloroform  parts  company  from  the  blood-protein,  and  enters  into  combination  with 
the  cell-protein,  limiting  its  activity  and  producing  quiescence  or  anaesthesia.  When 
the  administration  of  the  anaesthetic  ceases,  the  chloroform  tension  in  the  blood  is  no 
longer  maintained,  the  combination  between  cell-protein  and  chloroform  dissociates, 
and  anaesthesia  passes  off. 


CHAPTEE  XLIX 

FUNCTIONS  OF  THE  CEEEBELLUM 

In  past  times  there  have  been  several  views  held  as  to  the  functions 
of  the  cerebellum.  One  of  the  oldest  of  these  was  the  idea  that  the 
cerebellum  was  associated  with  the  function  of  generation ;  another 
view,  first  promulgated  by  Willis,  was  that  the  cerebellum  contained 
the  centres  which  regulate  the  functions  of  organic  life ;  this  arose 
from  the  circumstance  that  diseases  of  the  cerebellum  are  often 
associated  with  nausea  and  vomiting;  it  is  a  familiar  fact  that  in 
displacements  of  equilibrium  such  as  occur  on  board  ship  in  a  rough 
sea,  or  in  the  disease  called  Meniere's  disease,  sickness  is  a  frequent 
result ;  it  appears  from  this  that  the  cerebellum  does  receive  from  or 
send  to  the  viscera  certain  impulses.  The  third  and  last  of  these 
older  theories  was  that  the  cerebellum  was  the  centre  for  sensation. 
This  arose  from  the  fact  that  certain  of  the  afferent  channels  of  the 
spinal  cord  were  traced  into  the  cerebellum.  The  impulses  that  travel 
along  these,  however,  though  afferent,  are  not  truly  sensory,  and  their 
reception  in  the  cerebellum  is  not  associated  with  consciousness. 

The  true  function  of  the  cerebellum  was  first  pointed  out  by 
Flourens,  who  showed  that  the  cerebellum  is  the  great  centre  for  the 
co-ordination  of  muscular  movement,  and  especially  for  that  variety 
of  co-ordination  which  is  called  equilibration — that  is,  the  harmonious 
adjustment  of  the  working  of  the  muscles  which  maintain  the  body 
in  a  position  of  equihbrium. 

It  must  not  be  supposed  from  this  that  the  cerebellum  is  the  sole 
centre  for  co-ordination.  We  have  already  seen  that  all  the  machinery 
necessary  for  carrying  out  very  comphcated  locomotive  movements 
is  present  in  the  spinal  cord.  The  higher  centres  set  this  machinery 
going,  and  the  work  of  arranging  what  muscles  are  to  act,  and  in 
what  order,  is  carried  out  by  the  whole  of  the  grey  matter  from  the 
corpora  striata  to  the  end  of  the  spinal  cord,  including  such  out- 
growths as  the  corpora  quadrigemina  and  cerebellum.  An  instance 
of  a  complex  co-ordinated  movement  is  seen  in  what  we  learnt  to  call 
in  the  last  chapter  conjugate  deviation  of  head  and  eyes.  The  higher 
cortical  centre  gives  the  general  word  of  command  to  turn  the  head 


CH.  XLIX.]  FUNCTIONS   OF   THE   CEREBELLUM  717 

and  eyos  to  the  right :  the  subsidiary  centres  or  subordinate  officials 
arrange  that  this  is  to  be  accomplished  by  the  external  rectus  of  the 
right  eye  supplied  by  the  right  sixth  nerve,  the  internal  rectus  of  the 
left  eye  suppHed  by  the  left  third  nerve,  and  numerous  muscles  of 
neck  and  back  of  both  sides  supplied  by  numerous  nerves.  The 
relaxation  of  the  antagonistic  muscles  has  also  to  be  provided  for. 
We  thus  see  how  the  complicated  intercrossing  of  fibres  and  connec- 
tions of  the  centres  of  the  various  nerves  are  brought  into  play. 

The  functions  of  the  cerebellum  are  investigated  by  the  same  two 
methods  of  experiment  {stimulation  and  extirpation)  that  are  employed 
in  similar  researches  on  the  cerebrum.  The  anatomical  connections 
of  the  cerebellum  with  other  parts  of  the  cerebro-spinal  axis  (see 
p.   662)  have  been  chiefly  elucidated  by  the  degeneration  method. 


Fio.  500. — Pigeon  after  removal  of  the  cerebellum.    (Dalton.) 

Each  side  of  the  cerebellum  has  three  peduncles :  the  superior  peduncle 
connecting  it  to  the  opposite  hemisphere  of  the  cerebrum,  the  inferior 
peduncle  connecting  it  mainly  to  the  same  side  of  the  spinal  cord,  and 
the  middle  peduncle  contains  fibres  which  link  the  two  halves  of  the 
cerebellum  together  in  a  physiological  though  not  in  an  anatomical 
sense.  The  upper  end  of  the  inferior  peduncle  terminates  in  the 
vermis ;  in  some  of  the  lower  animals  the  vermis  is  practically  the 
only  part  of  the  cerebellum  which  is  present,  and  it  is  this  part  of 
the  cerebellum  which  is  principally  concerned  in  the  co-ordination 
of  the  bodily  movements.  The  cerebellar  hemispheres  are  especially 
connected  with  the  opposite  cerebral  hemispheres ;  and  possibly  just 
as  the  different  regions  of  the  body  have  corresponding  areas  in  the 
cerebrum,  so  also  they  are  similarly  represented  in  the  cerebellum ; 
but  localisation  of  function  in  the  cerebellum  has  not  gone  sufficiently 
far  yet  to  make  this  a  certainty. 

If  the  cerebellum  is  removed  in  an  animal,  or  if  it  is  the  seat  of 


718  FUNCTIONS  OF  THE  CEREBELLUM        [CH.  XLIX. 

disease  in  man,  the  result  is  a  condition  of  slight  muscular  weak- 
ness ;  but  the  principal  symptom  observed  is  inco-ordination,  chiefly 
evidenced  by  a  staggering  gait  similar  to  that  seen  in  a  drunken  man. 
It  is  called  cerebellar  ataxy. 

This  condition  is  well  illustrated  in  the  figure  on  p,  717  (fig.  509); 
the  disturbed  condition  of  the  animal  contrasts  very  forcibly  with 
the  sleepy  state  produced  by  removal  of  the  cerebrum  (see  fig.  493). 

In  order  that  the  cerebellum  may  duly  execute  its  function  of 
equilibration,  it  is  necessary  that  it  should  send  out  impulses ;  this  it 
does  by  fibres  that  leave  its  cells  and  pass  out  through  its  peduncles ; 
they  pass  out  to  the  opposite  cerebral  hemisphere,  and  so  influence 
the  discharge  of  the  impulses  from  the  cortex  of  the  cerebrum.  It 
is  also  probable  that  impulses  pass  out  to  the  cord  (see  dotted  line 

in  fig.  482),  but  the  exact  course  of 
these  fibres,  if  they  do  exist,  has  still  to 
be  worked  out. 

The  cerebellum  thus  acts  upon  the 
muscles  of  the  same  side  of  the  body 
in  conjunction  with  the  cerebral  hemi- 
sphere of  the  opposite  side.  The  close 
inter-relation  of  one  cerebral  with  the 
opposite  cerebellar  hemisphere  is  shown 
in  cases  of  brain  disease,  in  which 
atrophy  of  one  cerebellar  hemisphere 
Fio.  sio.-This  is  a  reproduction  of  a     follows    that    of   the    opposito   ccrobral 

ptiotograijh  of  a  lunatics  brain  lent       ,  .       ,  ,  „         1--1  a\ 

me  by  Dr  Fricke.    Ona  cerebral  and       hemisphere    (seO    fag.    OlU). 
are  a?r^£ed. '"'''''''"'   l^emisphere  j^     ^^^^^     ^-^^^     ^-^^    CerebcUum    may 

send  out  impulses  in  this  way,  it  is 
necessary  that  it  receive  impulses  which  guide  it  by  keeping  it 
informed  of  the  position  of  the  body  in  space.  These  afferent  im- 
pulses are  of  four  kinds,  namely : — 

1.  Tactile.  3.  Visual. 

2.  Motorial.  4.  Labyrinthine. 

1.  Tactile  impressions. — The  importance  of  the  tactile  sense  is 
obvious ;  and  in  diseases  of  the  afferent  tracts,  loss  of  that  sense  in 
the  lower  limbs  leads  to  disturbances  of  equilibrium ;  in  such  cases 
a  man  has  difficulty  in  balancing  himself  while  standing  with  his 
eyes  shut.  Sherrington,  however,  has  shown  how  comparatively 
unimportant  is  the  loss  of  tactile  sensibility  from  the  feet.  A  cat, 
in  which  the  feet  have  been  completely  desensitised  by  division  of 
all  their  nerves,  can  stand  and  walk  without  obvious  inconvenience. 
It  is  not  until  the  sensitiveness  of  the  joints,  especially  in  the  upper 
segments  of  the  limb,  is  interfered  with  that  marked  disturbances 
of  balance  are  noticeable. 


CH.  XLIX.] 


LABYRINTHINE   IMPHESSIONS 


719 


2.  Moforial  impressions. — Even  more  important  tliaii  the  tactile 
sense  frora  the  skin  is  the  sense  which  enables  us  to  know  what  we 
are  doing  with  our  muscles.  We  have  hitherto  chiefly  spoken  of  the 
muscular  nerves  as  being  motor;  they  also  contain  sensory  fibres; 
these  pass  from  the  muscles,  and  their  tendons  to  the  posterior  roots 
of  the  spinal  nerves,  and  the  impulses  ascend  the  sensory  tracts 
through  cord  and  brain  to  reach  the  cerel)ellum  and  the  Eolandic 
area.  In  many  cases  of  locomotor  ataxy  there  is  but  little 
loss  of  tactile  sensibihty,  and  the  condition  of  inco-ordination  is 
then  chiefly  due  to  the  loss  of  impressions  from  motorial  organs 
(muscles     and     joints,     see     further, 

p.  742). 

3.  Visual  impressions. — The  use  of 
visual  impressions  in  guiding  the 
nervous  centres  for  the  maintenance 
of  equilibrium  is  seen  in  those  cases 
of  locomotor  ataxy  where  there  is  loss 
of  equilibrium  when  the  patient  closes 
his  eyes.  Destruction  of  the  eyes  in 
animals  often  causes  them  to  spin 
round  and  lose  their  balance.  The 
giddiness  experienced  by  many  people 
on  looking  at  moving  water,  or  after 
the  onset  of  a  squint,  or  when  objects 
are  viewed  under  unusual  circum- 
stances, as  in  the  ascent  of  a  mountain 
railway,  is  due  to  the  same  thing.  The 
importance  of  keeping  one's  eyes  open 
is  brought  home  to  one  very  forcibly 
when  one  is  walking  in  a  perilous  posi- 
tion, as  along  the  edge  of  a  precipice, 
where  an  upset  of  the  equilibrium 
would  be  attended  with  serious  con- 
sequences. 

4.  Labyrinthine  impressions. — These  are  the  most  important  of 
all ;  they  are  the  impressions  that  reach  the  central  nervous  system 
from  that  part  of  the  internal  ear  called  the  labyrinth.  Here,  how- 
ever, we  must  pause  to  consider  first  some  anatomical  facts  in 
connection  with  the  semicircular  canals  that  make  up  the  labyrinth. 
Fig.  511  is  an  external  view  of  the  internal  ear;  it  is  enclosed  within 
the  petrous  portion  of  the  temporal  bone;  and  consists  of  three 
parts — the  vestibule  (1),  the  three  semicircular  canals  (3,  4,  5)  which 
open  into  the  vestibule,  and  the  tube,  coiled  like  a  snail's  shell,  called 
the  cochlea  (6,  7,  8).  The  cochlea  is  the  part  of  the  apparatus  which 
is  concerned  in  the  reception  of  auditory  impressions ;  it  is  supplied 


-Right  bony  labyrinth,  viewed 
from  the  outer  side.  The  specimen 
here  represented  was  prepared  by 
separating  piecemeal  the  looser  sub- 
stance of  the  petrous  bone  from  the 
dense  wgills  which  immediately  en- 
close the  labyrinth.  1,  the  vestibule; 
2,  fenestra  ovalis ;  3,  superior  semi- 
circular canal ;  4,  horizontal  or  ex- 
ternal canal ;  5,  posterior  canal ;  *, 
ampulla;  of  the  semicircular  canals ; 
6,  first  turn  of  the  cochlea ;  7,  second 
turn ;  8,  apex ;  9,  fenestra  rotunda. 
The  smaller  figure  in  outline  below 
shows  the  natural  size.    (Sommering.) 


720 


FUNCTIONS   OF  THE   CEREBELLUM 


[CH.  XLIX. 


by  the  cochlear  division  of  the  eighth  or  auditory  nerve.  The 
remainder  of  the  internal  ear  is  concerned  not  in  hearing,  but  in 
the  reception  of  the  impressions  we  are  now  studying.  Within  the 
vestibule  are  two  chambers  made  of  membrane,  called  the  utricle 

and  the  saccule;  these  com- 
municate with  one  another  and 
with  the  canal  of  the  cochlea. 
Within  each  bony  semicircular 
canal  is  a  membranous  semi- 
circular canal  of  similar  shape. 
Each  canal  is  filled  with  a 
watery  fluid  called  endolymph, 
and  separated  from  the  bony 
canal  by  another  fluid  called 
perilymph.  Each  canal  has  a 
swelling  at  one  end  called  the 
ampulla.  The  membranous 
canals  open  into  the  utricle ; 
the  horizontal  canal  by  each  of 
its  ends ;  the  superior  and  pos- 
terior vertical  canals  by  three 
openings,  these  two  canals  being 
connected  at  their  non-ampul- 
lary  ends. 

Fig.    512    shows   in   transverse   section   the  way  in   which  the 
membranous  is  contained  within  the  bony  canal ;  the  membranous 


Fig.  512.— Section  of  human  semicircular  canal. 
(After  Rtidinger.)  l,Bone;  2,  periosteum  ;  3,3, 
tlbrous  bands  connecting  the  periosteum  to  4,  the 
outer  fibrous  coat  of  the  membranous  canal ; 
5,  tunica  propria ;  6,  epithelium. 


Fio.  518.— Section  through  the  wall  of  the  ampulla  of  a  semicircular  canal,  passing  through  the  crista 
acoustica.  1,  Epithelium  ;  2,  tunica  propria  ;  3,  fibrous  layer  of  canal ;  N,  bundles  of  nerve-fibres  ; 
C,  cupula,  into  which  the  hairs  of  the  hair-cells  project.    (After  Schufer). 

canal  consists  of  three  layers,  the  outer  of  which  is  fibrous  and 
continuous  with  the  periosteum  that  lines  the  bony  canal ;  then  comes 
the  tunica  propria,  composed  of  homogeneous  material,  and  thrown 


CH.  XLIX.] 


THE  SEMICIRCULAR   CANALS 


721 


into  papillre  except  just  where  the  attachment  of  the  membranous  to 
the  bony  canal  is  closest;  and  the  innermost  layer  is  a  somewhat 
flattened  epithelium. 

At  the  ampulla  there  is  a  different  appearance ;  the  tunica 
propria  is  raised  into  a  hillock  called  the  crista  aciustica  (see  fig.  513) ; 
the  cells  of  the  epithelium  become  columnar  in  shape,  and  to  some 
of  them  fibres  of  the  auditory  nerve  pass,  arborising  round  them ; 
these  cells  are  provided  with  stiff  hairs,  which  project  into  what  is 
called  the  cupula,  a  mass  of  mucus-like  material  containing  otoliths 
or  crystals  of  calcium  carbonate.  Between  the  hair-cells  are  fibre- 
cells  which  act  as  supports  (fig.  514).  When  the  endolymph  in  the 
interior  of  the  canals  is  thrown  into  vibration,  the  hairs  of  the  hair- 
cells  are  affected,  and  a  nervous  im- 
pulse is  set  up  in  the  contiguous 
nerve-fibres,  which  carry  it  to  the 
central  nervous  system. 

The  walls  of  the  saccule  and 
utricle  are  similar  in  composition, 
and  each  has  a  similar  hillock,  called 
a  macula,  to  the  hair-cells  on  which 
nerve-fibres  are  distributed. 

The  macula  of  the  utricle  and 
the  cristas  of  the  superior  and  hori- 
zontal canals  are  supplied  by  the 
vestibular  division  of  the  eighth  or 
auditory  nerve.  The  macula  of  the 
saccule  and  the  crista  of  the  posterior 
canal  are  supplied  by  a  branch  of  the 
cochlear  division  of  the  same  nerve 
(see  p.  655). 

It  will  be  noticed  that  the  canals 
of  each  side  are  in  three  planes  at 
right  angles  to  each  other,  and  we 
learn  the  movements  of  our  body  with  regard  to  the  three  dimen- 
sions of  space  by  means  of  impressions  from  the  ampullary  endings 
of  the  auditory  nerve ;  these  impressions  are  set  up  by  the  varying 
pressure  of  the  endolymph  in  the  am  pull  se. 

Thus  a  sudden  turning  of  the  head  from  right  to  left  will  cause 
movement  of  the  endolymph  towards,  and  therefore  increased  pressure 
on,  the  ampullary  nerve-endings  of  the  left  horizontal  canal,  and 
diminished  pressure  on  the  corresponding  nerve-endings  of  the  right 
side.  It  is  probable  that  resulting  from  such  a  movement  two 
impulses  reach  the  brain,  one  the  effect  of  increased  pressure  in  one 
ampulla,  the  second  the  effect  of  decreased  pressure  in  its  fellow. 

"  One  canal  can  be  affected  by,  and  transmit  the  sensation  of 

2  Z 


Fig.  514. — 1,  Hair-cell ;  3,  hair-cell,  showing 
the  hair  broken,  and  the  base  of  the  hair 
split  into  its  constituent  fibrils;  2,  fibre- 
cell  ;  N,  bundle  of  nerve-tibres  which 
have  lost  their  medullary  sheath,  and 
terminate  by  arborising  round  the  base 
of  the  hair-cells  ;  A  B,  surface  of  tunica 
propria.    (After  Retzius.) 


'22 


FUNCTIONS   OF  THE   CEREBELLUM 


[CH.  XLIX. 


rotation  about  one  axis  in  one  direction  only;  and  for  complete 
perception  of  rotation  in  any  direction  about  any  axis,  six  canals  are 
required  in  three  pairs,  each  pair  being  in  the  same  or  parallel  planes, 
and  their  ampullae  turned  opposite  ways.  Each  pair  would  thus  be 
sensitive  to  any  rotation  about  a  line  at  right  angles  to  its  plane  or 
planes,  the  one  canal  being  influenced  by  rotation  in  one  direction, 
the  other  by  rotation  in  the  opposite  direction."     (Crum-Brown.) 

The  two  horizontal  canals  are  in  the  same  plane ;  the  posterior 
vertical  of  one  side  is  in  a  plane  parallel  to  that  of  the  superior 
vertical  of  the  other  side  (see  fig.  515). 


Pig.  515. — Diagram  of  semicircular  canals,  to  show  tlieir  positions  in  three  planes  at  right  angles  to 
each  other.  It  will  be  seen  that  the  two  horizontal  canals  (H)  lie  in  the  same  plane  :  and  that  the 
superior  vertical  of  one  side  (8)  lies  in  a  plane  parallel  to  that  of  the  posterior  vertical  (P)  of  the 
other.    (After  Ewald.) 

When  these  canals  are  diseased  in  man  as  in  Meniere's  disease, 
there  are  disturbances  of  equilibrium :  a  feeling  of  giddiness,  which 
may  lead  to  the  patient's  falling  down,  is  associated  with  nausea  and 
vomiting.  In  animals  similar  results  are  produced  by  injury,  and  the 
subject  has  been  chiefly  worked  out  on  birds  by  Flourens,  where  the 
canals  are  large  and  readily  exposed,  and  more  recently  in  fishes,  by  Lee. 

Thus,  if  the  horizontal  canal  is  divided  in  a  pigeon,  the  head  is 
thrown  into  a  series  of  oscillations  in  a  horizontal  plane,  which  are 
increased  by  section  of  the  corresponding  canal  of  the  opposite  side. 
After  section  of  the  vertical  canals,  the  forced  movements  are  in  a 
vertical  plane,  and  the  animal  tends  to  turn  somersaults. 

"When  the  whole  of  the  canals  are  destroyed  on  both  sides 
the  disturbances  of  equilibrium  are  of  the  most  pronounced  character. 
Goltz  describes  a  pigeon  so  treated  which  always  kept  its  head  with 
the  occiput  touching  the  breast,  the  vertex  directed  downwards,  with 
the  right  eye  looking  to  the  left  and  the  left  looking  to  the  right, 
the  head  being  incessantly  swung  in  a  pendulum-like  manner. 
Cyon  says  it  is  almost  impossible  to  give  an  idea  of  the  perpetual 
movements  to  which  the  animal  is  subject.  It  can  neither  stand, 
nor  lie  still,  nor  fly,  nor  maintain  any  fixed  attitude.  It  executes 
violent  somersaults,  now  forwards,  now  backwards,  rolls  round  and 
round,  or  springs  in  the  air  and  falls  back  to  recommence  anew.     It 


CH.  XLIX.]  THE   SEMICIRCULAR   CANALS  723 

is  necessary  to  envelop  the  animals  in  some  soft  covering  to  prevent 
them  dashing  themselves  to  pieces  by  the  violence  of  their  move- 
ments, and  even  then  not  always  with  success.  The  extreme 
agitation  is  manifest  only  during  the  first  few  days  following  the 
operation,  and  the  animal  may  then  be  set  free  without  danger ;  but 
it  is  still  unable  to  stand  or  walk,  and  tumultuous  movements  come 
on  from  the  slightest  disturbance.  But  after  the  lapse  of  a  fortnight 
it  is  able  to  maintain  its  upright  position.  At  this  stage  it  resembles 
an  animal  painfully  learning  to  stand  and  walk.  In  this  it  relies 
mainly  on  its  vision,  and  it  is  only  necessary  to  cover  the  eyes  with 
a  hood  to  dispel  all  the  fruits  of  this  new  education,  and  cause  the 
reappearance  of  all  the  motor  disorders."     (Ferrier.) 

It  is  these  canals  which  enable  all  of  us  to  know  in  which  direc» 
tion  we  are  being  moved,  even  though  our  eyes  are  bandaged,  and 
the  feet  are  not  allowed  to  touch  the  ground.  On  being  whirled 
round,  such  a  person  knows  in  which  direction  he  is  being  moved, 
and  feels  that  he  is  moving  so  long  as  the  rate  of  rotation  varies, 
but  when  the  whirling  stops  he  seems,  especially  if  he  opens  his 
eyes,  to  be  whirling  in  the  opposite  direction,  probably  owing  to  the 
rebound  of  the  fluid  in  the  canals.  The  forced  movements  just 
described  in  animals  are  due  both  to  the  absence  of  the  normal  sensa- 
tions from  the  canals  and  to  delusive  sensations  arising  from  their 
irritation,  and  the  animal  makes  efforts  to  correct  the  movement 
which  it  imagines  it  is  being  subjected  to. 

Artificial  stimulation  of  the  canals  produces  raoveraents  of  the  head  and  orbits, 
and  giddiness.  Similar  movements  occur  during  bodily  rotation,  and  giddiness  is 
the  result  of  a  rivalry  of  sensations  which  afford  conflicting  ideas  of  the  position  of 
the  body  relatively  to  external  objects.  A  certain  proportion  of  deaf  mutes  lose  their 
sense  of  direction  under  water,  cannot  maintain  their  equilibrium  when  their  eyes  are 
shut,  exhibit  no  orbital  movements  when  rotated,  and  never  suffer  from  sea-sickness 
or  giddiness.  This  proportion  is  approximately  the  frequency  in  which  abnormal 
conditions  of  the  canals  have  been  found  post-mortem  in  deaf  mutes. 

These  four  sets  of  impressions  (tactile,  motorial,  visual,  and 
labyrinthine)  reach  the  cerebellum  by  its  peduncles ;  from  the  eyes 
through  the  superior  peduncle,  from  the  semicircular  canals  through 
the  middle  and  inferior  peduncles,  and  from  the  body  generally 
through  the  restiform  body  or  inferior  peduncle.  Section  and 
stimulation  of  the  peduncles  cause  inco-ordination,  chiefly  evidenced 
by  rotatory  and  circus  movements  similar  to  those  that  occur  when 
the  nerve-endings  in  the  semicii'cular  canals  are  destroyed  or  stimu- 
lated. Stimulation  of  the  cerebellum  itself — and  this  has  been  done 
through  the  skull  in  man — causes  giddiness,  and  consequent  muscular 
efforts  to  correct  it.  The  results  of  stimulation,  indeed,  are  precisely 
analogous  to  those  of  extirpation,  only  in  the  reverse  direction.  Loss 
of  muscular  tone  which  follows  extirpation  of  the  canals  is  probably 
the  result  of  secondary  changes  in  the  brain. 


CHAPTER  L 

COMPARATIVE   PHYSIOLOGY   OF   THE    BRAIN 

It  will  have  been  noticed  in  the  preceding  chapters  how  much  of  our 
knowledge  of  cerebral  functions  is  derived  from  observations  and 
experiments  performed  upon  the  lower  animals.  I  propose  in  this 
chapter  to  expand  this  part  of  the  subject.  It  is  important  not  only 
because  of  its  intrinsic  interest,  but  also  because  a  wider  survey  of 
the  conditions  in  various  animals  throws  considerable  light  on  what 
is  found  in  man. 

The  brain  in  the  lower  vertebrata  is  composed  of  a  smaller 
number  of  cells  than  is  found  in  the  human  brain ;  one  notices  also 
that  the  massing  of  the  nerve  units  towards  the  cerebral  cortex  and 
in  relation  to  the  principal  sense  organs  has  gone  on  to  a  less  extent. 

The  doctrine  of  cerebral  localisation  is  not  accurately  expressed 
by  the  statement  that  a  cortical  centre  is  one,  the  stimulation  of 
which  produces  a  definite  response,  and  the  extirpation  of  which 
abolishes  the  response.  "We  have,  for  instance,  seen  that  the  stimu- 
lation of  certain  areas  in  the  dog's  brain  produces  certain  movements, 
but  Goltz  showed  that  in  his  dogs,  the  removal  of  an  entire  hemi- 
sphere did  not  cause  permanent  paralysis  of  the  opposite  side  of  the 
body. 

In  the  central  nervous  system  there  are  few  or  no  places,  where 
only  one  set  of  nerve  units  are  situated,  with  fibres  passing  to  and 
from  them.  Almost  every  locality  has  several  connections  with 
other  parts,  and  also  fibres  passing  through  it  which  connect  together 
the  parts  on  all  sides  of  it.  Hence  in  extirpating  even  a  limited 
area,  numerous  pathways  are  interrupted,  and  the  damage  is  con- 
sequently widespread.  Much  of  the  disturbance  produced  at  first 
gradually  passes  away,  and  the  temporary  effects  must  be  distinguished 
from  those  which  are  permanent ;  the  permanent  effects  have  the 
greater  significance  of  the  two.  Moreover,  it  is  clear  that  the  relative 
and  absolute  value  of  any  locality  in  the  central  nervous  system 
depends  largely  on  the  degree  to  which  centraKsation  has  progressed, 
and  on  the  amount  of  connection  between  the  various  areas.  The 
closer  the  connection,  the  more  numerous  and  intricate  the  path- 

T24 


CH.  L.]  COMPARATIVE   PHYSIOLOGY   OF  THE  BRAIN  725 

ways,  the  greater  will  be  the  periaaneiit  effects  of  an  extirjiation, 
and  the  recovery  of  function  the  more  remote.  The  lower  the 
animal  in  the  zoological  series,  or  the  less  the  age  of  the  animal,  the 
more  imperfectly  developed  will  be  the  connecting  strands,  and  so 
the  possibility  of  other  parts  taking  up  to  some  extent  the  functions 
of  those  that  are  removed  will  be  increased. 

If  the  cerebral  hemispheres  are  removed  in  a  teleostean  or  bony 
fish  (and  in  such  animals  there  is  practically  no  cortex),  the  animal 
is  to  all  intents  and  purposes  unaffected ;  it  can  distinguish  between 
a  worm  and  a  piece  of  string,  and  will  rise  to  red  wafers  in  preference 
to  those  of  another  colour.  The  operation  does  not  damage  the 
primary  centres  of  vision,  and  in  these  fishes  the  eye  is  the  most 
important  sense  organ. 

A  shark,  however,  subjected  to  the  same  operation,  is  reduced  to 
a  condition  of  complete  quiescence ;  this  is  due  to  the  circumstance 
that  in  this  fish  the  principal  sense  organ  is  that  of  smell,  and  sever- 
ance of  both  olfactory  tracts  produces  the  same  result  as  removal 
of  the  entire  hemispheres.  In  either  case  the  path  between  the 
olfactory  bulbs  and  the  centres  that  control  the  cord  are  interrupted. 

Going  higher  in  the  animal  scale  to  the  frog,  we  find  that  re- 
moval  of  the  hemispheres  only  does  not  entirely  abolish  its  apparent 
spontaneity;  it  still  continues  to  feed  itself,  for  instance,  by  catching 
passing  insects.  It  is  not  until  the  optic  thalami  are  removed  also 
that  it  becomes  the  purely  reflex  animal  described  on  p.  680. 

If  the  brain  and  the  anterior  end  of  the  bulb  are  removed  the 
frog  becomes  incessantly  active,  creeping  and  clambering  about  the 
room ;  but  if  the  whole  bulb  is  removed  strong  stimulation  is  required 
to  produce  movements ;  these,  however,  remain  co-ordinated. 

If  the  frog's  cerebellum  is  removed  there  is  some  tremor  of  the 
leg  muscles,  and  a  loss  of  co-ordination  in  jumping.  If  the  removal 
is  confined  to  one  side  of  the  twixt-brain,  mid -brain,  or  bulb,  there  is  a 
tendency  to  forced  positions  and  movements,  action  being  most  vigor- 
ous on  the  side  of  the  body  associated  with  the  uninjured  portions. 

We  thus  see  that  a  progressive  removal  of  portions  of  the  brain 
is  followed  by  a  progressive  loss  of  responsiveness,  until  we  reach  the 
anterior  end  of  the  bulb,  the  removal  of  which  sets  free  the  lower 
centres  of  the  cord,  and  the  result  is  incessant  movement  provoked 
by  slight  stimuli.  Further  removal,  however,  lessens  responsiveness, 
and  this  is  not  easy  to  explain. 

In  the  bird,  removal  of  the  hemispheres  and  basal  ganglia  pro- 
duces the  sleepy  condition  already  described  (p.  693) ;  when  the 
animal  is  made  to  fly  its  movements  are  directed  by  the  sense  of 
sight,  and  it  will  select  a  perch  to  settle  on  in  preference  to  the  floor. 
It  will  start  at  a  noise;  it  will  not  eat  voluntarily;  it  exhibits  no 
emotions  such  as  fear,  sexual  feeling,  or  maternal  instincts. 


726  COMPARATIVE   PHYSIOLOGY   OF   THE   BRAIN  [CH.  L. 

In  mammals,  the  difficulty  of  the  operation  has  been  overcome  by 
Goltz  in  dogs  by  removing  the  cerebrum  piecemeal.  One  dog  treated 
in  this  way  lived  in  good  health  for  eighteen  months,  when  it  was 
killed  in  order  that  a  thorough  examination  of  the  brain  might 
be  made.  It  was  then  found  that  not  only  the  hemispheres  but  the 
main  parts  of  the  optic  thalamus  and  corpus  striatum  had  been 
removed  also.  Though  it  could  still  carry  out  co-ordinated  move- 
ments, its  reactions  were  entirely  reflex,  and  emotions,  feelings,  or 
the  capacity  to  learn  were  absent. 

If  we  now  compare  these  effects,  it  is  seen  that  the  results  of  the 
operation  becomes  progressively  greater  as  we  ascend  the  scale.  The 
higher  the  animal,  the  more  fatal  the  effects,  the  immediate  disturb- 
ance more  severe,  the  return  of  function  slower,  and  the  permanent 
loss  greater.  The  long  life  of  Goltz's  dog  was  doubtless  due  to  the 
fact  that  the  removal  was  accomplished  by  several  operations. 

The  higher  animal  loses  just  those  characters  which  distinguish 
it  from  the  lower  ones.  It  is  difficult  to  prophesy  what  would 
happen  if  as  extensive  operations  were  carried  out  in  a  monkey  or  a 
man.  But  so  far  as  extirpation  has  been  observed,  the  initial  paralysis 
(which  is  seen  also  in  the  dog)  does  not  disappear  so  rapidly  or  so 
completely.     In  man,  the  tendency  to  recover  is  least. 

This  is  anatomically  explicable  when  we  remember  that  the 
anterior  horn  cells  are  influenced  chiefly  by  two  sets  of  impulses, 
those  which  enter  the  cord  by  the  posterior  roots,  and  those  which 
come  down  from  the  cerebrum  by  the  pyramidal  tracts.  In  the  lower 
animals  the  pyramidal  pathway  is  insignificant,  and  when  it  is  inter- 
rupted the  disturbance  is  consequently  slight.  In  animals  below 
the  mammals  it  is  absent,  and  going  up  the  mammalian  scale  it 
becomes  more  and  more  important,  as  the  following  figures  show : — 

In  the  mouse  the  pyramidal  fibres  constitute  I  "14  per  cent,  of  those  in  the  cord. 
,,      guinea-pig     ,,                         ,,                  3*0              ,,  ,, 

,,      rabbit  ,,  ,,  5  "3  ,,  ,, 

„      cat  „  „  7-76 

„      man  ,,  ,,  11'87  ,,  ,, 

We  can  therefore  quite  readily  understand  that  in  the  apes  and 
in  man,  a  damage  to  the  cortex  which  causes  degeneration  of  these 
tracts  will  cut  off  many  impulses  to-  the  anterior  cornual  cells,  and 
produce  a  greater  or  less  degree  of  paralysis. 

There  are  80,000  fibres  in  each  pyramidal  tract  of  the  human  cord.  They  are, 
moreover,  not  the  only  tracts  which  connect  the  cerebrum  to  the  spinal  cord,  and 
section  of  these  other  tracts  (see  p.  628)  may  produce  more  marked  and  more 
permanent  paralysis.  In  man,  it  appears  that  when  the  pyramidal  tracts  are 
diseased,  it  is  the  finer  and  more  dehcate  movements  which  are  permanently  lost. 
(Schafer.) 

"We  have  already  pointed  out  (p.  701)  that  the  size  of  the  cortical 
areas  does  not  vary  with  the  mere  mass  of  the  muscles  under  control, 


CII.  L.]  COMPARATIVE   PHYSIOLOGY    OF   THE    BRAIN  727 

but  with  tlio  increasing  complexity  and  delicacy  of  the  movement ; 
(compare  in  Hg.  498  the  relative  size  of  the  areas  which  control  the 
trunk  muscles  and  the  finger  movements).  It  is  just  these  move- 
ments which  are  most  affected  by  a  cortical  injury,  and  which  exhibit 
least  recovery ;  in  the  upper  limb,  for  instance,  the  shoulder  muscles 
will  be  the  least,  and  the  hand  the  most,  paralysed. 

On  the  sensory  side  of  the  cortex,  vision  alone  can  be  analysed 
with  sufficient  accuracy.  The  lower  the  animal  in  the  series,  the 
more  readily  can  its  actions  be  controlled  by  sensory  impulses  which 
have  not  passed  through  the  cortex  cerebri.  A  decerebrated  bony 
fish  can  distinguish  colours,  a  frog  can  catch  flies,  even  a  pigeon  will 
select  its  perch,  though  it  takes  no  notice  of  food  or  of  people  who  try 
to  frighten  it.  A  dog  similarly  operated  on  is  practically  blind, 
though  it  will  blink  at  a  bright  flash  of  light.  In  the  lower  animals 
the  impulses  pass  in  to  the  primary  visual  centre  which  acts  as  the 
centre  for  the  reflex;  the  higher  we  ascend  the  animal  scale,  the 
path  vid  the  cortex  becomes  more  permeable,  of  greater  value  or 
even  indispensable,  and  the  reflexes  through  the  lower  centres  of  less 
importance;  not  only  so,  but  there  are  subdivisions  of  the  visual 
cortical  area,  which  correspond  to  different  regions  of  the  retinse. 

In  the  fishes  which  have  no  cortex  cerebri,  the  optic  lobes,  analogous  to  the  C. 
quadrigcniina,  are  the  centres  for  vision.  In  some  fishes,  a  small  number  of  the 
fibres  of  the  optic  nerve  pass  into  the  geniculate  body,  which  forms  a  cell  station  on 
the  road  to  the  posterior  region  of  the  cerebrum,  where  a  primitive  cortex  begins  to 
appear.  On  ascending  the  animal  scale,  this  group  of  fibres  becomes  more  and  more 
abundant,  and  this  part  of  the  cortex  becomes  more  elaborate  in  structure.  When 
we  reach  the  monkeys,  this  part  of  the  brain  is  cut  off  from  the  rest  to  form  a  dis- 
tinct occipital  lobe  by  the  parieto-occipital  fissure,  which  is  frequently  called  the 
AfFenspalte  (ape's  split).  At  first  this  lobe  is  smooth  (fig.  497,  p.  699),  but  as  the 
great  parietal  association  centres  get  larger  with  increase  of  intelligence,  the  visuo- 
sensory  area  is  pushed  back,  and  is  thus  thrown  into  folds.  In  the  highest  apes, 
and  in  the  lower  races  of  mankind,  a  good  deal  of  the  visuo-sensory  sphere  is  still 
seen  on  the  external  cerebral  surface  ;  but  in  the  higher  races,  most  is  pushed  round 
on  to  the  mesial  surface  (area  4,  figs.  506,  .507,  p.  7io).  This  calcarine  area  is  better 
named  the  striate  area,  because  it  is  characterised  by  the  white  stripe  called  the  line 
of  Gennari  (see  p.  703). 

Some  animals  have  panoramic  and  others  stereoscopic  vision.  The  former 
(mainly  vegetable  feeders)  have  eyes  set  laterally;  each  eye  receives  a  different 
picture,  and  the  decussation  of  the  optic  nerves  is  complete;  each  eye  sends 
impulses  to  the  opposite  hemisphere.  Animals  with  stereoscopic  vision  have  the 
eyes,  as  in  man,  in  front,  and  the  optic  axes  can  be  converged  so  that  an  object  is 
focussed  with  both  eyes.  This  becomes  necessary  in  carnivora,  which  have  to  catch 
moving  prey;  the  more  complex  the  movements  of  the  fore-limb,  the  greater 
becomes  the  necessity  for  fixation  of  the  eyes  to  guide  them.  In  such  animals  each 
visual  area  corresponds  with  the  same  half  of  both  retinae,  that  is,  with  the  opposite 
half  of  the  visual  field  ;  the  lower  half  of  each  area  corresponds  with  the  upper  half 
of  each  half  field  of  vision,  and  vice  versa.  The  appearance  of  the  macula  lutea  (with 
cortical  representation  in  both  hemispheres)  in  the  primates  is  the  culminating  point 
in  visual  development  among  the  mammals. 

A  man  or  an  animal  who  loses  both  eyes  is  bhnd,  but  in  time  manages  to  find 
his  way  about.  This  is  not  the  case  when  blindness  is  produced  by  removal  or 
disease  of  both  occipital  lobes ;  here,  the  sense  of  orientation  is  lost  also,  for  the 
associa,tion  of  many  essential  sensory  and  motor  impulses  is  then  impossible. 


CHAPTER  LI 

SENSATION 

Befoke  passing  to  the  study  of  the  various  special  senses,  there  are 
a  number  of  general  considerations  in  connection  with  the  subject  of 
sensation  that  demand  our  attention. 

The  psychologist  divides  the  mental  phenomena,  which  the 
physiologist  localises  in  the  brain,  into  three  main  categories : — 

1.  Intellectual:  perceiving,  remembering,  reasoning,  etc. 

2.  Emotional :  joy,  love,  hate,  anger,  etc. 

3.  Volitional:  purposing,  deliberating,  doing. 

These  are  all  closely  connected  together,  and  are  all  present  in 
each  healthy  brain ;  but  according  as  one  or  other  may  predominate, 
we  speak  of  intellectual,  emotional,  or  strong-willed  individuals. 
The  connection  is  especially  close  between  intellect  and  will,  which 
represent  as  it  were  the  two  sides  of  what  we  may  call  a  conscious 
reflex  action ;  the  intellect  gives  the  reason  or  stimulus  for  the 
exercise  of  the  volitional  power.  The  emotions  are  more  complex 
mental  processes,  in  which  sensations  predominate. 

The  intellectual  faculties  are  derived  from  the  senses ;  sensations 
form  the  materials  for  intellect ;  in  other  words,  we  know  and  learn 
from  what  we  see,  feel,  hear,  taste,  and  smell.  People  born  blind  or 
deaf  thus  labour  under  the  great  disadvantage  of  having  one  or  the 
other  channel  of  knowledge  closed ;  they  can,  however,  make  up  for 
this  in  some  measure  by  an  education,  and  consequent  increased 
sensitiveness  of  the  channels  that  remain  open. 

The  simplest  mental  operation  is  a  sensation — that  is,  the 
conscious  reception  of  an  impression  from  the  external  world.  For 
this  the  following  things  are  necessary : — 

1.  A  stimulus. 

2.  A  nerve-ending  to  receive  it. 

3.  A  path  to  the  brain. 

4.  A  part  of  the  brain  to  receive  the  impulse. 

Partly  through  congenital,  partly  through  acquiretl  experience, 
the  brain  refers  the  sensation  to  the  nerve-ending  which  received 

728 


CII.  LI.]  SENSATION  729 

the  sliiiiulus;  thus  pain  in  the  linger  is  referred  to  the  finger, 
the  sight  of  an  object  to  the  eyes,  etc.  If  the  ulnar  nerve  is 
stimulated  by  a  knock  on  the  elbow,  the  sensation  is  referred  to 
the  fingers  where  the  nerve  is  distributed  ;  if  the  stump  of  a  recently 
amputated  leg  be  stimulated,  the  brain  not  having  got  used  to  the 
new  condition  of  things,  refers  the  sensation  to  the  toes,  which  still 
seem  to  be  present. 

Perception  is  a  more  complicated  mental  process ;  it  consists  in 
the  grouping  of  sensations  into  a  presentation  of  the  object  from 
which  they  arise,  and  which  is  called  the  percept.  The  smell,  the 
taste,  the  colour,  etc.,  of  an  orange  are  all  sensations  ;  the  grouping 
of  these  together  constitutes  the  perception  of  an  orange.  Each 
mental  process  leaves  an  impress  on  the  mind  ;  these  impressions 
allow  of  memory,  or  representative  imagination  ;  this  may  be  repro- 
ductive, as  in  recalling  a  friend's  face  ;  or  constructive,  as  in  picturing 
the  face  of  an  historical  person. 

During  the  whole  operation,  moreover,  there  must  be  attention ; 
it  is  quite  possible,  for  instance,  in  a  dreamy  person,  that  he  may 
look  at  a  thing  without  seeing  it,  or  be  present  at  a  lecture  without 
hearing  it. 

The  more  complex  intellectual  operations  consist  in  the  forma- 
tion of  concepts,  and  reasoning  is  the  grouping  and  discrimination  of 
conceptions.  Just  as  perception  is  built  up  of  sensations,  so 
conception  is  built  up  of  perceptions.  Thus  the  orange  of  our 
previous  example  is  learnt  to  be  one  of  similar  substances  called 
fruits ;  fruits  to  be  products  of  the  vegetable,  as  distinguished  from 
the  animal  world,  and  so  on. 

In  the  mental  development  of  a  child,  it  is  very  doubtful  whether 
he  ever  experiences  the  individual  sensations,  of  which  for  descrip- 
tive purposes  we  have  assumed  a  perception  is  built,  although  of 
course  it  is  only  by  education  that  he  learns  what  these  sensa- 
tions correspond  to  in  the  external  world,  and  how  they  may  be 
classified.  From  the  first,  perceptions  and  conceptions  find  an  outlet 
in  motor  activity;  at  length  the  conscious  realisation  of  ideas  of 
movement  culminate  in  the  purposeful  actions  of  volition.  More- 
over, every  experience  contains  its  own  quantum  of  pain  or  pleasure, 
and  produces  reflex  contractions  or  relaxations  in  vascular  and  other 
tissues,  which  in  their  turn  possess  a  painful  or  pleasurable  com- 
ponent. So,  too,  ideas  acquire  their  colouring  of  pain  or  pleasure, 
ultimately  elaborating  the  complex  emotions  of  sorrow,  joy,  etc. 

The  nerve-endings  that  receive  the  impression  from  the  external 
world  are  of  various  kinds.  They  may  be  simply  ramifying  and 
interlacing  plexuses  of  nerve-fibrils,  as  in  the  cornea,  parts  of  the 
skin,  and  in  the  interior  of  the  body ;  this  kind  of  nerve-ending  is 
chiefly  associated  with  general  sensibility,  that  vague  kind  of  seusa- 


730  SENSATION  [CH,  LI. 

tion  which  cannot  be  put  under  any  of  the  special  headings — sight, 
hearing,  labyrinthine,  taste,  smell,  touch,  temperature,  etc.  The 
nerve-endings  of  the  nerves  of  special  sense  are  usually  end-organs 
of  a  specialised  kind.  The  most  frequent  kind  of  sensory  end-organ 
is  made  of  what  is  called  nerve-epithelium ;  certain  epithelial  cells  of 
the  surface  of  the  body  become  peculiarly  modified,  and  grouped  in 
special  ways  to  receive  the  impressions  from  the  outer  world ;  these 
send  an  impulse  into  the  arborisations  at  the  termination  of  the 
axis-cylinders  of  the  nerves  which  envelop  the  cells.  One  of  these 
varieties  of  nerve-epithelium  we  have  already  made  the  acquaintance 
of,  in  the  hair-cells  of  the  semicircular  canals ;  we  shall  find  other 
kinds  in  the  hair-cells  of  the  cochlea,  in  the  rods  and  cones  of  the 
retina,  etc. 

Pain  may  be  due  to  an  excessive  stimulation  of  the  other  sensory 
nerves,  but  there  is  evidence  that  it  is  a  distinct  sensation.  Thus 
in  some  cases  of  diseases  of  sensory  channels,  tactile  sensation  may 
be  intact,  but  sensitiveness  to  pain  absent,  and  vice  versa ;  (see 
p.  679  and  also  p.  740). 

The  other  essential  anatomical  necessities  for  a  sensation  are  the 
channels  to  the  brain  with  their  numerous  cell-stations  on  the  road, 
and  the  parts  of  the  brain  to  which  these  tracts  pass.  Blindness,  for 
instance,  may  not  only  be  due  to  disease  of  the  eye,  but  also  to 
disease  of  the  optic  nerve,  or  of  the  parts  of  the  brain  to  which  the 
optic  nerve  passes. 

A  small  stimulus,  or  a  small  increase  or  decrease  in  a  big  stimulus, 
will  have  no  effect ;  a  light  touch,  a  feeble  light,  a  gentle  sound,  may 
be  so  slight  as  to  produce  no  effect  on  the  brain.  The  smallest 
stimulus  that  produces  an  effect  is  called  the  lower  limit  of  excitation 
or  the  liminal  (from  limen,  a  threshold)  intensity  of  the  sensation. 
The  height  of  sensibility  or  maximum  of  excitation  is  a  stimulus,  so 
strong  that  the  brain  is  incapable  of  recognising  any  increase  in  it; 
a  bright  light,  for  instance,  may  be  so  intense  that  any  increase  in 
its  brightness  is  not  perceptible.  Between  these  two  extremes  we 
have  what  is  called  the  range  of  sensibility.  Most  of  our  ordinary 
sensations  fall  somewhere  about  the  middle  of  the  range,  and  Weber's 
law  (as  expanded  by  Fechner)  is  a  law  that  regulates  the  proportion 
between  the  stimulus  and  the  sensation,  and  which  is  operative  for 
this  region  of  the  range  of  sensibihty.  In  general  terms  it  may  be 
stated  that  sensations  increase  as  the  logarithm  of  the  stimuli; 
or,  in  order  that  the  intensity  of  a  sensation  may  increase  in 
arithmetical  progression,  the  stimulus  must  increase  in  a  geometrical 
progression. 

A  definite  example  will  help  us  to  understand  these  mathemati- 
cal terms  a  little  better.  We  will  select  our  example  from  the 
sense  of  vision,  because  the  intensity  of  the  cause  of  visual  sensa- 


en.  LI.]  DISCRIMINATIVE   SENSIBILITY  731 

tions,  light,  is  easily  measurable.  Suppose  a  room  lighted  by  100 
candles,  and  one  candle  more  is  brought  in,  the  increase  of  light  pro- 
duced by  the  extra  candle  is  quite  perceptible  to  the  eye ;  or  if  a 
candle  were  removed,  the  decrease  in  light  would  be  perfectly 
appreciable.  Next  suppose  the  room  lighted  by  1000  candles,  and 
one  extra  was  brought  in,  no  difference  would  be  seen  in  the  amount 
of  illumination ;  in  order  to  notice  increase  or  decrease  in  the  light 
it  would  be  necessary  to  bring  in  ten  extra  candles,  or  take  away 
ten  of  the  candles,  as  the  case  might  be.  In  each  case  an  increment 
or  decrease  of  one-hundredth  of  the  original  light  is  necessary  to 
cause  an  increase  or  diminution  in  the  sensation. 

This  is  after  all  a  perfectly  familiar  fact ;  a  farthing  rushlight 
will  increase  the  illumination  in  a  dimly-lighted  cellar,  but  it  makes 
no  apparent  difference  in  the  bright  sunshine. 

The  magnitude  of  the  fraction  representing  the  increment  of 
stimulus  necessary  to  produce  an  increase  of  sensation  determines 
what  is  called  the  discriminative  sensibility.  This  fraction  differs 
considerably  for  different  sense-organs ;  thus  : — 

For  light  it  is  y^- 

For  weight  it  is  -^  to  yV  for  different  muscles. 

For  tactile  pressure  ^/o"  to  yV  i^i  different  parts  of  the  body. 

Another  general  consideration  in  connection  with  sensation  is 
that  the  sensation  lasts  longer  than  the  stimulus ;  a  familiar  instance 
of  this  is  the  sting  after  a  blow.  The  after-sensations,  as  they  are 
called,  have  been  specially  studied  in  connection  with  the  eye  (see 
After-images). 

Subjective  sensations  are  those  which  are  not  produced  by  stimuli 
in  the  external  world,  but  arise  in  one's  own  inner  consciousness ; 
they  are  illustrated  by  the  sensations  experienced  during  sleep 
(dreams),  and  in  the  hallucinations  to  which  mad  and  delirious  people 
are  subject. 

Homologous  stimuli. — Each  kind  of  peripheral  end-organ  is  speci- 
ally suited  to  respond  to  a  certain  kind  of  stimulus.  The  homo- 
logous stimuli  of  the  organs  of  special  sense  may  be  divided  into  : — 

1.  Vibrations  set  up  at  a  distance  without  actual  contact  with 
the  object;  for  instance,  light  and  radiant  heat. 

2.  Changes  produced  by  actual  contact  with  the  object;  for 
instance,  in  the  production  of  sensations  of  taste,  touch,  weight,  and 
alteration  of  temperature  by  conduction ;  in  the  case  of  the  olfactory 
end-organs,  the  sensation  is  also  excited  by  material  particles  given 
off  by  the  odoriferous  body,  and  borne  by  the  air  to  the  nostrils.  In 
sound  also,  though  there  is  no  actual  contact  of  the  ear  with  the 
vibrating  body  which  emits  the  sound,  the  organ  of  hearing  is  excited 
by  waves  of  material  substance,  first  of  air,  then  of  bones,  then  of 
endolymph,  and  these  excite  the  nerve-endings  of  the  internal  ear. 


732  SENSATION  [CH.  LI. 

When  the  eye  is  excited  by  any  other  kind  of  stimulus  than  by 
light,  which  is  its  adequate  or  homologous  stimulus,  the  sensation 
experienced  is  light  all  the  same ;  for  instance,  one  sees  sparks  when 
the  eyeball  is  struck ;  singing  in  the  ears,  the  result  of  an  accumula- 
tion of  wax  against  the  membrana  tympani,  is  a  similar  example. 

It  has  been  inferred  that  there  are  separate  nerve-fibres  for  the 
conveyance  of  each  kind  of  sensation,  and  Johannes  Muller  expressed 
this  idea  in  what  is  known  as  the  law  of  specific  nerve  energy.  He 
pointed  out  that  the  same  nerve  may  be  stimulated  by  mechanical  or 
electrical  means  as  well  as  in  the  normal  physiological  manner,  and 
that  in  all  cases  the  sensation — light,  sound,  taste,  contact,  etc.,  as 
the  case  might  be — is  the  same.  Hence  it  was  argued  that  the 
psychical  effect  or  sensation  is  independent  of  the  nature  of  the 
stimulus,  but  dependent  on  the  nature  of  the  activity  of  the  central 
cells  among  which  the  afferent  fibres  terminate.  We  have  no  observa- 
tions which  can  decide  whether  the  nerve  impulses  passing  along 
the  optic  fibres  are,  for  instance,  similar  to  or  different  from  those 
which  are  transmitted  by  the  auditory  fibres.  The  experiments  of 
Langley  and  others  on  nerve-crossing  (p.  173)  would  seem  to  indicate 
that  the  nervous  impulse  is  an  identical  process  in  all  nerves. 

It  is,  however,  possible  that  in  the  nerves  of  cutaneous  sensation,  the  psycliical 
process  is  determined  by  the  nature  of  the  peripheral  stimulus,  and  consequently 
different  branches  of  the  same  nerve-fibres  may  be  imagined  to  be  susceptible  to 
different  forms  of  stimulation,  and  thus  two  different  sensations  follow  from  the 
partial  stimulation  of  the  same  nerve-fibres.  Hering  even  argues  in  favour  of  the 
view  that  the  nerve  impulse  has  different  characters  in  different  afferent  nerves,  and 
further  that  it  may  be  modified  by  the  nature  of  the  normal  stimulus  (^.r/. .  in  the  skin, 
heat,  cold,  pain,  or  pressure).  In  the  absenc-e  of  direct  experimental  proof  of  such 
an  idea,  it  is  difficult  to  see  upon  what  grounds  it  can  rest 


CHAPTEE  LII 


CUTANEOUS    SENSATIONS 


The  tactile  end-organs  are  of  numerous  kinds,  but  the  following  are 
the  principal  ones  : — 

Pacinian  Corpuscles. — These  are  named  after  their  discoverer 
Pacini.  They  are  little  oval  bodies,  situated  on  some  of  the  cerebro- 
spinal and  sympathetic  nerves,  especially  the  cutaneous  nerves  of 
the  hands  and  feet,  where  they  lie  deeply 
placed  in  the  true  skin.  They  also  occur 
on  the  nerves  of  the  mesentery  of  some 
animals  like  the  cat.  They  have  been  ob- 
served also  in  the  pancreas,  lymphatic 
glands  and  thyroid  glands,  as  well  as  in  the 
penis.  They  are  about  ^  inch  long.  Each 
corpuscle  is  attached  by  a  narrow  pedicle  to 
the  nerve  on  which  it  is  situated,  and  is 
formed  of  several  concentric  sheaths  of  con- 
nective-tissue, each  layer  being  lined  by 
endothelium  (figs.  517,  518);  through  its 
pedicle  passes  a  single  nerve-fibre,  which 
loses  its  medullary  sheath  and  enters  a 
central  core,  at  or  near  the  distal  end  of 
which  it  terminates  in  an  arborisation.  Some 
of  these  layers  are  continuous  with  those 
of  the  perineurium,  but  some  are  super- 
added. In  some  cases  two  nerve-fibres 
have  been  seen  entering  one  Pacinian  body, 
and  in  others  a  nerve-fibre  after  passing 
through  it  has  been  observed  to  terminate 
in  a  second. 

The  corpuscles  of  Herbst  (fig.  519)  are 
closely  allied  to  Pacinian  corpuscles,  except  that  they  are  smaller 
and  longer,  with  a  row  of  nuclei  around  the  central  termination 
of  the  nerve  in  the  core.  They  have  been  found  chiefly  in  the 
tongues  and  bills  of  ducks. 

733 


Fig.  516. — Extremities  of  a  neire 
of  the  finger  with  Pacinian  cor- 
puscles attached,  about  the 
natural  size.  (Adapted  from 
Henle  and  KoUiker.) 


734 


CUTANEOUS    SENSATIONS 


[CH.  LII. 


End-bulbs  are  found  in  the  conjunctiva  (where  in  man  they  are 
spheroidal,  but  in  most  animals  oblong),  in  the  glans  penis  and 

clitoris,  in  the  skin,  in  the  lips,  in 
^^r^^sv^  the   epineurium   of   nerve-trunks, 

and  in  tendon ;    each  is  about  g-^ 
/'  '-^^'^^'^^  inch  in  diameter,  oval  or  spheroidal. 


'/lg.  517. — Pacinian  corpuscle  of  the  cat's  mesen- 
tery. The  stalk  consists  of  a  nen'e-fibrep<^) 
with  its  thick  outer  sheath.  The  peripheral 
capsules  of  the  Pacinian  corpuscle  are  con- 
tinuous with  the  outer  sheath  of  the  stalk. 
The  intermediarj'  part  becomes  much  nar- 
rower near  the  entrance  of  the  axis-cylinder 
into  the  clear  central  core.  A  hook-shaped 
termination  (T)  is  seen  in  the  upper  part.  A 
blood-vessel  (V)  enters  the  Pacinian  corpuscle, 
and  approaches  the  end  ;  it  possesses  a  sheath 
which  is  the  continuation  of  the  peripheral 
capsules  of  the  Pacinian  corpuscle.  xlOO. 
(Klein  and  Xoble  Smith.) 


Fig.  51S. — Summit  of  a  Pacinian  cor- 
puscle of  the  human  finger  sho^ving 
the  endothelial  membranes  lining  the 
capsules,  x  220.  (Klein  and  Xoble 
Smith.) 


and  is  composed  of  a  meduUated 
nerve  -  fibre,  which  terminates 
among  cells  of  various  shapes.  Its 
capsule  contains  a  transparent  or 
striated  core,  in  the  centre  of 
which  the  axis-cylinder  terminates 
(fig.  520). 

Touch-corpuscles  (Meissner's 
corpuscles),  (figs.  521,  523),  are 
found  in  the  papillae  of  the  skin 


of  the  fingers  and  toes.  They  are 
oblong,  about  -^^^  inch  long,  and  -g^  inch  broad,  and  composed 
of  connective-tissue,  surrounded  by  elastic  fibres  and  a  capsule  of 
nucleated  cells.  They  do  not  occur  in  all  the  papUlse  of  the 
parts  where  they  are  found,  and,  as  a  rule,  in  the  papillae  in  which 
they  are  present  there  are  no  blood-vessels. 


CH.  LII.] 


TACTILE   END-ORGANS 


735 


The  peculiar  way  in  which  the  medullated  nerve  winds  round 
and  round  the  corpuscle  before  it  enters  it  is  shown  in  fig.  523.     It 


Fig.  519. — A  corpuscle  of  Herbst,  from 
the  tongue  of  a  duck,  n,  Medullated 
nerve  cut  away.    (Klein.) 


Fig.  520. — End-bulb  of  Krause.  a,  Me- 
dullated nerve-flbre;  b,  capsule  of 
corpuscle. 


loses  its  sheath  before  it  enters  into  the  interior,  and  then  its  axis- 
cylinder  branches,  and  the  branches  after  either  a  straight  or  con- 
voluted course  terminate  within  the  corpuscle. 


:./ 


■Mmlm 


Fig.  5:-'1. — Papillee  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  Meissner's  corpuscles. 

1/1  b  I  A.  Simple  papula  with  fuur  nen'e-fibres  ;  a,  tactile  corpuscle  ;  b,  nerves  \vitb  winding  fibres  c  and  e. 

B.  Papilla  treated  with  acetic  acid  ;   a,  cortical  layer  with   cells  and   fine  elastic   filaments ;  h, 

tactile  corjjuscle  with  transverse  nuclei ;  c,  entering  nerve ;  d  and  e,  nerve-fibres  winding  round 

the  corpuscle,     x  350.    (Kolliker.) 

The  corpuscles  of  Grandry  (fig.  522)  form  another  variety,  and 
have  been  noticed  in  the  beaks  and  tongues  of  birds.  They  consist 
of  oval  or  spherical  cells,  two  or  more  of  which  compressed  vertically 


736 


CUTANEOUS   SENSATIONS 


[CH.  Lll. 


are  contained  within  a  delicate  nucleated  sheath.  The  nerve  enters 
on  one  side,  and,  laying  aside  its  medullary  sheath,  terminates 
between  the  cells  in  flattened  expansions. 


Fig.  522. — A  corpuscle  of 
Grandry,  from  the 
tongue  of  a  duck. 


Fig.  523.— a  touch-corpuscle  from  the  skin  of  the 
human  hand,  stained  with  gold  chloride. 


Sensory  nerve  -  endings  in  muscle.  —  Nerve  terminations, 
sensory  in  function,  are  found  in  tendon.  Some  of  these  are  end- 
bulbs,  and  others  appear  very  much  like  end-plates,  as  represented  in 
figs.  52-i  and  525.     The  neuro-muscular  spindles,  which  are  described 


k;  I 


L 


1/  m 


Fig.  524. — Termination  of  medullated 
nerve-fibres  in  tendon  near  the  mus- 
cular insertion.    (Golgi.) 


Fig.  525. — One  of  the  reticulated  end-plates 
of  fig.  524,  more  highly  niagiiifled.  c, 
Medullated  nerve-tlbre;  h,  reticulated 
end-plate.     (Golgi.) 


on  p.  86,  are  principally  found  in  muscles  in  the  neighbourhood  of 
tendons  and  aponeuroses.  One  of  these  spindles  is  shown  in  the 
accompanying  drawing  (fig.  526). 

The  principal  grounds  for  believing  the  neuro-muscular  spindles 
to  be  sensory  are"^  first,  that  the  nerve-fibres  that  supply  them  do 
not  degenerate  when  the  anterior  roots  of  the  spinal  nerves  are  cut, 
and  secondly,  that  they  do  degenerate  when  the  posterior  roots  are 
divided  (Sherrington).     They  also  undergo  degenerative  changes  in 


CH.  LII.] 


TACTILE   LOCALISATION 


737 


locomotor  ataxy,  which  is  a  disease  of  the  sensory  nerve-units,  and 
remain  healthy  in  infantile  paralysis,  which  is  a  disease  of  the 
motor  cells  of  the  anterior  horn  of  the  cord  (Batten). 


ntM-b 


Fio.  526. — Neuro-muscular  spindle,    c,  Capsule;  n.tr.,  nerve  trunk;  m.n.b.,  motor  nerve  bundle; 
pl.e.,  plate-ending;  jjr.c,  primary  nerve-ending;  s.e.,  secondary  ending.    (After  Ruffini.) 


sensory   fibres    may 


In  addition  to  the  special  end-organs, 
terminate  in  plexuses  of  fibrils,  as  in 
the  sub-epithelial  and  the  intra-epithelial 
plexus  of  the  cornea  (fig.  527)  and 
around  the  hair  follicles  in  the  skin 
generally.  In  some  cases  the  nerve-fibrils 
within  a  stratified  epithelium  end  in 
crescentic  expansions  {tactile  discs)  which 
are  applied  to  the  deeper  epithelium 
cells.  These  are  well  seen  in  the  skin 
of  the  pig's  snout. 

Localisation  of  Tactile  Sensations. 

The  localisation  of  a  tactile  sensation 
is  of  two  kinds,  absolute  and  relative. 
We  can  localise  a  touch  on  the  arm 
absolutely  by  indicating  the  exact  spot 
which  has  been  touched,  or  we  may 
localise  it  relatively  to  another  spot  on 
the  arm  which  is  simultaneously  or  suc- 
cessively touched  Generally  speaking, 
the  delicacy  of  these  two  kinds  of  locali- 
sation are  similarly  variable  in  different 
parts  of  the  body.  The  simplest  ex- 
periments which  have  been  made  to 
determine  the  spatial  relationships  of 
the  cutaneous  sense  consist  in  touching 
the  skin,  while  the  eyes  are  closed,  with 
the  points  of  a  pair  of  compasses,  and  in  ascertaining  how  close  the 

3A 


-X^?ie3S^S[Sr^?StseS!S^_  d 


Fig.  5-27. — Vertical  section  of  rabbit's 
cornea,  stained  with  gold  chloride. 
The  nerves  n,  terminate  in  a  plexus 
under  and  within  the  ei)ithelial 
layer,  e. 


738  CUTANEOUS   SENSATIONS  [CH.  LII. 

points  may  be  brought  to  each  other,  and  still  be  felt  as  two  points. 
(Weber.)     A  few  results  are  as  follow : — 


Tip  of  tongue A-inc 

Palmar  surface  of  third  phalanx  of  forefinger        .  ,'„ 

Palmar  surface  of  second  phalanges  of  fingers      .  i 

Palm  of  hand f\ 

Dorsal  surface  of  first  phalanges  of  fingers  .         .  /rr 

Back  of  hand I}, 

Upper  and  lower  parts  of  forearm          .         .         •  IJ^ 

Middle  of  thigh  and  back 21 


1  mm. 

2  „ 
4  „ 

10  „ 

14  „ 

25  „ 

37  „ 

62  „ 


Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they 
were  recognised  as  two,  the  points  of  the  compasses  had  to  he  further 
separated  when  the  line  joining  them  was  in  the  long  axis  of  the 
limb,  than  when  in  the  transverse  direction. 

We  may  thus  assume  that  minute  areas  of  the  body  surface  have 
each  their  "  local  sign,"  i.e.,  the  sensation  arising  from  stimulation  of 
one  area  differs  in  some  obscure  quality  from  the  sensations  arising 
from  stimulation  of  neighbouring  areas,  thereby  acquiring  its  own 
spatial  colouring  which  enables  us  to  identify  the  area  when  stimulated. 
The  difference  of  local  sign  between  two  near  points  may  be  imper- 
oeptible  in  one  region  of  the  body,  but  fully  recognisable  in  another. 
Again,  the  delicacy  of  the  sense  of  touch  may  be  very  much  increased 
by  practice.  A  familiar  illustration  occurs  in  the  case  of  the  blind, 
who,  by  constant  practice,  can  acquire  the  power  of  reading  raised 
letters,  the  forms  of  which  are  almost  if  not  quite  undistinguishable 
by  the  sense  of  touch  to  an  ordinary  person. 

The  power  of  correctly  localising  sensations  of  touch  is  gradually 
derived  from  experience.  Thus,  infants  when  in  pain  simply  cry 
but  make  no  effort  to  remove  the  cause  of  irritation,  as  an  older 
child  or  adult  would,  on  account  of  their  imperfect  knowledge 
of  its  exact  situation.  As  education  proceeds  the  brain  gets  to 
know  more  and  more  accurately  the  surface  of  the  body,  and  the 
map  of  the  surface  in  the  brain  is  most  accurately  known  where 
there  is  most  practice  of  the  sense  of  touch. 

The  different  degrees  of  sensitiveness  possessed  by  different  parts 
may  give  rise  to  errors  of  judgment  in  estimating  the  distance 
between  two  points  where  the  skin  is  touched.  Thus,  if  the  blunted 
points  of  a  pair  of  compasses  (maintained  at  a  constant  distance 
apart)  are  slowly  drawn  over  the  skin  of  the  cheek  towards  the  lips, 
it  is  almost  impossible  to  resist  the  conclusion  that  the  distance 
between  the  points  is  gradually  increasing.  When  they  reach  the 
lips  they  seem  to  be  considerably  further  apart  than  on  the  cheek. 
Then,  too,  our  estimate  of  the  size  of  a  cavity  in  a  tooth  is  usually 
exaggerated  when  based  upon  sensations  derived  from  the  tongue 
alone.  Another  curious  illusion  is  the  following: — If  we  close 
the  eyes,  and  place  a  marble  between  the  crossed  fore  and  middle 


CII.  LII.]  VARIETIES   OF   CUTANEOUS   SENSATIONS  739 

fingers,  we  seem  to  be  touching  two  marbles.  This  illusion  is  due 
to  an  error  of  judgment.  The  marble  is  touched  by  two  surfaces 
which,  under  ordinary  circumstances,  could  only  be  touched  by  two 
separate  marbles ;  hence,  the  mind,  taking  no  cognizance  of  the  fact 
that  the  fingers  are  crossed,  forms  the  conclusion  that  the  two 
sensations  are  due  to  two  marbles. 


Varieties  of  Cutaneous  Sensations. 

The  surface  of  the  skin  is  a  mosaic  of  tiny  sensorial  areas ;  but 
these  areas  are  not  set  edge  to  edge  as  in  the  retina,  but  separated 
by  relatively  wide  intervals  which  are  not  sensitive  to  stimuli  just 
above  liminal  intensity.  If  the  stimuli  are  made  nearly  minimal, 
the  individual  fields  are  reduced  to  small  spots.  Each  of  these  spots 
subserves  a  specific  sense,  touch,  cold,  heat  or  pain,  and  each 
doubtless  coincides  with  the  site  of  some  special  end-organ,  placed 
either  singly  or  in  clusters.  The  "touch  spots,"  "cold  spots," 
"heat  spots,"  and  "pain  spots"  are  intercommingled.  In  some 
districts  one  variety  predominates,  in  others  another.  "  Pain  spots  " 
are  the  most  and  "heat  spots"  the  least  numerous.  It  is  a 
matter  of  common  experience  that  the  sensitiveness  of  these  varieties 
of  cutaneous  sensation  differs  in  different  parts  of  the  body.  The 
tip  of  the  finger  which  is  very  sensitive  to  the  true  tactile  sense 
(sense  of  pressure  or  contact)  is  not  nearly  so  sensitive  to  alterations 
of  temperature  as  the  forearm  or  cheek  to  which  a  washerwoman 
generally  holds  her  iron  when  forming  a  judgment  of  its  temperature. 
Some  parts  of  the  skin  are  more  sensitive  to  pain  than  others,  and 
in  the  cornea  we  have  an  instance  of  a  surface  in  which  "  pain  spots  " 
alone  are  present. 

For  the  more  accurate  exploration  of  the  skin  cesthesiometers  of 
various  kinds  have  been  invented.  The  sense  of  pressure  may  be 
estimated  by  the  ability  of  the  skin  to  distinguish  different  weights 
placed  upon  it;  there  must  be  no  lifting  of  the  weight,  or  the 
motorial  sense  is  brought  into  play.  The  fraction  which  by  Weber's 
law  represents  the  discriminative  sensibility  (see  p.  731)  varies 
from  -^Q  to  more  than  -^  in  different  parts  of  the  body.  It  does  not, 
however,  follow  that  the  acuteness  of  the  pressure  sense  varies 
exactly  as  the  ability  of  accurately  localising  sensations ;  for  instance, 
the  skin  of  the  forearm  is  as  sensitive  to  pressure  changes  as  that 
of  the  palm ;  and  the  tip  of  the  tongue,  which  is  the  most  discrimi- 
native region  of  the  body  for  locality,  is  not  so  for  pressure.  For 
pressure  stimuli  which  are  near  the  limen  or  threshold  of  sensation, 
the  hair  sesthesiometer  is  much  used;  this  is  a  hair  or  bristle 
mounted  in  a  holder ;  the  bristle  can  be  shifted  backwards  or  for- 
wards in  the  holder,  and  the  amount  of  pressure  it  exercises  can 


740 


CUTANEOUS   SENSATIONS 


[CH.  LII. 


thus  be  varied.  It  is  used  for  the  exploration  of  "  touch  spots,"  and 
these  are  found  most  numerously  around  the  hair  follicles.  The 
touch  spots  are  more  numerous  in  some  parts  than  in  others,  but 
fifteen  for  each  square  centimetre  of  skin  is  a  rough  average.  To 
explore  "  pain  spots "  a  mounted  needle  is  used ;  in  Griesbach's 
instrument  the  needle  shifts  up  and  down  in  the  holder,  and  works 
against  a  spring  which  registers  the  amount  of  pressure  exerted  to 
evoke  a  painful  sensation.  In  a  "pain  spot"  the  sensation  is 
unaccompanied  by  "cold"  or  "heat,"  even  if  a  cold  or  hot 
needle  is  used.     For  the  exploration  of  "  heat  spots  "  a  small,  hollow, 

metallic  pencil  is  kept  warm  by  a  stream 
of  warm  water ;  this  is  moved  over  the 
surface;  there  are  some  points  where 
the  sensation  is  purely  tactile,  but  at 
the  "heat  spots"  the  pencil  will  feel 
uncomfortably  warm.  "  Cold  spots  " 
can  be  similarly  mapped  out  by  the  use 
of  a  cold  pencil.  The  accompanying 
figure  (fig.  528)  indicates  a  small  piece  of 
the  skin  of  the  thigh ;  the  areas  where 
heat  spots  are  numerous  are  shaded 
horizontally ;  the  areas  where  cold  spots 
are  numerous  are  shaded  vertically. 

All  these  facts  clearly  indicate  that 
different  varieties  of  sensation  are  the 
result  of  the  stimulation  of  different  end-organs,  and  that  the 
impulses  are  conveyed  to  the  central  nervous  system  by  different 
groups  of  nerve-fibres;  they  moreover  form  the  clearest  piece  of 
evidence  we  have  that  pain  is  a  distinct  kind  of  sensation. 

The  question  is  more  difficult  to  answer,  which  particular  end- 
organ  is  concerned  with  each  variety  of  sensation.  There  is,  how- 
ever, little  doubt  that  the  nerve-fibrils  around  the  hair  follicles  of 
the  short  hairs  are  the  terminations  most  affected  by  changes  of 
pressure,  and  also  that  Meissner's  corpuscles  are  purely  tactual, 
taking  the  place  of  hairs  in  hairless  parts.  In  the  palmar  surface 
of  the  last  phalanx  of  the  index  finger,  there  are  21  Meissner's 
corpuscles  per  square  centimetre ;  in  other  parts  of  the  palm  and 
sole  the  number  varies  from  2  to  8.  End-bulbs  are  believed  to 
be  the  organs  for  cold ;  they  are  most  numerous  in  the  conjunctiva 
and  glans  penis,  where  "  cold  spots  "  are  almost  exclusively  present. 
The  end-organs  in  "heat  spots"  have  not  been  identified  with 
certainty,  but  they  are  probably  larger  organs,  and  placed  more 
deeply  in  the  skin. 

We  have  spoken  of  the  pressure  sense  as  the  true  tactile  sense ; 
but  Meissner  pointed  out  many  years  ago  that  the  hand  immersed 


Fio.  52S. — Heat  and  cold  areas. 
(Waller,  after  Goldscheider.) 


CII.   LII.]  VARIETIES    OF   CUTANEOUS    SENSATFONS  741 

in  a  fluid  like  mercury  at  body  temperature,  does  not  feel  the  contact 
of  the  fluid,  although  the  fluid  pressure  may  be  far  above  the  limen ; 
it  is,  however,  ecjual  in  all  directions ;  it  is  therefore  clear  that  the 
adequate  stimulus  for  touch  organs  consists  in  a  deformation  of  the 
skin  surface. 

As  compared  with  the  sensation  obtained  from  pain  spots,  touch 
is  quicker  both  in  development  and  subsidence.  Thus  vibrations  of 
strings  are  recognisable  as  such  by  the  finger,  even  at  a  frequency 
of  1500  vibrations  per  second.  A  revolving  wheel  with  toothed  edge 
does  not  give  a  sensation  of  smoothness  till  the  teeth  meet  the  skin 
at  the  rate  of  from  480  to  640  per  second. 

Head,  in  his  recent  study  of  nerve-regeneration,  cut  one  of  the 
nerves  in  his  own  arm  and  noted  accurately  the  date  and  other 
particulars  of  return  of  function.  The  first  sensations  return  about 
the  eightieth  day  after  the  operation ;  they  are  of  a  vague  nature, 
and  are  termed  jirotoipatMr.  Head  associates  this  with  the  activity 
of  the  fine  medullated  nerve-fibres  which  replace  the  degenerated 
ones  at  this  early  stage.  The  more  elaborate  sensations  and  power 
to  localise  them  accurately  return  much  later,  and  this  cpicritic 
sensibility  is  usually  not  perfect  until  many  months  or  even  a  few 
years  after  the  regeneration  started.  By  this  time,  as  was  shown  in 
experiments  on  animals,  the  fine  nerve-fibres  which  subserve  proto- 
pathic  sensation  are  largely  admixed  with  a  later  growth  of  larger 
nerve-fibres,  and  Head  believes  epicritic  sensation  is  subserved  by 
these.  Quite  apart  from  these  two  forms  of  cutaneous  sensation  is 
the  deep  sensibility  of  subjacent  structures,  and  the  fibres  suljserving 
this  run  mainly  with  the  motor  nerves ;  this  form  of  sensation  is  not 
destroyed  by  division  of  all  the  nerves  to  the  skin.  The  three  kinds 
of  sensation  (deep,  protopathic,  and  epicritic)  are  doubtless  related  to 
different  kinds  of  end-organs  in  the  peripheral  structures. 

Adaptation  plays  a  part  as  important  in  cutaneous  as  in  other  sensations.  The 
same  room  feels  warm  to  a  man  who  enters  it  from  the  street,  and  cold  to  another  who 
has  been  in  a  conservatory.  Hering  calls  the  point  of  adaptation  to  temperature  "  the 
physiological  zero."  Thus  the  temperature  of  the  mouth  and  the  hps  may  actually 
differ  by  several  degrees,  yet  neither  of  them  will  feel  hot  or  cold  because  each  is  at 
the  physiological  zero  temperature.  Sensations  of  warmth  or  cold  arise  when  the 
physiological  zero  is  altered  :  they  persist  until  a  new  zero  is  formed,  i.e. ,  until  adapta- 
tion is  complete.  So,  too,  heavy  weights  feel  unduly  heavy  after  light  weights,  and 
rice  versa.  When  eyeglasses  or  false  teeth  are  first  worn,  their  contact  is  well-nigh 
unbearable ;  yet  later,  through  adaptation,  the  discomfort  becomes  negligible. 

It  is  very  difficult  to  draw  any  hard  and  fast  line  between  the  cutaneous  sensa- 
tions we  have  just  described,  and  those  which  are  grouped  under  the  name  "  common 
or  general  sensibility."  Sensations  which  are  difficult  to  describe  but  which  are 
perfectly  familiar,  such  as  those  accompanying  tickUng,  shivering,  shuddering,  and 
the  like,  are  regarded  as  varieties  of  "common  sensation."  Pain  may  be  looked 
upon  as  an  excessive  form  of  "common  sensation,"  but  cutaneous  pain  is  so  distinct 
a  sensation  that  most  psychologists  agree  to  place  it  under  a  "  special"  rather  than 
a  "  common  "  heading.  The  term  "common  sensation  "  is  most  frequently  employed 
in  reference  to  sensations  from  the  interior  of  the  body.     Each  viscus  stands  in 


742  CUTANEOUS    SENSATIONS  [CH.  LII. 

relation  with  a  definite  patch  of  skin ;  that  is  to  say,  tlie  afferent  fibres  from  the 
skin  and  from  the  viscera  belong  to  corresponding  spinal  nerve-roots.  Locahsation 
of  painful  or  uncomfortable  feelings  arising  from  disorders  of  internal  organs  is 
always  very  difficult ;  hence  the  associated  skin  ]>ains  play  an  important  part  in 
ascertaining  the  position  of  internal  maladies.    (Head,  see  also  p.  690.) 

Dniqs. — Cocaine  applied  locally  depresses  all  forms  of  cutaneous  sensibility, 
but  especially  the  true  tactile  sense  ;  carbolic  acid  acts  similarly  but  less  strongly. 
Chloroform  produces  a  temporary  burning  sensation,  and  then  blunts  sensibility 
especially  to  temperature  changes.  Menthol  produces  a  feeling  of  local  cold  because 
it  first  causes  hyperaesthesia  of  the  end-organs  for  cold  ;  this  is  followed  by  a  depres- 
sion of  the  activity  of  these  organs,  together  with  that  subserving  other  forms  of 
cutaneous  sensation. 

The  Motorial  or  Kinsesthetic  Sense. 

By  this  sense  we  become  aware  that  movement  is  taking  place  in 
some  part  of  the  body.  We  are  especially  conscious  of  willed  muscular 
action,  and  the  sense  has  thus  been  confused  and  identified  with  the 
"  feeling  of  innervation,"  or  "  sense  of  effort,"  which  accompanies  voli- 
tional movements.  By  some  this  feeling  has  been  attributed  to  a  direct 
discharge  from  the  motor  to  the  sensory  cells  of  the  cerebral  cortex 
occurring  at  the  very  birth  of  the  efferent  impulse.  But  most  physio- 
logists of  the  present  day  regard  the  sense  of  effort  as  due  to  afferent 
impulses  peripherally  generated  by  the  accompanjdng  respiratory  and 
other  strains;  and  they  no  longer  consider  it  as  a  very  important 
factor  in  effecting  or  estimating  movement.  It  is  in  the  estimation  of 
weights  that  the  value  of  peripheral  sensations  can  be  most  clearly  seen. 

When  a  weight  is  first  handled,  the  amount  of  force  necessary  to 
lift  it  is  estimated  in  the  light  of  past  experience.  As  it  is  being 
lifted,  sensations  from  the  moving  limb  guide  the  expenditure  of  force : 
a  weight  wliich  flies  uj)  too  fast  or  does  not  move  at  once,  calls  for  less 
or  more  muscular  force.  Similarly  the  motorial  sense  is  invoked 
when  we  estimate  the  extent  to  which  we  have  moved  our  limbs,  or 
to  which  they  have  been  passively  moved  by  others. 

These  guiding  sensations  are  not  merely  of  cutaneous  origin. 
Persons  whose  skin  has  been  rendered  insensitive  by  cocaine,  or  by 
certain  diseases,  yet  retain  the  power  of  estimating  weights  and  the 
extent  of  their  movement.  In  locomotor  ataxy  the  motorial  sense 
may  be  destroyed  while  the  skin  retains  its  usual  sensitiveness  to 
touch.  On  the  other  hand,  we  must  remember  that  it  is  not  at  all 
certain  that  the  muscles  are  solely  or  even  predominantly  the  seat  of 
these  peripheral  sensations ;  the  term  "  motorial "  or  "  kinaesthetic  " 
is  therefore  preferable  to  that  of  "  muscular  "  sense,  by  which  name 
it  was  formerly  known.  It  is  true  that  sensory  end-organs  and 
nerve-fibres  occur  in  muscles  and  tendons,  which  presumably  transmit 
impulses  upon  change  of  muscular  form  or  of  tendinous  strain.  But 
we  have  experimental  evidence  that  the  pressure  and  movement  of  joint- 
surfaces  are  most  important  factors  in  the  development  of  kinsesthetic 
sensations.     The  "  motorial  sense  "  is  thus  of  very  complex  origin. 


CHAPTER     LIII 


TASTE   AND    SMELL 


Taste. 

Certain  anatomical  facts  must  be  studied  first  in  connection  with 
the  tongue,  the  upper  surface  of  which  is  concerned  in  the  reception 
of  taste  stimuli. 

The  tongue  is  a  muscular  organ  covered  by  mucous  membrane. 
The  muscles,  which  form  the  greater  part  of  the  substance  of  the 
tongue  {intrinsic  muscles)  are  termed  linguales ;  and  by  these,  which 
are  attached  to  the  mucous  membrane,  its  smaller  and  more  delicate 
movements  are  performed. 

By  other  muscles  {extrinsic  muscles),  such  as  the  genio-hyoglossus, 
the  styloglossus,  etc.,  the  tongue  is  fixed  to  the  surrounding  parts ; 
and  by  these  its  larger  movements  are  performed. 

Its  mucous  membrane  resembles  other  mucous  membranes  in 
essential  points,  but  contains  papillce,  peculiar  to  itself.  The  tongue 
is  also  beset  with  mucous  glands  (fig.  530)  and  lymphoid  nodules. 

The  lingual  papillm  are  thickly  set  over  the  anterior  two-thirds 
of  its  upper  surface,  or  dorsum  (fig.  529),  and  give  to  it  its  character- 
istic roughness.  Three  principal  varieties  may  be  distinguished, 
namely,  the  (1)  circumvallate,  the  (2)  fungiform,  and  the  (3)  conical 
and  filiform  papillte.  They  are  all  formed  by  a  projection  of  the 
corium  of  the  mucous  membrane,  covered  by  stratified  epithelium ; 
they  contain  special  branches  of  blood-vessels  and  nerves.  The 
corium  in  each  kind  is  studded  by  microscopic  papillse. 

(1.)  Circumvallate. — These  papillae  (fig.  531),  eight  or  ten  in  number, 
are  situate  in  a  V-shaped  line  at  the  base  of  the  tongue  (1,  1,  fig.  529). 
They  are  circular  elevations,  from  ^Vth  to  yV^h  of  an  inch  wide  (1  to 
2  mm.),  each  with  a  slight  central  depression,  and  surrounded  by  a 
circular  moat,  at  the  outside  of  which  again  is  a  slightly  elevated 
ring  or  rampart;  their  walls  contain  taste-buds.  Into  the  moat 
that  surrounds  the  central  tower,  a  few  little  glands  (glands  of 
Ebner)  open.     They  form  a  thin,  watery  secretion. 


744 


TASTE 


[cn.  LIII. 


(2.)  Fungiform. — The  fungiform  papillfe  (3,  fig.  529)  are  scattered 
chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle  of  the 


"r- "\ 


Fig.  5'29. — Papillar  surface  of  the  tongue,  with  the  fauces  and  tonsils.  1,  1,  Circunivallate  papilla?  in 
front  of  2,  the  foramen  c»cum  ;  3,  fungiform  papilla.- ;  4,  filiform  and  conical  papilla  ;  6,  transverse 
and  oblique  rugfe  ;  li,  mucous  glands  at  the  base  of  the  tongue  and  in  the  fauces  ;  7,  tonsils  ;  S,  part 
of  the  epiglottis;  !i,  median  glosso-epiglottidean  fold  (froenum  epiglottidis).    (From  Sappey.) 


dorsum,  of  the  tongue ;  their  name  is  derived  from  their  being  shaped 
like  a  puff-ball  fungus.     (See  fig.  532,  B.) 

(3.)  Conical  and  Filiform. — These,  which  are  the  most  abundant 
papillae,  are  scattered  over  the  whole  upper  surface  of  the  tongue, 
but  especially  over  the  middle  of  the  dorsum.     They  vary  in  shape, 


CII.  LIII.] 


THE   LINGUAL  PAPILLA 


74J 


some  being  conical  (simple  or  compound)  and  others  filiform ;  they 
are  covered  by  a  thick  layer  of  epithelium,  which  is  either  arranged 
over  them,  in  an  imljricated  manner,  or  is  prolonged  from  their  sur- 
face in  the  form  of  fine  stiff  projections 
(fig.  533).  In  carnivora  they  are  devel- 
oped into  horny  spines.  From  their 
structure,  it  is  likely  that  these  papillae 
have  a  mechanical  and  tactile  function, 


Fio.  531.— Vertical  section  of  a  circumvallate  papilla 
of  the  calf.  1  and  3,  Epithelial  layers  covering  it ; 
■2,  taste-buds  ;  4  and  4',  duct  of  serous  gland  open- 
ing out  Into  the  pit  in  which  papilla  is  situated  ; 
5  and  C,  nerves  ramifying  within  the  papilla. 
(Engelmann.) 

rather  than  that  of  taste ;  the  latter 
sense  is  seated  especially  in  the  other 
two  varieties  of  papillae,  the  circumvallate 
and  t\iQ  fungiform. 

In  the  circumvallate  papillae  of  the 
tongue  of  man  peculiar  structures  known 
as  taste-huds  are  found.  They  are  of  an 
oval  shape,  and  consist  of  a  number  of 
closely  packed,  very  narrow  and  fusi- 
form, cells  (gustatory  cells).  This  central 
core  of  gustatory  cells  is  enclosed  in  a  single  layer  of  broader  fusi- 
form cells  (encasing  cells).  The  gustatory  cells  terminate  in  fine  stiff 
spikes  which  project  on  the  free  surface  (fig.  534,  a). 

These  bodies  also  occur  in  considerable  numbers  in  the  epithelium 
of  the  papilla  foliata,  which  is  situated  near  the  root  of  the  tongue 
in  the  rabbit,  and  is  composed  of  a  number  of  closely  packed  papillae 
very  similar  to  the  circumvallate  papillae  of  man.  Taste-buds  are  also 
scattered  over  the  posterior  third  of  the  tongue  and  the  pharynx,  as 
low  as  the  posterior  (laryngeal)  surface  of  the  epiglottis. 

The  gustatory  cells  in  the  interior  of  the  taste-buds  are  sm- 
rounded  by  arborisations  of  nerve-fibres. 


Fig.  530. — Section  of  a  mucous  gland 
from  the  tongue.  A,  Opening  of 
the  duct  on  the  free  surface ;  C, 
basement  membrane  with  nuclei ; 
B,  flattened  epithelial  cells  lining 
duct.  The  duct  divides  into  several 
branches,  which  are  convoluted  and 
end  blindly,  being  lined  through- 
out by  columnar  epithelium.  U, 
Lumen  of  one  of  the  tubuli  of  the 
gland.  ■.  '.lO.  (Klein  and  Noble 
Smith.) 


746 


TASTE 


[CH.  LIII. 


The  middle  of  the  dorsum  of  the  tongue  is  but  feebly  endowed 
with    the    sense    of    taste ;   the    tip   and    margins,   and    especially 


-r 


Fig.  532. — Surface  and  section  of  the  fongifonn  papfllee.  A,  The  surface  of  a  fungiform  papilla,  partially 
rlenuded  of  its  epithelium ;  p,  secondary  papUlse ;  e,  epithelium.  B,  Section  of  a  fungiform  papilla 
with  the  blood-vessels  injected ;  a,  artery ;  v,  vein ;  c,  capillary  loops  of  similar  papOlse  in  the 
neighbouring  structure  of  the  tongue ;  d,  capillary  loops  of  the  secondarj-  papill* ;  e,  epithelinm. 
(From  KiUliker,  after  Todd  and  Bowman.) 


the  posterior  third  of  the  dorsum  {i.e.,  in  the  region  of  the  taste- 
buds),  possess  this  faculty.  The  anterior  part  of  the  tongue  is 
supplied  by  the  lingual  branch  of  the  fifth  nerve  and  the  chorda 
tympani,  and  the  posterior  third  by  the  glosso-pharyngeal  nerve. 
Considerable  discussion  has  arisen  whether  there  is  more  than  one 
nerve  of  taste.  The  view  generally  held  is  that  the  glosso-pharyngeal 
nerve  is  the  ners-e  of  taste,  and  the  lingual  the  nerve  of  tactile  sensa- 
tion. Nevertheless,  the  lingual  and  the  chorda  tympani  do  contain 
taste-fibres,  which  probably  take  origin  from  the  .cells  of  the  geniculate 
ganglion ;  the  central  axons  of  these  cells  pass  by  the  pars  intermedia 
to  the  sensory  nucleus  of  the  glosso-pharyngeal  nerve.  Gowers  holds 
that  the  fifth  nerve  is  the  only  nerve  of  taste,  and  has  recorded  a  case 
of  loss  of  taste  where  the  fifth  nerve  alone  was  the  seat  of  disease ; 
other  cases,  however,  do  not  support  this  view. 


Tastes  may  be  classified  into- 

1.  Sweet. 
3.  Acid. 


2.  Bitter. 
4.  Saline. 


Whether  alkaline  and  metallic  tastes  are  elementary,  is  as  yet 
imdecided.  All  the  above  affect  to  a  varying  extent  the  nerves  of 
tactile  sense  as  well  of  those  of  touch  proper,  sweet  ha\-ing  the  least, 
acids  the  most  marked  action  upon  the  latter.  Sweet  tastes  are  best 
appreciated  by  the  tip,  acid  by  the  side,  and  bitter  tastes  by  the 
back  of  the  tongue. 

The  substance  to  be  tasted  must  be  dissolved ;  here  there  is  a 


CH.  LIII.] 


VAUIETIES    OF   TASTE 


74'; 


striking  contrast  to  the  sense  of  smell ;  tiavours  are  really  odours. 

In   testing  the  sense  of  taste  in  a  patient,  the  tongue  should  be 

protruded,  and  drops  of  the 
substance  to  be  tasted  ap- 
plied with  a  camel's  hair 
brush  to  the  different  parts ; 
the  subject  of  the  experi- 
ment must  signify  his  sen- 
sations   by  signs,   for    if    he 


P'iG.  534. — Taste-bud  from  dog's  epiglottis 
(larj'ngeal  surface  near  the  base),  precisely 
similar  in  structure  to  those  found  in 
the  tongue,  a,  Depression  in  epithelium 
over  bud ;  below  the  letter  are  seen  the 
line  hair-like  processes  in  which  the  cells 
terminate ;  c,  two  nuclei  of  the  axial 
(gustatorj')  cells.  The  more  superficial 
nuclei  belong  to  the  superficial  (encasing) 
cells ;  the  converging  lines  indicate  the 
fusiform  shape  of  the  encasing  cells,  x  400. 
(Schofield.) 


Fig.  533. — Filiform  papillae,  one  with  epithelium, 
the  other  without.  -Y. — p,  The  substance  of  the 
papillse  dividing  at  their  upper  extremities  into 
secondary  papillaj ;  a,  arterj',  and  v,  vein,  dividing 
into  capillary  loops ;  f ,  epithelial  covering,  lamin- 
ated between  the  papillae,  but  extended  into  hair- 
like processes,  /,  from  the  extremities  of  the 
secondary  papillaj.  (From  KuUiker,  after  Todd 
and  Bowman.) 


withdraws  the  tongue  to 
speak,  the  material  gets 
widely  spread.  The  more 
concentrated  the  solution, 
and  the  larger  the  surface 
acted  on,  the  more  intense 
is  the  taste;  some  tastes  are  perceived  more  rapidly  than  others, 
saline  tastes  the  most  rapidly  of  all.  The  best  temperature  of  the 
substance  to  be  tasted  is  from  10°  to  35'  C.  Very  high  or  very  low 
temperatures  deaden  the  sense. 

Individual  papillae,  when  thus  treated  with  various  solutions,  show 
great  diversity:  from  some  only  one  or  two  tastes  can  be  evoked, 
from  others  all  four.  The  papillse  may  also  be  stimulated  electrically. 
It  is  possible  by  chewing  the  leaves  of  a  certain  plant  called  the 
Gymnema  sylvestre  to  do  away  with  the  power  of  tasting  bitters 
and  sweets,  while  the  taste  for  acids  and  salts  remains. 


748 


SMELL 


[CH.  Lin. 


It  will  thus  be  seen  that  there  are  many  facts  pointing  to  the 
conclusion,  that  the  varieties  of  gustatory  like  those  of  cutaneous 
sensation  are  due  to  the  stimulation  of  different  end-organs. 

When  diluted  sweet  and  salt  solutions  are  simultaneously  applied 
to  the  tongue,  they  tend  to  neutralise  one  another,  but  a  true  indifferent 
point  is  difficult  or  impossible  to  reach.  Sweet  and  bitter,  sweet  and 
acid-tasting  substances  are  antagonistic  to  a  similar  but  less  perfect 
extent.  Contrast-effects  of  one  taste  upon  another  are  matters  of 
common  observation,  but  can  only  be  experimentally  investigated  with 
great  difficulty. 

Smell. 

The  entrance  to  the  nasal  cavity  is  lined  with  a  mucous  membrane 
closely  resembling  the  skin.     The  greater  part  of  the  rest  of   the 

cavity  is  Imed  with  ciliated  epi- 
thelium ;  the  corium  is  thick  and 
contains  numerous  mucous  glands. 
The  olfactory  region  in  man  is 
limited  to  a  portion  of  the  mem- 
l)rane  covering  the  upper  turbinal 
bone,  and  is  only  245  square  milli- 
metres in  area.  This  area  is  larger 
in  animals  with  a  keener  sense  of 
smell  than  we  possess.  The  cells 
of  the  epithelium  here  are  of  several 
kinds : — first,  columnar  cells  not 
ciliated  (fig.  535,  st),  with  the  broad 
end  at  the  surface,  and  below 
tapering  into  an  irregular  branched 
process  or  processes,  the  termina- 
tions of  which  pass  into  the  next  layer:  the  second  kind  of  cell 
(fig.  535,  r)  consists  of  a  small  cell  body  with  large  spherical  nucleus, 
situated  between  the  ends  of  the  first  kind  of  cell,  and  sending 
upwards  a  process  to  the  surface  between  the  cells  of  the  first 
kind,  and  from  the  other  pole  of  the  nucleus  a  process  towards 
the  corium.  The  latter  process  is  very  delicate  and  may  be  varicose. 
The  upper  process  is  prolonged  beyond  the  surface,  where  it  becomes 
stiff,  and  in  some  animals,  such  as  the  frog,  is  provided  with  hairs. 
These  cells,  which  are  called  olfadorial  cells,  are  numerous,  and  the 
nuclei  of  the  cells  not  being  on  the  same  level,  a  comparatively 
thick  nuclear  layer  is  the  result  (fig.  537,  h).  In  the  corium  are 
a  number  of  serous  glands  called  Bowman's  glands.  They  open 
upon  the  surface  by  fine  ducts  passing  up  between  the  epithelium 
cells. 

The   distribution   of   the   olfactory  nerves  which  penetrate  the 


FiQ.  535. — Cells  from  the  olfactory  region  of 
the  rabbit,  st,  Supporting  cells ;  r,  r' , 
olfactorial  cells  ;  /,  ciliated  cells ;  s,  cilia- 
like  processes ;  h,  cells  from  Bowman's 
gland.    (Stdhr.) 


CII.  LIII.] 


THE   OLFACTORY   APl'AKATUS 


749 


cribriform  plate  of  the  ethmoid  bono  and  pass  to  this  region  of  the 
nasal  mucous  membrane  is  shown  in  fig.  536.     The  nerve-fibres  are 


Fig.  53l>. — Nen'es  of  tlie  sei)tum  nasi,  seen  from  the  right  side.  g. — I,  The  olfactory  bulb;  ],  the 
olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  to  be  distri- 
buted on  the  septum  ;  2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthalmic  nerve ;  3, 
naso-palatine  nerves.    (Prom  Sappey,  after  Hirschfeld  and  Leveille.) 


continuous  with  the  inner  processes  of  the  cells  we  have  termed 
olfactorial ;  the  columnar  cells  between  these  act  as  supports  to  them. 

The  olfactory  tract  is  an  outgrowth  of 
the  brain  which  was  originally  hollow,  and 
remains  so  in  many  animals  ;  in  man  the 
cavity  is  obliterated,  and  the  centre  is  occu- 
pied by  neuroglia :  outside  this  the  white 
fibres  lie,  and  a  thin  superficial  layer  of 
neuroglia  covers  these.  The  three  "  roots  " 
of  the  olfactory  tract  have  been  traced  to 
the  uncinate  gyrus  and  hippocampal  regions 
of  the  same  side  of  the  brain,  which  is  the 
portion  experimentally  found  to  be  associ- 
ated with  the  reception  of  olfactory  impulses 
(see  pp.  677  and  703).  From  the  cells  of  the 
grey  matter  here  fibres  pass  by  a  complex 
path  to  the  corresponding  regions  of  the 
opposite  side.  There  is  also  a  communica- 
tion via  the  corpora  mammillaria  with  the 
optic  thalamus  and  tegmentum  of  the  mid- 
brain. 

The  olfactory  bulb  has  a  more  complicated  structure ;  above  there 
is  first  a  continuation  of  the  olfactory  tract  (white  fibres  enclosing 
neuroglia) ;    below   this   four   layers   are  distinguishable ;  they  are 


Fig.  6:j'r.  — Smii  -  iliagraimiiatic 
section  through  the  olfactory 
mucous  membrane  of  the  new- 
bom  child,  a,  Non-nuclear; 
and  h,  nucleated  portions  of  the 
epithelium  ;  c,  nerves  ;  dd,  Bow- 
man's glands.    (M.  Scbultze.) 


750  SMELL  [CH.  LIIL 

shown  in  the  accompanjdng  diagram  from  Eamon  y  Cajal's  work, 
the  histological  method  used  being  Golgi's. 

(1)  A  layer  of  white  fibres  containing  numerous  small  cells,  or 
"granules"  (d). 

(2)  A  layer  of  large  nerve-cells  called  "  mitral  cells "  (c),  with 
smaller  cells  {a)  mixed  with  them.  The  axis-cylinder  processes  of 
these  cells  pass  up  into  the  layer  above  and  eventually  become  fibres 


Fig.  538. — Nenous  mechanism  of  the  olfactory  apparatus,  a,  Bipolar  cells  of  the  olfactory  apparatus 
(Max  Schultze's  olfactorial  cells) ;  b,  olfactory  glomeruli ;  c,  mitral  cells ;  d,  granule  of  white 
layer ;  e,  external  root  of  the  olfactory  tract ;  f,  grey  matter  of  the  sphenoidal  region  of  the 
cortex  ;  a,  small  cell  of  the  mitral  layer ;  h,  basket  of  a  glomerulus  ;  c,  spiny  basket  of  a  granule  ; 
e,  collateral  of  the  axis-cylinder  process  of  a  mitral  ceU ;  /,  collaterals  terminating  in  the  molecular 
layer  of  the  frontal  and  sphenoidal  convolutions ;  g,  superficial  triangular  cells  of  the  cortex ; 
h,  supporting  epithelium  cells  of  the  olfactorj'  mucous  membrane.    (Ramon  y  Cajal.) 

of  the  olfactory  tract  E,  which  passes  to  the  grey  matter  of  the  base 
of  the  brain  f.     They  give  off  numerous  collaterals  on  the  way  {e,  f). 

(3)  The  layer  of  olfactory  glomeruli  (b).  Each  glomerulus  is  a 
basket-work  of  fibrils  derived  on  the  one  hand  from  the  terminal 
arborisations  of  the  mitral  cells,  and  on  the  other  from  similar 
arborisations  of  the  non-medullated  fibres  which  form  the  next  layer. 

(4)  Tlie  layer  of  olfactory  nerve-fibres. — These  are  non-medullated  ; 
they  continue  upwards  the  bi23olar  olfactory  cells,  or  as  we  have 
already  termed  them,  the  olfactorial  cells  of  the  mucous  membrane. 

Animals  may  be  di\ided  into  three  classes : — those  which,  like  the 
porpoise,  have  no  sense  of  smell  {anosmatic) ;  those  wliich  possess  it  in 
comparatively  feeble  degree  (man,  most  primates,  monotremes,  and 
some  cetacea) ;  those  are  called  microsmatie.  In  man  the  thickness 
of  the  olfactory  membrane  is  only  0"06  mm.  Most  mammals  are  in 
contradistinction  rnacrosmatic,  the  thickness  of  the  membrane  being 
0  1  mm.  or  more,  and  its  area  larger. 

The  mucous  membrane  must  be  neither  too  dry  nor  too  moist ;  if 
we  have  a  cold  we  are  unable  to  smell  odom-s  or  flavours  (which  are 


CH.  LIII.]  SMELL  751 

really  odours).  When  liquids  are  poured  into  the  nose,  their  smell  is 
imperceptible,  as  they  damage  the  olfactory  epithelium,  owing  to  the 
difference  of  osmotic  pressure.  But  even  if  a  "  normal "  saline  solu- 
tion of  an  odorous  substance  be  substituted,  the  sense  of  smell  is  still 
lost  so  long  as  air-bubbles  are  carefully  excluded  from  the  nasal 
cavity.  It  is  therefore  necessary  that  odorous  substances  should  be 
in  a  gaseous  state  in  order  to  act  upon  the  olfactory  epithelium ;  they 
are  propagated  mainly  by  diffusion. 

Generally,  the  odours  of  homologous  series  of  compounds  increase 
in  intensity  with  increase  of  molecular  weight,  but  bodies  of  very  low 
molecular  weight  are  odourless,  while  vapours  of  very  high  molecular 
weight,  which  escape  and  diffuse  slowly  have  little  or  no  smell.  A  slight 
change  in  chemical  constitution  may  produce  marked  alteration  in 
the  character  of  the  odour  of  a  substance ;  certain  modes  of  atomic 
grouping  within  the  molecule  appear  to  be  more  odoriferous  than 
others.  Attempts  have  been  made  to  discover  the  elementary  sensa- 
tions of  smell,  but  hitherto  with  scant  success.  Many  odours  have 
unquestionably  a  complex  physiological  effect.  For  example,  when 
nitrobenzol  is  held  before  the  nose,  it  yields  first  the  smell  of  helio- 
trope, next  the  smell  of  bitter  almonds,  and  finally  the  smell  of 
benzene;  just  as  if  different  end-organs  became  successively  ex- 
hausted. Some  substances  have  a  very  different  smell  according  to 
their  concentration.  Chemical  dissociation,  too,  unquestionably  plays 
a  prominent  part. 

Nevertheless,  there  are  certain  points  which  indicate  the  existence 
of  primary  sensations  of  smell.  First,  some  persons  are  congenitally 
insensible  to  one  or  more  odours,  but  yet  smell  others  quite  normally. 
Hydrocyanic  acid,  mignonette,  violet,  vanilla,  benzoin,  are  substances 
which  appear  to  certain  people  to  have  no  smell.  Secondly,  some  odor- 
ous bodies,  when  simultaneously  given,  antagonise  one  another ;  others 
produce  a  mixed  smell.  Thirdly,  fatigue  of  the  epithelium  with  one 
odour  will  modify  or  abolish  the  effect  of  some  smells,  but  will  leave 
that  of  others  untouched. 

The  delicacy  of  the  sense  of  smell  is  most  remarkable.  Valentin 
calculates  that  even  ^qo  qqo  oqq  of  a  grain  of  musk  can  be  distinctly 
smelled.  Solutions  of  camphor  afford  a  good  means  of  testing 
olfactory  acuity.  One  tube  of  camphor  solution  is  presented  to  the 
subject  along  with  three  tubes  of  water,  and  the  former  is  replaced 
with  weaker  and  weaker  solutions  until  it  is  indistinguishable  from 
the  tubes  containing  water.  Pungent  substances,  like  ammonia,  are 
unsuited  for  olfactometrical  experiment.  They  stimulate  the  endings 
of  the  fifth  as  well  as  those  of  the  olfactory  nerve. 


CHAPTER  LIV 

HEARING 

Anatomy  of  the  Ear. 

The  Organ  of  Hearing  (tig.  539)  is  divided  into  three  parts,  (1)  the 
external,  (2)  the  middle,  and  (3)  the  internal  ear.  The  two  first  are 
only  accessory  to  the  third  or  internal  ear,  which  contains  the 
essential  parts  of  the  organ  of  hearing. 

External  Ear. — The  external  ear  consists  of  the  pinna  and  the 
external  auditory  meatus.  The  central  hollow  of  the  former  is  named 
the  concha.  From  the  concha,  the  auditory  canal,  with  a  slight 
arch  directed  upwards,  passes  inwards  and  a  little  forwards  to 
the  membrana  tympani,  to  which  it  thus  serves  to  convey  the 
vibrating  air. 

Middle  Ear  or  Tympanum. — The  middle  ear,  or  tympanum  or 
drum  (3,  fig.  539),  is  separated  by  the  membrana  tympani  from  the 
external  auditory  meatus.  It  is  a  cavity  in  the  temporal  bone, 
opening  through  its  anterior  and  inner  wall  into  the  Eustachian  tube, 
a  cylindriform  flattened  canal,  dilated  at  both  ends,  composed  partly 
of  bone  and  partly  of  elastic  cartilage,  and  lined  with  mucous  mem- 
brane, which  forms  a  communication  between  the  tympanum  and  the 
pharynx.  It  opens  into  the  cavity  of  the  pharynx  just  behind  the 
posterior  aperture  of  the  nostrils.  The  cavity  of  the  tympanum 
communicates  posteriorly  with  air-cavities,  the  mastoid  cells  in  the 
mastoid  process  of  the  temporal  bone ;  but  its  only  opening  to  the 
external  air  is  through  the  Eustachian  tube  (4,  fig.  539).  The  walls 
of  the  tympanum  are  osseous,  except  where  apertures  in  them  are 
closed  with  membrane,  as  at  the  fenestra  rotunda,  and  fenestra  oralis, 
and  at  the  outer  part  where  the  bone  is  replaced  by  the  membrana 
tympani.  The  cavity  of  the  tympanum  is  lined  with  mucous  mem- 
brane, the  epithelium  of  which  is  ciliated  and  continuous  through 
the  Eustachian  tube  with  that  of  the  pharynx.  In  some  parts,  how- 
ever, viz.,  over  the  roof,  promontory,  ossicles,  and  membrana  tympani, 
the  epithelium  is  of  the  pavement  variety.  A  chain  of  small  bones 
extends  from  the  membrana  tympani  to  the  fenestra  ovalis. 


CH.  LIT.] 


ANATOMY   OF   THE   EAR 


753 


The  memhrana  tympani  is  placed  in  a  slanting  direction  at  the 
bottom  of  the  external  auditory  canal,  its  plane  being  at  an  angle 
of  about  45°  with  the  lower  wall  of  the  canal.  It  is  formed  of  fibres, 
some  running  radially,  some  circularly ;  its  margin  is  set  in  a  bony 


Fig.  539. — Diagrammatic  view  from  before  of  the  parts  composing  the  organ  of  hearing  of  the  left  side. 
The  temporal  bone  of  the  left  side,  with  the  accompanying  soft  parts,  has  been  detached  from  the 
head,  and  a  section  has  been  carried  through  it  transversely,  so  as  to  remove  the  front  of  the 
meatus  extemus,  half  the  tympanic  membrane,  the  upper  and  anterior  wall  of  the  tympanum  and 
Eustachian  tube.  The  meatus  intemus  has  also  been  opened,  and  the  bony  labyrinth  exposed  by 
the  removal  of  the  surrounding  parts  of  the  petrous  bone.  1 ,  The  pinna  and  lobe ;  2,  meatus 
extemus  ;  2',  membrana  tympani ;  3,  cavity  of  the  tympanum  ;  3',  its  opening  backwards  into  the 
mastoid  cells  ;  between  3  and  3',  the  chain  of  small  bones  ;  4,  Eustachian  tube  ;  5,  meatus  intemus, 
containing  the  facial  (uppermost)  and  the  auditorj' nen-es ;  6,  placed  on  the  vestibule  of  the  laby- 
rinth above  the  fenestra  ovalis  ;  a,  apex  of  the  petrous  bone ;  h,  internal  carotid  artery  :  c,  styloid 
process  ;  d,  facial  nen'e  issuing  from  the  stylo-mastoid  foramen ;  e,  mastoid  process ;  /,  squamous 
part  of  the  bone  covered  by  integument,  etc.    (Arnold.) 

groove;  its  outer  surface  is  covered  with  a  continuation  of  the 
cutaneous  lining  of  the  auditory  canal,  its  inner  surface  with  the 
mucous  membrane  of  the  tympanum. 

The  ossicles  are  three  in  number;  named  malleus,  incus,  and 
stapes.  The  malleus,  or  hammer-bone,  has  a  long  slightly-curved 
process,  called  its  handle,  which  is  inserted  between  the  layers  of 
the  membrana  tympani ;  the  line  of  attachment  is  vertical,  including 
the  whole  length  of  the  handle,  and  extending  from  the  upper 
border  to  the  centre  of  the  membrane.  The  head  of  the  malleus  is 
irregularly  rounded ;  its  neck,  or  the  line  of  boundary  between  the 
head  and  the  handle,  supports  two  processes:  a  short  conical  one, 
and  a  slender  one,  processus  gracilis,  which  extends  forwards,  and  is 
attached  to  the  wall  of  the  cavity  at  the  Glaserian    fissure.     The 


754 


HEARING 


[CH.  LIY. 


incus,  or  anvil-bone,  shaped  like  a  bicuspid  molar  tooth,  is  articulated 
by  its  broader  part,  corresponding  with  the  surface  of  the  crown  of 
the  tooth,  to  the  malleus.  Of  its  two  fang-like  processes,  one, 
directed  backwards,  has  a  free  end  attached  by  ligament  to  a  depres- 


Fio.  540. — The  hammer- 
bone  or  malleus,  seen 
from  the  front.  1,  The 
head ;  2,  neck ;  3, 
short  process ;  4, 
handle.    (Schwalbe.) 


Fig.  541. — The  incus,  or  anvil-bone. 
1,  Body;  2,  ridged  articulation 
for  the  malleus ;  4,  processus 
bre\-is,  ■with  5,  rough  articular 
surface  for  ligament  of  incus ; 
6,  processus  magnus,  with  articu- 
lating surface  for  stapes ;  7,  nu- 
trient foramen.    (Schwalbe.) 


Fig.  542. — The  stapes,  or 
stirrup  •  bone.  1,  Base  ; 
2  and  3,  arch;  4,  head 
of  bone,  which  articu- 
lates with  orbicular 
process  of  the  incus ; 
5,  constricted  part  of 
neck;  6,  one  of  the 
crura.    (Schwalbe.) 


sion  in  the  mastoid  bone ;  the  other,  curved  downwards,  longer  and 
more  pointed,  articulates  by  means  of  a  roundish  tubercle,  formerly 
called  OS  orUculare,  with  the  stapes,  a  little  bone  shaped  like  a  stirrup, 
of  which  the  base  fits  into  the  mem^      ne  of  the  fenestra  ovalis.     To 

tht    neck   of   the   stapes,  a  short 
,,   h       process,    corresponding    with    the 
loop  of  the  stirrup,  is  attached  the 
_  ^      stapedius  muscle. 
e  The  micscles  of  the  tympanum 

y  are  two  in  number.  The  tensor 
tympani  arises  from  the  cartila- 
ginous end  of  the  Eustachian  tube 
and  the  adjoining  surface  of  the 
sphenoid,  and  from  the  sides  of 
the  canal  in  which  the  muscle  lies  ; 
'^'  the  tendon  of  the  muscle  bends  at 

nearly  a  right  angle  over  the  end 
of  the  processus  cochleariformis, 
and  is  inserted  into  the  inner  part 
of  the  handle  of  the  malleus.  The 
stapedius  is  concealed  within  a 
canal  in  the  bone  in  front  of  the  aqueductus  Fallopii  The  tendon 
issues  from  the  aperture  of  this  canal  and  is  inserted  into  the  neck 
of  the  stapes  posteriorly. 

The  Internal  Ear. — The  proper  organ  of  hearing  is  formed  by  the 


Fig.  543. — Interior  view  of  the  tympanum,  with 
membrana  tympani  and  bones  in  natural  posi- 
tion. 1,  Membrana  tympani  ;  2,  Eustachian 
tube ;  3,  tensor  tympani  muscle  ;  4,  lig.  mallei 
erter. ;  5,  lig.  maUei  super. ;  6,  chorda-tympani 
nerve;  a,  h,  and  e,  sinuses  about  ossicles. 
(Schwalbe.) 


CH.  Lrv.] 


THE   INTERNAL    EAR 


755 


distribution  of  the  auditory  uerve,  within  the  internal  ear,  or  laby- 
rinth, a  set  of  cavities  within  the  petrous  portion  of  the  temporal 
bone.  The  bone  which  forms  the  walls  of  these  cavities  is  denser 
than  that  around  it,  and  forms  the  osseous  labyrinth ;  the  membrane 
within  the  cavities  forms  the  membranous  labyrinth.  The  mem- 
branous labyrinth  contains  a  fluid  called  endolymph ;  while  outside 
it,  between  it  and  the  osseous  labyrinth,  is  a  fluid  called  perilymph. 
This  fluid  is  not  pure  lymph,  as  it  contains  mucin. 

The  Osseous  Labyrinth  consists  of  three  principal  parts,  namely, 
the  vestibule,  the  cochlea,  and  the  semicircular  canals. 

The  vestibule  is  the  middle  cavity  of  the  labyrinth,  and  the 
central  chamber  of  the  auditory  apparatus.  It  presents,  in  its 
inner  wall,  several  openings  for  the  entrance  of  the  divisions  of  the 
auditory  nerve ;  in  its  outer  wall,  the  fenestra  ovalis  (2,  fig.  544a)^ 


Fig.  544a. — Right  bony  labyrinth,  viewed 
from  the  outer  side.  The  specimen 
here  represented  is  prepared  by  sepa- 
rating piecemeal  the  looser  substance 
of  the  petrous  bone  from  the  dense 
walls  which  immediately  enclose  the 
labyrinth.  1,  The  vestibule;  2,  fen- 
estra ovalis ;  3,  superior  semicircular 
canal ;  4,  horizontal  or  external  canal ; 
5,  posterior  canal ;  *,  ampullae  of  the 
semicii'cular  canals ;  5,  first  turn  of 
the  cochlea ;  7,  second  turn ;  8,  apex ; 
9,  fenestra  rotunda.  The  smaller  figure 
in    outline     below    shows     the     natural 

size,     -r*    (Sommering.)        | 


Fig.  5446.— View  of  the  interior  of  the  left 
labyrinth.  The  bony  wall  of  the  laby- 
rinth is  removed  superiorly  and  exter- 
nally. 1,  Fovea  hemielliptica ;  2,  fovea 
hemispherical  3,  common  opening  of 
the  superior  and  posterior  semicircular 
canals ;  4,  opening  of  the  aqueduct  of 
the  vestibule ;  5,  the  superior ;  6,  the 
posterior,  and  7,  the  external  semicir- 
cular canals ;  8,  spiral  tube  of  the 
cochlea  (scala  tympani) ;  9,  opening  of 
the  aqueduct  of  the  cochlea ;  10,  placed 
on  the  lamina  spiralis  in  the  scala  ves- 

21 
tibuli.    -p*     (Sommering.) 


an  opening  filled  by  membrane,  in  which  is  inserted  the  base  of  the 
stapes ;  in  its  posterior  and  superior  walls,  five  openings  by  which 
the  semicircular  canals  communicate  with  it :  in  its  anterior  wall, 
an  opening  leading  into  the  cochlea.  The  semicircular  canals  are 
described  in  Chapter  XLIX. 

The  cochlea  (6,  7,  8,  fig.  544a,  and  8,  fig.  5445)  is  shaped  like  a 


756 


HEARING 


[CH.  LIV. 


snail-shell,  and  is  situated  in  front  of  the  vestibule ;  its  base  rests  on 
the  bottom  of  the  internal  meatus,  where  some  apertures  transmit 
the  cochlear  filaments  of  the  auditory  nerve.  In  its  axis,  the  cochlea 
is  traversed  by  a  conical  column,  the  modioltis,  around  which  a 
spiral  canal  winds  with  two  turns  and  a  half  from  the  base  to  the 
apex.  At  the  apex  of  the  cochlea  the  canal  is  closed ;  at  the  base  it 
presents  three  openings,  of  which  one,  already  mentioned,  communi- 
cates with  the  vestibule  ;  another,  called  fenestra  rotunda,  is  separated 
by  a  membrane  from  the  cavity  of  the  tympanum ;  the  third  is  the 
orifice  of  the  aquceductus  cochlece,  a  canal  leading  to  the  jugular  fossa 
of  the  petrous  bone.  The  spiral  canal  is  divided  into  two  passages, 
or  scales  (staircases),  by  a  partition  formed  partly  of  bone,  the  lamina 
spiralis,  connected  with  the  modiolus,  and  partly  of  a  membrane 
called  the  hasilar  memhrane. 

The    Membranous    Labyrinth. — The     membranous     labyrinth 
corresponds  generally  with  the  form  of  the  osseous  labyrinth,  so  far 

as  regards  the  vestibule  and  semicircular 
canals,  but  is  separated  from  the  walls 
of  these  parts  by  perilymph,  except 
where  the  nerves  enter  into  connection 
with  it.  The  labyrinth  is  a  closed 
membrane  containing  endolymph,  which 
is  of  much  the  same  composition  as  peri- 
lymph, but  contains  less  solid  matter. 
In  the  cochlea,  the  membranous  labyrinth 
completes  the  septum  between  the  two 
scalce,  and  encloses  a  spiral  canal,  called 
the  canalis  cochlece  (fig.  545).  The  fluid 
in  the  scalce  of  the  cochlea  is  continuous 
with  the  perilymph  in  the  vestibule  and 
semicircular  canals.  The  vestibular  por- 
tion of  the  membranous  labyrinth  com- 
prises two  communicating  cavities,  of 
which  the  larger  and  upper  is  named 
the  utricle ;  the  lower,  the  saccule.  They 
are  lodged  in  depressions  in  the  bony 
in  the  whole  length  of  the  canal  of    labyrinth,  termed  respectively  foxca  hemi- 

the  cochlea.    (After  Schaffr.)  ,,."'.  i       ^  7  ■      7        ■  rrn. 

elhpticu  and  fovea  hemispherica.  Ine 
membranous  semicircular  canals  open  into  the  utricle ;  the  canal  of 
the  cochlea  opens  by  the  canaHs  reimiens  into  the  saccule.  The 
accompanying  diagram  (fig.  545)  shows  the  relationship  of  all  these 
parts  to  one  another. 

Auditory  Nerve. — All  the  organs  now  described  are  provided 
for  the  appropriate  exposure  of  the  filaments  of  the  auditory  nerve 
to  vibrations.     It   enters    the  meatus   auditorius  internum  with  the 


Fig.  545.— Diagram  of  the  right  mem- 
branous labjTinth.  U,  Utricle,  into 
which  the  three  semicircular  canals 
open ;  S,  saccule,  communicating 
with  the  cochlea  (0)  by  C.R.,  the 
canaUs  reuniens,  and  with  the  utricle 
by  a  canal  having  on  it  an  enlarge- 
ment, the  saccus  endolymphaticus 
(S.E.).  The  black  shading  repre- 
sents the  places  of  termination  of 
the  auditory  nerve,  namely,  in  the 
maculfe  of  the  utricle  and  saccule ; 
the  cristae  in  the  ampullary  ends  of 
the  three  semicircular  canals;   and 


CH.  LIV.] 


THE   COCHLEA 


757 


Fio.  546. — View  of  the  osseous  cochlea 
divided  through  the  middle.  1,  Central 
caual  of  the  modiolus  ;  2,  lamina  spiralis 
ossea ;  3,  scala  tympani ;  4,  scala  vesti- 
buli ;  5,  porous  substance  of  the  modiolus 
near  one  of  the  sections  of  the  canalis 
spiralis  modioli,     j    (Arnold.) 


facial  nerve  and  the  nervus  intermedins,  and,  traversing  the  bone, 
enters  the  labyrinth  at  the  angle  between  the  base  of  the  cochlea 
and  the  vestibnle,  in  two  divisions ;  one  for  the  vestibule  and  semi- 
circular canals,  and  the  other  for  the  cochlea. 

There  are  two  branches  for  the  vestibule,  one,  superior,  distri- 
buted to  the  utricle  and  to  the  superior  and  horizontal  semicircular 
canals,  and  the  other,  inferior,  which 
arises  from  the  cochlear  nerve,  ends  in 
the  saccule  and  posterior  semicircular 
canal.  The  inferior  nerve,  although  it 
is  contained  for  some  distance  in  the 
sheath  of  the  cochlear  nerve,  is  really 
composed  of  vestibular  fibres.  The  ter- 
minations of  the  nerve  in  the  saccule, 
utricle,  and  semicircular  canals  have 
been  already  described  in  page  721 ; 
80  we  can  pass  at  once  to  the  cochlea. 
This  is  best  seen  in  vertical  section ; 
the  cavity  is  divi<led  partly  by  bone 
(the  sjjiral  lamina),  partly  by  membrane  (the  basilar  membrane),  into 
two  spiral  scalse,  the  scala  tymjMni  and  scala  vestibuli  (fig.  546).  The 
basilar  membrane  increases  in  breadth  from  the  base  towards  the  apex 
of  the  cochlea.     It  contains  fibres  (about  24,000  in  all)  embedded 

in  a  homogeneous  matrix, 
and  running  radially,  from 
the  spiral  lamina  to  the 
spiral  ligament,  where  its 
other  end  is  again  attached 
to  the  bone.  At  the  apex  of 
the  cochlea,  the  lamina  ends 
in  a  small  hamulus,  the  inner 
and  concave  part  of  which 
being  detached  from  the  sum- 
mit of  the  modiolus,  leaves 
a  small  aperture  named  the 
helicotrema,  by  which  the  two 
scalse,  separated  in  all  the 
rest  of  their  length,  com- 
municate. 

Besides  the  scala  vestibuli 
and  scala  tympani,  there  is  a 
third  space  between  them, 
called  scala  media  or  canal  of  the  cochlea  {CC,  fig.  547).  In  section 
it  is  triangular,  its  external  wall  being  formed  by  the  wall  of  the 
cochlea,  its  upper  wall  (separating  it  from  the  scala  vestibuli)  by 


Fig.  547. — ^ecti<jn  thpjuuh  one  of  liie  i- vil.^  of  the  cochlea 
(diagrammatic).  .ST,  Scala  tyinpani ;  SF,  scala  vesti- 
buli ;  CC,  canalis  cochlea  or  canalis  membranaceus  ; 
R,  membrane  of  Reissner ;  Iso,  lamina  spiralis  ossea ; 
Us,  limbus  laminae  spiralis ;  ss,  sulcus  spiralis ;  nc, 
cochlear  nerve ;  gs,  ganglion  spirals ;  t,  membrana 
tectoria  (below  the  membrana  tectoria  is  the  lamina 
reticularis) ;  b,  membrana  basilaris  ;  Co,  rods  of  Corti ; 
Up,  ligamentum  spirale.     ((^uain.) 


758 


HEAEING 


[CH.  LIV. 


the  membrane  of  Eeissner,  and  its  lower  wall  (separating  it  from 
the  scala  tympani)  by  the  basilar  membrane,  these  two  meeting  at 
the  outer  edge  of  the  bony  lamina  spiralis.  Following  the  turns  of 
the  cochlea  to  its  apex,  the  scala  media  there  terminates  blindly; 
while  towards  the  base  of  the  cochlea  it  is  also  closed,  with  the 
exception  of  a  very  narrow  passage  (canalis  reuniens)  uniting  it 
with  the  saccule.  The  scala  media  (like  the  rest  of  the  membranous 
labyrinth)  contains  endolymph. 

Organ  of  Corti. — Upon  the  basilar  membrane  are  arranged  cells 
of  various  shapes.  About  midway  between  the  outer  edge  of  the 
lamina  spiralis  and  the  outer  wall  of  the  cochlea  are  situated  the 


Fig.  548.— Vertical  section  of  the  organ  of  Corti  from  the  dog.  1  to  2,  Homogeneous  layer  of  the 
membrana  basilaris  ;  k,  vestibular  layer ;  t;,  tympanal  layer,  with  nuclei  and  protoplasm;  a,  pro- 
longation of  tympanal  periosteum  of  lamina  spiralis  ossea  ;  e,  thickened  commencement  of  the 
membrana  basilaris  near  the  point  of  perforation  of  the  nerves  h ;  d,  blood-vessel  (vas  spirale) ;  c, 
blood-vessel ;  /,  nerves  ;  g,  the  epithelium  of  the  sulcus  spiralis  intemus;  i,  internal  hair-cell,  with 
basal  process  k,  surrounded  with  nuclei  and  protoplasm  (of  the  granular  layer),  into  which  the 
nerve-tlbres  radiate  ;  I,  hairs  of  the  internal  hair-cell ;  n,  base  or  foot  of  inner  pillar  of  organ  of  Corti ; 
m,  head  of  the  same  uniting  with  the  corresponding  part  of  an  external  pillar,  whose  under  half  is 
missing,  while  the  next  pillar  beyond,  o,  presents  both  middle  portion  and  base;  r,  s,  d,  three 
external  hair-cells  ;  t,  bases  of  two  neighbouring  hair  or  tufted  cells  ;  x,  supporting  cell  of  Deiters  ; 
w,  nerve-tibre  arborising  round  the  first  of  the  external  hair-cells ;  I  I  to  I,  lamina  reticularis. 
X  800.    (Waldeyer.) 

o'ods  of  Corti.  Viewed  sideways,  they  are  seen  to  consist  of  an 
external  and  internal  pillar,  each  rising  from  an  expanded  foot  or 
hase  attached  to  the  basilar  membrane  (o,  n,  fig.  548).  They  slant 
inwards  towards  each  other,  and  each  ends  in  a  swelling  termed  the 
head ;  the  head  of  the  inner  pillar  overlies  that  of  the  outer  (fig.  548). 
Each  pair  of  pillars  forms  a  pointed  roof  arching  over  a  space,  and 
by  a  succession  of  them  a  tunnel  is  formed. 

There  are  about  3000  of  these  pairs  of  pillars,  in  proceeding  from 
the  base  of  the  cochlea  towards  its  apex.  They  are  found  pro- 
gressively to  increase  in  length,  and  become  more  oblique ;  in  other 
words,  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
approach  the  apex  of  the  cochlea.    Leaning  against  the  rods  of  Corti 


CH.  LIV.]  PHYSIOLOGY   OF   HEARING  759 

are  certain  other  cells  called  hair-cells,  which  terminate  in  small 
hair-like  processes.  There  are  several  rows  of  these  on  the  outer 
and  one  row  on  the  inner  side.  Between  them  are  certain  sup- 
porting cells  called  cells  of  Deiters  (fig.  548,  x).  This  structure  rests 
upon  the  basilar  membrane ;  it  is  roofed  in  by  a  fenestrated  mem- 
brane or  lamina  reticularis  into  the  fenestrae  of  which  the  tops  of 
the  various  rods  and  cells  are  received.  When  viewed  from  above, 
the  organ  of  Corti  shows  a  remarkable  resemblance  to  the  key- 
board of  a  piano.  The  top  of  the  organ  is  roofed  by  the  membrana 
teetoria  (fig.  547,  t)  which  extends  from  the  end  of  the  limbus 
{lis,  fig.  547),  a  connective  tissue  structure  on  the  spiral  lamina. 
The  spiral  ganglion  from  which  the  cochlear  nerve-fibres  originate  is 
situated  in  the  spiral  lamina.  The  peripheral  axons  of  its  bipolar 
cells  arborise  around  the  hair-cells  of  the  organ  of  Corti :  the  central 
axons  pass  down  the  modiolus,  and  thence  to  the  pons  (see  p.  654). 

Physiology  of  Hearing. 

Sounds  are  caused  by  vibrations ;  when  a  piano-string  is  struck, 
it  is  thrown  into  a  series  of  rapid  regular  vibrations ;  the  more 
rapidly  the  vibrations  occur  the  liigher  is  the  pitch  of  the  musical 
note;  the  greater  the  amplitude  of  the  vibration,  the  louder  or 
more  intense  is  the  tone;  if  the  vibrations  are  regular  and  simple 
(pendular),  the  tone  is  pure ;  if  they  are  regular  but  compomid,  the 
tone  is  impure,  and  its  quality  or  timhre  is  dependent  on  the  rate 
and  amplitude  of  the  simple  -vibrations  of  which  the  compound 
vibrations  are  composed.  The  vibrations  are  transmitted  as  waves, 
and  ultimately  affect  the  hair-cells  at  the  extremities  of  the 
auditory  nerve  in  the  cochlea.  The  semicircular  canals  are  not 
concerned  in  the  sense  of  hearing ;  their  function  in  connection  with 
equilibration  is  described  in  Chapter  XLIX.  The  external  and 
middle  ears  are  conducting;  the  internal  ear  is  conducting  and 
receptive.  In  the  external  ear  the  vibrations  travel  through  air ;  in 
the  middle  ear  through  solid  structures — membranes  and  bones  ;  and 
in  the  internal  ear  through  fluid,  first  through  the  perilymph  on  the 
far  side  of  the  fenestra  ovalis ;  and  then  the  vibrations  pass  through 
the  basilar  membrane  and  membrane  of  Eeissner,  and  set  the  endo- 
lymph  of  the  canal  of  the  cochlea  in  motion. 

This  is  the  normal  way  in  which  the  vibrations  pass,  but  the  endolymph  may  be 
affected  in  other  ways,  for  instance  through  the  other  bones  of  the  head ;  one  can, 
for  example,  hear  the  ticking  of  one's  watch  when  it  is  placed  between  the  teeth, 
even  when  the  ears  are  stopped.  From  this  fact  is  derived  a  valuable  practical 
method  of  distinguishing  in  a  deaf  person  what  part  of  the  organ  of  hearing  is  at 
fault.  The  patient  may  not  be  able  to  hear  a  watch  or  a  tuning-fork  when  it  is  held 
close  to  the  ear  ;  but  if  he  can  hear  it  when  it  is  placed  between  his  teeth,  or  on  his 
forehead,  the  malady  is  localised  in  either  the  external  or  middle  ear  ;  if  he  can  hear 
it  in  neither  situation,  it  is  a  much  more  serious  case,  for  then  the  internal  ear  or  the 


760  HEARING  [CH.  LIV. 

nervous  mechanism  of  hearing  is  at  fault.  In  disease  of  the  middle  ear  the  hearing 
of  low  tones  is  especially  affected  ;  high  tones  appear  to  be  transmissible  by  bone- 
conduction  more  readily  than  loTt^. 

In  connection  with  the  external  ear  there  is  not  much  more  to  be 
said ;  the  pinna  in  many  animals  is  large  and  acts  as  a  kind  of  natural 
ear-trumpet  to  collect  the  vibrations  of  the  air ;  in  man  this  function 
is  to  a  very  great  extent  lost,  and  though  there  are  muscles  present  to 
move  it  into  appropriate  postures,  they  are  not  under  the  control  of  the 
will  in  the  majority  of  people,  and  are  functionless,  ancestral  vestiges. 

In  the  middle  ear,  however,  there  are  several  points  to  be  con- 
sidered, namely,  the  action  of  the  membrana  tympani,  of  the  ossicles, 
of  the  tympanic  muscles,  and  of  the  Eustachian  tube. 

TJie  Membrana  Tympani. — This  membrane,  unlike  that  of 
ordinary  drums,  can  take  up  and  vibrate  in  response  to,  not  only  its 
own  fundamental  tone,  but  to  an  immense  range  of  tones  differing 
from  each  other  by  many  octaves.  This  would  clearly  be  impos- 
sible if  it  were  an  evenly  stretched  membrane.  It  is  not  evenly  nor 
very  tightly  stretched,  but  owing  to  its  attachment  to  the  chain  of 
ossicles  it  is  slightly  funnel-shaped :  the  ossicles  also  damp  the  con- 
tinuance of  the  vibrations. 

When  the  membrane  gets  too  tightly  stretched,  by  increase  or 
decrease  of  the  pressure  of  the  air  in  the  tympanum,  then  the  sense 
of  hearing  is  dulled.  The  pressure  in  the  tympanic  cavity  is  kept 
the  same  as  that  of  the  atmosphere  by  the  Eustachian  tube,  which 
leads  from  the  cavity  to  the  pharynx,  and  so  to  the  external  air. 
The  Eustachian  tube  is  not,  however,  always  open ;  it  is  opened  by 
the  action  of  the  tensor  palati  during  swallowing.  Suppose  it  were 
closed  owing  to  swelling  of  its  mucous  membrane — this  often 
happens  in  inflammation  of  the  throat — the  result  would  be  what  is 
called  Eustachian  or  throat  deafness,  and  this  is  relieved  by  passing 
a  catheter  so  as  to  open  the  tube.  When  the  tube  is  closed,  an 
interchange  of  gases  takes  place  between  the  imprisoned  air  and  the 
blood  of  the  tympanic  vessels.  In  time,  as  in  the  aerotomometer 
(see  p.  381),  equilibrium  is  established  and  the  tension  of  the 
imprisoned  gases  becomes  equal  to  that  of  the  blood-gases,  not  to 
that  of  the  atmosphere.  The  membrane  is  therefore  cupped  inwards 
by  the  atmospheric  pressure  on  its  exterior ;  it  is  this  increased 
tightening  of  the  membrane  that  produces  deafness.  There  is  also 
an  accumulation  of  mucus.  When  one  makes  a  violent  expiration, 
as  in  sneezing,  some  air  is  often  forced  through  the  Eustachian  tube 
into  the  tympanum.  The  ears  feel  as  though  they  were  bulged  out, 
as  indeed  the  membrana  tympani  is,  and  there  is  again  partial  deaf- 
ness, which  sensations  are  at  once  relieved  by  swallowing,  so  as  to 
open  the  Eustachian  tube  and  thus  re-establish  equality  of  pressure. 

The    ossicles    communicate    the    vibrations     of    the    membrana 


CH.  LIV.]  MECUANISM   OF   THE   TYMPANUM  761 

tympaiii  (to  which  the  handle  of  the  malleus  is  fixed)  to  the  mem- 
brane which  closes  the  fenestra  ovalis  (to  which  the  foot  of  the 
stapes  is  attached).  Thus  the  vibrations  are  communicated  to 
the  fluid  of  the  internal  ear  which  is  situated  on  the  other  side  of 
the  oval  window. 

The  accompanying  diagram  will  assist  us  in  understanding  how 
this  is  brought  about.  The  bones  all  vibrate  as  if  they  were  one, 
the  slight  movements  between  the  individual  bones  being  inappreci- 
able. The  utility  of  there  being  several  bones  is  seen  when  the 
vibrations  are  excessive;  the  small  amount  of  "give"  at  the 
articulations  is  really  protective  and  tends  to  prevent  fractures. 

The  handle  of  the  malleus  is  inserted  between  the  layers  of  the 
tympanic  membrane ;  the  processus  gracilis  (p.  g.)  has  its  end  A 
attached  to  the  tympanic  wall  on 
the  inner  aspect  of  the  Glaserian 
fissure ;  the  end  B  of  the  short  pro- 
cess (s.  p.)  of  the  incus  is  fastened 
by  a  ligament  to  the  opposite  wall 
of  the  tympanic,  cavity ;  the  end 
D  of  the  long  process  of  the  incus 
articulates  with    the  stirrup,  the 

base  of  which  is  turned  towards      ^  \\     I  [\;J\-Foot  of 

the  reader.     The  handle  vibrates  \\?  \\^  j   Stapes 

with  the  membrana  tympani ;  and 
the  vibrations  of  the  whole  chain 
take  place  round  the  axis  of  rota- 
tion    AB.       Every    time     C     comes  Fig.  349.— Diagrammatic  view  of  ear  ossicles. 

forwards  D  comes  forwards,  but 

by  drawing  perpendiculars  from  C  and  D  to  the  axis  of  rotation,  it  is 
found  that  D  is  about  f  of  the  distance  from  the  axis  that  C  is.  So 
in  the  transmission  of  the  vibrations  from  membrane  to  membrane 
across  the  bony  chain,  the  amplitude  of  the  vibration  is  decreased  by 
about  ;^,  and  the  force  is  correspondingly  increased.  This  increase  of 
power  is  augmented  by  the  fact  that  the  tympanic  membrane  concen- 
trates its  power  upon  an  area  (the  membrane  of  the  oval  window)  only 
one-twentieth  of  its  size.  The  final  movement  of  the  stapes  is,  however, 
always  very  small ;  it  varies  from  yV  to  less  than  j^oloo  of  a  millimetre. 

The  action  of  the  tensor  tympani,  by  pulling  in  the  handle  of  the 
malleus,  increases  the  tension  of  the  membrana  tymj)ani.  It  is 
supplied  by  the  fifth  nerve.  It  is  opposed  by  the  strong  external 
ligament  of  the  malleus.  The  stapedius  attached  to  the  neck  of  the 
stapes  tilts  it  backwards  and  diminishes  the  intra-tympanic  air- 
pressure.     It  is  supplied  by  the  seventh  nerve. 

The  next  very  simple  diagram  (fig.  550)  will  explain  the  use  of 
the  fenestra  rotunda. 


762  HEARING  [CH.  LIY. 

The  cochlea  is  supposed  to  be  uncoiled ;  the  scala  vestibuli  leads 
from  the  fenestra  ovalis,  to  the  other  side  of  which  the  stapes  is 
attached ;  the  scala  tympani  leads  to  the  fenestra  rotunda ;  the  two 
scalse  communicate  at  the  helicotrema,  and  are  separated  from  the 
canal  of  the  cochlea  by  the  basilar  membrane,  and  the  membrane  of 
Eeissner.     C.R.  is  the  canalis  reuniens  leading  to  the  saccule.     The 

F.  Ovalis 
Stapes     I 


m 


Scale    Vestibuli    (Perilymph) 

-Canal    of-Coclilea     (-£Traonrwpl> }  ~ 


CR       ll  Scala    Tympani    (Perilymph) 


F.  Rotunda 

Fig.  550. — Diagram  to  illustrate  the  use  of  the  fenestra  rotunda. 

cochlea  is  filled  with  incompressible  fluid  in  an  inexpansible  bony 
case,  except  where  the  windows  are  closed  by  membranes.  Hence 
every  time  the  membrane  of  the  oval  window  is  bulged  in  by  the 
stirrup,  the  membrane  of  the  round  window  is  simultaneously  bulged 
out  to  the  same  extent,  and  vice  versd.  These  changes  of  pressure 
are  transmitted  from  one  scala  to  the  other  directly  through  the 
cochlear  canal,  setting  it  into  vibration,  and  through  the  helicotrema. 

The  range  of  hearing  extends  over  10  or  11  octaves;  the  lowest 
audible  tone  having  about  20,  the  highest  about  25,000,  vibrations 
per  second.  The  range  varies  in  different  people,  and  diminishes 
from  childhood  onwards.  The  upper  limit  of  hearing  may  be  tested 
by  minute  tuning-forks,  metal  rods,  or  by  Galton's  wliistle.  Many 
animals  appear  to  be  able  to  detect  high  tones  which  lie  beyond  the 
human  limit.  The  lower  limit  may  be  determined  by  very  large  tuning- 
forks,  or  by  employing  very  low  difference-tones. 

Difference-tones  are  produced  when  two  tones  of  different  pitch, 
m  and  n,  are  sounded  together.  A  tone  having  the  pitch  m  minus  7i 
is  then  heard  in  addition  to  the  tones  m  and  n :  also  a  summation 
tone  of  pitch  m  plus  n  may  be  heard,  but  with  greater  difficulty. 
When  m  and  n  are  nearly  equal,  a  beating  tone,  instead  of  a  difference- 
tone,  results,  having  a  pitch  somewhere  intermediate  between  m  and  n. 
If  the  difference  between  m  and  n  is  exceedingly  small,  this  beating- 
tone  alone  is  heard.  The  frequency  of  the  beats  corresponds  to  the 
difference  in  vibration-rates,  m  and  n.  Under  certain  conditions  the 
difference  and  summation-tones  (which  are  collectively  called  combina- 
tion-tones) exist  in  the  air;  then-  presence  being  demonstrable  by 
their  re-inforcement  before  appropriate  resonators.  More  generally, 
however,  they  appear  to  be  produced  within  the  ear,  i.e.,  they  have 
merely  a  subjective  origin.  The  smallest  perceptible  difference  in 
pitch  between  two  successive  tones  is  about  0"2  vibrations  in  the 


CH.  LIV.]  THEORIES   OF   THE   COCHLEA  763 

middle  region  of  the  piano  for  trained  subjects.  Practice  effects 
extraordinary  improvement,  even  among  the  most  unmusical. 

There  can  be  little  doubt  that  the  cochlea  is  the  organ  specially 
concerned  in  hearing.  It  first  appears  among  vertebrata  in  certain 
fishes  as  a  very  rudimentary  structure.  If  the  cochlea  is  removed 
from  dogs,  they  become  deaf. 

There  are  two  classes  of  theories  of  hearing,  in  both  of  which  the 
basilar  membrane  of  the  cochlea  plays  the  essential  part. 

The  one  class  comprises  the  many  "sound-picture"  theories 
which  have  been  advanced  in  very  various  forms  by  Eutherford, 
Waller,  Hurst,  Ewald,  and  Meyer.  The  entire  basilar  membrane  is 
supposed  to  vibrate  either  as  a  telephone  plate,  or  as  an  elastic  mem- 
brane, different  tones  or  combinations  of  tones  giving  rise  to  different 
patterns  of  vibrations  which  are  communicated  to  the  hair-cells 
and  thence  by  the  auditory  nerve-fibres  to  the  brain,  where  (in 
Rutherford's  theory)  the  analysis  of  these  patterns  is  held  to  take  place. 

The  other  is  the  resonance-theory  of  Helmholtz,  in  which  the 
pitch  of  a  tone,  or  the  analysis  of  a  complex  sound  into  its  constituent 
tones,  is  determined  not  in  the  brain  but  in  the  cochlea.  It  depends 
on  the  principle  of  sympathetic  vibration.  As  is  well  known,  if  a 
tone  is  sung  in  front  of  a  piano  (best  with  the  loud  pedal  held  down), 
the  string  of  the  piano  which  is  attuned  to  that  tone  will  immediately 
respond;  another  tone  will  elicit  response  from  another  string.  So 
in  the  cochlea  the  appropriate  fibre  of  the  basilar  membrane  is  thrown 
into  vibration  when  the  tone  to  which  it  is  attuned  reaches  it.  The 
fibre  thus  stimulated  affects  the  hair-cells  above  it,  whence  the  stimulus 
is  conducted  to  the  brain.  If  two  tones  are  sounded  together,  the  two 
appropriate  fibres  respond,  and  the  analysis  of  the  now  more  complex 
stimulus  is  performed  in  the  cochlea.  The  fibres  of  the  basilar  mem- 
brane increase  in  radial  length  from  the  base  towards  the  apex  of  the 
cochlea.  According  to  the  resonance-theory,  the  upper  part  of  the 
organ  would  thus  be  affected  by  low  tones,  the  lower  part  by  liigh  tones. 

The  first  of  these  two  classes  of  theory  makes  it  difficult  or 
impossible  for  us  to  explain  our  ability  to  analyse  complex  chords 
into  their  component  tones.  The  full  acceptance  of  the  second  is 
difficult  in  the  face  of  the  small  difference  of  length  (at  most  1  :  12) 
between  the  shortest  and  the  longest  of  the  basilar  fibres.  On  the 
other  hand,  it  gains  support  from  the  effects  of  experiment  on,  and 
disease  of,  different  portions  of  the  cochlea.  For  instance,  the  deaf- 
ness to  high-pitched  tones  (seen  in  boiler-makers)  is  stated  to  be 
associated  with  disease  of  the  lower  whorl  of  the  cochlea. 

It  may  be  that  the  fibres  of  the  basilar  membrane  do  not 
vibrate  as  Helmholtz  supposed,  but  that  the  hair-cells  themselves 
are  each  in  some  unknown  way  specially  attuned  to  respond  only  to 
one  of  the  many  tonal  stimuli  which  may  reach  them  (Myers). 


C  H  A  P  T  E  E     L  V 


VOICE   AND    SPEECH 


The  fundamental  tones  of  the  voice  are  produced  by  the  current  of 
expired  air  causing  the  vibration  of  the  vocal  cords,  two  elastic  bands 
contained  in  a  cartilaginous  box  placed  at  the  top  of  the  wind-pipe 
or  trachea.  This  box  is  called  the  larynx.  The  sounds  produced 
here  are  modified  by  other  parts  such  as  the  tongue,  teeth,  and  lips, 
as  will  be  explained  later  on. 

Anatomy  of  the  Larynx. 

The  cartilages  of  the  larynx  are  the  thyroid,  the  cricoid,  the  two  arytenoids. 
These  are  the  most  important  for  voice  production  ;  they  are  made  of  hyaline  carti- 


m.  Sterno-liyoideus. 


m.  Thyi'o-hyoideus. 


m.  Sterno-hyoideus. 
in.  Crico-thyroideus. 


Lig.  cricu-thyr.  med. 

Cart,  cricoidea  .. 
Lig.  crico-tracheiE 

Cart,  tracheale 


Kio.  651.— The  larynx,  as  seen  from  the  front  showing  the  cartilages  and  ligaments.     The  muscles,  with 
the  exception  of  one  crico-thyroid,  are  cut  off  short.    (Stoerk.) 

lage.     Then  there  are  the  epiglottis,  two  cornicular,  and  two  cuneiform  cartilages. 
These  are  made  of  yellow  fibro-cartilage. 

The  thyroid  cartilage  (fig.  552, 1  to  4)  does  not  form  a  complete  ring  around  the 

704 


CH.  LV.] 


THE   LARYNX 


765 


larynx,  but  only  covers  the  front  portion.  It  forms  the  prominence  in  front  of  the 
throat  known  as  Adam's  apple.  The  rncovl  cartilage  (fig.  r)52,  5,  6),  on  the  other 
hand,  is  a  complete  ring ;  the  back  part  of  tlie  ring  is  much  broader  than  the  front. 
On  the  top  of  this  broad  portion  of  the  cricoid  are  the  arylimovl  cartilages  (fig. 
552,  7) ;  the  <'onneetion  between  the  cricoid  below  and  arytenoid  cartilages  above 
is  a  joint  with  synovial  membrane  and  ligaments,  the  latter  permitting  tolerably  free 


Fia.  552. — Cartilatjes  of  the  larynx  seen  from  the  front.  1  to  4,  Thyroid  cartilage  ;  1 ,  vertical  ridge  or 
pomum  Adami ;  2,  right  ala;  3,  superior,  and  4,  inferior  comu  of  the  right  side  ;  5,  6,  cricoid  carti- 
lage ;  5,  inside  of  the  posterior  part ;  (3,  anterior  narrow  part  of  the  ring  ;  7,  arytenoid  cartilages,    x  |. 

motion  between  them.  But  although  the  arytenoid  cartilages  can  move  on  the 
cricoid,  they  accompany  the  latter  in  all  its  movements.  The  base  by  means  of 
which  each  arytenoid  cartilage  sits  on  the  cricoid  is  triangular  ;  the  anterior  angle  is 
often  called  the  vocal  process  :  to  it  the  posterior  ends  of  the  true  vocal  cords  are 
attached.     The  outer  angle  is  thick  and  called  the  muscular  process. 

The  cornicular  cartilages,  or  cartilages  of  Santorini,  are  perched  on  the  top  of 


Lig.  ary-epiglott.  ,^ 


Cart.  Wrisbergu 
Cart.  Santorini 

Cart,  aryten. 

Proc.  muscul. 

Lig.  crico-aryten 
Lig.  cerato-crico.  post,  sup 

Cornu  infei . 

Lig.  cerato-crico.  post,  inf 


Cart  traclipfe 


Pars  menibran. 


Fig.  r.53.— The  larynx  as  seen  from  behind  after  removal  of  the  muscles.    The  cartilages  and  ligaments 

only  remain.    (Stoerk.) 

the  arytenoids  ;  the  cuneiform  cartilages,  or  cartilages  of  Wrisberg,  are  in  a  fold  of 
mucous  membrane  ;  the  epiglottis  looks  like  a  lid  to  the  whole  (fig.  553). 

The  thyroid  cartilage  is  connected  with  the  cricoid,  by  the  crico-thyroid  mem- 
brane, and  also  by  joints  with  synovial  membranes  ;  the  lower  cormia  of  the  thyroid 
clasp  the  cricoid  between  them,  yet  not  so  tightly  but  that  the  thyroid  can  revolve, 
within  a  certain  range,  around  an  axis  passing  transversely  through  the  two  joints 


766 


VOICE   AND    SPEECH 


[CH.  LV. 


F.V.C.- 


at  which  the  cricoid  is  clasped.  The  vocal  cords  are  attached  behind  to  the  front 
portion  of  the  base  (vocal  process)  of  the  arytenoid  cartilages,  and  in  front  to  the 
re-entering  angle  at  the  back  of  the  thyroid  ;  it  is  evident,  therefore,  that  all  move- 
ments of  either  of  these  cartilages  must  produce  an  effect  on  them  of  some  kind  or 
other.  Inasmuch,  too,  as  the  arytenoid  cartilages  rest  on  the  top  of  the  back  portion 
of  the  cricoid  cartilage,  and  are  connected  with  it  by  capsular  and  other  ligaments, 
all  movements  of  the  cricoid  cartilage  must  move  the  arytenoid  cartilages,  and  also 
produce  an  effect  on  the  vocal  cords. 

Mucous  membrane.  — The  larynx  is  lined  with  a  mucous  membrane  continuous 
with  that  of  the  trachea ;  this  is  covered  with  ciliated  epithehum  except  over  the  vocal 

cords  and  epiglottis,  where  it  is 
stratified.  The  vocal  cords  are 
thickened  bands  of  elastic  tissue  in 
this  mucous  membrane  which  run 
from  before  back.  They  are  at- 
tached behind  to  the  vocal  processes 
of  the  arytenoid  cartilages,  and  in 
front  to  tlie  angle  where  the  two 
wings  of  the  thyroid  meet.  The 
chink  between  them  is  called  the 
rima  f/lof/u/is  (see  fig.  554).  Two 
ridges  of  mucous  membrane  above 
and  parallel  to  these  are  called  the 
false  vocal  cords :  between  the  true 
and  false  vocal  cord  on  each  side  is 
a  recess  called  the  t-entricle. 

Muscles. — The  muscles  of  the 
larynx  are  divided  into  intrinsic  and 
extrinsic.  The  intrinsic  are  named 
from  their  attachments  to  the  various 
cartilages ;  the  extrinsic  are  those 
which  connect  the  larynx  to  other 
parts  like  the  hyoid  bone. 

The  intrinsic  muscles  of  the 
larynx  are  as  follows : — 

1.  Crico-thyroid. 

2.  Posterior  crico-arytenoid. 

3.  Lateral  crico-arytenoid. 

4.  Thyro-arytenoid. 
.").  Arjiienoid. 
All    these    muscles  except   the 

arytenoid  are  in  pairs. 

Their  attachments  and  actions 
are  as  follows  : — 

1.  Crico-tln/roid. — This  is  a 
short,  thick  triangular  muscle,  at- 
tached below  to  the  cricoid  cartilage ; 
this  attachment  extends  from  the  middle  line  backwards.  The  fibres  pass  upwards 
and  outwards,  diverging  sUghtly  to  be  attached  above  to  the  inferior  border  of  the 
thyroid  cartilage,  and  to  the  anterior  border  of  its  lower  cornu.  In  the  latter  portion 
of  the  muscle  the  fibres  are  nearly  horizontal.  Some  of  the  superficial  fibres  are 
continuous  with  those  of  the  inferior  constrictor  of  the  pharynx. 

The  thyroid  cartilage  being  fixed  by  extrinsic  muscles,  the  contraction  of  this 
muscle  draws  upwards  the  anterior  part  of  the  cricoid  cartilage,  and  depresses  the 
posterior  part,  and  with  it  the  arytenoid  cartilages,  so  that  the  vocal  cords  are 
stretched.  Paralysis  of  these  muscles  therefore  causes  an  inability  to  produce  high- 
pitched  tones. 

2.  Postei-ior  crico-arytenoid. — This  arises  from  the  broad  depression  on  the 
corresponding  half  of  the  posterior  surface  of  the  cricoid  cartilage ;  its  fibres  con- 
verge upwards  and  outwards,  and  are  inserted  into  the  outer  angle  of  the  base  of  the 


Fig.  554. — Vertical  section  through  the  larynx,  passing 
from  side  to  side.  H,  Hyoid  bone ;  T.,  thyroid  carti- 
lage ;  T.C.M.,  thyro-cricoid  membrane  ;  C,  cricoid 
cartilage;  Tr.,  first  ring  of  trachea;  T.A.,  thyro- 
arytenoid muscle ;  R.G.,  rima  glottidis;  V.C.,  vocal 
cord;  V.,  ventricle;  F.V.C.,  false  vocal  cord.  (After 
Allen  Thomson.) 


CH.  LV.] 


MUSCLES   OF   THE   LARYNX 


767 


arytenoid  cartilage  behind  the  attachment  of  the  lateral  crico-arytenoid  muscle. 
Near  their  insertion  the  upper  fibres  are  blended  with  the  lower  fibres  of  the  ary- 
tenoid muscle. 

These  muscles  draw  the  outer  angles  of  the  arytenoid  cartilages  backwards  and 
inwards,  and  thus  rotate  tiie  anterior  or  vocal  processes  outwards,  and  widen  the 
riraa  glottidis.  They  come  into  action  during  deep  inspiration.  If  they  are  paralysed, 
the  lips  of  the  glottis  approach  the  middle  line  and  come  in  contact  during  each 
inspiration,  so  that  d^yspnoea  is  produced. 

3.  Lalcral  cricu-dn/foioid. — This  arises  from  tiie  sloping  upper  border  of  the 
cricoid  cartilage,  and  is  inserted  into  tlie  muscular  process  of  the  arytenoid  carti- 
lage, and  the  adjacent  part  of  its  anterior  surface.  Its  upper  part  is  more  or  less 
blended  with  the  thyro-arytenoid,  and  a  few  of  its  fibres  are  continuous  round  the 
outer  side  of  the  arytenoid  cartilage  with  the  arytenoid  muscle. 

These  muscles  draw  the  muscular  processes  of  the  arytenoid  cartilages  forwards 
and   downwards,  and   thus  ap- 
proximate the  vocal  cords.    They 
are  antagonistic  to  the  posterior 
crico-arytenoids. 

4.  Thi/ro  -  arytenoid.  —  This 
consists  of  two  portions,  inner 
and  outer.  The  inner  portion 
arises  in  the  lower  half  of  the 
angle  formed  by  the  alae  of  the 
thyroid  cartilage,  and  passing 
backwards  is  attached  behind  to 
the  vocal  process  and  to  the  ad- 
jacent parts  of  the  outer  surface 
of  the  arytenoid  cartilage.  These 
fibres  are  joined  internally  by 
short  fibres  which  are  attached 
in  front  to  the  vocal  cord,  and 
behind  to  the  vocal  process. 
Some  oblique  fibres  pass  from 
the  sloping  portion  of  the  crico- 
thyroid membrane  below  the 
vocal  cord,  upwards,  outwards, 
and  somewhat  backwards,  to 
end  in  the  tissue  of  the  false 
vocal  cord.  The  fibres  of  the 
outer  portion  arise  in  front  from 
the  thyroid  cartilage  close  to  the 
origin  of  the  inner  portion  and  from  the  crico-thyroid  membrane.  They  pass  back- 
wards to  be  inserted  in  part  into  the  lateral  border  and  muscular  process  of  the 
arytenoid  cartilage,  and  in  part  they  pass  obliquely  upwards  towards  the  aryteno- 
epiglottidean  fold,  ending  in  the  false  vocal  cord.  The  portion  of  this  muscle  which 
extends  towards  the  epiglottis  is  often  described  as  a  separate  muscle  (thj/ro- 
epujlottidean) ;  it  resembles  the  crico-arytenoid  in  that  some  of  its  fibres  are  con- 
tinuous with  those  of  the  arytenoid  muscle. 

The  antero-posterior  fibres  will  tend  to  draw  forward  the  arytenoid  cartilage, 
and  with  it  the  posterior  part  of  the  cricoid  cartilage,  rotating  the  latter  upwards 
and  antiigonising  the  action  of  the  crico-thyroid  muscle,  the  effect  being  to  relax  the 
vocal  cords.  But  if  the  latter  are  kept  stretched  those  fibres  of  the  inner  portion  of 
the  muscle  which  are  inserted  into  the  vocal  cord  may  serve  to  modify  its  elasticity, 
tightening  the  parts  of  the  cord  in  front  of,  and  relaxing  those  behind,  its  attach- 
ment. The  vertical  fibres  of  the  muscle  which  extend  from  the  crico-thyroid  mem- 
brane across  the  base  of  the  vocal  fold  and  over  the  ventricle  into  the  false  vocal 
cord,  render  the  free  edge  of  the  former  more  prominent.  Then  the  fibres  which  are 
inserted  into  the  muscular  process  and  outer  surface  of  the  arytenoid  cartilage  will 
tend  to  draw  the  arytenoid  cartilage  forwards  and  rotate  it  inwards  ;  finally,  the  fibres 
which  pass  into  the  aryteno-epiglottidean  fold  may  assist  in  depressing  the  epiglottis. 


Lig.  ary-epiglott.   - 

Cart.  Wrisbergil 
Cart.  Santorini 

mm.  Aryten.  obliqu. 

Crico-arytenoid.  post. 

Comu  inferior 

Lig.  cerato-cric. 

Tars  post.  inf.  membrani 
Pars  cartilag. 


Fio.  555. — The  larynx  as  seen  from  behind.    To  show  the 
intrinsic  muscles  posteriorly.    (Stoerk.) 


768  VOICE   AND    SPEECH  [CH.  LV. 

If  these  muscles  are  paralysed,  the  lips  of  the  glottis  are  no  longer  parallel,  but 
are  curved  with  the  concavity  inwards,  and  a  much  stronger  blast  of  air  is  required 
for  the  production  of  the  voice. 

^K  A/yft-nc/uL — When  the  mucous  membrane  is  removed  from  the  back  of  the 
arjiienoid  cartilages,  a  band  of  transverse  fibres  is  exposed,  on  the  dorsal  surface  of 
which  are  two  slender  decussating  obhque  bundles.  These  are  often  described  as 
separate  muscles  (ar\'tenoid  and  aryteno-epiglottidean),  but  they  are  intimately 
blended  together.  The  ventral  fibres  (arj-lenoid  proper)  pass  straight  across  from 
the  outer  half  of  the  concave  surface  on  the  back  of  one  arytenoid  cartilage  to  the 
corresponding  surface  of  the  other.  The  dorsal  fibres  can  be  followed  to  the  lateral 
walls  of  the  larynx,  the  uppermost  ones  to  the  cartilage  of  Santorini.  the  intermediate 
ones  run  with  the  uppermost  fibres  of  the  th}TO-ar\i;enoid  muscle  forming  the  so- 
called  aryteno-epiglottidean  muscle,  and  the  lowest  fibres  blend  at  the  level  of  the 
true  vocal  cords  with  the  thyro-arytenoid  and  lateral  crico-arytenoid  muscles. 

The  arj^tenoid  muscle  draws  the  arytenoid  cartilages  together.  If  it  is  paralysed, 
the  intti-rcartllaginous  part  of  the  glottis  remains  open,  although  the  membranous  lips 
can  still  be  approximated  during  vocalisation. 

It  has  been  generally  supposed  that  the  epiglottis  is  depressed  as  a  hd  over  the 
glottis  during  swallowing.  This  may  be  so  in  some  animals,  but  in  man  it  is  not 
the  case  :  the  epiglottis  projects  upwards  in  close  contact  with  the  base  of  the  tongue. 
The  necessary  closure  of  the  glottis  during  swallowing  is  brought  about  by  the  con- 
traction of  the  arytenoid  and  thyro-arytenoid  muscles  :  by  this  means  the  ar\-tenoid 
cartilages  are  drawn  towards  each  other,  and  also  forwards  into  contact  with  the 
posterior  surface  of  the  epiglottis  (Anderson  Stuart).  Henle  remarks  that  "the 
muscles  which  lie  in  the  space  enclosed  by  the  laminae  of  the  thyroid  cartilage  and 
above  the  cricoid  may  be  regarded  in  their  totahty  as  a  kind  of  sphincter  such  as  is 
found  in  its  simplest  form  embracing  the  entrance  of  the  larynx  in  reptiles  "'  (Quain's 
Anatomy). 

Nerves. — The  larynx  is  supplied  by  two  branches  of  the  vagus ;  the  superior 
htnjnf/i^alis  the  sensory  nerve  ;  by  its  <>:rti>rnnl  branch,  it  supplies  one  muscle,  namely, 
the  crico-thyroid.  These  fibres,  however,  probably  arise  from  gloss o-pharyngeal  root- 
lets (see  p.  <V)^).  The  rest  of  the  muscles  are  supplied  by  the  inferior  lari^ngeal 
ru-rr-,  the  fibres  of  which  come  from  the  spinal  accessory,  not  the  vagus  proper. 

The  laryngoscope  is  an  instrument  employed  in  investigating  during  life  the 
condition  of  the  pharynx,  larynx,  and  trachea.  It  consists  of  a  large  concave  mirror 
with  perforated  centre,  and  of  a  smaller  mirror  fixed  in  a  long  handle.  The  patient 
is  placed  in  a  chair,  a  good  light  (argand  burner,  or  electric  lamp)  is  arranged  on  one 
side  of.  and  a  httle  above,  his  head.  The  operator  fixes  the  large  mirror  round  his 
head  in  such  a  manner,  that  he  looks  through  the  central  aperture  with  one  eye. 
He  then  seats  himself  opposite  the  patient,  and  so  alters  the  position  of  the  mirror, 
which  is  for  this  purpose  provided  with  a  ball-and-socket  joint,  that  a  beam  of  light 
is  reflected  on  the  lips  of  the  patient. 

The  patient  is  now  directed  to  throw  his  head  slightly  backwards,  and  to  open  his 
mouth  ;  the  reflection  from  the  mirror  lights  up  the  cavity  of  the  mouth,  and  by  a 
little  alteration  of  the  distance  between  the  operator  and  the  patient  the  point  at 
which  the  greatest  amount  of  light  is  reflected  by  the  mirror — in  other  words,  its 
foc-al  length — is  readily  discovered.  The  small  mirror  fixed  in  the  handle  is  then 
warmed,  either  by  holding  it  over  the  lamp,  or  by  putting  it  into  a  vessel  of  warm 
water ;  this  is  necessary  to  prevent  the  condensation  of  breath  upon  its  surface. 
The  degree  of  heat  is  regulated  by  appl}'ing  the  back  of  the  mirror  to  the  hand  or 
cheek,  when  it  should  feel  warm  without  being  painful 

.\fter  these  preUminaries  the  patient  is  directed  to  put  out  his  tongue,  which  is 
held  by  the  left  hand  gently  but  firmly  against  the  lower  teeth  by  means  of  a 
handk-'rchief.  The  warm  mirror  is  passed  to  the  back  of  the  mouth,  until  it  rests 
upon  and  shghtly  raises  the  base  of  the  uvula,  and  at  the  same  time  the  hght  is 
directed  upon  it :  an  inverted  image  of  the  laryn.x  and  trachea  will  be  seen  in  the 
mirror.  If  the  dorsum  of  the  tongue  is  alone  seen,  the  handle  of  the  mirror  must 
be  slightly  lowered  until  the  larynx  comes  into  view ;  care  should  be  taken,  how- 
ever, not  to  move  the  mirror  upon  the  uvula,  as  it  excites  retching.  The  observa- 
tion should  not  be  prolonged,  but  should  rather  be  repeated  at  short  intervals. 


CH.  LV.] 


THE    LAKYNGOSCOPE 


769 


Tlie  structures  seen  will  vary  somewhat  according  to  the  condition  of  the  parts 
as  to  inspiration,  expiration,  phoiiation,  etc.  ;  they  are  (fig.  i'>'>8)  first,  and  apparently 
at  the  posterior  part,  the  base  of  /Jin  tomjue,  immediately  below  which  is  the  arcuate 


Fig.  556. — The  parts  of  the  Laryngoscope. 

outline  of  the  epiglottis,  with  its  cushion  or  tubercle.     Then  are  seen  in  the  central 
line  the  true  vocal  cords,  white  and  shining  in  their  normal  condition.     The  cords 


Fig.  557. — To  show  the  position  of  the  operator  and  patient  when  using  the  Laryngoscope. 

approximate  (in  the  inverted  image)  posteriorly;   between  them  is  left  a  chink, 
narrow  whilst  a  high  note  is  being  sung,  wide  during  a  deep  inspiration.     On  each 

^   C 


770 


VOICE   AND   SPEECH 


[CH.  LV. 


side  of  the  true  vocal  cords,  and  on  a  higher  level,  are  the  pink,  false,  vocal  cords. 
Still  more  externally  than  the  false  vocal  cords  is  the  ari/teno-cpiqlottidcan  fold,  in 
which  are  situated  upon  each  side  three  small  elevations  ;  of  these  the  most  external 
is  the  cartilac/e  of  Wrishn-f/,  the  intermediate  is  the  cartilage,  of  Saniorini,  whilst 
the  summit  of  the  arj/fenoid  cartilage  is  in  front,  and  somewhat  below  the  preceding, 
being  only  seen  during  deep  inspiration.  The  rings  of  the  trachea,  and  even  the 
bifurcation  of  the  trachea  itself,  if  the  patient  be  directed  to  draw  a  deep  breath, 
may  be  seen  in  the  interval  between  the  true  vocal  cords. 


Movements  of  the  Vocal  Cords. 

In  Respiration. — The  position  of  the   vocal  cords  in   ordinary 
tranquil  breathing  is  so  adapted  by  the  muscles,  that  the  opening 


Fio.  558. — Three  laryngoscopic  views  of  the  superior  aperture  of  the  larynx  and  surrounding  parts.  A, 
The  glottis  during  the  emission  of  a  high  note  in  singing ;  B,  in  easy  and  quiet  inhalation  of  air  ;  C, 
in  the  state  of  widest  possible  dilatation,  as  in  inhaling  a  very  deep  breath.  The  diagrams  A',  B',  and 
C,  show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal  cords  and  ai^ytenoid  cartilages 
in  the  three  several  states  represented  in  the  other  ligures.  In  all  the  figures  so  far  as  marked,  the 
letters  indicate  the  parts  as  follows,  viz.  :  I,  the  base  of  the  tongue ;  c,  the  upper  free  part  of  the 
epiglottis;  c',  the  tubercle  or  cushion  of  the  ejiiglottis;  ph,  part  of  the  anterior  wall  of  the 
pharynx  behind  the  larynx ;  in  the  margin  of  the  aryteno-epiglottidean  fold,  w,  the  swelling  of  the 
membrane  caused  by  the  cartilages  of  Wrisberg ;  s,  that  of  the  cartilages  of  Santorini ;  a,  the  tip  or 
summit  of  the  arytenoid  cartilages  ;  c  v,  the  true  vocal  cords  or  lips  of  the  rima  glottidis  ;  c  v  s,  the 
superior  or  false  vocal  cords  ;  between  them  the  ventricle  of  the  larynx  ;  in  C,  tr  is  placed  on  the 
anterior  wall  of  the  receding  trachea,  and  6  indicates  the  commencement  of  the  two  bronchi  beyond 
the  bifurcation  which  may  be  brought  into  view  in  this  state  of  extreme  dilatation.  (Quain,  after 
Czermak.) 

of  the  glottis  is   wide  and  triangular  (fig.    558,   b).      The   glottis 
remains    unaltered   during   ordinary   quiet  breathing,  though  in  a 


CH.  LV.]  MOVEMENTS  OF  THE  VOCAL  CORDS  771 

small  proportion  of  people  it  becomes  a  little  wider  at  each  inspira- 
tion, and  a  little  narrower  at  each  expiration.  In  the  cadaveric 
position  the  glottis  has  about  half  the  width  it  has  during  ordi- 
nary breathing ;  during  life,  therefore,  except  durmg  vocalisation, 
the  abductors  of  the  vocal  cords  (posterior  crico-arytenoids)  are  in 
constant  action.  (F.  Semon.)  On  making  a  rapid  and  deep  inspira- 
tion the  opening  is  widely  dilated  (fig.  558,  c),  and  somewhat 
lozenge-shaped. 

In  Vocalisation. — At  the  moment  of  the  emission  of  a  note,  the 
chink  is  narrowed,  the  margins  of  the  arytenoid  cartilages  being 
brought  into  contact,  and  the  edges  of  the  vocal  cords  approximated 
and  made  parallel  (fig.  558,  a);  at  the  same  time  their  tension  is 
much  increased.  The  higher  the  note  produced,  the  tenser  do  the 
cords  become ;  and  the  range  of  a  voice  depends,  in  the  main,  on 
the  extent  to  which  the  degree  of  tension  of  the  vocal  cords  can 
be  thus  altered.  In  the  production  of 
a  high  note  the  vocal  cords  are  brought 
well  within  sight,  so  as  to  be  plainly 
visible  w4th  the  help  of  the  laryngo- 
scope. In  the  utterance  of  low-pitched 
tones,  on  the  other  hand,  the  epiglottis 
is  depressed  and  brought  over  them,  and  «  "^^^ 

the  arytenoid  cartilages  look  as  if  they  fig.  559.— view  of  the  upper  part  of  the 
were  trying  to  hide  themselves  under       i??p:7urinrttTtt™'of\^fss 

it  (fio".  559).  note,    f,  Epiglottis  ;  s,  tubercles  of  the 

^  _^'  '  .  .  „    ,  ,  ,  cartilages  of  Santorini ;   a,  arytenoid 

i he  approximation  01  the  vocal  cords  cartilages;    z.   base    of   the    tongue; 

also  usually  corresponds  with  the  height       S^erma^°f' "°' ""''  °*  *""'  ^'''''■^''• 

of  the  note  produced ;  but  the  width  of 

the  aperture  has  no  essential  influence  on  the  pitch  of  the  note,  as 

long  as  the  vocal  cords  have  the  same  tension :  only  with  a  wide 

aperture  the  tone  is  more  difficult  to  produce  and  is  less  perfect,  the 

rushing  of  the  air  through  the  aperture  being  heard  at  the  same 

time. 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the 
aperture  of  the  glottis,  that,  viz.,  which  is  formed  by  the  space 
between  the  arytenoid  cartilages. 

The  Voice. 

The  human  musical  instrument  is  often  compared  to  a  reed  organ- 
pipe  :  certainly  the  notes  produced  by  such  pipes  in  the  vox  humana 
stop  of  organs  is  very  like  the  human  voice.  Here  there  is  not  only 
the  vibration  of  a  column  of  air,  but  also  of  a  reed,  which  corre- 
sponds to  the  vocal  cords  in  the  air-chamber  composed  of  the  trachea 
and  the   bronchial   system  beneath  it.     The  pharynx,  mouth,  and 


772 


VOICE   AND    SPEECH 


[CH.  LV. 


nasal  cavities  above  the  glottis  are  resonating  cavities,  which,  by 
alterations  in  their  shape  and  size,  are  able  to  pick  out  and  emphasize 
certain  component  parts  of  the  fundamental  tones  produced  in  the 
larynx.  The  natural  voice  is  often  called  the  chest  voice.  The 
falsetto  voice  is  differently  explained  by  different  observers;  on 
laryngoscopic  examination,  the  glottis  is  found  to  be  widely  open,  so 
that  there  is  an  absence  of  chest  resonance ;  some  have  supposed 
that  the  attachment  of  the  thyro-arytenoid  muscle  to  the  vocal  cord 
renders  it  capable  of  acting  like  the  finger  on  a  violin  string, 
part  of  the  cord  being  allowed  to  vibrate  while  the  rest  is  held  still. 


Fig.  560. — Konig's  apparatus  for  obtaining  flame  pictures  of  musical  notes. 

Such  a  shortening  of  a  vibrating  string  would  produce  a  higher  note 
than  is  natural. 

Musical  sounds  differ  from  one  another  in  three  ways  : — 

1.  In  pitch. — This  depends  on  the  rate  of  vibration ;  and  in  the 
case  of  a  string,  the  pitch  increases  with  the  tension,  and  diminishes 
with  the  length  of  the  string.  The  vocal  cords  of  a  woman  are  shorter 
than  those  of  a  man,  hence  the  higher  pitched  voice  of  women.  The 
average  length  of  the  female  cord  is  11  "5  millimetres;  this  can  be 
stretched  to  14;  the  male  cord  averages  15  "5,  and  can  be  stretched 
to  19'5  millimetres. 

2.  In  loudness. — This  depends  on  the  amplitude  of  the  vibrations, 
and  is  increased  by  the  force  of  the  expiratory  blast  which  sets  the 
cords  in  motion. 

3.  In  "  timbre." — This  is  the  difference  of  character  which  dis- 
tinguishes one  voice,  or  one  musical  instrument,  from  another.  It 
is  due  to  admixture  of  the  primary  vibrations  with  secondary  vibra- 


CH.  LV.]  SPEECH  773 

tions  or  overtones.  If  one  takes  a  tracing  of  a  tuning-fork  on  a 
revolving  cylinder,  it  writes  a  simple  series  of  up  and  down  waves 
corresponding  in  rate  to  the  note  of  the  fork.  Other  musical  instru- 
ments do  not  lend  themselves  to  this  form  of  graphic  record,  but  their 
vibrations  can  be  rendered  visible  by  allowing  them  to  act  on  a  small 
sensitive  gas-flame ;  this  bobs  up  and  down,  and  if  the  reflection  of 
this  flame  is  allowed  to  fall  on  a  series  of  mirrors,  the  top  of  the  con- 
tinuous image  formed  is  seen  to  present  waves.  The  mirrors  are 
usually  arranged  on  the  four  lateral  sides  of  a  cube  which  is  rapidly 
rotated.  If  one  sings  a  note  on  to  the  membrane  in  the  side  of  the 
gas-chamber  with  which  the  flame  is  in  connection,  the  waves  seen 
are  not  simple  up  and  down  ones,  but  the  primary  large  waves  are 
complicated  by  smaller  ones  on  their  surface,  at  twice,  thrice,  etc., 
the  rate  of  the  primary  vibration.  The  richer  a  voice,  the  richer  the 
sound  of  a  musical  instrument,  the  more  numerous  are  these  over- 
tones or  harmonics.  The  range  of  the  voice  is  seldom,  except  in 
celebrated  singers,  more  than  two-and-a-half  octaves,  and  for  different 
voices  this  is  in  different  parts  of  the  musical  scale. 

Speech. 

This  is  due  to  the  modification  produced  in  the  fundamental 
laryngeal  notes,  by  the  resonating  cavities  above  the  vocal  cords. 
By  modifying  the  size  and  shape  of  the  pharynx,  mouth,  and  nose, 
certain  overtones  or  harmonics  are  picked  out  and  exaggerated :  this 
gives  us  the  vowel  sounds ;  the  consonants  are  produced  by  inter- 
ruptions, more  or  less  complete,  of  the  outflowing  air  in  different 
situations.  When  the  larynx  is  passive,  and  the  resonating  cavities 
alone  come  into  play,  then  we  get  whispering. 

The  pitch  of  the  Vo-wels  has  been  estimated  musically ;  u  has  the  lowest  pitch, 
then  0,  a  (as  in  father),  a  (as  in  cane),  i,  and  a.  We  may  give  a  few  examples  of 
the  shape  of  the  resonating  cavities  in  pronouncing  vowel  sounds,  and  producing 
their  characteristic  timbre  :  when  sounding  a  (m  father)  the  mouth  has  the  shape  of 
a  funnel  wide  in  front ;  the  tongue  Ues  on  the  floor  of  the  mouth  ;  the  lips  are  wide 
open  ;  the  soft  palate  is  moderately  and  the  larynx  slightly  raised. 

In  pronouncing  u  (oo),  the  cavity  of  the  mouth  is  shaped  like  a  capacious  flask 
with  a  short  narrow  neck.  The  whole  resonating  cavity  is  then  longest,  the  lips 
being  protruded  as  far  as  possible ;  the  larynx  is  depressed  and  the  root  of  the  tongue 
approaches  the  fauces. 

In  pronouncing  o,  the  neck  of  the  flask  is  shorter  and  wider,  the  lips  being 
nearer  the  teeth  ;  the  larynx  is  slightly  higher  than  in  sounding  oo. 

In  pronouncing  e,  the  flask  is  a  small  one  with  a  long  narrow  neck.  The 
resonating  chamber  is  then  shortest  as  the  larynx  is  raised  as  much  as  possible,  and 
the  mouth  is  bounded  by  the  teeth,  the  Ups  being  retracted ;  the  approach  of  the 
tongue  near  the  hard  palate  makes  the  long  neck  of  the  flask. 

The  Consonants  are  produced  by  a  more  or  less  complete  closure  of  certain 
doors  on  the  course  of  the  outgoing  blast.  If  the  closure  is  complete,  and  the  blast 
suddenly  opens  the  door,  the  result  is  an  explosive  ;  if  the  door  is  partly  closed,  and 
the  air  rushes  with  a  hiss  through  it,  the  result  is  an  aapirate  ;  if  the  door  is  nearly 
closed  and  its  margins  are  thrown  into  vibration,  the  result  is  a  vibrative  ;  if  the 


774  VOICE   AND    SPEECH  [CH.  LV. 

mouth  is  closed,  and  the  sound  has  to  find  its  way  out  through  the  nose,  the  result 
is  a  resonant. 

These  doors  are  four  in  number  ;  Briicke  called  them  the  artirulation  positions. 
They  are — 

1.  Between  the  lips. 

2.  Between  the  tongue  and  hard  palate. 

3.  Between  the  tongue  and  soft  palate. 

4.  Between  the  vocal  cords. 

The  following  table  classifies  the  principal  consonants  according  to  this 
plan  : — 

Hosition  Explosives.  A.spirates.  Vibratives.  Resonants. 

1  '  B,  P.  F,  V,  W.  ...  M. 

2  T,  D.  S,  Z,  L,  Sch,  Th.  R.  N. 

3  K,  G.  J,  Ch.  Palatal  R.  Ng. 

4  ...  H.  R  of  lower  Saxon 

The  introduction  of  the  phonograph  has  furnished  us  with  an  instrument  which 
it  is  hoped  in  the  future  will  enable  us  to  state  more  accurately  than  has  hitherto 
been  possible,  the  meaning  of  the  changes  in  nature  and  intensity  of  the  complex 
vibrations  which  constitute  speech.  The  microscopic  study  of  the  tracing  on  the 
recording  phonographic  cylinder,  and  various  methods  of  obtaining  a  high  magnifi- 
cation of  the  movements  of  the  recording  style  have  been  carried  out  by  M'Kendrick 
and  others.  The  subject  is,  however,  not  yet  sufficiently  ripe  for  definite  statements 
to  be  made. 

Defects  of  Speech. 

Speech  may  be  absent  in  certain  forms  of  lunacy,  and  temporarily  in  that  defect 
of  will  called  ]tystnria. 

It  may  be  absent  owing  to  congenital  defects.  Children  born  deaf  are  dumb 
also.  This  is  because  we  tiiink  with  remembered  sounds,  and  in  a  person  born  deaf 
the  auditory  centres  are  never  set  into  activity.  By  educating  the  child  by  the 
visual  inlet,  it  can  be  taught  to  think  with  the  remembered  shapes  of  the  mouth 
and  expressions  of  the  face  produced  in  the  act  of  speaking,  and  so  can  itself  speak 
in  time. 

If  a  child  becomes  deaf  before  it  is  six  or  seven  years  old,  there  is  a  liability  it 
will  forget  the  speech  it  has  learnt,  and  so  become  dumb. 

In  congenital  hemiplegia  there  may  be  speechlessness,  especially  if  the  injury  is 
due  to  meningeal  haemorrhage  affecting  the  grey  cortex  of  the  left  hemisphere. 
These  children  generally  talk  late,  the  right  side  of  the  brain  taking  on  the  function 
of  the  left. 

Disorders  of  speech  and  voice  occur  from  affections  of  the  larynx,  and  of  the 
nerves  which  supply  the  larynx.  Stammering  is  a  want  of  co-ordination  between 
the  various  muscles  employed  in  the  act  of  speaking. 

Perhaps  the  most  interesting  of  the  disorders  of  speech,  however,  are  those  due 
to  brain  disease  in  adults.     These  fall  into  three  principal  categories  : — 

1.  Aphemia. — A  difficulty  or  inabiUty  to  utter  or  articulate  words.  It  is  often 
associated  with  difficulty  of  swallowing,  and  occurs  in  lesions  of  the  base  of  the 
brain,  especially  of  pons  and  bulb.  The  blurring  of  speech  noticed  in  most  cases  of 
apoplexy  may  also  be  included  under  this  head. 

2.  Aphasia. — This  is  a  complex  condition  in  which  the  will  to  speak  exists,  and 
also  the  ability  to  speak,  but  the  connection  between  the  two  is  broken  down. 
When  the  patient  speaks,  the  words  which  he  utters  are  well  pronounced,  but  are 
not  those  he  wishes  to  utter.  This  is  often  associated  with  Agraphia,  a  similar 
condition  in  respect  to  writing.  It  is  the  form  of  disordered  speech  associated  with 
disorganisation  of  Broca's  convolution. 

3.  Amnesia. — This  term  includes  a  large  class  of  cases  in  which  the  main 
symptom  is  loss  of  memory  for  words,  or  a  defect  of  the  association  of  ideas  of 
things  with  ideas  of  words,  not,  as  in  aphasia,  with  ideas  of  verbal  action.     Amnesia 


en.  LV.]  DEFECTS    OF   SPEECH  775 

is  associated  with  lesions  of  the  intellectual,  i.f.,  the  sensory  centres  of  the  cortex 
beiiind  the  Rolandic  area.  We  have  seen  that  in  this  region  of  the  brain  there  are 
two  important  centres,  the  visual  and  the  auditory,  and  the  parts  of  these  which  are 
associated  with  words  may  be  called  the  rv>nal  v^ord-nmlre  and  the  aiulifori/  worclr- 
centre.  In  amnesia  (sometimes  called  sensory  aphasia),  either  these  centres  them- 
selves, or  the  tracts  that  connect  them,  are  diseased  or  broken  down.  See 
p.  70S. 

With  regard  to  the  auditory  word-centre,  impressions  for  the  sounds  of  words 
are  revived  in  one  of  three  ways  : — 

a.  Spontaneous  or  volitional ;  owing  to  accumulated  traces  which  constitute 
memory,  a  man  when  he  wants  to  express  his  thoughts  in  words  remembers  the 
sounds  it  is  necessary  to  use  ;  impulses  pass  to  the  motor-centre  (Broca's  convolu- 
tion), thence  to  the  nerve-centres,  nerves,  and  muscles  of  the  larynx,  mouth,  chest, 
etc. ,  and  the  man  speaks. 

h.  In  slight  disease  of  the  auditory  word-centre,  he  is  unable  to  do  this,  but  if 
his  mind  is  set  into  a  certain  groove  he  will  speak  ;  thus  if  the  alphabet  or  a  well- 
known  piece  of  poetry  be  started  for  him  he  will  finish  it  by  himself. 

c.  Mimetic.  In  more  severe  cases,  a  more  powerful  stimulus  still  is  needed  ;  he 
will  repeat  any  words  after  another  person,  but  forget  them  immediately  afterwards. 

With  regard  to  the  visual  word-centre  as  tested  by  writing,  there  are  also  three 
ways  of  reviving  impressions  for  written  words  or  letters. 

(a)  Spontaneous  or  normal. 

(6)  A  train  of  thought  must  first  be  set  going;  as,  for  instance,  converting 
printed  words  into  written  characters. 

(c)  Mimetic ;  he  can  only  write  from  a  copy. 

Some  operations,  such  as  reading  aloud,  and  writing  from  dictation  require 
the  combined  activity  of  both  centres.  This,  however,  we  have  previously  considered 
in  connection  with  the  subject  of  association  in  the  brain  (see  p.  70S). 

In  the  investigation  of  any  case  of  defective  speech  there  are  always  the  follow- 
ing six  things  to  be  inquired  into  : — 

1.  Can  the  patient  understand  spoken  words  ?  (The  patient,  of  course,  not 
being  deaf.)     If  he  cannot,  the  auditory  word-centre  is  deranged. 

2.  Can  he  repeat  words  when  requested  ?  This  tests  the  emission  fibres  from 
the  auditory  word-centre  which  pass  through  the  motor-centres  for  speech  in  Broca's 
convolution.     If  he  cannot  do  this,  the  patient  has  aphasia. 

3.  Can  he  write  from  dictation?  If  he  cannot,  either  the  auditory  or  visual 
word-centre,  or  the  fibres  passing  from  the  one  to  the  other,  are  injured. 

4.  Does  he  understand  printed  matter,  and  can  he  point  out  printed  letters  and 
words?  Can  he  read  to  himself?  (The  patient,  of  course,  not  being  blind.)  This 
tests  the  visual  word-centre. 

5.  Can  he  copy  written  words  ?  This  tests  the  channels  from  the  visual  word- 
centre  to  the  motor-centres  for  movements  of  the  hand  in  writing. 

6.  Can  he  read  aloud,  or,  what  is-  the  same  thing,  name  objects  he  sees  ?  This 
is  the  opposite  to  writing  from  dictation,  and  tests  the  healthiness  of  the  word-centres 
or  the  fibres  which  connect  the  visual  to  the  auditory  word-centre. 


CHAPTER  LVI 


THE   EYE   AND   VISION 


The  eyeball  is  contained  in  the  cavity  of  the  skull  called  the  orbit ; 
here  also  are  vessels  and  nerves  for  the  supply  of  the  eyeball, 
muscles  to  move  it,  and  a  quantity  of  adipose  tissue.  In  the  front 
of  the  eyeball  are  the  lids  and  lacrimal  apparatus. 

The  eyelids  consist  of  two  movable  folds  of  skin,  each  of  which  is 
kept  in  shape  by  a  thin  plate  of  fibrous  tissue  called  the  tarsus. 
Along  their  free  edges  are  inserted  a  number  of  curved  hairs  {eye- 
lashes), which,  when  the  lids  are  half  closed,  serve  to  protect  the 
eye  from  dust  and  other  foreign  bodies :  the  tactile  sensibility  of  the 
lids  is  very  delicate.  Imbedded  in  the  tarsus  are  a  number  of  long 
sebaceous  glands  {Meibomian),  the  ducts  of  which  open  near  the  free 
edge  of  the  lid.  In  the  loose  connective  tissue  in  front  of  the 
tarsus,  the  bundles  of  the  orbicularis  muscle  are  situated. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly 
sensitive  mucous  membrane  {conjunctiva),  which  is  continuous  with 
the  skin  at  the  free  edge  of  each  lid,  and  after  lining  the  inner 
surface  of  the  eyelid  is  reflected  on  to  the  eyeball,  being  somewhat 
loosely  adherent  to  the  sclerotic  coat.  Its  epithelium,  which  is 
columnar,  is  continued  over  the  cornea  as  its  anterior  epithelium, 
where  it  becomes  stratified.  At  the  inner  edge  of  the  eye  the 
conjunctiva  becomes  continuous  with  the  mucous  lining  of  the 
lacrimal  sac  and  duct,  which  again  is  continuous  with  the  mucous 
membrane  of  the  nose. 

The  eyelids  are  closed  by  the  contraction  of  a  sphincter  muscle 
{orbicularis),  supplied  by  the  facial  nerve ;  the  upper  lid  is  raised  by 
the  levator  palpebrce  superioris,  supplied  by  the  third  nerve. 

The  lacrimal  gland,  composed  of  lobules  made  up  of  acini  resembling 
the  serous  salivary  glands,  is  lodged  in  the  upper  and  outer  angle  of 
the  orbit.  Its  secretion,  which  issues  from  several  ducts  on  the 
inner  surface  of  the  upper  lid,  under  ordinary  circumstances  just 
sufi&ces  to  keep  the  conjunctiva  moist.  It  passes  out  through  two 
small  openings  (puncta  lacrimalia)  near  the  inner  angle  of  the  eye, 


CH.  LVI.] 


THE   EYEBALL 


777 


one  in  each  lid,  into  the  lacrimal  sac,  and  thence  along  the  nasal 
duct  into  the  inferior  meatus  of  the  nose.  The  excessive  secretion 
poured  out  under  the  influence  of  an  irritating  vapour  or  painful 
emotion  overflows  the  lower  lid  in  the  form  of  tears.  The  secretory 
nerves  are  contained  in  the  lacrimal  and  subcutaneous  malar  branches 
of  the  fifth  nerve,  and  in  the  cervical  sympathetic. 


The  Eyeball. 
The  eyeball  (fig.  561)  consists  of  the  following  structures : — 


Ciliary  muscle — 

Ciliary  process- 
Canal  of  Petit- 
Cornea— 
Anterior  chamber- 


Lens —  SB — 


Iris- 


Ciliary  process- 
Ciliary  muscle — 


—Sclerotic  coat. 
-Choroid  coat. 
—Retina. 


— \itreous  humour. 


Fig.  561. — Section  of  tin-  anterior  four-fifths  of  the  eyeball. 

The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths  of  the 
eyeball :  continuous  with  it,  in  front,  and  occupying  the  remaining 


Fig.  562. — Vertical  section  of  rabbit's  cornea,    a,  Anterior  epithelium,  showing  the  different  shapes  of 
the  cells  at  various  depths  from  the  free  surface  ;  h,  portion  of  the  substance  of  cornea.    (Klein.) 

sixth,  is  the  cornea.     Immediately  within  the  sclerotic  is  the  choroid 
coat,  and  within  the    choroid   is   the  retina.     The   interior   of   the 


78 


THE   EYE   AND    VISION 


[CH.  LVL 


eyeball  is  filled  by  the  aqueous  and  mtreous  humours  and  the 
crystalline  lens;  but,  also,  there  is  suspended  in  the  interior  a 
contractile  and  perforated  curtain, — the  iris,  for  regulating  the 
admission  of  light,  and  behind  at  the  junction  of  the  sclerotic  and 


K- 


Fig.  563. — Horizontal  preparation  of  cornea  of  frog ;  showing  the  network  of  branched  cornea-corpuscles. 
The  ground  substance  is  completely  colourless,     x  400.    (Klein.) 

cornea  is  the  ciliary  muscle,  the  f imction  of  which  is  to  adapt  the  eye 
for  seeing  objects  at  various  distances. 

The  sclerotv:  coat  is  composed  of  white  fibrous  tissue,  with  some 
elastic  fibres  near  the  inner  surface,  arranged  in  variously  disposed 
and  interlacing  layers.     Many  of  the  bundles    of   fibres   cross   the 


Fig.  564. — Surface  view  of  part  of  lamella  of  kitten's  cornea,  prepared  first  with  caustic  potash  and  then 
with  nitrate  of  silver.  (By  this  method  the  branched  comea-corpuscles  with  their  granular  proto- 
plasm and  large  oval  nuclei  are  brought  out.)     x  450.    (Klein  and  Xoble  Smith.) 

others  almost  at  right  angles.  It  is  separated  from  the  choroid  by 
a  l}Tnphatic  space  (perichoroidal),  and  this  is  in  connection  with 
smaller  spaces  lined  with  endothelium  in  the  sclerotic  coat  itself. 
There  is  a  lymphatic  space  also  outside  the  sclerotic,  separating  it 
from  a  loose  investment  of  connective  tissue,  containing  some  smooth 


CH.  LVI.] 


THE   CORNEA 


779 


muscular  fibres,  called  the  capside  of  Tenon.  The  innermost  layer  of 
the  sclerotic  is  made  up  of  loose  connective  tissue  and  pigment-cells, 
and  is  called  the  lamina  fusca. 

The  cornea  is  a  transparent  membrane  which  forms  a  segment  of 
a  smaller  spliere  than  the  rest  of  the  eye- 
ball, let  in,  as  it  were,  into  the  sclerotic, 
with  which  it  is  continuous  all  round.  It 
is  covered  by  stratified  epithelium  (a,  fig. 
562),  consisting  of  seven  or  eight  layers 
of  cells,  of  which  the  superficial  ones  are 
flattened  and  scaly,  and  the  deeper  ones 
more  or  less  columnar.  Immediately 
beneath  this  is  the  anterior  homogeneous 
lamina  of  Boivman,  which  differs,  only  in 
being  more  condensed  tissue,  from  the 
rest  of  the  cornea. 

The  rest  of  the  cornea  consists  of  many 
layers  of  connective  tissue  fibres  arranged 
parallel  to  the  free  surface,  the  direction 
of  the  fibres  crossing  one  another  at  right 
angles  in  the  alternate  laminae.  The 
corneal  corpuscles  lie  in  branched  anasto- 
mosing spaces  between  the  laminae.  They 
have  been  seen  to  execute  amoeboid  move- 
ments. At  its  posterior  surface  the  cornea 
is  limited  by  the  posterior  homogeneous 
lamina,  or  membrane  of  Descemet,  which 
is  elastic  in  nature,  and  lastly  a  single 
stratum  of  cubical  epithelial  cells  (fig. 
565,  d). 

The  nerves  of  the  cornea  are  both  large 
and  numerous :  they  are  derived  from  the 
ciliary  nerves.  They  traverse  the  sub- 
stance of  the  cornea,  in  which  some  of 
them  near  the  anterior  surface  break  up 
into  axis  cylinders,  and  their  primitive 
fibrillae.  The  latter  form  a  plexus  im- 
mediately beneath  the  epithelium,  from 
which  delicate  fibrils  pass  up  between 
the  cells  anastomosing  with  horizontal 
branches,  and  forming  an  intra-epithelial  plexus.  Most  of  the 
primitive  fibrillae  have  a  beaded  or  varicose  appearance.  The  cornea 
has  no  blood-vessels  or  lymphatics,  but  is  nourished  by  the  circulation 
of  lymph  in  the  spaces  in  which  the  corneal  corpuscles  lie.  These 
communicate  freely  and  form  a  lymph-canalicular  system. 


[G.  565. — Vertical  section  of  rabbit's 
cornea,  stained  with  gold  chloride. 
e,  Stratified  anterior  epithelium. 
Immediately  beneath  this  is  the 
anterior  homogeneous  lamina  of 
Bowman.  n.  Nerves  forming  a 
delicate  sub-epithelial  plexus,  and 
sending  up  fine  twigs  between  the 
epithelial  cells  to  end  in  a  second 
plexus  on  the  free  surface;  d, 
Descemet's  membrane,  consisting 
of  a  fine  elastic  layer,  and  a  single 
layer  of  epithelial  cells ;  the  sub- 
stance of  the  cornea,  /,  is  seen  to 
be  fibrillated,  and  contains  many 
layers  of  branched  corpuscles,  ar- 
ranged parallel  to  the  free  surface, 
and  here  seen  edgewise. 

(Schofield.) 


780 


THE   EYE   AKD   VISION 


[CH.  LVL 


I%e  Choroid  Coat  (tunica  vasculosa)  is  attached  to  the  inner  layer 
of  the  sclerotic  in  front  at  the  corneo-scleral  junction  and  behind  at 
the  entrance  of  the  optic  nerve ;  elsewhere 
it  is  connected  to  it  only  by  loose  connective 
tissue.  Its  external  coat  is  formed  chiefly 
of  elastic  fibres  and  large  pigment  cor- 
puscles loosely  arranged;  it  contains  lym- 
phatic spaces  lined  with  endothelium.  This 
is  the  lamina  suprachoroidea.  More  inter- 
nally is  a  layer  of  arteries  and  veins 
arranged  in  a  system  of  venous  whorls, 
together  with  elastic  fibres  and  branched 
pigment  cells.  The  lymphatics,  too,  are  well 
developed  around  the  blood-vessels,  and 
there  are  besides  distinct  lymph  spaces 
lined  with  endothelium.  Internal  to  this 
is  a  layer  of  fine  capillaries,  very  dense, 
and  derived  from  the  arteries  of  the  outer 
coat  and  ending  in  veins  in  that  coat.  It 
corpuscles  without  pigment,  and  lymph  spaces  which 
the    blood-vessels    (memhrana    chorio-capillaris).      It    is 


Fig.  566. — Section  through'  the 
choroid  coat  of  the  human  eye. 
1,  Membrane  of  Bruch ;  2, 
chorio-capillaris  or  tunica  Ruy- 
schiana ;  3,  proper  substance  of 
the  choroid  with  large  vessels 
cut  through;  4,  suprachoroidea; 
5,  sclerotic.    (Schwalbe.) 


contams 
surround 
separated  from  the  retina  by  a  fine  elastic  membrane  (membrane  of 


Fig.  567. — Section  through  the  eye  carried  through  the  ciliary  processes.  1,  Cornea;  2,  membrane  of 
Descemet ;  3,  sclerotic ;  3',  comeo-scleral  junction ;  4,  canal  of  Schlemm ;  5,  vein ;  6,  nucleated 
network  on  inner  wall  of  canal  of  Schlemm  ;  7,  lig.  pectinatum  iridis,  a  b  c;  8,  iris ;  9,  pigment  of 
iris  (uvea);  10,  ciliary  processes ;  11,  ciliary  muscle;  12,  choroid  tissue;  13,  meridional,  and  14, 
radiating  fibres  of  ciliarj-  muscle;  15,  ring-muscle  of  Miiller;  16,  circular  or  angular  bundles  of 
ciliary  muscle.    (.Schwalbe.) 

Bruch),  which   is    either   structureless    or   finely   fibrillated.      (Fig. 
566,  1.) 

The  choroid  coat  ends  in  front  in  what  are  called  the  ciliary 
processes  (figs.  567,  568).  These  consist  of  from  70  to  80  meridion- 
ally  arranged  radiating  plaits,  which  consist  of  blood-vessels,  fibrous 


CH.    LVI.] 


THE    IRIS   AND    LENS 


781 


Fig.  508. — Giliar>-  iiroecsses,  as  seen  from 
behind.  1,  Posterior  surface  of  the  iris, 
with  the  sphincter  muscle  of  the  pupil ; 
2,  anterior  part  of  the  choroid  coat ;  3, 
one  of  the  ciliary  processes,  of  which 
about  seventy  are  represented. 


connective  tissue,  and   pigment   corpuscles.     They  are   lined    by  a 
continuation    of   the   membrane   of   Bruch.     The    ciliary    processes 
terminate  abruptly  at  the  margin  of 
the  lens.     The  ciliary  muscle  (13,  14,  -^~^ — -- 

and  15,  fig.  567),  takes  origin  at  the 
corneo-scleral  junction.  It  is  a  ring 
of  muscle,  3  mm.  broad  and  8  mm. 
thick,  made  up  of  fibres  running  in 
three  directions.  {a)  Meridional 
fibres  near  the  sclerotic  and  passing 
to  the  choroid ;  (&)  radial  fibres  in- 
serted into  the  choroid  behind  the 
ciliary  processes ;  and  (c)  circular 
fibres  (muscle  of  Miiller),  more  in- 
ternal ;  they  constitute  a  sphincter. 

The  Iris  is  a  continuation  of  the 
choroid  inwards  beyond  the  ciliary 
processes.  It  is  a  fibro-muscular 
membrane  perforated  by  a  central 
aperture,  the  pupil. 

Posteriorly  is  a  layer  of  pigment  cells  {uvea),  which  is  a  con- 
tinuation forwards  of  the  pigment  layer  of  the  retina.  The  structure 
of  the  iris  proper  is  made  of  connective  tissue  in  front  with  corpuscles 
which  may  or  may  not  be  pigmented,  and  behind  of  similar  tissue 
supporting  blood  -  vessels.  The  pigment  cells  are  usually  well 
developed  here,  as  are  also  many  nerve-fibres  radiating  towards 
the  pupil.  Surrounding  the  pupil  is  a  layer  of  circular  unstriped 
muscle,  the  sphincter  pupillce.  In  some  animals  there  are  also 
muscle-fibres  which  radiate  from  the  sphincter  in  the  substance 
of  the  iris  forming  the  dilator  pupillce.  The  iris  is  covered 
anteriorly  by  a  layer  of  epithelium  continued  upon  it  from  the 
posterior  surface  of  the  cornea. 

The  Lens  is  situated  behind  the  iris,  being  enclosed  in  a  distinct 
capsule,  the  posterior  layer  of  which  is  not  so  thick  as  the  anterior. 
It  is  supported  in  place  by  the  suspensory  ligament,  fused  to 
the  anterior  surface  of  the  capsule.  The  suspensory  ligament  is 
derived  from  the  hyaloid  membrane,  which  encloses  the  vitreous 
humour. 

The  lens  is  made  up  of  a  series  of  concentric  laminae  (fig.  569), 
which,  when  it  has  been  hardened,  can  be  peeled  off  like  the  coats  of 
an  onion.  The  laminae  consist  of  long  ribbon-shaped  fibres,  which  in 
the  course  of  development  have  originated  from  cells. 

The  fibres  near  the  margin  have  nuclei  and  are  smooth,  those 
near  the  centre  are  without  nuclei  and  have  serrated  edges.  They 
are  hexagonal  in  transverse  section.     The  fibres  are  united  together 


782 


THE   EYE   AND   VISION 


[CH.  LVI. 


by  a   scanty   amount   of   cement   substance.     The   central   portion 
{nucleus)  of  the  lens  is  the  hardest. 

The  epithelium  of  the  lens  consists  of  a  layer  of  cubical  cells 
anteriorly,  which  merge  at  the  equator  into 
the  lens  fibres.  The  development  of  the 
lens  explains  this  transition.  The  lens  at 
first  consists  of  a  closed  sac  composed  of 
a  single  layer  of  epithelium.  The  cells  of 
the  posterior  part  soon  elongate  forwards 
and  obliterate  the  cavity ;  the  anterior  cells 
do  not  grow,  but  at  the  edge  they  become 
continuous  with  the  posterior  cells,  which 
are  gradually  developed  into  fibres  (fig. 
570).  The  principal  chemical  constituent 
of  the  lens  is  a  protein  of  the  globulin  class 
called  crystallin. 

Corneoscleral  junction. — At  this  junction 
the  relation  of  parts  (fig.  567)  is  so  important 
as  to  need  a  short  description.  In  this  neigh- 
bourhood, the  iris  and  ciliary  processes  join  with  the  cornea.  The 
proper  substance  of  the  cornea  and  the  posterior  elastic  lamina 
become  continuous  with  the  iris,  at  the  angle  of  the  iris,  and  the  iris 
sends  forwards  processes  towards  the  posterior  elastic  lamina,  form- 


PiG.  569. — Laminated  structure  of 
the  crystalline  lens.  The  laminte 
are  split  up  after  hardening  in 
alcohol.  1,  The  denser  central 
part  or  nucleus ;  2,  the  succes- 
sive external  layers,    f . 

(Arnold.) 


Fig.  570. — Meridional  section  through  the  lens  of  a  rabbit.    1,  Lens  capsule ;  2,  epithelium  of  lens; 
3,  transition  of  the  epithelium  into  the  fibres  ;  4,  lens  fibres.    (Bubuchin.) 


ing  the  ligamentum  pectinatum  iridis,  and  these  join  with  fibres  of 
the  elastic  lamina.  The  epithelial  covering  of  the  posterior  surface 
of  the  cornea  is,  as  we  have  seen,  continuous  over  the  front  of  the 
iris.  At  the  iridic  angle,  the  compact  inner  substance  of  the  cornea 
is  looser,  and  between  the  bundles  are  lymph  spaces  called  the  spaces 
of  Fontana.     They  are  little  developed  in  the  human  cornea. 

The  spaces  which  are  present  in  the  broken-up  bundles  of  corneal 
tissue  at  the  angle  of  the  iris  are  continuous  with  the  larger 
lymphatic  space  of  the  anterior  chamber.  Above  the  angle  at  the 
corneo-scleral  junction  is  a  canal,  which  is  called  the  canal  of 
Schlemm.     It  is  a  lymphatic  channel. 

The  retina  (fig.  571)  apparently  ends  in  front,  near  the  outer 
part   of   the  ciliary  processes,  in  a   finely-notched   edge, — the   ora 


CH.  LVI.] 


THE   RETINA 


783 


serrata,  but  is  really  represented  by  the  uvea  to  the  very  margin 
of  the  pupil.  The  nerve-cells  in  the  retina  remind  us  that  the  optic, 
like  the  olfactory  nerve,  is  not  a  mere 
nerve,  but  an  outgrowth  of  the  brain. 

In  the  centre  of  the  retina  is  a  round 
yellowish  elevated  spot,  about  ^^i-  of  an 
inch  (1  mm.)  in  diameter,  having  a  de- 
pression in  the  centre,  called  after  its 
discoverer  the  macula  lutea  or  yellow  spot 
of  Soemmering.  The  depression  in  its 
centre  is  called  t\\Q  fovea  centralis.  About 
•jV  of  an  inch  (2'5  mm.)  to  the  inner  side 
of  the  yellow  spot,  is  the  point  {optic  disc 
or  white  spot)  at  which  the  optic  nerve 
leaves  the  eyeball.  The  optic  nerve-fibres 
are  the  axons  of  the  nerve-cells  of  the 
retina;  the  dendrons  of  these  cells  ulti- 
mately communicate  with  the  visual  nerve- 
epithelium  (rods  and  cones). 

The  optic  nerve  passes  backwards  to 
the  ventral  surface  of  the  cerebrum  en- 
closed in  prolongations  of  the  membranes, 
which  cover  the  brain.  This  external 
sheath  at  the  exit  of  the  nerve  from  the 
eyeball  becomes  continuous  with  the 
sclerotic,  which  at  this  part  is  perforated 
by  holes  to  allow  of  the  passage  of  the 
optic  nerve-fibres,  the  perforated  part 
being  the  lamina  crihrosa.  The  pia  mater 
here  becomes  incomplete,  and  the  subar- 
achnoid and  the  superarachnoid  spaces 
become  continuous.  The  pia  mater  sends 
in  processes  into  the  nerve  to  support  the  fibres.  The  fibres  of  the 
nerve  themselves  are  exceedingly  fine,  and  are  surrounded  by  the 
myelin  sheath,  but  do  not  possess  the  ordinary  external  nerve 
sheath.  In  the  retina  itself  they  have  no  myelin  sheaths.  In  the 
centre  of  the  nerve  is  a  small  artery,  the  arteria  centralis  retince.  The 
number  of  fibres  in  the  optic  nerve  is  said  to  be  upwards  of  500,000. 

The  retina  consists  of  certain  elements  arranged  in  ten  layers 
from  within  outwards  (figs.  571,  572,  573). 

1.  Membrana  limitans  interna. — This  so-called  membrane  in  con- 
tact with  the  vitreous  humour  is  formed  by  the  junction  laterally  of 
the  bases  of  the  sustentacular  or  supporting  fibres  of  Midler,  which 
bear  the  same  relation  to  the  retina  as  the  neuroglia  does  to  the 
brain.     The  character  of  these  fibres  may  be  seen  in  fig.  572. 


Fig.  571.  —  Diagrammatic  section  of 
human  retin:i(M.  Sclmltze).  1,  Mem- 
brana limitans  interna ;  2,  layer  of 
optic  nerve-tibres ;  3,  layer  of  optic 
nerve-cells  ;  4,  inner  synapse  or  mole- 
cular layer ;  5,  inner  nuclear  or 
bipolar  layer;  6,  outer  synapse  or 
molecular  layer;  7,  outer  nuclear 
layer;  8,  membrana  limitans  ex- 
terna ;  9,  layer  of  rods  and  cones ; 
10,  layer  of  pigment  cells. 


784 


THE  EYE  AUD   VISION 


[CH.  LVI. 


2.  Optic  nerve-fibres. — This  layer  is  of  very  varying  thickness  in 
different  parts  of  the  retina  :  it  consists  of  non-medullated  fibres 
which  interlace,  and  most  of  which  are  the  axons  of  the  large 
nerve-cells  forming  the  next  layer.  The  fibres  are  supported  by  the 
sustentacular  fibres.     They  are  less  and  less  numerous  anteriorly, 


J"- 


lUlL^.......  / 


-    Outer  mole- 
cular layer. 


Spongio- 
blasts. 


Inuer    mole- 
cular layer. 


Fig.  572. — Diagram  showing  the  susten- 
tacular fibres  of  the  retina ;  /,  fibre- 
basket  above  the  external  limiting 
membrane ;  m,  nucleus  of  the  libre ; 
r,  base  of  the  fibre. 

(From  M'Kendrick,  after  Stohr.) 


Bipolar  cell. 


Fig.  573. — Diagram  showing  the  nervous  elements 
of  retina.  1,  Nerve-fibre  of  ganglion  cell;  2,  pro- 
cesses of  ganglion  cell  going  outwards  ;  3,  nerve- 
fibre  passing  from  bipolar  cell  in  inner  nuclear 
layer ;  4,  process  of  ganglion  cell  towards  bipolar 
cell ;  5,  arborisations  of  fibres  from  rods  and 
cones  with  the  branches  of  bipolar  cells. 

(From  M'Kendrick,  after  Stohr.) 


and  end  at  the  ora  serrata.     They  all  converge  towards  the  optic 
disc,  where  they  leave  the  retina  as  the  optic  nerve. 

3.  Layer  of  ganglion  cells. — This  consists  of  large  multipolar  nerve- 
cells  with  large  and  round  nuclei,  forming  either  a  single  layer,  or  in 
some  parts  of  the  retina,  especially  near  the  macula  lutea,  where  this 
layer  is  very  thick,  it  consists  of  several  strata  of  nerve-cells.  They 
are  arranged  with  their  single  axis-cylinder  processes  inwards. 
These  pass  into  and  are  continuous  with  the  layer  of  optic  nerve- 
fibres.  Externally  the  cells  send  off  several  branched  processes 
which  pass  into  the  next  layer. 


CH.  LVI.]  THE   RETINA  785 

4.  Inner  molecular  layer. — This  presents  a  finely  granulated 
appearance.  It  consists  of  neuroglia  traversed  by  numerous  fibrillar 
processes  of  the  nerve-cells  just  described,  and  the  minute  branch- 
ings of  the  processes  of  the  bipolar  cells  of  the  next  layer. 

5.  Inner  nuclear  layer. — This  consists  chiefly  of  numerous  small 
round  cells,  each  with  a  very  small  quantity  of  protoplasm  surround- 
ing a  large  ovoid  nucleus  ;  they  are  generally  bipolar,  giving  off  one 
process  outwards  and  another  inwards.  One  process  passes  inwards 
to  form  a  synapse  with  the  arborisation  of  a  ganglion  cell,  the  other 
outwards  to  similarly  arborise  with  the  branchings  of  the  rod  and 
cone  fibres.  Some  cells,  called  spongioblasts,  or  amacrine  cells,  how- 
ever, only  send  off  one  process,  which  passes  inwards  (fig.  572). 
The  large  oval  nuclei  (fig.  572)  belonging  to  the  Miillerian  fibres 
occur  in  this  layer. 

6.  Outer  molecular  layer. — This  layer  closely  resembles  the  inner 
molecular  layer,  but  is  much  thinner.  It  contains  the  branchings  of 
the  rod  and  cone  fibres  on  the  one  hand  and  of  the  bipolar  cells  on 
the  other. 

7.  External  nuclear  layer. — This  layer  consists  of  small  cells 
resembling  at  first  sight  those  of  the  internal  nuclear  layer;  they 
are  classed  as  rod  and  cone  granules,  according  as  they  are  connected 
with  the  rods  and  cones  respectively,  and  will  be  described  with 
them.  They  are  lodged  in  the  meshes  of  a  frame-work,  which  is 
formed  by  the  breaking  up  of  the  Miillerian  fibres. 

8.  Memhrana  limitans  externa. — This  is  a  well-defined  membrane, 
marking  the  internal  limit  of  the  rod  and  cone  layer,  and  made  up 
of  the  junction  of  the  sustentacular  fibres  externally. 

9.  Layer  of  rods  and  cones. — This  layer  is  the  nerve-epithelium 
of  the  retina.  It  consists  of  two  kinds  of  cells,  rods  and  cones, 
which  are  arranged  at  right  angles  to  the  external  limiting  mem- 
brane, and  supported  by  hairlike  processes  (basket)  proceeding  from 
the  latter  for  a  short  distance  (fig.  572). 

Each  rod  (fig.  573)  is  made  up  of  two  parts,  very  different  in 
structure,  called  the  outer  and  inner  limbs.  The  outer  limb  of  the 
rods  is  about  SO/ul  long  and  2/ut.  broad,  is  transparent,  and  doubly 
refracting.  It  is  said  to  be  made  up  of  fine  superimposed  discs. 
It  stains  brown  with  osmic  acid  but  not  with  hsematoxylin,  and 
resembles  in  some  ways  the  myelin  sheath  of  a  medullated  nerve. 
It  is  the  part  of  the  rod  in  which  the  pigment  called  visual  pitrple  is 
found.  In  some  animals,  a  few  rods  have  a  greenish  pigment  instead. 
The  inner  limb  is  about  as  long  but  slightly  broader  than  the  outer, 
is  longitudinally  striated  at  its  outer,  and  granular  at  its  inner  part. 
It  stains  with  haematoxylin,  but  not  with  osmic  acid.  Each  rod  is 
connected  internally  with  a  rod  fibre,  very  fine,  but  here  and  there 
varicose;  in  the  middle  of  the  fibre  is  a  rod  granule,  really  the 

3D 


786 


THE   EYE   AND    VISION 


[CH.  LVI. 


nucleus  of  the  rod,  striped  broadly  transversely,  and  situated  about 
the  middle  of  the  external  nuclear  layer ;  the  internal  end  of  the 
rod  fibre  terminates  in  branchings  in  the  outer  molecular  layer. 

Each  cone  (fig.  573),  like  the  rods,  is  made  up  of   two  limbs, 

outer  and  inner.  The  outer 
limb  is  tapering  and  not 
cylindrical  like  the  corre- 
sponding part  of  the  rod, 


Fig.  574. — The  poi:=rior  half  of  the  retina  of 
the  left  eye,  viewed  from  before;  s,  the  cut 
edge  of  the  sclerotic  coat;  ch,  the  choroid;  r, 
the  retina ;  in  the  interior  at  the  middle  the 
macula  lutea  with  the  depression  of  the  fovea 
centralis  is  represented  by  a  slight  oval  shade ; 
towards  the  left  side  the  light  spot  indicates 
the  colliculus  or  eminence  at  the  entrance  of 
the  optic  nerve,  from  the  centre  of  which  the 
arteria  centralis  is  seen  spreading  its  branches 
into  the  retina,  leaving  the  part  occupied  by 
the  macula  comparatively  free.   (After  Henle.) 


Fig.  575. — Pigment-cells  from  the  retina. 
A,  Cells  still  cohering,  seen  on  their 
surface ;  a,  nucleus  indistinctly  seen. 
In  the  other  cells  the  nucleus  is  con- 
cealed by  the  pigment  granules,  b, 
Two  cells  seen  in  profile ;  a,  the  outer 
or  posterior  part  containing  scarcely 
any  pigment,     x  370.    (Henle.) 


and  about  one-third  only 
of  its  length.  There  is, 
moreover,  no  visual  purple 
found  in  the  cones.  The 
inner  limb  of  the  cone  is 
broader  in  the  centre.  It  is  protoplasmic,  and  under  the  influence 
of  light  has  been  seen  to  execute  movements.  In  birds,  reptiles 
and  amphibia,  there  is  often  a  coloured  oil  globule  present  here. 
Each  cone  is  in  connection  by  its  internal  end  with  a  cone  fibre, 
which  has  much  the  same  structure  as  the  rod  fibre,  but  is  much 
stouter  and  has  its  nucleus  (cone  granule)  quite  near  to  the  ex- 
ternal limiting  membrane.  Its  inner  end  terminates  by  branchings 
in  the  external  molecular  layer. 

In  the  rod  and  cone  layer  of  birds,  the  cones  usually  pre- 
dominate largely  in  number,  whereas  in  man  the  rods  are  by  far 
the  more  numerous,  except  in  the  fovea  centralis,  where  cones  only 
are  present.  The  number  of  cones  has  been  estimated  at  3,000,000. 
10.  Figment-cell  layer  consists  of  a  single  layer  of  polygonal  cells, 
mostly  six-sided,  which  send  down  a  beard-like  fringe  to  surround 
the  outer  ends  of  the  rods.  It  is  this  layer  which  is  continuous 
with  the  uvea,  where,  however,  the  cells  become  rounded,  and 
arranged  two  or  three  deep. 

Differences  in  Structure  of  different  parts. — Towards  the  centre 


CH.  LVI.] 


THE   FOVEA 


787 


of  the  macula  lutea  all  the  layers  of  the  retina  become  greatly 
thinned  out  and  almost  disappear,  except  the  rod  and  cone  layer, 
and  at  the  fovea  centralis  the  rods  disappear,  and  the  cones  are  long 
and  narrow.     At  the  margin   of 


s^rl'^^UMii 


the  fovea  the  layers  increase  in 
thickness,  and  in  the  rest  of  the 
macula  lutea  are  thicker  than 
elsewhere.  The  ganglionic  layer 
is  especially  thickened,  the  cells 
being  six  to  eight  deep  (2,  fig. 
576).  The  bipolar  inner  gran- 
ules (cone  nuclei)  are  obliquely 
disposed  (figs.  576  and  577)  on 
the  course  of  the  cone  fibres,  and 
are  situated  at  some  distance 
from  the  memhrana  limitans  ex- 
terna, which  is  cupped  towards 
the  fovea  (fig.  576).  The  yellow 
tint  of  the  macula  is  due  to  a  diffuse  colouring  matter  in  the  interstices 
of  the  four  or  five  inner  layers  ;  it  is  absent  at  the  centre  of  the  fovea. 
It  is  important  to  notice  what  is  clearly  brought  out  in  fig.  577, 
that  at  the  fovea   each  cone  is  connected   to  a  separate  chain  of 


Fig.  576. — Diagram  of  a  section  through  half  the 
fovea  centralis.  2,  Ganglionic  layer;  4,  inner 
nuclear;  6,  outer  nuclear  layer,  the  cone  fibres 
forming  the  so-called  external  fibrous  layer ; 
7,  cones;  m.l.e.,  membrana  limitans  externa; 
m.l.i.,  membrana  limitans  interna.  (Schafer  and 
Golding  Bird.) 


Fig.  .^77. — Scheme  of  the  retinal  elements.  A,  Cones  of  the  fovea  centralis;  B,  granules  (nuclei)  of 
these  cones  ;  0,  synapse  between  the  cones  and  bipolar  cells  in  external  molecular  layer ;  D,  synapse 
between  the  bipolar  and  ganglion  cells  in  the  internal  molecular  layer;  a  and  h,  rods  and  cones  in 
other  regions  of  the  retina ;  <•,  bipolar  cell  destined  for  the  cones ;  d,  bipolar  cell  destined  for  the 
rods  ;  E,  c,  ganglion  cells  ;  /,  spongioblast ;  q,  efferent  fibre  (?  trophic),  originating  from  the  cell  m, 
in  geniculate  body ;  h,  optic  nerve ;  i,  terminal  arborisations  of  optic  nerve-fibres  in  geniculate 
body ;  j,  fibres  from  the  cells  of  geniculate  body  on  the  way  to  cerebral  cortex.     (R.  y  Cajal.) 

neurons,  whereas  in  other  regions  the  rods  and  cones  are  connected 
in  groups  to  these  chains ;  this  explains  the  greater  sensitiveness  of 
foveal  vision. 

At  the  ora  serrata  the  layers  are  not  perfect,  and  disappear  in 
this  order :  nerve-fibres  and  ganglion  cells,  then  the  rods,  leaving 
only  the  inner  limbs  of  the  cones,  next  these  cease,  then  the  outer 


788  THE   EYE   AND   VISION  [CH.  LVL 

molecular  layer,  the  inner  and  outer  nuclear  layers  coalescing,  and 
finally  the  inner  molecular  layer  also  is  unrepresented. 

At  the  pars-ciliaris  retince,  the  retina  consists  of  a  layer  of 
columnar  cells,  which  probably  represent  the  Miillerian  fibres.  These 
cells  externally  are  in  contact  with  the  pigment  layer  of  the  retina, 
which  is  continued  over  the  ciliary  processes  and  back  of  the  iris. 
Nervous  structures  are  absent. 

At  the  exit  of  the  optic  nerve  the  only  structures  present  are 
nerve-fibres. 

The  anterior  chamber  is  the  space  behind  the  cornea  and  in  front 
of  the  iris.     It  is  filled  with  aqueous  humour  (dilute  lymph). 

The  vitreous  humour,  which  is  a  jelly-like  connective  tissue  (see 
p.  48),  is  situated  behind  the  crystalline  lens.  It  is  enclosed  in  a 
membrane  called  membrana  hyaloidea,  which  in  front  is  continuous 
with  the  capsule  of  the  lens ;  round  the  edge  of  the  lens  the  canal 
left  is  called  the  Canal  of  Petit  (fig.  561,  p.  765),  the  membrane  itself 
being  the  Zonule  of  Zinn.  The  hyaloid  membrane  separates  the 
vitreous  from  the  retina. 

Blood-vessels  of  the  Eyeball.— The  eye  is  very  richly  supplied  with  blood- 
vessels. In  addition  to  the  conjunctival  vessels  which  are  derived  from  the  palpe- 
bral and  lacrimal  arteries,  there  are  at  least  two  other  distinct  sets  of  vessels 
supplying  the  tunics  of  the  eyeball. 

(i)  These  are  the  short  and  long  posterior  ciliary  arteries  which  pierce  the 
sclerotic  in  the  posterior  half  of  the  eyebaU,  and  the  anterior  ciliary  which  enter 
near  the  insertions  of  the  recti.  These  vessels  anastomose  and  form  a  rich  choroidal 
plexus ;  they  also  supply  the  iris  and  cihary  processes,  forming  a  highly  vascular 
circle  round  the  outer  margin  of  the  iris  and  adjoining  portion  of  the  sclerotic.  The 
distinctness  of  these  vessels  from  those  of  the  conjunctiva  is  well  seen  in  the 
diflference  between  the  bright  red  of  blood-shot  eyes  (conjunctival  congestion),  and 
the  pink  zone  surrounding  the  cornea  which  indicates  deep-seated  ciliary  congestion. 

(2)  The  rffinal  vessels  (fig.  574)  are  derived  from  the  arteria  centralis  retince, 
which  enters  the  eyeball  along  the  centre  of  the  optic  nerve.  They  ramify  all  over 
the  retina,  in  its  inner  layers.     They  can  be  seen  by  ophthalmoscopic  examination. 

The  Eye  as  an  Optical  Instrument. 

In  a  photographic  camera  images  of  external  objects  are  thrown 
upon  a  screen  at  the  back  of  a  box,  the  interior  of  which  is  painted 
black.  In  the  eye,  the  camera  is  represented  by  the  eyebaU  with  its 
black  pigment,  the  screen  by  the  layer  of  rods  and  cones  of  the  retina, 
and  the  lens  by  the  refracting  media.  In  the  case  of  the  camera, 
the  screen  is  enabled  to  receive  clear  images  of  objects  at  different 
distances,  by  an  apparatus  for  focussing.  The  corresponding  con- 
trivance in  the  eye  is  called  accommodation. 

The  iris,  which  allows  more  or  less  light  to  pass  into  the  eye, 
corresponds  with  the  diaphragms  used  in  the  photographic  apparatus. 

The  refractive  media  are  the  cornea,  aqueous  humour,  crystalline 
lens,  and  vitreous  humour.  The  most  refraction  or  bending  of  the 
rays  of  light  occurs  where  they  pass  from  the  air  into  the  cornea ;  they 


CH.  LVI.] 


REFKACTION   OF   LIGHT 


789 


are  again  bent  slightly  in  passing  through  the  lens.  Alterations  in 
the  anterior  curvature  of  the  lens  lead  to  accommodation. 

We  may  first  consider  the  refraction  through  a  transparent 
spherical  surface,  separating  two  media  of  different  density. 

Tlie  rays  of  light  which  fall  upon  the  surface  exactly  perpendicu- 
larly do  not  suffer  refraction,  but  pass  through,  cutting  the  optic 
axis  (0  A,  fig.  578),  a  line  which  passes  exactly  through  the  centre 


Fig.  578. — Diagram  of  a  simple  optical  system  (after  M.  Foster).  The  curved  surface,  6,  d,  is  supposed 
to  separate  a  less  refractive  medium  towards  the  left  from  a  more  refractive  medium  towards  the 
right. 

of  the  surface,  at  a  certain  point,  the  nodal  point  (fig.  578,  N),  or 
centre  of  curvature.  Any  rays  which  do  not  so  strike  the  curved 
surface  are  refracted  towards  the  optic  axis.  Eays  which  impinge 
upon  the  spherical  surface  parallel  to  the  optic  axis,  will  meet  at  a 
point  behind,  upon  the  said  axis  which  is  called  the  chief  posterior 
focus  (fig.  578,  F^);  and  again  there  is  a  point  on  the  optic  axis  in 
front  of  the  surface,  rays  of  light  from  which  so  strike  the  surface 
that  they  are  refracted  in  a  line  parallel  with  the  axis  d  f"\  this 
point  (fig.  578,  F2)  is  called  the  chief  anterior  focus.  The  optic  axis 
cuts  the  surface  at  what  is  called  the  principal  point. 

It  is  quite  obvious  that  the  eye  is  a  much  more  complicated 
optical  apparatus  than  the  one  described  in  the  figure.  It  is,  how- 
ever, possible  to  reduce  the  refractive  surfaces  and  media  to  a  simpler 
form  when  the  refractive  indices  of  the  different  media  and  the 
curvature  of  each  surface  are  known.     These  data  are  as  follows : — 


Index  of  refraction  of  cornea .... 
„  „  aqueous  and  vitreous  . 

,,  „  lens      .... 

Radius  of  curvature  of  cornea .... 

,,  ,,  anterior  surface  of  lens 

,,  ,,  posterior 

Distance  from  anterior  surface  of  cornea  to 

anterior  surface  of  lens  .... 

Distance  from  posterior  surface  of  cornea  to 

posterior  surface  of  lens        .... 

Distance   from   posterior   surface   of  lens   to 

retina    ........ 


1-37 

1-34  to  1-36 
/I '4  in  outer  to  1  "45 
t     in  inner  part. 

7 '8  mm. 
10 


=     3-6 


=   15-0 


790 


THE   EYE  ANt)   VISION 


[CH.  LVL 


With  these  data  it  has  been  found  comparatively  easy  to  reduce 
by  calculation  the  different  surfaces  of  different  curvature  into  one 
mean  curved  surface  of  known  curvature,  and  the  differently  refracting 
media  into  one  mean  medium  the  refractive  power  of  which  is  known. 


Pig.  579. — If  P  P'  is  a  line  which  separates  two  media,  the  lower  oue  being  the  denser,  and  A  O  is  a  ray 
of  light  falling  on  it,  it  is  bent  at  O  towards  the  normal  or  perpendicular  line  N  N'.  A  O  is  called 
the  incident  ray,  and  O  B  the  refracted  ray  ;  A  O  N  is  called  the  angle  of  incidence  (O,  N'  O  B  the 
angle  of  refraction  (r\     If  any  distance  O  X  is  measured  oil'  along  O  A,  and  an  equal  distance  O  X' 

X  Y 
along  O  B  and  perpendiculars  drawn  to  In  N';  then  ^7^=  index  of  refraction. 


The  simplest  so-called  schematic  eye  formed  upon  this  principle, 
suggested  by  Listing  as  the  reduced  eye,  has  the  following  dimen- 
sions : — 

From  anterior  surface  of  cornea  to  the  principal  point  =  2 '3448  mm. 

From  the  nodal  point  to  the  posterior  surface  of  lens  =       '4764    ,, 

Posterior  chief  focus  lies  behind  cornea        .         .         .  =  22"8237    ,, 

Anterior  chief  focus  in  front  of  cornea          .         .         .  =  12'8326    ,, 

Radius  of  curvature  of  ideal  surface     .         .         .         .  —  5'1248    ,, 

The  term  index  of  refraction  means  the  ratio  of  the  sine  of  the 
angle  of  incidence  to  that  of  the  angle  of  refraction ;  this  is  explained 
in  the  small  text  beneath  fig.  579. 

In  this  reduced  or  simplified  eye,  the  principal  posterior  focus, 
about  23  mm.  behind  the  spherical  surface,  would  correspond  to  the 
position  of  the  retina  behind  the  anterior  surface  of  the  cornea.  The 
refracting  surface  would  be  situated  about  midway  between  the 
posterior  surface  of  the  cornea  and  the  anterior  surface  of  the  lens. 


CH.  LVI.] 


REFlwVCTION    OF   LIGHT 


791 


The  optical  axis  of  the  eye  is  a  line  drawn  through  the  centres  of 
curvature  of  the  cornea  and  lens,  prolonged  backwards  to  touch  the 
retina  between  the  porus  opticus  and  fovea  centralis,  and  this  differs 
from  the  visual  axis  which  passes  through  the  nodal  point  of  the 
reduced  eye  to  the  fovea  centralis;  this  forms  an  angle  of  5°  with 
the  optical  axis.  But  for  practical  purposes  the  optical  axis  and  the 
visual  axis  may  be  considered  to  be  identical. 

The  visual  or  optical  angle  (fig.  580)  is  included  between  the  lines 
drawn  from  the  borders  of  any  object  to  the  nodal  point;  if  the 
lines  are  prolonged  backwards  they  include  an  equal  angle.  It  has 
been  shown  by  Helmholtz  that  the 
smallest  angular  distance  between 
two  points  which  can  be  appreci- 
ated as  two  distinct  points  =  50 
seconds,  the  size  of  the  retinal 
image  being  3"65^c ;  this  is  a  little 
more  than  the  diameter  of  a  cone 
at  the  fovea  centralis  which  =  3//, 
the  distance  between  the  centres  of 
two  adjacent  cones  being  =  4^.  If  the  two  points  are  so  close 
together  that  they  subtend  a  visual  angle  less  than  50  seconds,  both 
images  will  fall  upon  one  cone,  and  the  two  points  will  therefore 
appear  as  one. 

Any  object,  for  example,  the  arrow  A  B  (fig.  581),  may  be  con- 
sidered as  a  series  of  points  from  each  of  which  a  pencil  of  light 


Fig.  580.— Diagram  of  the  optical  angle. 


-Diagram  of  the  course  of  the  rays  of  light,  to  show  how  an  Image  is  formed  upon  the  retina. 
The  surface  C  0  should  be  supposed  to  represent  the  ideal  curvature. 


diverges  to  the  eye.  Take,  for  instance,  the  rays  diverging  from  the 
tip  of  the  arrow  A ;  C  C  represents  the  curvature  of  the  schematic 
or  reduced  eye ;  the  ray  which  passes  through  the  centre  of  the  circle 
of  which  C  C  is  part  is  not  refracted ;  this  point  is  represented  as 
an  asterisk  in  fig.  581 ;  it  is  near  the  posterior  surface  of  the  crystal- 


792  THE   EYE   AND   VISION  [ciI.  LVI. 

line  lens ;  the  ray  A  C,  which  is  parallel  to  the  optic  axis  0  0',  is 
refracted  through  the  principal  posterior  focus  P,  and  cuts  the  first 
ray  at  the  point  A'  on  the  retina.  All  the  other  rays  from  A  meet 
at  the  same  point.  Similarly  the  other  end  of  the  arrow  B  is  focussed 
at  B',  and  rays  from  all  other  points  have  corresponding  focusses. 

It  will  thus  be  seen  that  an  inverted  image  of  external  objects  is 
formed  on  the  retina.  The  retina  is  a  curved  screen,  but  the  images 
fall  only  on  a  small  area  of  the  retina  under  normal  circumstances ; 
hence,  for  practical  purposes,  this  small  area  may  be  regarded  as  flat. 

The  question  then  arises.  Why  is  it  that  objects  do  not  appear  to 
us  to  be  upside  down  ?  This  is  easily  understood  when  we  remember 
that  the  sensation  of  sight  occurs  not  in  the  eye,  but  in  the  brain. 
By  education  the  brain  learns  that  the  tops  of  objects  excite  certain 
portions  of  the  retina,  and  the  lower  parts  of  objects  other  portions 
of  the  retina.  That  these  portions  of  the  retina  are  reversed  in 
position  to  the  parts  of  the  object  does  not  matter  at  all,  any  more 
than  it  matters  when  one's  photograph  arrives  home  from  the 
photographer's  that  it  was  wrong  way  up  in  the  photographer's 
camera — one  puts  it  right  way  up  in  the  photograph  album. 

Accommodation 

The  power  of  accommodation  is  primarily  due  to  an  ability  to 
vary  the  shape  of  the  lens ;  its  front  surface  becomes  more  or  less 
convex,  according  as  the  distance  of  the  object  looked  at  is  near  or 
far.     The  nearer  the  object,  the  more  convex,  up  to  a  certain  limit, 

the  front  surface  of  the  lens  becomes,  and 
vice  versd ;  the  back  surface  takes  no  share 
in  the  production  of  the  effect  required. 
The  posterior  surface,  which  during  rest  is 
more  convex  than  the  anterior,  is  thus  ren- 
dered the  less  convex  of  the  two  during 
accommodation.  The  following  simple  ex- 
periment illustrates  this  point :  If  a  lighted 
candle  be  held  a  little  to  one  side  of  a 
Fig.  582.-Diagram  showing  three  pcrsou's  QjQ  an  obscrvcr  looking  at  the  eye 
reflections  of  a  candle    1,  Prom     fj-Qin  the  othcr  sido  sccs  thrcc  images  of  the 

the  anterior  surface  of  cornea;  -r^^x         mi         r.  t    i     •    i  j_      j_   • 

2,  from  the  anterior  surface  of       flame  (tig.   582).        Ihe    tirst    and    brightest  IS 

faceof\ns.°^  e  pos  enor  sur-  ^^^  ^  small  crcct  image  formed  by  the  an- 
terior convex  surface  of  the  cornea;  the 
second  (2)  is  also  erect,  but  larger  and  less  distinct  than  the  pre- 
ceding, and  is  formed  at  the  anterior  convex  surface  of  the  lens ; 
the  third  (3)  is  smaller,  inverted,  and  indistinct;  it  is  formed  at 
the  posterior  surface  of  the  lens,  which  is  concave  forwards,  and 
therefore,  like   all   concave   mirrors,  gives   an  inverted  image.     If 


CH.  LVI.] 


ACCOMMODATION 


793 


now  the  eye  under  observation  is  made  to  look  at  a  near  object,  the 
second  image  becomes  smaller,  clearer,  and  approaches  the  first.  If 
the  eye  is  now  adjusted  for  a  far  point,  the  second  image  enlarges 
again,  becomes  less  distinct,  and  recedes  from  the  first.  In  both 
cases  the  first  and  third  images  remain  unaltered  in  size,  distinct- 
ness, and  position.  This  proves  that  during  accommodation  for  near 
objects  the  curvature  of  the  cornea,  and  of  the  posterior  surface  of  the 
lens,  remain  unaltered,  while  the  anterior  surface  of  the  lens  becomes 
more  convex  and  approaches  the  cornea. 

The  experiment  is  more  striking  when  two  bright  images  (repre- 
sented by  arrows  in  fig.  583)  are  used ;  the  two  images  from  the  front 


Fia.  588. — Diagram  of  Sanson's  images.  A,  When  the  eyes  are  not,  and  B,  when  they  are  focussed  for 
near  objects.  The  flg.  to  the  right  in  A  and  B  is  the  inverted  image  from  the  posterior  surface  of 
the  lens. 

surface  of  the  lens  during  accommodation  not  only  approach  those 
from  the  cornea,  but  also  approach  one  another,  and  become  some- 
what smaller.  {Sanson's  Images.)  Helmholtz's  Phakoscope  (fig.  584) 
is  a  triangular  box  with  arrangements  for  demonstrating  this 
experiment. 

Mechanism  of  Accommodation. — The  lens  having  no  inherent 
power  of  contraction,  its  changes  of  outline  must  be  produced  by 
some  power  from  without ;  this  power  is  supplied  by  the  ciliary 
muscle.  Its  action  is  to  draw  forwards  the  choroid,  and  by  so 
doing  to  slacken  the  tension  of  the  suspensory  ligament  of  the 
lens  which  arises  from  it.  The  anterior  surface  of  the  lens  is 
kept  flattened  by  the  action  of  this  ligament.  The  ciliary  muscle 
during  accommodation,  by  diminishing  the  tension  of  this  ligament, 
diminishes  to  a  proportional  degree  the  flattening  of  which  it  is  the 
cause.  On  diminution  or  cessation  of  the  action  of  the  ciliary 
muscle,  the  lens  returns  to  its  former  shape,  by  virtue  of  the  elas- 
ticity of  the  suspensory  ligament  (fig.  585).  From  this  it  will 
appear  that  the  eye  is  usually  focussed  for  distant  objects.  In  view- 
ing near  objects  the  ciliary  muscle  contracts ;  the  ciliary  muscle 
relaxes  on  withdrawal  of  the  attention  from  near  to  distant  objects. 

It  is  possible  to  calculate  the  curvature  of  the  lens  or  cornea  in  the  body,  by 
measuring  the  size  of  the  image  of  an  object  upon  it     The  radius  (r)  of  curvature 


794 


THE   EYE   AND   VISION 


[CH.  LVI. 


of  a  convex  reflecting  surface  is  given  by  the  formula  r=  — ;  a  is  the  distance  of 

the  object  from  the  surface,  ''  the  diameter  of  the  image,  and  c  that  of  the  object. 
a  and  r  are  easily  measured  ;  h  is  measured  by  Helmholtz's  ophthalmometer,  the 


Fig.  584.— Phakoscope  of  Helmholtz.  At  i"  B'  are  two  prisms,  by  which  the  light  of  a  candle  is  con- 
centrated on  the  eye  of  the  person  experimented  with,  which  is  looking  through  a  hole  in  the  third 
angle  of  the  box  opposite  to  the  window  C.  A  is  the  aperture  for  the  eye  of  the  observer.  The 
observer  notices  three  double  images,  represented  by  arrows,  in  fig.  5S3,  reflected  from  the  eye 
under  examination  when  the  eye  is  fixed  upon  a  distant  object ;  the  position  of  the  images  having 
been  noticed,  the  eye  is  made  to  focus  a  near  object,  such  as  a  reed  pushed  up  at  C ;  the  images 
from  the  anterior  surface  of  the  lens  will  be  observed  to  move  as  described  in  the  text. 

principle  of  which  is  as  follows  :— If  a  line  is  looked  at  through  a  plate  of  glass 
placed  obliquely  between  it  and  the  eye.  the  line  is  shifted  sideways  to  either  right 


Fig.  585.— Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  leas  on  accommo- 
dation for  near  objects.    (E.  Landolt.) 

or  left ;  if  the  glass  plate  is  then  placed  obliquely  at  right  angles  to  its  previous 
position,  the  line  is  shifted  in  the  opposite  direction.     In  the  ophthalmometer  there 


CH.  LVI.]  SCIIEINEK'S  EXPERIMENT  795 

are  two  jjlass  plates  intersecting  each  otiier  at  an  an{;le;  the  iniafje  of  a  bright 
horizontal  line  upon  the  lens  or  cornea  is  looked  at  throuj^h  the  junction  between 
the  two  plates;  one  plate  shifts  the  image  to  the  right,  the  other  to  the  left;  the 
angle  between  the  two  i)lates  is  altered  until  the  line  appears  as  two  distinct  lines 
just  touching  each  other.  The  amount  of  shifting  of  each,  which  unist  therefore  be 
half  the  length  of  the  image  of  the  line,  can  be  easily  calculated  if  the  thickness  of 
the  glass  plates,  their  refractive  index,  and  the  angle  between  them  are  known. 
Double  this  result  gives  the  size  of  the  image  on  the  surface  under  investigation. 

Range  of  Distinct  Vision.  Near-point. — In  every  eye  there  is  a 
limit  to  the  power  of  accommodation.  If  a  book  be  brought  nearer 
and  nearer  to  the  eye,  the  type  at  last  becomes  indistinct,  and  cannot 
be  brought  into  focus  by  any  effort  of  accommodation,  however 
strong.  This,  which  is  termed  the  near-point,  can  be  determined  by 
the  following  experiment  {Scheiner).  Two  small  holes  are  pricked  in 
a  card  with  a  pin  not  more  than  a  twelfth  of  an  inch  (2  mm.)  apart ; 
at  any  rate  their  distance  from  each  other  must  not  exceed  the 
diameter  of  the  pupil.  The  card  is  held  close  in  front  of  the  eye, 
and  a  small  needle  viewed  through  the  pin-holes.  At  a  moderate 
distance  it  can  be  clearly  focussed,  but  when  brought  nearer,  beyond 
a  certain  point,  the  image  appears  double,  or  at  any  rate  blurred. 
This  point  where  the  needle  ceases  to  appear  single  is  the  near-point. 
Its  distance  from  the  eye  can  of  course  be  readily  measured.  It  is 
usually  about  5  or  6  inches  (13  cm.).  In  the  accompanying  figure 
(tig.  586)  the  lens  h  represents  the  refractive  apparatus  of  the  eye ; 


Fig.  586. — Diagram  of  experiment  to  ascertain  the  minimum  distance  of  distinct  vision. 

e  and/  the  two  pin-holes  in  the  card,  nn  the  retina ;  a  represents  the 
position  of  the  needle.  When  the  needle  is  at  a  moderate  distance, 
the  two  pencils  of  light  coming  from  e  and /are  focussed  at  a  single 
point  on  the  retina  nn.  If  the  needle  is  brought  nearer  than  the 
near-point,  the  strongest  effort  of  accommodation  is  not  sufficient  to 
focus  the  two  pencils,  they  meet  at  a  point  behind  the  retina.  The 
effect  is  the  same  as  if  the  retina  were  shifted  forward  to  mm:  Two 
images  h.g.  are  formed,  one  from  each  hole.  It  is  interesting  to  note 
that  when  two  images  are  produced,  the  lower  one  g  really  appears 
in  the  position  Q,  while  the  upper  one  appears  in  the  position  p.  This 
may  be  readily  verified  by  covering  the  holes  in  succession. 

During  accommodation  two  other  changes  take  place  in  the  eyes : 


796  THE   EYE   AND    VISION  [CH.  LVI. 

(1)  The  eyes  converge  owing  to  the  action  of  the  internal  rectus  muscle 
of  each  eyeball.     (2)  The  pupils  contract. 

The  contraction  of  all  of  the  muscles  which  have  to  do  with 
accommodation,  viz.,  of  the  ciliary  muscle,  of  the  internal  recti 
muscles,  and  of  the  sphincter  pupillse,  is  under  the  control  of  the 
third  nerve.  It  should  further  be  noted  that  although  the  act  is  a 
voluntary  one,  the  fibres  of  the  ciliary  muscle  and  of  the  sphincter 
pupillce  are  of  the  plain  variety. 

The  account  of  accommodation  as  given  in  the  preceding  pages  is  true  for  man 
and  other  mammals,  birds,  and  certain  reptiles. 

Beer  has,  however,  shown  that  in  many  animals  lower  in  the  scale,  the 
mechanism  of  accommodation  varies  a  good  deal,  and  is  often  very  diiTerent  from 
that  just  described,  consisting,  in  fact,  in  a  power  of  altering  the  distance  between 
the  lens  and  the  retina. 

In  bony  fishes,  the  eye  at  rest  is  accommodated  for  near  objects ;  in  focussing 
for  distant  objects  the  lens  is  drawn  nearer  to  the  retina  by  a  special  muscle  called 
the  retractor  lentis.  In  cephalopods  the  same  occurs,  but  the  retractor  lentis  is 
absent ;  here  the  approach  of  the  lens  to  the  retina  is  brought  about  by  an  alteration 
of  intra-ocular  tension.  In  Amphibia  and  most  snakes,  the  eye  at  rest  is  focussed 
for  distant  objects ;  in  accommodating  for  near  objects  the  lens,  by  alteration  of 
intra-ocular  tension,  is  brought  forward,  that  is,  the  distance  between  it  and  the 
retina  is  increased.  There  appear  to  be  not  a  few  animals  in  all  classes  which  do  not 
possess  the  power  of  accommodation  at  all.  Indeed,  Barrett  states  this  is  so  for 
most  mammals. 

Defects  in  the  Optical  Apparatus 

Under  this  head  we  may  consider  the  defects  known  as  (1) 
Myopia,  (2)  Hypermetropia,  (3)  Astigmatism,  (4)  Spherical  Aber- 
ration, (5)  Chromatic  Aberration. 

The  normal  {emmetropic)  eye  is  so  adjusted  that  at  rest  parallel 
rays  are  brought  exactly  to  a  focus  on  the  retina  (1,  fig.  587). 
Hence  all  objects  except  near  ones  (practically  all  objects  more  than 
twenty  feet  off)  are  seen  without  any  effort  of  accommodation ;  in 
other  words,  the  far-point  of  the  normal  eye  is  at  an  infinite  distance. 
In  viewing  near  objects  we  are  conscious  of  the  effort  (the  contraction 
of  the  ciliary  muscle)  by  which  the  anterior  surface  of  the  lens  is 
rendered  more  convex,  and  rays  which  would  otherwise  be  focussed 
behind  the  retina  are  converged  upon  the  retina  (see  dotted  lines, 
2,  fig.  587). 

1.  Myopia  (short-sight),  (4,  fig.  587). — This  defect  is  due  to  an 
abnormal  elongation  of  the  eyeball.  The  retina  is  too  far  from  the 
lens,  and  consequently  parallel  rays  are  focussed  in  front  of  the 
retina,  and,  crossmg,  form  little  circles  on  the  retina ;  thus  the  images 
of  distant  objects  are  blurred  and  indistinct.  The  eye  is,  as  it  were, 
permanently  adjusted  for  a  near-point.  Eays  from  a  point  near  the 
eye  are  exactly  focussed  on  the  retina.  But  those  which  issue  from 
any  object  beyond  a  certain  distance  (far-point)  cannot  be  distinctly 
focussed.     This  defect  is  corrected  by  concave  glasses  which  cause  the 


CII.  LVI.]  ERRORS  OF  REFRACTION  797 

rays  entering  the  eye  to  diverge :  hence  they  do  not  come  to  a  focus 
so  soon.  Such  glasses,  of  course,  are  only  needed  to  give  a  clear 
vision  of  distant  objects.  For  near  objects,  except  in  extreme  cases, 
they  are  not  required. 

2.  Hypermetropia  (3,  fig.  687). — This  is  the  reverse  defect.     The 


Fio.  587. — Diagram  showing — 1,  normal  (cinmeiTOpic)  eye  bringing  parallel  rays  exactly  to  a  focus  on 
the  retina ;  2,  normal  eye  adapted  to  a  near-point ;  without  accommodation  the  rays  would  be 
focussed  behind  the  retina,  but  by  increasing  the  curvature  of  the  anterior  surface  of  the  lens 
(shown  by  a  dotted  line)  the  rays  are  focussed  on  the  retina  (as  indicated  by  the  meeting  of  the  two 
dotted  lines) ;  3,  hypermetropic  eye ;  in  this  case  the  axis  of  the  eye  is  shorter  than  normal ;  parallel 
rays  are  focussed  behind  the  retina ;  4,  myopic  eye  ;  in  this  case  the  axis  of  the  eye  is  abnormally 
long ;  parallel  rays  are  focussed  in  front  of  the  retina.  The  figure  incorrectly  represents  the 
refraction  as  occurring  only  in  the  crystalline  lens ;  the  principal  refraction  really  occurs  at  the 
anterior  surface  of  the  cornea. 

eyeball  is  too  short.  Parallel  rays  are  focussed  behind  the  retina : 
an  effort  of  accommodation  is  required  to  focus  even  parallel  rays  on 
the  retina ;  and  when  they  are  divergent,  as  in  viewing  a  near  object, 
the  accommodation  is  insufficient  to  focus  them.  Thus,  in  well- 
marked  cases,  distant  objects  require  an  effort  of  accommodation,  and 


798  THE   EYE  AND   VISION  [CH.  LVL 

near  ones  a  very  powerful  effort,  and  the  ciliary  muscle  is,  therefore, 
constantly  acting.  This  defect  is  obviated  by  the  use  of  convex 
glasses,  which  render  the  pencils  of  light  more  convergent.  Such 
glasses  are,  of  course,  especially  needed  for  near  objects,  as  in  reading, 
etc.  They  rest  the  eye  by  relieving  the  ciliary  muscle  from  excessive 
work. 

3.  Astigmatism. — This  defect,  which  was  first  discovered  by 
Airy,  is  due  to  a  greater  curvature  of  the  eye  in  one  meridian  than 
in  others.  The  eye  may  be  even  myopic  in  one  plane,  and  hyper- 
metropic in  others.  Thus  vertical  and  horizontal  lines  crossing  each 
other  cannot  both  be  f ocussed  at  once ;  one  set  stand  out  clearly, 
and  the  others  are  blurred  and  indistinct.  This  defect,  which  is 
present  in  a  slight  degree  in  all  eyes,  is  generally  seated  in  the 
cornea,  but  occasionally  in  the  lens  as  well ;  it  may  be  corrected  by 
the  use  of  cylindrical  glasses  (i.e.,  curved  only  in  one  direction). 

4.  Spherical  Aberration. — The  rays  of  a  cone  of  light  from  an 
object  situated  at  the  side  of  the  field  of  vision  do  not  meet  all  in 
the  same  point,  owing  to  their  unequal  refraction ;  for  the  refraction 
of  the  rays  which  pass  through  the  circumference  of  a  lens  is 
greater  than  that  of  those  traversing  its  central  portion.  This 
defect  is  known  as  spherical  aberration,  and  in  the  camera,  telescope, 
microscope,  and  other  optical  instruments,  it  is  remedied  by  the 
interposition  of  a  screen  with  a  circular  aperture  in  the  path  of  the 
rays  of  light,  cutting  off  all  the  marginal  rays,  and  only  allowing  the 
passage  of  those  near  the  centre.  Such  correction  is  effected  in  the 
eye  by  the  iris,  which  prevents  the  rays  from  passing  through  any 
part  of  the  refractive  apparatus  but  its  centre.  The  image  of  an 
object  will  be  most  defined  and  distinct  when  the  pupil  is  narrow, 
the  object  at  the  proper  distance  for  vision,  and  the  light  abundant ; 
so  that,  while  a  sufficient  number  of  rays  are  admitted,  the  narrow- 
ness of  the  pupil  may  prevent  the  production  of  indistinctness  of 
the  image  by  spherical  aberration. 

Distinctness  of  vision  is  further  secured  by  the  pigment  of  the 
outer  surface  of  the  retina,  the  posterior  surface  of  the  iris  and  the 
ciliary  processes,  which  absorbs  most  of  the  light  which  is  reflected 
within  the  eye,  and  prevents  its  being  thrown  again  upon  the  retina 
so  as  to  interfere  with  the  images  there  formed. 

5.  Chromatic  Aberration. — In  the  passage  of  light  through  an 
ordinary  convex  lens,  decomposition  of  each  ray  into  its  elementary 
colours  commonly  ensues,  and  a  coloured  margin  appears  around 
the  image,  owing  to  the  unequal  refraction  which  the  elementary 
colours  undergo.  In  optical  instruments  this,  which  is  termed 
chromatic  aberration,  is  corrected  by  the  use  of  two  or  more  lenses, 
differing  in  shape  and  density,  the  second  of  which  continues  or 
increases  the  refraction  of  the  rays  produced  by  the  first,  but  by 


CH.  LVI.]  FUNCTIONS    OF   THE   IRIS  799 

recombining  the  individual  parts  of  each  ray  into  its  original  white 
light,  corrects  any  chromatic  aberration  which  may  have  resulted 
from  the  first.  It  is  proba])le  that  the  unequal  refractive  power  of 
the  transparent  media  in  front  of  the  retina  may  be  the  means  by 
which  the  eye  is  enabled  to  guard  against  the  effect  of  chromatic 
aberration.  The  human  eye  is  achromatic,  however,  only  so  long  as 
the  image  is  received  at  its  focal  distance  upon  the  retina,  or  so 
long  as  the  eye  is  properly  accommodated.  If  these  conditions 
are  interfered  with,  a  more  or  less  distinct  appearance  of  colours  is 
produced. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white 
object,  it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This 
phenomenon  is  termed  Irradiation.  It  is  partly  for  this  reason  that 
a  white  square  on  a  black  ground  appears  larger  than  a  black  square 
of  the  same  size  on  a  white  ground.  The  phenomenon  is  naturally 
more  marked  when  the  white  object  is  a  little  out  of  focus. 

Defective  Accommodation — Presbyopia. — This  condition  is  due  to 
the  gradual  loss  of  the  power  of  accommodation  which  is  an  early 
sign  of  advancing  years.  In  consequence,  the  person  is  obliged  in 
reading  to  hold  the  book  further  and  further  away  in  order  to  focus 
the  letters,  till  at  last  the  letters  are  held  too  far  for  distinct  vision. 
The  defect  is  remedied  by  weak  convex  glasses.  It  is  due  chiefly  to 
the  gradual  increase  in  density  of  the  lens,  which  is  unable  to  swell 
out  and  become  convex  when  near  objects  are  looked  at,  and  also  to 
a  weakening  of  the  ciliary  muscle,  and  a  general  loss  of  elasticity  in 
the  parts  concerned  in  the  mechanism. 


Functions  of  the  Ieis 

The  iris  has  the  following  uses : — 

1.  To  act  as  a  diaphragm  in  order  to  lessen  spherical  aberration 
in  the  manner  just  described.  This  is  specially  necessary  when  one 
wishes  to  obtain  a  clearly  defined  image  of  an  object;  the  pupil 
therefore  contracts  "when  accommodation  for  a  near  object  takes 
place. 

2.  To  regulate  the  amount  of  light  entering  the  eye.  In  a  bright 
light  the  pupil  contracts ;  in  a  dim  light  it  enlarges.  This  may  be 
perfectly  well  seen  in  one's  own  iris  by  looking  at  it  in  a  mirror 
while  one  alternately  turns  a  gas-light  up  and  down. 

The  muscular  fibres  (unstriped  in  mammals,  striped  in  birds)  of 
the  iris  are  arranged  circularly  around  the  margin  of  the  pupil,  and 
radiatingly  from  its  margin.  The  radiating  fibres  are  best  seen  in 
the  eyes  of  birds  and  otters ;  some  look  upon  them  as  elastic  in 
nature,  but  there  is  little  doubt  that  they  are  contractile.     Those 


800 


THE   EYE   AND   VISION 


[CH.  LVI. 


MID-BRAIN 


who  believe  they  are  not  contractile  explain  dilatation  of  the  pupil 
as  due  to  inhibition  of  the  circular  fibres.  But  if  the  iris  is  stimu- 
lated near  its  outer  margin  at  three  different  points  simultaneously 

the  pupil  assumes  a  triangular 
shape,  the  angles  of  the  triangle 
corresponding  to  the  points  stimu- 
lated ;  this  must  be  due  to  con- 
traction of  three  strands  of  the 
radiating  muscle ;  inhibition  of  the 
circular  fibres  would  occur  equally 
all  round. 

The  iris  is  supplied  by  three 
sets  of  nerve-fibres  contained  in 
the  ciliary  nerves. 

(a)  The   third    nerve    via   the 

Diagram  of  the  motor  nerves  of  the    short    ciHary    UCrVCS    SUpplieS    the 

circular  fibres. 

(b)  The  cervical  sympathetic 
supplies  the  radiating  fibres.  The 
cilio-spinal  centre  which  governs 
them  is  in  the  cervical  region  of 
the  cord  (see  p.  690).  The  fibres 
leave  the  cord  by  the  anterior  root 

of  the  second  thoracic  nerve,  pass  into  the  cervical  sympathetic,  and 
reach  the  eyeball  via  the  ophthalmic  branch  of  the  fifth,  and  long 
ciliary  nerves. 

(c)  Fibres  of  the  fifth  nerve  which  are  sensory. 

The  experiments  on  the  motor  nerves  are  those  of  section  and 
stimulation  of  the  peripheral  ends ;  the  usual  experiments  by  which 
the  functions  of  such  nerves  are  discovered. 


C.G. 


Fm.  588, 

iris.  Around  the  upper  half  of  the  pupil  the 
circular  fibres  (C)  only  are  indicated.  These 
are  supplied  by  the  tliird  nerve,  one  fibre  of 
which  (111.)  is  seen  issuing  from  tlie  mid-brain  ; 
the  cell-station  for  these  fibres  is  in  the  ciliary 
ganglion  (C.G. ).  Around  the  lower  half  of  the 
pupil,  the  radiating  fibres  (R)  are  indicated  ; 
these  are  supplied  by  the  cervical  sympathetic 
(Sy),  one  fibre  of  which  is  shown  with  its  cell- 
station  in  the  superior  cervical  ganglion  (S. C.G.) 
(After  Dixon.) 


Nerve. 

Experiment.    - 

Eflect  on  pupil. 

Third 
Third 

Sympathetic 
Sympathetic 

Both  nerves  together 

Section   . 
Stimulation     . 
Section   . 
Stimulation     . 

Stimulation     < 

Dilatation. 
Contraction. 
Contraction. 
Dilatation. 

Contraction  overcomes 
the  dilatation. 

Certain  drugs  dilate  the  pupil.  These  are  called  mydriatics; 
atropine  is  a  well-known  example.  Others  cause  the  pupil  to 
contract.  These  are  called  myotics ;  physostigmine  and  opium 
(taken  internally)  are  instances.  Different  myotics  and  mydriatics 
act  in  different  ways,  some  exerting  their  activity  on  the  muscular, 
and  others  on  the  nervous  structures  of  the  iris. 


en.  LVl.]  FUNCTIONS   OF   THE   IRIS    AND    iiETINA  801 

Rejiex  actions  of  the  iris. — When  the  iris  contracts  under  the 
influence  of  light,  the  sensory  nerve  is  the  optic,  and  the  motor  the 
third  nerve.  The  central  connection  of  the  two  nerves  in  the 
region  of  the  mid-brain  we  shall  see  later  on.  The  iris  also  contracts 
on  accommodation ;  and  the  reflex  path  concerned  in  this  action  is  a 
different  one  from  that  concerned  in  the  light  reflex,  as  this  reflex 
often  remains,  in  cases  of  locomotor  ataxy,  after  there  is  an  entire 
loss  of  the  refliix  to  light  (Argyll-Eobertson  pupil). 

On  painful  stimulation  of  any  part  of  the  body,  there  is  reflex 
dilatation  of  the  pupil.  This  is  accompanied  by  starting  of  the 
eyeballs,  due  to  contraction  of  the  plain  muscle  in  the  capsule  of 
Tenon,  which,  like  the  dilator  fibres  of  the  iris,  is  supplied  by  the 
cervical  sympathetic  nerve. 

We  may  sum  up  the  principal  conditions  under  which  the  pupil 
contracts  and  dilates  in  the  following  table : — 

Causes  of — 

Contraction  of  the  Pupil.  i  Dilatation  of  the  Pupil. 

1.  Stimulation  of  third  nerve.  I    1.  Paralysis  of  the  third  nerve. 

2.  Paralysis  of  cervical  sympathetic.  2,  Stimulation  of  the  cervical  synipa- 

3.  When  the  eye  is  exposed  to  light.  thetic. 

4.  When  accommodation  occurs.  3.  In  the  dark. 

5.  Under    the     local     influence     of  4.  When     the     accommodation     is 

physostigniine.  relaxed. 

6.  Under  the  influence  of  opium.  5.  Under  the  local  influence  of  atro- 

7.  During  sleep.  j  pine.     This  drug  also  paralyses 

the  ciliary  muscle. 

6.  In  the  last  stage  of  asphyxia. 

7.  In  deep  chloroform  narcosis. 

8.  Under   the    influence    of   certain 
I  emotions,  such  as  fear. 

'   9.  During  pain. 

There  is  a  close  connection  of  the  centres  that  govern  the  activity 
of  the  two  irides.  If  one  eye  is  shaded  by  the  hand,  its  pupil  will 
of  course  dilate,  but  the  pupil  of  the  other  eye  will  also  dilate. 
The  two  pupils  always  contract  or  dilate  together  unless  the  cause 
is  the  local  injury  to  the  nerves  of  one  side  or  the  local  action  of 
drugs. 

Functions  of  the  Ketina 

The  Retina  is  the  nervous  coat  of  the  eye ;  it  contains  the  layer 
of  nerve-epithelium  (rods  and  cones)  which  is  capable  of  receiving 
the  stimulus  of  light,  and  transforming  it  into  a  nervous  impulse 
which  passes  to  the  brain  by  the  optic  nerve. 

The  bacillary  layer,  or  layer  of  rods  and  cones,  is  at  the  back 
of  all  the  other  retinal  layers,  which  the  light  has  to  penetrate 
before  it  can  affect  this  layer.     The  proofs  of  the  statement  that  this 


802  THE   EYE   AND    VISION  [CH.  LVI. 

is  the  layer  of  the  retina  which  is  capable  of  stimulation  by  light  are 
the  following : — 

(1)  The  point  of  entrance  of  the  optic  nerve  into  the  retina, 
where  the  rods  and  cones  are  absent,  is  insensitive  to  light,  and  is 
called  the  Uind  spot.  This  is  readily  demonstrated  by  what  is  known 
as  Mariotte's  experiment.  If  we  direct  one  eye,  the  other  being 
closed,  upon  a  point  at  such  a  distance  to  the  side  of  any  object, 
that  the  image  of  the  latter  must  fall  upon  the  retina  at  the  point  of 
entrance  of  the  optic  nerve,  this  image  is  lost.  If,  for  example,  we 
close  the  left  eye,  and  look  steadily  with  the  right  eye  at  the  dot 


here  represented,  while  the  page  is  held  about  six  inches  from  the 
eye,  both  dot  and  cross  are  visible.  On  gradually  increasing  the 
distance  between  the  page  and  the  eye,  still  keeping  the  right  eye 
steadily  on  the  dot,  it  wiU  be  found  that  suddenly  the  cross  dis- 
appears from  view,  because  its  image  has  faUen  on  the  blind  spot ; 
on  removing  the  book  still  farther,  it  comes  in  sight  again.  The 
question  has  arisen  why  we  are  not  normally  conscious  of  a  gap  in 
the  image.  The  gap  is  not  felt  for  the  reason  that  a  defect  of  light 
sensations  at  a  spot  blmd  from  the  beginning  can  no  more  be  per- 
ceived as  a  gap  in  the  image  than  the  blindness,  say,  of  the  skin  of 
the  back  or  foot  can  be  so  perceived. 

(2)  In  the  fovea  centralis  which  contains  the  bacillary  layer, 
but  in  which  the  other  layers  of  the  retina  are  thinned  down  to  a 
minimum,  light  produces  the  greatest  effect.  In  the  macula  lutea, 
cones  occur  in  large  numbers,  and  in  the  fovea  centralis  cones 
without  rods  are  found,  whereas,  in  the  rest  of  the  retina  which  is 
not  so  sensitive  to  light,  there  are  fewer  cones  than  rods. 

(3)  If  a  small  lighted  candle  is  moved  to  and  fro  at  the  side  of 
and  close  to  one  eye  in  a  darkened  room,  while  the  eyes  look  steadily 
forward  on  to  a  dull  background,  a  remarkable  branching  figure 
{Purkinje' s  figures)  is  seen  floating  before  the  eye,  consisting  of  dark 
lines  on  a  reddish  ground.  As  the  candle  moves,  the  figure  moves 
in  the  opposite  direction,  and  from  its  whole  appearance  there  can 
be  no  doubt  that  it  is  a  reversed  picture  of  the  retinal  vessels  pro- 
jected before  the  eye.*  This  remarkable  appearance  is  due  to 
shadows  of  the  retinal  vessels  cast  by  the  candle ;  and  it  is  only 
when  they  are  thrown  upon  the  retina  in  an  unusual  slanting 
direction  that  they  are  perceived.  The  branches  of  these  vessels  are 
distributed  in  the  nerve-fibre  and  ganglionic  layers ;  and  since  the 

*  Purkinje's  figures  can  be  much  more  readily  seen  by  simply  looking  steadily 
down  a  microscope,  and  moving  the  whole  Instrument  backwards  and  forwards,  or 
from  side  to  side,  while  so  doing. 


CH.  LVI.]  VISUAL  SENSATIONS   AND   STIMULI  803 

light  of  the  candle  falls  on  the  retinal  vessels  from  in  front,  the 
shadow  is  cast  behind  them,  and  hence  those  elements  of  the  retina 
which  perceive  the  shadows  must  also  lie  behind  the  vessels.  Here, 
then,  we  have  a  clear  proof  that  the  light-perceiving  elements  are 
not  the  inner,  but  one  of  the  external  layers  of  the  retina ;  further 
than  this,  calculation  has  shown  it  is  the  layer  of  rods  and  cones. 
The  data  for  such  a  calculation  are — the  dimensions  of  the  eyeball, 
the  distance  of  the  screen  from  the  eye,  the  angle  through  which  the 
candle  is  moved,  and  the  displacement  of  the  figure  seen. 

Duration  of  Visual  Sensations. — The  duration  of  the  sensation 
produced  by  a  luminous  impression  on  the  retina  is  always  greater 
than  that  of  the  impression  which  produces  it.  However  brief  the 
luminous  impression,  the  effect  on  the  retina  always  lasts  for  about 
one-eighth  of  a  second.  Thus,  supposing  an  object  in  motion,  say  a 
horse,  to  be  revealed  on  a  dark  night  by  a  flash  of  lightning.  The 
object  would  be  seen  apparently  for  an  eighth  of  a  second,  but  it 
would  not  appear  in  motion ;  because,  although  the  image  remained 
on  the  retina  for  this  time,  it  was  really  revealed  for  such  an 
extremely  short  period  (a  flash  of  lightning  lasting  only  a  millionth 
of  a  second)  that  no  appreciable  movement  on  the  part  of  the  object 
could  have  taken  place  in  the  period  during  which  it  was  revealed  to 
the  retina  of  the  observer.  The  same  fact  is  proved  in  a  reverse 
way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as 
distinct  objects,  because  at  every  point  of  the  field  of  vision  over 
which  the  revolving  spokes  pass,  a  given  impression  has  not  faded 
before  another  replaces  it.  Thus  every  part  of  the  interior  of  the 
wheel  appears  occupied. 

The  stimuli  which  excite  the  retina  are  exceedingly  slight ;  for  instance,  the 
minimum  stimulus  in  the  form  of  green  light  is  equal  in  terms  of  work  to  that  which 
is  done  in  raising  a  ten-millionth  part  of  a  milligramme  to  the  height  of  a  millimetre, 
and  even  some  of  this  is  doubtless  Masted  in  the  form  of  heat.  The  time  during 
which  the  stimulus  acts  may  be  excessively  small ;  thus  light  from  a  rapidly  rotating 
mirror  is  visible  even  when  it  only  falls  upon  the  retina  for  one  eight-millionth  part 
of  a  second.  Some  physiologists  have  drawn  an  analogy  between  retinal  and 
muscular  excitations.  There  is  no  complete  analogy,  but  the  following  points  of 
resemblance  may  be  noted  : — 

1.  The  retina  like  the  muscle  possesses  a  store  of  potential  energy,  which  the 
stimidus  serves  to  fire  off. 

2.  Fatigue  on  action,  and  recovery  after  rest  are  noticeable  in  both. 

3.  The  curve  of  retinal  excitation,  like  the  muscle  curve,  rises  not  abruptly  but 
gradually  to  its  full  height,  and  on  the  cessation  of  the  stimulus  takes  a  measurable 
time  to  fall  again,  the  retinal  impression  outlasting  the  stimulus  by  about  one-eighth 
of  a  second. 

4.  With  comparatively  slow  intermittent  excitation,  the  phenomenon  known  as 
flicker  takes  place ;  this  may  be  shown  by  the  slow  rotation  on  Maxwell's  machine 
of  a  disc  painted  with  alternate  black  and  white  sectors.  This  roughly  corresponds 
with  what  in  a  muscle  is  called  incomplete  tetanus. 

5.  When  the  rate  of  stimulation  is  increased,  as  by  increasing  the  speed  of  rota- 
tion of  the  disc  just  alluded  to  (say  to  twenty  or  thirty  times  a  second)  the  resulting 
sensation  is  a  smooth  one  of  greyness.     This  fusion  of  individual  stimuli  into  a  con- 


804  THE   EYE   AND   VISION  [CH.  LVI. 

tinuous  sensation,  does  not  by  any  means  correspond  to  the  complete  tetanus  of 
muscle,  for  the  resultant  sensation  has  a  brightness  corresponding  not  to  a  summa- 
tion of  the  individual  fusing  sensations,  but  to  a  brightness  which  would  ensue  if  the 
stimuli  were  spread  evenly  over  the  surface  of  the  disc  (Talbot's  Law). 

The  Ophthalmoscope. 

Every  one  is  perfectly  familiar  with  the  fact,  that  it  is  quite  im- 
possible to  see  the  fundiLS  or  back  of  another  person's  eye  by  simply 
looking  into  it.  The  interior  of  the  eye  forms  a  perfectly  black 
background.*  The  same  remark  applies  to  the  difficulty  we  experi- 
ence in  seeing  into  a  room  from  the  street  through  the  window  unless 
the  room  is  lighted  within.  In  the  case  of  the  eye  this  fact  is  partly 
due  to  the  feebleness  of  the  light  reflected  from  the  retina,  most  of  it 
being  absorbed  by  the  retinal  pigment ;  but  far  more  to  the  fact  that 
every  such  ray  is  reflected  straight  to  the  source  of  light  (e.g., 
candle),  and  cannot,  therefore,  be  seen  by  the  unaided  eye  without 
intercepting  the  incident  light  from  the  candle,  as  well  as  the 
reflected  rays  from  the  retina.  This  difficulty  is  surmounted  by  the 
use  of  the  ophthalmoscope. 

The  ophthalmoscope  was  invented  by  Helmholtz ;  as  a  mirror  for 
reflecting  the  light  into  the  eye,  he  employed  a  bundle  of  thin  glass 
plates ;  this  mirror  was  transparent,  and  so  he  was  able  to  look 
through  it  in  the  same  direction  as  that  of  the  rays  of  the  light  it 
reflected.  It  is  almost  impossible  to  over-estimate  the  boon  this 
instrument  has  been  to  mankind ;  previous  to  this  in  the  examina- 
tion of  cases  of  eye  disease,  the  principal  evidence  on  which  the 
surgeon  had  to  rely  was  that  derived  from  the  patient's  sensations ; 
now  he  can  look  for  himself. 

The  instrument,  however,  has  been  greatly  modified  since  Helni- 
holtz's  time ;  the  principal  modification  is  the  substitution  of  a  con- 
cave mirror  of  silvered  glass  for  the  bundle  of  glass  plates ;  this  is 
mounted  on  a  handle,  and  is  perforated  in  the  centre  by  a  small  hole 
through  which  the  observer  can  look. 

The  methods  of  examining  the  eye  with  this  instrument  are — the  dirert  and  the 
indirect :  both  methods  of  investigation  should  be  employed.  A  drop  of  a  solution 
of  atropine  (two  grains  to  the  ounce)  or  of  homatropine  hydrobromate,  should  be 
instilled  about  twenty  minutes  before  the  examination  is  commenced ;  the  ciliary 
muscle  is  thereby  paralysed,  the  power  of  accommodation  is  abolished,  and  the 
pupil  is  dilated.  This  will  materially  facilitate  the  examination ;  but  it  is  quite 
possible  to  observe  all  the  details  to  be  presently  described  without  the  use  of  such 


*  In  some  animals  {e.y. ,  the  cat),  the  pigment  is  absent  from  a  portion  of  the 
retinal  epithehum;  this  forms  the  Tapetum  lucidum.  The  use  of  this  is  supposed  to 
be  to  increase  the  sensitiveness  of  the  retina,  the  light  being  reflected  back  through 
the  layer  of  rods  and  cones.  It  is  probably  the  case  that  these  animals  are  able  to  see 
clearly  with  less  hght  than  we  can,  hence  the  popular  idea  that  a  cat  can  see  in  the 
dark.'  In  fishes  a  tapetum  lucidum  is  often  present ;  here  the  brightness  is  increased 
by  crystals  of  guanine. 


CS.  LVI.] 


THE  OPHTHALMOSCOt'E 


805 


drugs.     The  room  being  now  darkened,  the  observer  seats  himself  in  front  of  the 

E)erson  whose  eye  he  is  about  to  examine,  placing  himself  upon  a  somewhat  higher 
evil.  Let  us  suppose  that  the  right  eye  of  the  patient  is  being  examined.  A 
brilliant  and  steady  light  is  placed  close  to  the  left  ear  of  the  patient.  Taking  the 
mirror  in  his  right  hand,  and  looking  through  the  central  hole,  the  operator  directs 
a  beam  of  light  into  the  eye  of  the  patient.  A 
red  glare,  known  as  the  refi'x,  is  seen  ;  it  is  due 
to  the  illumination  of  the  retina.  The  patient 
is  then  told  to  look  at  the  little  finger  of  the 
observer's  right  hand  as  he  holds  the  mirror ; 
to  effect  this  the  eye  is  rotated  somewhat  in- 
wards, and  at  the  same  time  the  reflex  changes 
from  red  to  a  lighter  colour,  owing  to  the  re- 
flection from  the  optic  disc.  The  observer  now 
approximates  the  mirror,  with  his  eye  to  the 
eye  of  the  patient,  taking  care  to  keep  the 
light  fixed  upon  the  pupil,  so  as  not  to  lose 
the  reflex.  At  a  certain  point,  which  varies 
with  different  eyes,  but  is  usually  reached  when 
there  is  an  interval  of  about  two  or  three  inches 
between  the  observed  and  the  observing  eye,  the, 
vessels  of  the  retlud  become  visible.  Examine 
carefully  the  fundus  of  the  eye,  i.e.,  the  red 
surface — until  the  optic,  disc  is  seen ;  trace  its 
circular  outline,  and  observe  the  small  central 
white  spot,  the  porus  opticus,  or  physiological 
pit :  near  the  centre  is  the  central  artery  of  the 
retina  breaking  up  upon  the  disc  into  branches  ; 
veins  also  are  present,  and  correspond  roughly 
to  the  course  of  the  arteries.  Trace  the  vessels 
over  the  disc  on  to  the  retina.  Somewhat  to 
the  outer  side,  and  only  visible  after  some 
practice,  is  the  yellovj  spot,  with  the  smaller 
lighter-coloured  fove.a  centralis  in  its  centre. 
This  constitutes  the  direct  method  of  examina- 
tion ;  by  it  the  various  details  of  the  fundus  are 
seen  as  they  really  exist,  and  it  is  this  method 
which  should  be  adopted  for  ordinary  use. 

If  the  observer  is  myopic  or  hypermetropic, 
he  will  be  unable  to  employ  the  direct  method 
of  examination  until  he  has  remedied  his  de- 
fective vision  by  the  use  of  proper  glasses. 

In  the  indirect  method  the  patient  is  placed  as  before,  and  the  operator  holds  the 
mirror  in  his  right  hand  at  a  distance  of  twelve  to  eighteen  inches  from  the  patient's 
right  eye.  At  the  same  time  he  rests  his  left  little  finger  lightly  upon  the  patient's  right 
temple,  and  holding  a  convex  lens  between  his  thumb  and  forefinger,  two  or  three 
inches  in  front  of  the  patient's  eye,  directs  the  light  through  the  lens  into  the  eye. 
The  red  reflex,  and  subsequently  the  white  one,  having  been  gained,  the  operator 
slowly  moves  his  mirror,  and  with  it  his  eye,  towards  or  away  from  the  face  of  the 
patient,  until  the  outline  of  one  of  the  retinal  vessels  becomes  visible,  when  very 
slight  movements  on  the  part  of  the  operator  will  suffice  to  bring  into  view  the 
details  of  the  fundus  above  described,  but  the  image  will  be  much  smaller  and  in- 
verted. The  appearances  seen  are  depicted  in  fig.  574.  The  lens  should  be  kept 
fixed  at  a  distance  of  two  or  three  inches,  the  mirror  alone  being  moved  until  the 
disc  becomes  visible  :  should  the  image  of  the  mirror,  however,  obscure  the  disc,  the 
lens  may  be  slightly  tilted. 

The  two  next  figures  show  diagrammatically  the  course  of  the  rays  of  light. 

Fig.  590  represents  what  occurs  when  employing  the  direct  method.  S  is  the 
source  of  light,  and  M  M  the  concave  mirror  with  its  central  aperture,  which  reflects 
the  rays  ;  these  are  focussed  by  the  eye  E,  which  is  being  examined,  toapointin  the 


Fio.  589.--The  Ophthalmoscope.  The 
small  upper  mirror  is  for  direct,  the 
larger  for  indirect,  illumination. 


806 


THE   EYE   ANt)   VlSlON 


[cH.  vn. 


vitreous  humour,  and  this  produces  a  diffuse  lighting  of  the  interior  of  the  eyeball. 
Rays  of  light  issuing  from  the  point  p  emerge  from  the  eye  parallel  to  one  another, 
and  enter  the  observer's  eye  E^ ;  they  are  brought  to  a  focus  p^  on  the  retina  as  the 


Fio.  590.— The  course  of  the  light  in  examining  the  eye  by  the  direct  method.    (T.  G.  Brodie.) 


eye  is  accommodated  for  distant  vision.     Similarly  the  point  vi  and  n  will  give  rise 
to  images  at  m}  and  v}  respectively. 

Fig.  591  represents  what  occurs  in  examining  the  eye  by  the  indirect  method. 


Fig.  591.— Tlie  course  of  the  light  in  examining  the  eye  by  the  indirect  method.     (T.  G.  Brodie.) 

S  is  the  source  of  light,  M  M  the  mirror,  E  the  observed,  and  E'  the  observing 
eye  as  before.  The  rays  of  light  are  reflected  from  the  mirror  and  form  an  image 
at  o^ ;  they  then  diverge  and  are  again  made  convergent  by  the  lens  L  held  in  front 
of  the  eye  by  the  observer ;  by  this  means  a  second  image  is  focussed  just  behind 
the  crystaUine  lens  of  the  eye  E.  They  then  again  diverge  and  diffusely  light  up 
the  interior  of  the  eyeball.  The  rays  of  light  reflected  from  two  points  i  and  m  on 
the  retina  diverging  from  the  eye  are  refracted  to  the  glass  lens  L,  and  give  an 
inverted  real  image  i'  /;i'  larger  than  the  object  i  m.  These  latter  rays  then  diverge, 
and  are  collected  and  focussed  by  the  observing  eye  E^  to  give  an  image  i-  m'  on  th e 
retina.     (T.  G.  Brodie.) 

The  Perimeter. 

This  is  an  instrument  for  mapping  out  tlie  field  of  vision.  It 
consists  of  a  graduated  arc,  which  can  be  moved  into  any  position, 
and  which  when  rotated  traces  out  a  hollow  hemisphere.  In  the 
centre  of  this  the  eye  under  examination  is  placed,  the  other  eye 


CH.  I-VI.] 


THE    PERIMETER 


807 


Fig.  592.— Priestley  Smith's  Perimeter. 


100 


180 

Fio.  503.— Periiueter  chart  for  the  right  eye. 


808  THE   EYE   AND   VISION  [CH.  LVI. 

being  closed.  The  examiner  then  determines  on  the  surface  of  the 
hemisphere  those  points  at  which  the  patient  just  ceases  or  just 
begins  to  see  a  small  object  moved  along  the  arc  of  the  circle.  These 
points  are  plotted  out  on  a  chart  graduated  in  degrees,  and  by  con- 
necting them  the  outline  of  the  field  of  vision  is  obtained. 

Fig.  592  shows  one  of  the  forms  of  perimeter  very  generally 
employed,  and  fig.  593  represents  one  of  the  charts  provided  with 
the  instrument.  The  blind  spot  is  shown,  and  the  dotted  line 
represents  the  normal  average  field  of  vision  for  the  right  eye. 

It  will  be  seen  that  the  field  of  vision  is  most  extensive  on  the 
outer  side ;  it  is  less  on  the  inner  side  because  of  the  presence  of  the 
nose. 

By  the  use  of  the  same  instrument,  it  is  found  that  the  colour 
of  a  coloured  object  is  not  distinguishable  at  the  margin,  but  only 
towards  the  centre  of  the  field  of  vision,  but  there  are  differences 
for  different  colours ;  thus  a  blue  or  yellow  object  is  seen  to  be 
blue  or  yellow  over  a  wider  field  than  a  red  or  green  object. 

In  disease  of  the  optic  nerve,  contraction  of  the  field  of  vision 
for  white  and  coloured  objects  is  found.  This  is  often  seen  before 
any  change  in  the  optic  nerve  is  discoverable  by  the  ophthalmoscope. 

The  yellow  spot  of  one's  own  eye  can  be  rendered  evident  by 
what  is  called  Clerk-Maxwell's  experiment : — On  looking  through  a 
solution  of  chrome-alum  in  a  bottle  with  parallel  sides,  an  oval 
purplish  spot  is  seen  in  the  green  colour  of  the  alum.  This  is  due 
to  the  pigment  of  the  yellow  spot. 

Visual  Sensations. 

Visual  sensations  are  of  two  kinds,  colour  sensations  and  colour- 
less sensations.  Colour  sensations  differ  (1)  in  hue,  for  instance,  blue, 
red,  yellow  ;  (2)  in  saturation,  for  instance,  pale  green  and  f uU  green ; 
this  depends  upon  the  degree  of  admixture  with  white  light ;  and  (3) 
in  intensity,  for  instance,  a  weak  sensation  or  a  strong  sensation. 
These  differences  are  in  part  dependent  respectively  on  the  length, 
the  purity,  and  the  amplitude  of  the  light- wave ;  but  they  are  also 
dependent  on  the  local  or  general  condition  of  the  cerebro-retinal 
apparatus  at  the  time  of  stimulation.  Colours  also  differ  (4)  in 
brightness  or  luminosity;  this  is  a  purely  psychological  quality 
devoid  of  any  known  physical  counterpart.  The  brightness  of  a 
colour  may  be  measured  by  determining  the  shade  of  grey  to  which 
it  appears  equivalent.  Even  the  most  saturated  colours  (for 
instance,  yellow  and  blue)  have  different  degrees  of  brightness. 
Colourless  sensations  include  the  grey  series  from  the  deepest  black 
to  the  most  blinding  white. 

If  a  ray  of  sunlight  is  allowed  to  pass  through  a  prism,  it  is 


CH.  LVI.]  COLOUR  SENSATIONS  809 

decomposed  by  its  passage  into  rays  of  different  colours,  which  are 
called  the  colours  of  the  spectrum;  they  are  red,  orange,  yellow, 
green,  blue,  indigo,  and  violet.  The  red  rays  are  the  least  turned  out 
of  their  course  by  the  prism,  and  the  \dolet  the  most,  whilst  the  other 
colours  occupy  in  order  places  between  these  two  extremes.  The 
differences  in  the  colour  of  the  rays  depend  upon  the  rapidity  of 
vibrations  producing  each,  the  red  rays  being  the  least  rapid 
and  the  violet  the  most.  In  addition  to  these,  there  are  other  rays 
which  are  invisible  but  which  have  definite  properties ;  those  to  the 
left  of  the  red  are  less  refrangible,  being  the  calorific  rays  which  act 
upon  the  thermometer,  and  those  to  the  right  of  the  violet,  which 
are  called  the  actinic  or  chemical  rays,  have  a  powerful  chemical 
action. 

White  light  may  be  built  from  its  constituents  in  several  ways, 
for  instance,  by  a  second  prism  reversing  the  dispersion  produced  by 
the  first,  or  by  causing  the  colours  of  the  spectrum  to  fall  on  the 
retina  in  rapid  succession.  The  best  way  to  study  the  effects  of 
compounding  successive  colour  stimuli  is  by  means  of  a  rapidly 
revolving  disc  to  which  two  or  more  coloured  sectors  are  fixed. 
Each  colour  is  viewed  in  rapid  succession,  but  owing  to  the  per- 
sistence of  retinal  impressions,  the  constituent  colour  stimuli  give  a 
single  sensation  of  colour. 

A  colourless  sensation  can  be  produced  by  the  mixture  of  three 
colours,  or  even  of  two  colours  in  certain  hues  and  proportions. 
These  pairs  of  colours,  of  which  red  and  greenish-blue,  orange 
and  blue,  and  violet  and  yellow  are  examples,  are  called  comjyle- 
mentary. 

Thus  blue  and  orange,  when  rotated  on  the  colour-wheel,  produce  a  colourless 
sensation  ;  but  it  is  well  known  that  a  mixture  of  blue  and  orange  paint  gives  green. 
This  is  explained  on  the  supposition  that  the  colours  used  are  not  pure  and  that 
each  contains  green ;  the  true  blue  and  orange  present  neutralise  each  other  to 
produce  white,  and  thus  green  is  the  only  colour  sensation  obtained. 

Three  properly  chosen  colours  will  not  only  produce  a  colourless 
sensation,  but  when  combined  in  appropriate  amounts  they  can  be 
made  to  yield  any  other  colour  sensation.  It  is  on  this  principle 
that  Thomas  Young  based  his  trichromatic  theory  of  colour  vision, 
which  was  subsequently  elaborated  by  Helmholtz  and  Clerk-Maxwell. 
It  is  known  as  the  Young-Helmholtz  theory.  The  theory  selects 
as  the  three  above-mentioned  colours  red,  green,  and  violet,  and 
terms  these  the  three  primary  colours.  These  three  particular 
colours  are  chosen,  partly  because  of  their  position  within  the 
spectrum,  partly  on  account  of  the  phenomena  of  colour-blindness, 
and  for  other  reasons. 

The  Young-Helmholtz  theory  teaches  that  there  are  in  the  retina 
certain  elements  (?  within  the  cones)  which  answer  to  each  of  these 


810 


THE   EYE   AXD    VISION 


[cn.  LVI. 


Fig.  594. — Diagram  of  the  three  primary  colour 
sensations.  (Young-Helmholtz  theory.)  1  is 
the  red ;  2,  green,  and  3,  violet,  primary 
colour  sensation.  The  lettering  indicates  the 
colours  of  the  spectrum.  The  diagram  indi- 
cates by  the  height  of  the  curve  to  what 
extent  the  several  primary  sensations  of 
colour  are  excited  by  vibrations  of  different 
wave  lengths. 


primary  colours,  whereas  the  innumerable  intermediate  shades  of 
colour  are  produced  by  stimulation  of  the  three  primary  colour 
terminals  in  different  degrees,  the  sensation  of  white  being  produced 
when  the  three  elements  are  equally  excited.     Thus,  if  the  retina  is 

stimulated  by  rays  of  certain  wave 
length,  at  the  red  end  of  the  spec- 
trum, the  terminals  of  the  other 
colours,  green  and  violet,  are  hardly 
stimulated  at  all,  but  the  red 
terminals  are  strongly  stimulated, 
the  resulting  sensation  being  red. 
The  orange  rays  excite  the  red 
terminals  considerably,  the  green 
rather  more,  and  the  \dolet  slightly, 
the  resulting  sensation  being  that 
of  orange,  and  so  on  (fig.  59-i). 

Another  theory  of  colour  vision 
(Hering's)  supposes  that  there  are 
six  primary  colour  sensations,  viz. : 
three  antagonistic  (complemen- 
tary) pairs,  black  and  white,  red  and  green,  and  yellow  and  blue ; 
and  that  these  are  produced  by  the  changes  either  of  disin- 
tegration or  of  assimilation  takmg  place  in  certain  substances, 
which  (the  theory  supposes)  exist  in  the  cerebro-retinal  apparatus. 
Each  of  the  substances  corresponding  to  a  pair  of  colours  is 
capable  of  undergoing  two  changes,  one  of  disintegration,  and 
the  other  of  construction,  with  the  result  of  producing  one  or 
other  colour.  For  instance,  in  the  white-black  substance,  when 
disintegi'ation  is  in  excess  of  construction  or  assimilation,  the 
sensation  is  white,  and  when  assimilation  is  in  excess  of 
disintegration  the  reverse  is  the  case ;  and  similarly  with  the  red- 
green  substance,  and  with  the  yellow-blue  substance.  When  the 
repair  and  disintegration  are  equal  with  the  first  substance,  the  visual 
sensation  is  grey ;  but  in  the  other  pairs,  when  this  is  the  case,  no 
colour  sensation  occurs.  The  rays  of  the  spectrum  to  the  red  end 
produce  changes  in  the  red-green  substance,  with  a  resulting 
sensation  of  red,  whilst  the  (orange)  rays  further  to  the  right  affect 
both  the  red-green  and  the  yellow-blue  substances ;  blue  rays  cause 
constructive  changes  in  the  yellow-blue  substances,  but  none  in  the 
red-green,  and  so  on.  All  colours  act  on  the  white-black  substance 
as  well  as  on  the  red-green  or  yellow-blue  substance. 

Xeither  theory  satisfactorily  accounts  for  all  the  numerous 
complicated  problems  presented  in  the  physiology  of  colour  \'ision. 
One  of  these  problems  is  colour  blindness,  a  by  no  means  uncommon 
visual  defect.     Some  people  are  completely  colour  blind,  but  the 


CH.  LVI.]  THEORIES    OF   COLDUR   VISION  811 

commonest  form  is  the  inability  to  distinguish  between  red  and 
green.  Hehnholtz's  explanation  of  such  a  condition  is,  that  the 
elements  of  the  retina  which  receive  the  impression  of  red  or  green 
are  absent,  or  very  imperfectly  developed,  and  Hering's  would  be 
that  the  red-green  substance  is  absent  from  the  cerebro-retinal 
apparatus.  Other  varieties  of  colour-blindness,  in  which  the  other 
colour-perceiving  elements  are  absent,  have  been  shown  to  exist 
occasionally. 

Hering's  theory  appears  to  meet  the  difficulty  best,  for  if  the  red 
element  of  Helmholtz  were  absent,  the  patient  ought  not  to  be  able 
to  perceive  white  sensations,  of  which  red  is  a  constituent  part ; 
whereas,  according  to  Hering's  theory,  the  white-black  visual  sub- 
stance remains  intact. 

These  two  theories  have  been  for  a  long  time  before  the  scientific 
world.  As  facts  have  accumulated,  it  has  been  for  some  years 
recognised  that  many  facts  could  not  be  reconciled  with  either ; 
and  modifications  of  one  or  the  other  have  been  from  time  to  time 
introduced. 

C.  J.  Burch  found  that  by  exposing  the  eye  to  bright  sunlight  in  the  focus  of  a 
burning  glass  behind  transparent  coloured  screens,  it  is  possible  to  produce 
temporary  colour  blindness.  After  red  light,  the  observer  is  for  some  minutes  red- 
blind,  scarlet  geraniums  look  black,  yellow  flowers  green,  and  purple  Howers  violet. 
After  violet  light,  violet  looks  black,  purple  flowers  crimson,  and  green  foliage 
richer  than  usual.  After  light  of  other  colours,  corresponding  effects  are  produced. 
If  one  eye  is  made  purple-blind,  and  the  other  green-blind,  all  objects  are  seen  in 
their  natural  colours,  but  in  exaggerated  perspective,  due  to  the  difficulty  the  brain 
experiences  in  combining  the  images  from  the  two  eyes. 

By  using  a  brightly-illuminated  spectrum,  and  directing  the  eye  to  certain  of  its 
colours,  the  eye  in  time  becomes  fatigued  and  blind  for  that  colour,  so  that  it  is  no 
longer  seen  in  the  spectrum.  Thus,  after  green  blindness  is  induced  the  red 
appears  to  meet  the  blue,  and  no  green  is  seen.  If,  however,  the  eye  is  exposed  to 
yellow  light,  it  does  not  similarly  become  blind  for  yellow  only,  but  for  red  and 
green  too.  This  supports  the  Young-Helmholtz  theory,  that  the  sensation  yellow 
is  one  compounded  of  the  red  and  green  sensations.  By  an  exhaustive  examination 
of  the  different  parts  of  the  spectrum,  in  this  way  it  thus  becomes  possible  to 
differentiate  between  the  primary  colour  sensations  and  those  whic-h  are  compound. 
By  a  study  of  this  kind,  Burch  concludes  that  the  phenomena  of  colour  vision  are 
in  accordance  with  the  Young-Helmholtz  theory,  with  the  important  addition  that 
there  is  a  fourth  primary  colour  sensation,  namely,  blue.  He  could  not  discover 
that  colour  sensations  are  related  to  each  other  in  the  sense  indicated  by  Hering. 
Each  may  be  exhausted  without  either  weakening  or  strengthening  the  others. 
These  observations  were  confirmed  by  examining  in  a  similar  way  the  colour 
sensations  of  seventy  other  people,  but  there  are  individual  differences  in  the 
extent  to  which  the  colour  sensations  overlap. 

After-images. — These  are  the  after-effects  of  retinal  excitation, 
and  are  divided  into  2J0sUive  and  negative.  Positive  after-images 
resemble  the  original  image  in  distribution  of  brightness  and  colour. 
In  negative  after-images  bright  parts  appear  dark,  dark  parts  bright, 
and  coloured  parts  in  the  complementary  or  contrast  colours. 

If  a  bright  white  object  is  looked  at,  and  the  eyelids  are  then 


81 2  THS  tTE  AND  VISION  [cH.  LVI. 

closed,  a  positive  after-image  is  seen  which  fades  gradually,  but  as  it 
fades  it  passes  through  blue,  violet  or  red,  to  orange ;  according  to 
the  Young-Helmholtz  theory,  this  is  explained  on  the  hypothesis 
that  the  excitation  does  not  decline  with  equal  rapidity  in  the  three 
colour  terminals.  A  positive  after-image  is  readily  obtained  by 
momentarily  looking  at  a  bright  object,  e.g.,  a  window,  after  waking 
from  sleep.  Negative  after-images  may  be  seen  either  by  closing 
the  eyes  or  by  turning  them  to  a  uniform  grey  surface  after  viewing 
an  object  steadily. 

If  the  object  looked  at  is  coloured,  the  negative  after-image  seen 
upon  such  a  background  is  in  its  complementary  colour;  this  is 
explained  by  the  Young-Helmholtz  theory,  by  the  supposition  that 
the  colour-perceiving  element  for  the  colour  looked  at  is  the  most 
fatigued,  and  the  terminals  for  its  complementary  colour  least 
fatigued.  On  the  Hering  theory,  one  colour  produces  anabolic  or 
katabolic  effects  as  the  case  may  be ;  on  withdrawing  the  eye  from 
stimulation  by  that  particular  colour,  the  opposite  phase  of  meta- 
bolism takes  place  and  produces  the  complementary  colour.  One 
has  an  analogy  to  this  in  the  case  of  the  heart ;  when  that  organ  has 
been  thrown  into  an  anabohc  state  by  the  stimulation  of  the  vagus, 
it  will  beat  better  when  the  stimulation  stops  owing  to  increase  of 
katabolic  processes. 

Simultaneous  Contrast. — Negative  after-images  are  frequently 
spoken  of  as  phenomena  of  successive  contrast.  Somewhat  more 
complex  than  these  are  the  phenomena  of  simultaneous  contrast.  A 
grey  object  looks  whiter  when  viewed  against  a  dark  background 
than  when  seen  against  a  white  background ;  the  colour  of  an  object 
is  intensified  by  viewing  it  against  a  background  of  its  comple- 
mentary hue.  Another  familiar  experiment  is  the  following: — A 
piece  of  grey  paper  is  placed  on  a  green  sheet,  and  the  whole  covered 
with  tissue  paper ;  the  grey  patch  then  appears  to  be  reddish,  that 
is,  of  the  colour  complementary  to  green.  Helmholtz  regarded  such 
phenomena  as  the  result  of  false  judgment,  and  not  of  changes  in 
excitability  of  the  different  parts  of  the  retina.*  It  certainly 
appears  easier  to  explain  contrast  by  the  Hering  theory ;  excitation 
by  one  colour  induces  an  opposite  metabolic  process  in  neighbouring 
areas  of  the  retina ;  if  two  stimuli  of  opposite  character  are  presented 
.simultaneously  side  by  side,  the  contrast  effect  will  be  most  marked. 
In  the  experiment  with  tissue  paper,  the  greater  part  of  the  retina 
is  being  excited  by  green,  and  the  part  of  the  retina  stimulated  by 
the  feeble  white  light  from  the  grey  paper  will  undergo  the  opposite 
change  and  produce  a  sensation  of  red. 

*  By  "retina"  here  and  elsewhere  we  mean  "  cerebro-retinal  apparatus.*'  We 
have  no  knowledge  of  the  precise  share  of  retina  and  brain  in  the  development  of 
visual  sensations  and  after-sensations. 


CH.  LVI.]  THE   VISUAL   PURPLE  813 

Binocular  colour-mixture. — By  means  of  the  stereoscope,  l)inocular 
comlnnatioiis  of  colour  can  be  obtained.  Thus,  if  one  eye  is  exposed 
to  a  red  disc,  and  the  corresponding  portion  of  the  other  eye  to  a 
yellow  one,  the  mind  usually  perceives  one  disc  of  an  orange  tint; 
but  frequently,  especially  if  there  be  differences  of  brightness  or  of 
form  in  the  two  objects,  we  notice  that  "  rivalry  of  the  fields  of 
vision  "  occurs,  first  one  then  the  other  disc  rising  into  consciousness. 
A  stereoscopic  combination  of  black  and  white  produces  the  appear- 
ance of  metallic  lustre ;  this  is  very  beautifully  shown  with  figures  of 
crystals,  one  black  on  a  white  ground,  the  other  white  on  a  black 
ground.  Probably  the  combination  of  black  and  white  is  interpreted 
as  indicating  a  polished  surface,  because  a  polished  surface  reflects 
rays  irregularly  so  that  the  two  eyes  receive  stimuli  of  unequal 
intensity. 

Changes  in  the  Retina  during  Activity. 

The  method  by  which  a  ray  of  light  is  able  to  stimulate  the 
endings  of  the  optic  nerve  in  the  retina  in  such  a  manner  that  a 
visual  sensation  is  perceived  by  the  cerebrum,  is  not  yet  understood. 
It  is  supposed  that  the  change  effected  by  the  agency  of  the  light 
which  falls  upon  the  retina  is  in  fact  a  chemical  alteration  in  the 
protoplasm,  and  that  this  change  stimulates  the  optic  nerve-endings. 
The  discovery  of  a  certain  temporary  reddish-purple  pigmentation  of 
the  outer  limbs  of  the  retinal  rods  in  certain  animals  {e.g.,  frogs) 
which  had  been  killed  in  the  dark,  forming  the  so-called  rhodopsin  or 
visual  purple,  appeared  likely  to  offer  some  explanation  of  the 
matter,  especially  as  it  was  also  found  that  the  pigmentation  dis- 
appeared when  the  retina  was  exposed  to  light,  and  reappeared  when 
the  light  was  removed,  and  also  that  it  underwent  distinct  changes 
of  colour  when  other  than  white  light  was  used.  It  was  also  found 
that  if  the  operation  were  performed  quickly  enough,  the  bleached 
image  of  a  bright  object  (optogram)  might  be  fixed  on  the  retina  by 
soaking  the  retina  of  an  animal  which  has  been  killed  in  the  dark,  in 
alum  solution. 

The  rhodopsin  is  derived  in  some  way  from  the  black  pigment 
(melanin  or  fuscin)  of  the  polygonal  epithelium  of  the  retina,  since 
the  colour  is  not  renewed  after  bleaching,  if  the  retina  is  detached 
from  its  pigment  layer. 

Certain  pigments,  not  sensitive  to  light,  are  contained  in  the 
inner  segments  of  the  cones.  These  are  oU  globules  of  various 
colours,  red,  green,  and  yellow,  called  chromophanes,  and  are  found 
in  the  retinae  of  marsupials  (but  not  other  mammals),  birds,  reptiles, 
and  fishes.  Nothing  is  known  about  the  yellow  pigment  of  the 
yellow  spot. 

Another  change  produced  by  the  action  of  the  light  upon  the 


814  THE    EYE   AND    VISION  [CH.  LVI. 

retina  is  the  movement  of  the  pigment  cells.  On  being  stimulated  by 
light  the  granules  of  pigment  in  the  cells  which  overlie  the  outer 
part  of  the  rod  and  cone  layer  of  the  retina  pass  down  into  the 
processes  of  the  cells,  which  hang  down  between  the  rods :  these 
inelanin  ov  fuscin  granules  are  generally  rod-shaped,  and  look  almost 
like  crystals.  In  addition  to  this,  a  movemetit  of  the  cones  and  possibly 
of  the  rods  occurs,  as  has  been  already  mentioned ;  in  the  light  the 
cones  shorten,  and  in  the  dark  they  lengthen  (Engelmann). 

Dewar  and  McKeudrick  were  the  first  to  show  that  the  chemical 
changes  in  the  retina  are  accompanied  with  an  electrical  change. 

Red  light  has  no  ac±ion  on  visual  purple ;  the  maximum  bleaching  eflFect  takes 
place  in  greenish-yellow  light.  Now.  when  the  Uving  eye  is  brought  into  a  condition 
of  '"dark  adaptation,"  that  is,  when  the  retina  has  become  adapted  to  hght  of  low 
intensity,  the  colours  of  the  spectrum  alter  in  brightness  ;  the  red  end  becomes 
shortened  and  much  darker :  the  blue  end  becomes  brighter,  and  the  region  of 
maximum  brightness  is  in  the  green.  This  change  of  brightness  with  change  of 
adaptation  is  absent  in  the  fovea,  where  there  are  no  rods.  The  selective  action  of  the 
colours  of  the  spectrum  on  the  visual  purple  is  so  strikingly  similar  to  the  altered 
conditions  of  brightness  just  described,  that  changes  in  the  visual  purple  of  the  rods 
have  been  supposed  to  be  the  cause  of  sensations  excited  by  feeble  illumination  (i.e., 
in  the  "  dark-adapted  "  eyej,  while  the  cones  are  affected  under  more  ordinary  con- 
ditions of  Uluimnation.  This  conclusion  gains  support  from  several  interesting  facts. 
Visual  purple  is  specially  abundant  in  the  retinae  of  almost  all  animals  whose  habits 
are  nocturnal,  or  who  hve  underground.  Further,  if  the  intensity  of  a  colour  stimulus 
is  gradually  increased,  it  at  first  is  too  faint  to  produce  any  sensation ;  then  it  pro- 
duces a  sensation  of  grejTiess,  and  at  last  the  colour  itself  is  seen ;  the  interval 
between  the  appearance  of  the  grey  or  white-black  effect  and  of  the  true  colour 
effect  of  the  stimulus  is  spoken  of  as  the  " pJioto-'hro-matic  int'^rcal."  Red  hght  has 
no  effect  on  visual  purple,  and  has  no  photonhromatic  interval  (that  is,  it  appears 
either  red  or  nothing),  and  according  to  several  observers,  there  is  no  such  interval 
at  the  fovea,  where  the  rods  and  therefore  \isual  purple,  are  absent  Thirdly,  a  very 
similar  effect  has  been  described  by  M'DougaU,  when  the  retina  is  momentarily 
stimulated  by  a  coloured  light :  the  sensation  arising  from  the  stimulus  is  followed 
by  a  series  of  "  primary  responses  "  or  after-sensations ;  the  first  members  of  the 
series  have  the  same  colour  as  the  stimulus,  and  these  are  sometimes  followed  by  a 
series  of  colourless  (grey)  sensations  :  these  grey  sensations  are  only  present  outside 
the  fovea,  and  under  conditions  of  *  •  dark  adaptation  "  are  absent  with  red  and  bright- 
est with  green  stimuh.  Here  again  we  are  able  to  differentiate  between  a  \isual- 
purple  (rod)  effect,  and  a  cone  effect,  the  former,  active  under  conditions  of  feeble 
illumination,  affected  most  by  green,  and  unaffected  by  red  light,  and  yielding  colour- 
less sensations  ;  the  latter  being  more  specially  concerned  in  developing  sensations 
of  colour  under  conditions  of  adaptation  to  ordinary  light  The  fovea  centrahs  thus 
becomes  the  region  where  the  colours  of  objects  are  best  distinguishable,  and  where 
with  ordinary  lUummation  \isual  acuity  is  most  marked.  In  the  dark,  however, 
extra-foveal  (rod)  vision  is  more  sensitive  than  fo^eal  (cone)  \-ision  :  astronomers  see 
faint  stars  more  readily  in  the  periphery  of  the  field  of  vision. 

Two  abnormal  conditions  may  be  described  here,  for  they  throw  light  on  these 
phenomena.  In  cases  oi  achromatopsia  itotal  colour  blindness  i  the  spectrum  is  seen 
as  a  band  of  light  differing  only  in  brightness  ;  the  region  of  maximum  brightness 
is  the  same  as  in  extra-foveal  vision  of  the  normal  eye  :  in  many  of  these  cases  there 
is  a  central  scotoma  ibhnd  spots  that  is,  the  rodless  fovea  is  blind  ;  there  isre  duced 
acuity  of  vision  as  in  the  "  dark-adapted  "  eye,  and  photophobia  (fear  of  strong  hght): 
nystagmus  (oscillating  movements  of  the  eye)  also  occurs,  due  to  absence  of  an  area  of 
distinct  vision.  We  are  thus  in  typical  cases  of  achromatopsia  dealing  with  cases 
of  cone  blindness.  In  nyctalopia  (night  blindness)  on  the  other  hand,  we  meet  the 
converse  condition.    Here  there  is  an  abnormal  slowness  of  "dark  adaptation,"  and 


en.  LVI.]  MOVEMENTS    OF   THE   EYEBALL  815 

ii  pathological  chaufje  known  as  relhiitis  pigmfutosa  is  present,  suggesting  an  im- 
paired function  of  the  visual  purple.  Pilocarpine  has  been  found  an  effective  drug 
in  such  casts,  and  this  is  also  interesting  because  it  hastens  the  regeneration  of  visual 
purple  in  the  extirpated  eye. 

The  electrical  variations  m  the  retina  under  the  influence  of  light  have  been 
recently  reinvestigated  by  Waller.  The  excised  eyeball  of  a  frog  is  led  off  by  non- 
polarisable  electrodes  to  a  galvanometer.  One  electrode  is  placed  on  the  front,  the 
other  on  the  back  of  the  eye.  If  the  eyeball  is  quite  fresh,  a  current  is  observed 
passing  through  the  eyeball  from  back  to  front.  ^Vhen  light  falls  on  the  eye  this 
current  is  increased  ;  on  shutting  off  the  light  there  is  a  momentary  further  increase, 
and  then  the  current  slowly  returns  back  to  its  previous  condition.  Waller  explains 
this  by  supposing  that  anabolic  changes  in  the  eye  predominate  during  stimulation 
by  light.  With  the  onset  of  darkness,  the  katabolic  changes  cease  at  once,  and  the 
anabolic  more  slowly  ;  hence  a  further  positive  variation. 

As  already  stated,  the  current  in  a  fresh  eyeball  passes  from  back  to  front  before 
the  stimulus  is  applied,  but  this  cannot  be  regarded  as  a  true  current  of  rest,  but  as 
a  current  due  to  previous  action  which  very  slowly  subsides.  When  this  has 
subsided,  the  true  current  of  rest  is  from  cornea  to  fundus,  />.,  it  is  hke  that  of  the 
skin  (see  p.  484)  ingoing — the  response  to  stimulation  is  like  that  of  the  skin  out- 
going. Waller  has  also  studied  the  electrical  responses  of  the  eyeball  to  other 
methods  of  stimulation ;  if  electrical  currents  are  employed,  and  the  eyeball  is  still 
healthy,  the  response  is  always  an  outgoing  current,  whatever  may  be  the  direction 
of  the  electrical  current  used  as  the  stimulus.  These  currents  of  action  are  no  doubt 
mainly  of  retinal  origin,  but  later  Waller  showed  that  the  anterior  portions  of  the 
eye,  especially  the  crystalline  lens,  participate  in  their  causation.  The  response  of 
the  eye  to  non-luminous  stimuli  lasts  some  time,  and  is  spoken  of  as  a  "  blaze  current. " 
An  analogous  response  has  been  seen  in  skin,  plant-tissues,  etc. 

Gotch  has  studied  the  photo-electric  changes  in  the  frog's  eyeball  with  the 
capillary  electrometer.  He,  hke  Waller,  draws  attention  to  the  long  latent  period  and 
sustained  character  of  the  response.  The  photo-electric  changes  are  all  monophasic 
effects,  whether  produced  by  illumination,  or  by  shutting  off  the  light.  Gotch 
suggests  there  are  two  chemical  substances  in  the  retina,  one  of  which  reacts  to  light, 
the  other  to  darkness.  Each  reaction  is  a  change  of  the  same  type,  but  for  the  change 
to  occur  markedly,  the  eye  must  be  previously  adapted,  i.e.,  the  substances  must 
undergo  a  phase  of  metabolism  under  conditions  opposite  to  those  which  evoke  the 
reaction  effects.  Observations  with  red  and  green  light  do  not  support  the  view 
that  the  photo-chemical  changes  are  of  opposite  characters,  for  the  photo-electric 
change  is  always  in  the  same  direction,  differing  only  in  period  of  latency,  that  for 
red  being  the  longer. 

Movements  of  the  Eyeball 

Frotrusion  of  the  eyeballs  occurs  (1)  when  the  blood-vessels  of 
the  orbit  are  congested ;  (2)  when  contraction  of  the  plain  muscular 
fibres  of  the  capsule  of  Tenon  takes  place ;  these  are  innervated  by 
the  cervical  sympathetic  nerve;  and  (3)  in  the  disease  called 
exophthalmic  goitre. 

Retraction  occurs  (1)  when  the  lids  are  closed  forcibly;  (2) 
when  the  blood-vessels  of  the  orbit  are  comparatively  empty ; 
(3)  when  the  fat  in  the  orbit  is  reduced  in  quantity,  as  during 
starvation;  and  (4)  on  section  or  paralysis  of  the  cervical  sympa- 
thetic nerves. 

The  most  important  movements,  however,  are  those  produced  by 
the  six  ocular  muscles. 

The  internal  rectus  turns  the  eyeball  inwards,  the  external  rectus 


816  THE   EYE   AND    VISION  [CH.  LVI. 

turns  it  outwards.  If  the  superior  rectus  acted  alone,  it  would  turn 
the  eyeball  not  only  upwards,  but  owing  to  the  sloping  direction  of 
the  muscle,  the  eyeball  would  be  turned  inwards  also;  in  turning 
the  eyeball  directly  upwards,  this  inward  movement  is  arrested  by 
the  outward  tendency  of  the  inferior  oblique.  Similarly,  in  turning 
the  eyeball  directly  downwards,  the  inferior  rectus  acts  in  conjunc- 
tion with  the  superior  oblique.  Movements  in  intermediate  directions 
are  produced  by  other  combinations  of  the  muscles. 

These  muscles  are  all  supplied  by  the  third  nerve  except  the 
superior  oblique,  which  is  supplied  by  the  fourth  and  the  external 
rectus  by  the  sixth  nerve. 

The  muscles  of  the  two  eyes  act  simultaneously,  so  that  images 
of  the  objects  looked  at  may  fall  on  corresponding  points  of  the 
two  retinae.  The  inner  side  of  one  retina  corresponds  to  the 
outer  side  of  the  other,  so  that  any  movement  of  one  eye  inwards 
must  be  accompanied  by  a  movement  of  the  other  eye  outwards. 
If  one  eyeball  is  forcibly  fixed  by  pressing  the  finger  against  it  so 
that  it  cannot  follow  the  movement  of  the  other,  the  result  is 
double  vision  {diplopia),  because  the  image  of  the  objects  looked  at 
will  fall  on  points  of  the  two  retinae  which  do  not  correspond.  The 
same  is  experienced  in  a  squint,  until  the  subject  learns  to  disregard 
the  image  from  one  eye. 

If  the  external  rectus  is  paralysed,  the  eye  will  squint  inwards ; 
if  this  occurs  in  the  right  eye  the  false  image  wUl  lie  on  the  left  side 
of  the  yellow  spot,  and  appear  in  the  field  of  vision  to  the  right  of 
the  true  image.  If  the  third  nerve  is  paralysed,  the  case  is  a  more 
complicated  one :  owing  to  the  paralysis  of  the  levator  palpebrse 
superioris,  the  patient  will  be  unable  to  raise  his  upper  lid  (ptosis), 
and  so  in  order  to  see  will  walk  with  his  chin  in  the  air.  If  the 
paralysis  is  on  the  right  side,  the  eyeball  will  squint  downwards  and 
to  the  right ;  the  false  image  will  be  formed  below  and  to  the  right 
of  the  yellow  spot,  and  the  apparent  image  in  the  field  of  vision  will 
consequently  appear  above  and  to  the  left  of  the  true  image,  and 
owing  to  the  squint  being  an  oblique  one,  the  false  image  will  slant 
in  a  corresponding  direction. 

Various  Positions  of  the  Eyeballs. 

All  the  movements  of  the  eyeball  take  place  around  the  point  of 
rotation,  which  is  situated  1'77  mm.  behind  the  centre  of  the  visual 
axis,  or  10*9  mm.  behind  the  front  of  the  cornea. 

The  three  axes  around  which  the  movements  occur  are : — 

1.  The  visual  or  antero-posterior  axis.     (A  P,  fig.  595). 

2.  The  transverse  axis,  which  connects  the  points  of  rotation  of 
the  two  eyes.     (Tr,  fig.  595). 


en.  Lvi.] 


POSITIONS    OF   THE    EYEBALLS 


817 


3.  The  vertical  axis,  which  passes  at  right  angles  to  the  other 
two  axes  through  their  point  of  intersection. 

The  line  which  connects  the  fixed  point  in  the  outer  world  at 
which  the  eye  is  looking  to  the  point  of  rotation  is  called  the  visual 


Fig.  595. 


-Diagram  of  the  axes  &f  rotation  to  the  eye.    The  thin  lines  indicate  axes  of  rotation,  the 
thick  the  position  of  muscular  attachment. 


line.  The  plane  which  passes  through  the  two  visual  lines  is  called 
the  visual  plane. 

The  various  positions  of  the  eyeballs  are  designated  primary, 
secondary,  and  tertiary. 

The  primary  position  occurs  when  both  eyes  are  parallel,  the 
visual  lines  being  horizontal  (as  in  looking  at  the  horizon). 

Secondary  positions  are  of  two  kinds: — 

(1)  The  visual  lines  are  parallel,  but  directed  either  upwards  or 
downwards  from  the  horizontal  (as  in  looking  at  the  sky). 

(2)  The  visual  lines  are  horizontal,  but  converge  towards  one 
another  (as  in  looking  at  a  small  object  near  to  and  on  the  same 
level  as  the  eyes). 

Tertiary  positions  are  those  in  which  the  visual  lines  are  not 
horizontal,  and  converge  towards  one  another  (as  in  looking  at  the 
tip  of  the  nose). 

It  is  possible  to  conceive  positions  of  the  eyeballs  in  which  the 
visual  lines  diverge  from  one  another;  but  such  positions  do  not 
occur  in  normal  vision  in  man. 

Both   eyes   are    moved    simultaneously,   even   if    one   of   them 

3F 


818 


THE    EYE   AND    VISION 


[CH.  LVI. 


happens  to  be  blind.  They  are  moved  so  that  the  object  in  the 
outer  world  is  focussed  on  the  two  yellow  spots,  or  other  corre- 
sponding points  of  the  two  retinae.  The  images  which  do  not  fall 
on  corresponding  points  are  seen  double,  but  these  are  to  a  great 
extent  disregraded  by  the  brain,  which  pays  particular  attention  to 
those  images  which  fall  on  corresponding  points. 

The  accompanying  diagrams  will  assist  us  in  understanding 
what  is  meant  by  corresponding  or  identical  points  of  the  two 
retinae. 

If  E  and  L  (fig.  596)  represent  the  right  and  left  retinae 
respectively,  0  and  0'  the  two  yellow  spots  are  identical ;  so  are  A 


Fig.  596. — Identical  points  of  the  retina;. 

and  A',  both  being  the  same  distance  above  0  and  0'.  But  the 
corresponding  point  to  B  on  the  inner  side  of  0  in  the  right  retina, 
is  B',  a  point  to  the  same  distance  on  the  outer  side  of  0'  in  the  left 
retina ;  similarly  C  and  C  are  identical.  The  two  blind  spots  X  and 
X'  are  not  identical. 

Fig.  597  shows  the  same  thing  in  rather  a  different  way ;  A  and 
B  represent  horizontal  sections  through  the  two  retinae;  the  points 

a  a',  b  b',  and  c  c',  being  identicaL 
In  the  lower  part  of  the  diagram  is 
shown  the  wa^  in  which  the  brain 
combines  the  images  in  the  two  retinae, 
one  overlapping  so  as  to  coincide  with 
the  other. 

The  Horopter  is  the  name  given  to 
the  surface  in  the  outer  world  which 
contains  all  the  points  which  fall  on 
the  identical  points  of  the  retinae. 
The  shape  of  the  horopter  will  vary  with  the  position  of  the  eye- 
balls, in  the  primary  position,  and  in  the  first  variety  of  the 
secondary  position,  the  visual  lines  are  parallel ;  hence  the  horopter 
will  be  a  plane  at  an  infinite  distance. 

In  the  other  variety  of  the  secondary  position,  and  in  tertiary 


Fig.  597. — Diagram  to  show  the  correspond 
ing  parts  of  both  retinae. 


CH.  LVL] 


PATHS  IN  THE  OPTIC  NERVES 


819 


positions  in  which  the  visual  lines  converge,  as  when  looking  at  a 

near  object,  the  horopter  is  a  circle  (fig.  598)  which  passes  through  the 

nodal  points  of  the  two  eyes,  and  through 

the  fixed  point  (I)  in  the  outer  world  at 

which  the   eyes   are   looking,  and  which 

will  consequently  fall  on  the  two  yellow 

spots  (0  and   0').     All   other   points  in 

this  circle  (II,  III)  will  fall  on  identical 

points  of  the   retinae.     The  image  of  II 

will  fall  on  A  and  A' ;  of  III  on  B  and  B' ; 

it  is  a  simple  mathematical  problem  to 

prove  that  OA  =  O'A',  and  OB  =  O'B'. 

In  those  animals  in  which  the  eyes 
are  lateral  in  position,  and  the  visual 
lines  diverge,  the  problem  of  binocular 
vision  is  a  very  different  one  (see  also 
p.  727). 


O    A         ti       o 

Fig.  598.— The  Horopter,  when  the 
eyes  are  convergent. 


Left   Retina 


Right  Retina 


Nervous  Paths  in  the  Optic  Nerves. 

The  correspondence  of  the  two  retinae  and  of  the  movements  of 
the  eyeballs  is  produced  by  a  close  connection  of  the  nervous  centres 
controlling  these  phenomena,  and  by  the  arrangement  of  the  nerve- 
fibres  in  the  optic  nerves.  The  crossing  of  the  nerve-fibres  at  the 
optic  chiasma  is  incomplete,  and  the  next  diagram  (fig.  599) 
gives  a  simple  idea  of  the  way  the  fibres  go. 

It  will  be  seen  that  it  is  only  the  fibres  from  the  inner  portions 
of  the  retinae  that  cross;  and  that  those 
represented  by  continuous  lines  from  the 
right  side  of  the  two  retinae  ultimately  reach 
the  right  hemisphere,  and  those  represented 
by  interrupted  lines  from  the  left  side  of  the 
two  retinae  ultimately  reach  the  left  hemi- 
sphere. The  two  halves  of  the  retinae  are 
not,  however,  separated  by  a  hard-and-fast 
line  from  one  another;  this  is  represented 
by  the  two  halves  being  depicted  as  slightly 
overlapping,  and  this  comes  to  the  same 
thing  as  saying  that  the  central  region  of 
each  retina  is  represented  in  each  hemisphere. 
The  part  of  the  hemisphere  concerned  in 
vision  is  the  occipital  lobe,  and  the  reader 
should  turn  back  to  our  previous  consideration  of  this  subject  in 
connection  with  cen  bral  localisation,  the  phenomena  of  hemian- 
opsia (p.  703)  and  the  conjugate  deviation  of  head  and  eyes 
(pp.  703,  717). 


Left 
Hemisphere 


Right 
Hemisphere 


Fig.  599.— Course  of  fibres  at 
optic  chiasma. 


820 


THE  EYE   AND   VISION 


[CH.  LVI. 


Fig.  600,  though  diagrammatic,  will  assist  the  reader  in  more 
fully  comprehending  the  paths  of  visual  impulses,  and  the  central 
connections  of  the  nerves  and  nerve-centres  concernediin  the  process. 
The  fibres  from  the  retina  to  the  external  geniculate  body  end 
there  by  arborising  around  its  cells,  and  a  fresh  relay  of  fibres  from 


F[0.  600. — Relations  of  nerve  cells  and  fibres  of  visual  apparatus.    (Schafer.) 

these  cells  passes  in  the  posterior  part  of  the  internal  capsule  to  the 
cortex  of  the  occipital  lobe.  Those  to  the  anterior  corpus  quadrige- 
minum  are  continued  on  by  a  fresh  relay  to  the  nuclei  of  the  nerves 
concerned  in  eye-movements  (represented  by  the  oculo-motor  nucleus 
in  the  diagram) ;  the  axons  of  the  cortical  cells  pass  to  the  tegmentum, 
whence  a  fresh  relay  continues  the  impidse  to  the  oculo-motor 
nucleus. 

Sherrington's  observations  on  binocular  flicker  have  shown  that  there  are 
difficulties  in  accepting  fig.  600  as  a  complete  anatomical  basis  for  the  psychological 
processes  involved  in  binocular  vision,  although  it  is  probably  correct  so  far  as  the 
motor  mechanisms  involved  are  concerned. 


Visual  Judgments. 

The  psychical  or  mental  processes  which  constitute  the  visual 
sensation  proper  have  been  studied  to  a  far  greater  degree  than  ia 
possible  in  connection  with  other  forms  of  sensation. 


CH.  LVI.]  VISUAL  JUDGMENTS  821 

We  have  already  seen  that  in  spite  of  the  reversion  of  the  image 
in  the  retina,  the  mind  sees  objects  in  their  proper  position ;  this 
is  (3xplained  on  p.  792. 

We  are  also  not  conscious  of  the  blind  spot.  This  is  partly  due 
to  the  fact  that  those  images  which  fall  on  the  blind  spot  of  one  eye 
are  not  focussed  there  in  the  other  eye.  But  even  when  one  looks 
at  objects  with  one  eye,  there  is  no  blank,  for  the  reason  explained 
on  p.  802. 

Our  estimate  of  the  size  of  various  objects  is  based  partly  on  the 
visual  angle  (p.  791)  under  which  they  are  seen,  but  much  more  on  the 
estimate  we  form  of  their  distance.  Thus  a  lofty  mountain  many 
miles  off  may  be  seen  under  the  same  visual  angle  as  a  small  hill 
near  at  hand,  but  we  infer  that  the  former  is  much  the  larger 
object  because  we  know  it  is  much  farther  off  than  the  hill.  Our 
estimate  of  distance  is  often  erroneous,  and  consequently  the 
estimate  of  size  also.  Thus  persons  seen  walking  on  the  top  of 
a  small  hill  against  a  clear  twilight  sky  appear  unusually  large, 
because  we  over-estimate  their  distance,  and  for  similar  reasons 
most  objects  in  a  fog  appear  immensely  magnified.  The  same  mental 
process  gives  rise  to  the  idea  of  depth  in  the  field  of  vision ;  this 
idea  is  fixed  in  our  mind  principally  by  the  circumstance  that,  as 
we  ourselves  move  forwards,  different  images  in  succession  become 
depicted  on  our  retina,  so  that  we  seem  to  pass  between  these  images, 
which  to  the  mind  is  the  same  thing  as  passing  between  the  objects 
themselves. 

The  action  of  the  sense  of  vision  in  relation  to  external  objects 
is,  therefore,  quite  different  from  that  of  the  sense  of  touch.  The 
objects  of  the  latter  sense  are  immediately  present  to  it ;  and 
our  own  body,  with  which  they  come  in  contact,  is  the  measure  of 
their  size.  The  part  of  a  table  touched  by  the  hand  appears  as  large 
as  the  part  of  the  hand  receiving  an  impression  from  it,  for  the  part 
of  our  body  in  which  a  sensation  is  excited,  is  here  the  measure  by 
which  we  judge  of  the  magnitude  of  the  object.  In  the  sense  of 
vision,  on  the  contrary,  the  images  of  objects  are  mere  fractions  of 
the  objects  themselves,  realised  upon  the  retina,  the  extent  of  which 
remains  constantly  the  same.  But  the  imagination,  which  analyses 
the  sensations  of  vision,  invests  the  images  of  objects,  together  with 
the  whole  field  of  vision  in  the  retina,  with  very  varying  dimensions ; 
the  relative  size  of  the  image  in  proportion  to  the  whole  field  of 
vision,  or  of  the  affected  parts  of  the  retina  to  the  whole  retina, 
alone  remains  unaltered. 

The  estimation  of  the  form  of  bodies  by  sight  is  the  result  partly 
of  the  mere  sensation,  and  partly  of  the  association  of  ideas.  Since 
the  form  of  the  images  perceived  by  the  retina  depends  wholly  on 
the  outline  of  the  part  of  the  retina  affected,  the  sensation  alone  is 


822 


THE   EYE   AND    VISION 


[CH.  LVI. 


adequate  to  the  distinction  of  superficial  forms  from  each  other,  as 
of  a  square  from  a  circle.  But  the  idea  of  a  solid  body  like  a  sphere, 
or  a  cube,  can  only  be  attained  by  the  action  of  the  mind  construct- 
ing it  from  the  different  superficial  images  seen  in  different  positions 
of  the  eye  with  regard  to  the  object,  and,  as  shown  by  Wheatstone 
and  illustrated  in  the  stereoscope,  from  two  different  perspective  pro- 
jections of  the  object  being  presented  simultaneously  to  the  mind  by 
the  two  eyes. 

Thus,  if  a  cube  is  held  at  a  moderate  distance  before  the  eyes, 
and  viewed  with  each  eye  successively  while  the  head  is  kept 
perfectly  steady,  a  (fig.  601)  will  be  the  picture  presented  to  the 
right  eye,  and  B  that  seen  by  the  left  eye.  Wheatstone  has  shown 
that  on  this  circumstance  depends  in  a  great  measure  our  conviction 
of  the  solidity  of  an  object,  or  of  its  projection  in  relief.     If  different 


'      \ 


Fig.  GOl. — Diagrams  to  illustrate  how  a  judgment  of  a  figure  of  three  dimensions  is  obtained. 


perspective  drawings  of  a  solid  body,  one  representing  the  image 
seen  by  the  right  eye,  the  other  that  seen  by  the  left  (for  example, 
the  drawing  of  a  cube.  A,  B,  fig.  601)  be  presented  to  corresponding 
parts  of  the  two  retinse,  as  may  be  readily  done  by  means  of  the 
stereoscope,  the  mind  will  perceive  not  merely  a  single  representa- 
tion of  the  object,  but  a  body  projecting  in  relief,  the  exact  counter- 
part of  that  from  which  the  drawings  were  made. 

By  transposing  two  stereoscopic  pictures  a  reverse  effect  is  pro- 
duced; the  elevated  parts  appear  to  be  depressed,  and  vice  versd. 
An  instrument  contrived  with  this  purpose  is  termed  a  pseudoscope. 
Viewed  with  this  instrument  a  bust  appears  as  a  hollow  mask,  and 
as  may  readily  be  imagined  the  effect  is  most  bewildering. 

The  clearness  with  which  the  details  of  an  object  is  perceived 
irrespective  of  accommodation,  would  appear  to  depend  largely  on 
the  number  of  rods  and  cones  which  its  retinal  image  covers.  Hence 
the  nearer  an  object  is  to  the  eye  (within  moderate  limits)  the  more 
clearly  are  all  its  details  seen.  Further,  if  we  want  carefully  to 
examine  any  object,  we  always  direct  the  eyes  straight  to  it,  so  that 
its  image  shall  fall  on  the  two  yellow  spots,  where  an  image  of  a 
given  area  will  cover  a  larger  number  of  cones  than  anywhere  else 


CH.  LVI.] 


VISUAL   JUDGMENTS 


823 


in  the  retina.     Moreover,  as  previously  pointed  out,  each  tone  in  the 
macula  lutea  is  connected  to  a  separate  chain  of  neurons. 

The  importance  of  hinocular  vision  is  very  great.  If  an  ohject  is 
looked  at  with  one  eye  only,  it  is  impossible  to  estimate  its  distance 
by  the  sense  of  vision  alone.  For  instance,  if  one  eye  is  closed 
and    the   other   looks    at   a    wire   or   bar,   it   is   impossible   to   tell 

ABC 


D 


Fifi.  602.— Diagrams  to  illustrate  visual  illusions, 


whether,  if  some  one  drops  a  small  object,  it  falls  in  front  of  or 
behind  the  bar. 

Visual  judgments  are  not  always  correct;  there  are  a  large 
number  of  puzzles  and  toys  which  depend  on  visual  illusions.  One 
or  two  of  the  best  known  are  represented  in  the  accompanying 
diagrams. 

In  fig.  602,  A,  B,  and  c  are  of  the  same  size ;  but  A  looks  taller 
than  B,  while  c  appears  to  cover  a  less  area  than  either.     The  sub- 


y/A^'7/'//,^^y7. 


SSSiSJ^J^^>:SSSii^SSSS:^^ 


'mmmmmmmm. 

Fio.  603. — Parallel  puzzle. 

division  of  a  space  or  line  increases  its  apparent  size  or  length. 
In  fig.  602  D,  ah  is  equal  to  Ic.  Vertical  distances  also  are  usually 
over-estimated.  In  fig.  603,  the  horizontal  lines  are  parallel,  though 
they  do  not  appear  so,  owing  to  the  mind  being  distracted  by  the 
intercrossing  lines. 


CHAPTER  LVII 

TROPHIC   NERVES 

Nerves  exercise  a  trophic  or  nutritive  influence  over  the  tissues  and 
organs  they  supply.  Some  nerves  increase  the  building-up  stage  of 
metabolism ;  these  are  termed  anabolic.  Such  a  nerve  is  the  vagus 
in  reference  to  the  heart ;  when  it  is  stimvdated  the  heart  beats 
more  slowly  or  may  stop,  and  is  thus  enabled  to  rest  and  repair  its 
waste.  The  opposite  kind  of  nerves  (katabolic)  are  those  which  lead 
to  increase  of  work,  and  so  mcreased  wear  and  tear  and  formation  of 
waste  products.  Such  a  nerve  in  reference  to  the  heart  is  the 
sympathetic. 

There  has  been  considerable  diversity  of  opinion  as  to  whether 
trophic  nerve-fibres  are  a  distinct  anatomical  set  of  nerve-fibres,  or 
whether  all  nerves  in  addition  to  their  other  functions  exercise  a 
trophic  influence. 

When  a  nerve  going  to  an  organ  is  cut,  the  wasting  of  the  nerve 
itself  beyond  the  cut  constitutes  what  we  have  learnt  to  call 
Wallerian  degeneration,  but  the  wasting  process  continues  beyond 
the  nerve ;  the  muscles  it  supplies  waste  also,  and  waste  much  more 
rapidly  than  can  be  explained  by  simple  disuse.  The  same  is  seen 
in  the  testicle  after  section  of  the  spermatic  cord ;  and  in  the  disease 
of  joints  called  Charcot's  disease,  the  trophic  changes  are  to  be 
explained  by  disease  of  the  nerves  supplying  them. 

From  these,  and  numerous  other  instances  that  might  be  given, 
there  is  no  question  that  nerves  do  exert  a  trophic  influence; 
the  question,  however,  whether  this  is  due  to  special  nerve-fibres 
has  been  chiefly  worked  out  in  connection  with  the  fifth  cranial 
nerve. 

After  the  division  of  this  nerve  there  is  loss  of  sensation  in  the 
corresponding  side  of  the  face:  the  cornea  in  two  or  three  days 
begins  to  get  opaque,  and  this  is  followed  by  a  slow  inflammatory 
process  which  may  lead  to  a  destruction  not  only  of  the  cornea,  but 
of  the  whole  eyeball.  The  same  is  seen  in  man ;  when  the  fifth  nerve 
is   diseased   or   pressed   upon    by  a   tumour  beyond  the  Gasserian 


CII.  LVII.]  TROPHIC    NEltVES  825 

ganglion,  the  result  is  loss  of  sensation  iu  the  face  and  conjunctiva, 
an  eruption  (herpes)  appears  on  the  face,  and  ulceration  of  the 
cornea  leading  in  time  to  disintegration  of  the  eyeball  may  occur  too. 
In  disease  such  as  haemorrhage  in  the  spinal  ganglia  there  is  a  similar 
herpetic  eruption  on  the  skin  (shingles). 

In  the  case  of  the  fifth  nerve  the  evidence  that  there  are  special 
nerve-fibres  to  which  these  trophic  changes  are  due,  is  an  experiment 
by  Meissner  and  Biittner,  who  found  that  division  of  the  most 
internal  fibres  is  most  potent  in  producing  them. 

Those,  however,  who  do  not  believe  in  special  trophic  nerves, 
attribute  the  changes  in  the  eyeball  to  its  loss  of  sensation.  Dust, 
etc.,  is  not  felt  by  the  cornea,  and  is  therefore  allowed  to  accumulate 
and  set  up  inflammation.  This  is  supported  by  the  fact  that  if  the 
eyeball  is  protected  by  sewmg  the  eyelids  together  the  trophic  results 
do  not  ensue.  On  the  other  hand,  in  paralysis  of  the  seventh  nerve, 
the  eyeball  is  much  more  exposed,  and  yet  no  trophic  disorders 
follow. 

Others  have  attributed  the  change  to  increased  vascularity  due 
to  disordered  vaso-motor  changes ;  against  this  is  the  fact  that  in 
disease  of  the  cervical  sympathetic,  the  disordered  vaso-motor 
phenomena  which  ensue  do  not  lead  to  the  disorders  of  nutrition  we 
have  described.  Nevertheless  in  trophic  disorders,  it  is  very  difficult 
to  be  sure  that  the  disordered  metabolism  is  not  in  part  due  to 
vascular  disturbances. 

There  can,  therefore,  be  but  little  doubt  that  we  have  to  deal 
with  the  trophic  influence  of  nerves ;  *  but  the  dust,  etc.,  which  falls 
on  the  cornea  must  be  regarded  as  the  exciting  cause  of  the  ulceration. 
The  division  or  disease  of  the  nerve  acts  as  the  predisposing  cause. 
The  eyeball  is  more  than  usually  prone  to  undergo  inflammatory 
changes,  with  very  small  provocation. 

The  same  explanation  holds  in  the  case  of  the  influence  of  the 
vagi  on  the  lungs.  If  both  these  nerves  are  divided,  the  animal 
usually  dies  within  a  week  or  a  fortnight  from  a  form  of  pneumonia 
called  vagus  pneumonia,  in  which  gangrene  of  the  lung  substance  is 
a  marked  characteristic.  Here  the  predisposing  cause  is  the  division 
of  the  trophic  fibres  in  the  pneumogastric  nerves ;  the  exciting  cause 
is  the  entrance  of  particles  of  food  into  the  air  passages,  which  on 
account  of  the  loss  of  sensation  in  the  larynx  and  neighbouring  parts 
are  not  coughed  up.  Another  trophic  disturbance  that  follows 
division  of  the  vagi  is  fatty  degeneration  of  the  heart. 

Many  bedsores  are  due  to  prolonged  confinement  in  bed  with 
bad  nursing ;  these  are  of  slow  onset.  But  there  is  one  class  of  bed- 
sores which  are  acute;    these  are  especially  met  with  in  cases  of 

*  The  proof,  however,  that  there  are  distinct  nerve-fibres  anatomically  is  not 
very  conclusive. 


826  TROPHIC   NERVES  [CH.  LVII. 

paralysis,  due  to  disease  of  the  spinal  cord ;  they  come  on  in  three  or 
four  days  after  the  onset  of  the  paralysis  in  spite  of  the  most  careful 
attention ;  they  cannot  be  explained  by  vaso-motor  disturbance,  nor 
by  loss  of  sensation ;  there  is,  in  fact,  no  doubt  they  are  of  trophic 
origin ;  the  nutrition  of  the  skin  is  so  greatly  impaired  that  the  mere 
contact  of  it  with  the  bed  for  a  few  days  is  sufficient  to  act  as  the 
exciting  cause  of  the  sore. 

It  will  be  noticed  that  in  some  instances  of  trophic  disorder  the  nerves  which  are 
injured  are  efferent ;  the  muscular  wasting  that  occurs  when  a  muscular  nerve  is  cut 
is  the  best  marked  example  of  this.  In  nerve  itself  Wallerian  degeneration  follows 
the  direction  of  growth,  which,  as  a  rule,  is  the  direction  in  which  the  nerve  transmits 
impulses.  The  acute  Wallerian  change  does  not  actually  leap  synapses,  still  the 
trophic  influence  of  one  set  of  neurons  upon  a  second  set  among  which  the  axons  of 
the  first  set  terminate  is  shown  by  a  slow  wasting  process,  of  which  chromatolysis 
is  an  early  visible  sign.  In  the  peripheral  axons  of  the  cells  of  the  sjnnal  and 
corresponding  cranial  gangha,  the  trophic  disorder  follows  a  peripheral  direction, 
whUe  impulses  are  carried  in  the  opposite  or  afferent  direction.  The  trophic  influence 
here  travels  against  the  stream  of  impulse.  It  cannot  fail  to  be  a  striking  fact  that 
the  most  marked  trophic  disorders  with  which  we  are  acquainted,  herpes,  acute 
bedsores,  Charcot's  disease,  eye  changes  after  division  or  injury  to  the  fifth  nerve, 
vagus  pneumonia,  etc.,  are  due  to  interference  with  sensory  channels.  Loss  of 
sensation  is  the  great  predisposing  cause  of  nutritive  mischief. 


CHAPTEE  LVIII 


THE   REPRODUCTIVE   ORGANS 


The  reproductive  organs   consist   in   the   male   of   the   two   testes 
which  produce  spermatozoa,  and  the  ducts  which  lead  from  them, 


Fig.  604.— Plan  of  a  vertical 
section  of  the  testicle, 
showing  the  arrangement 
of  the  ducts.  The  true 
length  and  diameter  of  the 
ducts  have  been  disre- 
garded, a  a,  Tubuli  semi- 
niferi  coiled  up  in  the 
separate  lobes ;  b,  tubuli 
recti ;  c,  rete  testis  ;  d,  vasa 
efferentia  ending  in  the  coni 
vasculosi ;  I,  c,  g,  convo- 
luted canal  of  the  epidi- 
dymis;  h,  vas  deferens; 
/,  section  of  the  back  part 
of  the  tunica  albuginea ; 
i  i,  fibrous  processes  run- 
ning between  the  lobes ; 
s,  mediastinum. 


\  ■><>»<» 


Fig.  605. — Section  of  the  epididymis  of 
a  dog. — The  tube  is  cut  in  several 
places,  both  transversely  and  ob- 
liquely ;  it  is  seen  to  be  lined  by  a 
ciliated  epithelium,  the  nuclei  of 
which  are  well  shown,  c,  Connec- 
tive tissue.    (Schofield.) 


and   in    the   female   of   the    two   ovaries   which   produce   ova,    the 
Fallopian  tubes  or  oviducts,  the  uterus,  and  the  vagina. 


828 


THE  EEPRODUCTIVE   ORGANS 


[CH.  LVin, 


Male  Organs 

The  testis  is  enclosed  in  a  serous  membrane  called  the  tunica 
vaginalis,  originally  a  part  of  the  peritoneum,  which  descends  into  the 
scrotum  before  the  testis  and  subsequently  gets  entirely  cut  off 
from  the  remainder  of  the  peritoneum.  There  are,  however,  many 
animals  in  which  the  testes  remain  permanently  in  the  abdomen. 
The  external  covering  of  the  testicle  itself  is  a  strong  fibrous  capsule, 
called,  on  account  of  its  white  appearance,  the  tunica  albuginea. 
Passing  from  its  inner  surface  are  a  number  of  septa  or  trabeculse, 
which  divide  the  organ  imperfectly  into  lobules.  On  the  posterior 
aspect  of  the  organ  the  capsule  is  greatly  thickened,  and  forms  a  mass 
of  fibrous  tissue  called  the 


Corpus  Highmorianum  (body 
of  Highmore)  or  mediastinuin 
testis.  Attached  to  this  is  a 
much  convoluted  tube,  which 
forms  a  mass  called  the  epi- 
didymis. This  receives  the 
ducts  of  the  testis,  and  is 
prolonged  into  a  thick  walled 
tube,  the  vas  deferens,  by 
which  the  semen  passes  to 
the  urethra. 

Each  lobule  of  the  testicle 
contains  several  convoluted 
tubes.  Every  tube  commences 
near  the  tunica  albuginea,  and 
terminates  after  joining  with 
others  in  a  straight  tubule, 
which  passes  into  the  body 
of  Highmore,  where  it  ends 
in  a  network  of  tubes,  the  rete 
testis.  From  the  rete  about 
fifteen  efferent  ducts  (vasa 
efferentia)  arise,  which  become 
convoluted  to  form  the  coni 
vasculosi,  and  then  pass  into 
the  tube  of  the  epididymis. 


Fig.  606.— Dissection  of  tlie  base  of  the  bladder  and  pro- 
state gland,  showing  the  veslculEe  seminales  and 
vasa  deferentia.  o,  Lower  surface  of  the  bladder  at 
the  place  of  reflexion  of  the  peritoneum  ;  b,  the  part 
above  covered  by  tlie  peritoneum  ;  i,  left  vas  deferens, 
ending  in  e,  the  ejaculatory  duct;  the  vas  deferens 
has  been  divided  near  i,  and  all  except  the  vesical 
portion  has  been  taiien  away ;  s,  left  vesicula  semi- 
nalis  joining  the  same  duct ;  s  s,  the  right  vas  de- 
ferens and  right  vesicula  seminalis,  which  has  been 
unravelled ;  p,  under  side  of  the  prostate  gland ; 
m,  part  of  the  urethra  ;  u  ti,  the  ureters  (cut  short), 
the  right  one  turned  aside.    (Haller.) 


The  convoluted  or  semi- 
niferous tubes  (fig.  607)  have  the  following  structure :  each  consists 
of  (1)  an  outer  boundary  of  flattened  connective  tissue  cells  inter- 
mingled with  elastic  fibres;  (2)  a  fine  membrana  propria;  (3)  a 
lining  epithelium  of  many  layers  of  germinal  cells.  JSText  to  the 
membrana  propria  is  a  layer   of   cells,   some  of   which   are   prim- 


CH.  LVIII.] 


THE   TESTIS 


829 


ordial  germinal  cells,  others  are  spermatogonia  produced  from  the 
primordial  germinal  cells,  but  differing  from  them  in  structure,  and 
the  remainder  are  supporting  or  nurse  cells  which  provide  nutri- 
ment for  the  developing  spermatozoa.     More  internally,  between  the 


^ 


Fio.  607.— Diagram  of  a  portion  of  a  seminal  tubule  showing  development  of  spermatozoa.  1,  Primi- 
tive germ  cell ;  2,  spermatogonia  ;  3,  spermatocysts  of  the  first  order  ;  4,  spermatocysts  of  the  second 
order  ;  5,  spermatids,  some  with  commencement  of  axial  filament ;  G,  a  nurse  cell  with  spermatids 
and  spermatozoa  in  various  stages  of  development ;  7,  free  spermatozoa  in  lumen  of  tube  ;  8,  por- 
tions of  nurse  cells.    (After  Waldeyer.) 

projecting  processes  of  the  nurse  cells,  are  large  spermatocysts  of  the 
first  order,  derived  from  the  spermatogonia  by  karyokinesis  and 
growth.  Still  nearer  the  lumen  of  the  tube  lie  the  spermatocysts 
of  the  second  order,  which  are  the  daughter-cells  of  the  spermato- 


Fio.  608. — A  spermatid  largely 
magnified.  1,  nucleus;  2, 
nucleolus ;  3,  chromatoid 
body ;  4,  idiosome ;  5,  centro- 
somes  ;  6,  commencement  of 
axial  filament.  (After  Meves.) 


Fig.  600.— Cells  of  the 
interstitial  tissue  of 
the  testis  with  crj-stal- 
loid  bodies. 


cysts  of  the  first  order,  and  the  spermatocysts  of  the  second  order 
give  rise   by  division  to  the  spermatids  which  lie  next  the  lumen. 


830 


THE  REPEODUCTIVE   ORGANS 


[CH.  LVIII. 


The  spermatids  become  embedded  in  the  inner  ends  of  the  nurse 
cells,  where  they  lose  their  distinct  cellular  characters  and  become 
converted  into  spermatozoa.  Every  spermatid  consists  of  a  cell  body 
and  a  nucleus  with  a  nucleolus.  In  the  cell  body  near  the  nucleus 
is  another  structure  called  an  idiosome,  containing  a  number  of 
microsomes.  There  are  also  a  coloured  or  chromatoid  body  whose 
function  is  not  known,  and  two  centrosomes  (see  fig.  608). 

The  interstitial  connective  tissue  of  the  testis  is  loose,  and  con- 
tains numerous  lymphatic  clefts.  Lying  in  it,  accompanying  the  blood- 
vessels, are  strands  of  polyhedral  epithelial  cells,  of  a  yellowish  colour 
{interstitial  cells),  which  frequently  contain  crystalloid  bodies  (fig.  609). 
The  straight  tubules  consist  of  basement  membrane  and  lining 
cubical  epithelium  only.  The  tubules  of  the  rete  testis  are  lined  by 
cubical  epithelium ;  the  basement  membrane  is  absent.  The  vasa 
efferentia,  coni  vasculosi,  and  epididymis  are  lined  by  columnar  cells, 
some  of  which  are  ciliated,  whilst  others  are  devoid  of  cilia,  and  prob- 
ably possess  secretory  functions.  There  is  a  good  deal  of  muscular 
tissue  in  their  walls.  The  vas  deferens  consists  of  a  muscular  wall 
(outer  layer  longitudinal,  middle  circular,  inner  longitudinal),  lined 
by  a  mucous  membrane,  the  inner  surface  of  which  is  covered  by 
columnar  epithelium. 

The  vesiculce  seminales  (fig.  606)  are  outgrowths  of  the  vasa  def  erentia. 
Each  is  a  much  convoluted,  branched,  and  sacculated  tube  of  structure 

similar  to  that  of  the  vas  deferens, 
except  that  the  wall  is  thinner,  and 
the  lining  epithelium  is  often  of 
transitional  character. 

The  penis  is  composed  of  cavernous 
tissue  covered  by  skin.  The  caver- 
nous tissue  is  collected  into  three 
tracts,  the  two  corpora  cavernosa  and 
the  corpus  spongiosum  in  the  middle 
line  inferiorly.  All  these  are  en- 
closed in  a  capsule  of  fibrous  and  plain 
muscular  tissue;  the  septa  which 
are  continued  in  from  this  capsule, 
form  the  boundaries  of  the  cavernous 
venous  spaces  of  the  tissue.  The 
arteries  run  in  the  septa ;  the  capil- 
laries open  into  the  venous  spaces. 
The  arteries  are  often  called  helicine, 
as  in  injected  specimens  they  form  twisted  loops  projecting  into  the 
cavernous  spaces  (see  also  p.  313).  The  structure  of  the  urethra  and 
prostate  is  described  on  pp.  551-553. 

The  Spermatozoa,  suspended  in  a  richly  albuminous  fluid,  con- 


FiG.  610. — Erectile  tissue  of  the  human  penis. 
a,  Fibrous  trabecula;  with  their  ordinary 
capillaries ;  b,  section  of  the  venous  sinuses ; 
c,  muscular  tissue.    (Cadiat.) 


CH.  LVIII.] 


THE   SPERMATOZOA 


831 


Btitute  the  semen.  Each  spermatozoon  consists  of  a  head,  a  very 
short  neck,  a  body,  a  tail,  and  an  end-piece.  The  head  is  of  flattened 
ovoid  shape,  and  in  the  anterior  two- thirds  of  its  extent  is  surmounted 
by  a  head-cap  which,  sliarpencd  at  its  extremity,  forms  a  cutting 
edge.  The  neck  is  very  short,  but  contains  two  centrosomes.  The 
body  is  about  the  same  length  as  the  head ;  it  is  traversed  by  an 
axial  filament  and  a  spiral  fibril  wound  round   the  sheath  of  the 


Fig.  Oil. — Senii-diasrammatic  representation  of 
human  spermatozoa.  A,  Front  view  ;  B,  side 
view.  1,  Head  cap  surrounding  head;  2, 
neck  ;  3,  body  ;  4,  tail ;  5,  end-piece.  The 
axial  filament  runs  through  the  body  and 
tail  into  the  end-piece. 


Fig.  612.— Diagram  of 
part  of  a  human  sper- 
matozoon highly  mag- 
nified (after  Meves). 
1,  Head  cap  ;  2,  head  ; 
3,  anterior  centrosome 
in  neck ;  4,  posterior 
centrosome  in  neck  ;  5, 
axial  filament;  6,  spiral 
sheath ;  7,  sheath  of 
axial  filament  in  body  ; 
8, mitochondrial  sheath; 
9,  annulus  ;  10,  thick 
sheath  of  axial  filament 
in  taU. 


axial  filament.  More  externally  is  a  layer  of  punctiform  substance 
called  the  mitochondrial  sheath,  which  terminates  at  the  junction 
with  the  tail  on  an  annular  disc.  The  axial  filament  is  continued 
tlrrough  the  tail  into  the  end  -  piece,  and  in  the  tail  is  sur- 
rounded by  thick  sheath.  In  some  animals,  newts  and  sala- 
manders, the  tail  is  surrounded  by  a  spiral  membrane,  but  this 
is   not   present   in    the   human    spermatozoon.      The   head   of    the 


832 


THE   REPRODUCTIVE   ORGANS 


[CH    LVIII. 


spermatozoon  is  formed  from  the  nucleus  of  the  spermatid,  the 
head-cap  from  the  idiosome ;  the  centrosomes  of  the  spermatid 
I^ass  to  the  neck,  and  the  cytoplasm  of  the  spermatid  is  transformed 
into  the  parts  of  the  body  and  tail  of  the  spermatozoon. 


Female  Organs 

The  Ovary  is  composed  of  fibrous  tissue  (stroma)  containing, 
near  its  attachment  to  the  broad  ligament,  a  number  of  plain 
muscular  fibres.  It  is  covered  by  a  layer  of  cubical  cells,  called 
the  germinal  epithelium,  which,  in  young  animals,  is  seen  dipping 
down,  here  and  there,  into  the  stroma.  The  stroma  contains  a 
number  of  yellow  polyhedral  cells  similar  to  the  interstitial  cells 
of  the  testicle. 

Sections  of  the  ovary  show  that  the  stroma  is  crowded  with  a 


Fig.  613. — Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The  uterus  and 
upper  part  of  the  vagina  have  been  laid  open  by  removing  the  posterior  wall ;  the  Fallopian  tube, 
round  ligament,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  ligament  removed  on  the 
leftside;  w,  the  upper  part  of  the  uterus  ;  c,  the  cervix  opposite  the  os  internum;  the  triangular 
shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical  cavity  with  the  rugae  termed 
arbor  vitfe  ;  v,  upper  part  of  the  vagina  ;  od.  Fallopian  tube  or  oviduct ;  the  narrow  communication 
of  its  cavity  with  that  of  the  coniu  of  the  uterus  on  each  side  is  seen  ;  I,  round  ligament ;  lo,  liga- 
ment of  the  ovary ;  o,  ovary  ;  i,  wide  outer  part  of  the  right  Fallopian  tube ;  fi,  its  fimbriated 
extremity  ;  po,  parovarium  ;  h,  one  of  the  hydatids  frequently  found  connected  with  the  broad  liga- 
ment,    h.    (Allen  Thomson.) 

number  of  rounded  cells,  the  oocytes,  derived  from  primitive  germ 
cells,  which,  in  the  early  stages,  were  intermingled  with  the  cells  of 
the  germinal  epithelium.  There  are  also  numerous  vesicles  of  differ- 
ent sizes  which  are  called  Graafian  foUidcs.  The  smallest  follicles 
are  near  the  surface,  the  largest  are  deeply  placed,  but  as  they  ex- 
pand they  again  approach  the  surface,  and  ultimately  rupture  upon  it. 
A  Graafian  follicle  has  an  external  wall  formed  by  the  stroma ; 
this  is  lined  internally  by  a  layer  of  cells,  derived  from  the  germinal 
epithelium,  which  surrounds  the  oocyte.     At  a  later  stage  there  are 


CH.  Lvm.] 


THE   OVARY 


833 


two  layers  of  cells,  one  lining  the  cavity,  and  the  other  surrounding 
the  oocyte,  but  the  two  are  close  together.  A  viscid  fluid  collects 
between  the  two,  and  as  the  follicle  grows,  separates  them. 


Fio.  614.— View  of  a  section  of  tlie  ovaiy  of  the  cat.  1,  Outer  covering  and  free  border  of  the  ovary  ;  1', 
attached  border ;  2,  the  ovarian  stroma,  presenting  a  fibrous  and  vascular  structure  ;  3,  granular 
substance  lying  extt-rnal  to  the  fibrous  stroma  ;  4,  blood-vessels  ;  5,  ovigerms  in  their  earliest  stages 
occupying  a  part  of  the  granular  layer  near  the  surface  ;  6,  ovigerms  which  have  begun  to  enlarge 
and  to  pass  more  deeply  into  the  ovary ;  7,  ovigerms  round  which  the  Graafian  follicle  and  tunica 
granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper  into  the  ovary  and  are  surrounded 
by  the  fibrous  stroma;  8,  more  advanced  Graafian  follicle  with  the  ovum  imbedded  in  the  layer  of 
cells  constituting  the  proligerous  disc;  9,  the  most  advanced  follicle  containing  the  ovum,  etc.;  9', 
a  follicle  from  which  the  ovum  has  accidentally  escaped  ;  10,  corpus  luteum.    (Schnin.) 

The  cells  in  each  layer  multiply,  and  are  eventually  arranged  in 
several  strata.     The  lining  epithelium  of   the  follicle  is  then  called 


e,.'^* 


Fig.  615. — Section  of  the  ovarj'  of  a  cat.  A,  germinal  epithelium  ;  B,  immature  Graafian  follicle ;  C, 
stroma  of  ovary;  D,  zona  pellucida  containing  the  ovum;  E,  Graafian  follicle  showing  lining 
cells ;  F,  follicle  from  which  the  ovum  has  fallen  out.    (V.  D.  Harris.) 

the  merribrana  granulosa,  and  the  heaped  mass  of  cells  around  the 
ovum,  the  discus  proligerus.     The  fluid  increases  in   quantity,  the 


'834 


THE   EEPRODUCTIVE   ORGANS 


[CH.  LVIII. 


follicle  becomes  tenser,  and  finally  it  reaches  the  surface  of  the  organ 
and  bursts ;  the  ovum  is  thus  set  free,  and  is  seized  by  the  fringed 
ends  of  the  Fallopian  tube  and  thence  passes  to  the  uterus.  The 
bursting  of  a  follicle  usually  occurs  about  the  time  of  menstruation. 
After  the  rupture  of  the  Graafian  follicle,  it  is  filled  up  with  what 
is  known  as  a  corpses  luteum.  This  is  derived  from  the  wall  of  the 
follicle,  and  consists  of  columns  of  yellow  cells  developed  from  the 
yellow  cells  of  the  membrana  granulosa ;  it  contains  a  blood-clot  in 
its  centre.  These  cells  multiply,  and  their  strands  get  folded  and 
converge  to  a  central  strand  of  connective  tissue;  between  the 
columns  there  are  septa  of  connective  tissue  with  blood-vessels.  The 
corpus  luteum  after  a  time  gradually  disappears ;  but  if  pregnancy 
supervenes  it  becomes  larger  and  more  persistent  (see  fig.  616).     The 


Fig.  616.— Corpora  lutea  of  different  periods.  B,  Corpus  luteum  of  about  the  sixth  week  after  impreg- 
nation, showing  its  plicated  form  at  that  period.  1,  Substance  of  the  ovary;  2,  sub>tance  of  the 
corpus  luteum  ;  3,  a  greyish  coagulum  in  its  cavity.  (Patersoii.)  A,  Corims  luteum  two  days  after 
delivery  ;  D,  iu  the  twelfth  week  after  delivery.    (Montgomery.) 


following  table  gives  the  chief  facts  in  the  life-history  of  the  ordinary 
corpus  luteum  of  menstruation,  compared  with  that  of  pregnancy : — 


At  the  end  of 

three  weeks. 

One  month     . 


Two  months 


Six  months 


Nine  months . 


Corpus  Luteum  of 
Menstruation. 


Corpus  Luteum  of 
Pregnancy. 


Three-quarters  of  an  inth  in  diameter 
convoluted  wall  pale. 

Smaller  ;  convoluted  wall 
bright  yellow ;  clot  still 
reddish. 

Reduced  to  the  condition 
of  an  insignificant  cica- 
trix. 

Absent. 


central  clot  reddish  ; 


Larger ;    convoluted  wall  bright 
yellow  ;  clot  still  reddish. 


Seven-eighths  of  an  inch  in  dia- 
meter ;  convoluted  wall  bright 
yellow ;    clot  decolorised. 

Still  as  large  as  at  end  of  second 
raontli ;  clot  fibrinous  ;  convo- 
luted wall  paler. 

One  half  an  inch  in  diameter ; 
central  clot  converted  into  a 
radiating  cicatrix  ;  the  external 
wall  tolerably  thick  and  con- 
voluted, but  without  any  bright 
yellow  colour. 


CH.   LVIIl.] 


THE   OVUM 


835 


The  corpus  lutcum  possibly  yields  an  internal  secretion,  the 
effect  of  which  is  to  assist  gestation  in  some  at  present  unknown 
way. 

Many  Graalian  follicles  never  burst ;  they  attain  a  certain  degree 
of  maturity  even  during  childhood,  and  then  atrophy. 


Nucleus  or  gormiiial  vesiclo. 
Nucleolus  or  germinal  spot. 

Space  left   by   retraction   of 
protoplasm. 

Protoplasm   containing  yolk 
spherules. 


/. Zona  pi'Uucida. 


Fig.  617. — A  human  ovum.     (Cadiat.) 


The  ovarian  ovum  or  oocyte  of  the  first  order  (tig.  617)  is  a  large 
spheroidal  cell  surrounded  by  a  transparent  striated  membrane  called 


Fig.  618.— Diagram  showing  mode  of  development  of  oocytes  of  the  first  order  from  primitive  germ  cells 
in  mammalian  ovary.  1,  germinal  epithelium  ;  2,  primitive  germ  cells  ;  3,  oogonia  ;  4,  oocytes  of 
the  first  order.  In  A,  two  primitive  germ  cells  are  seen  imbedded  in  the  germinal  epithelium.  In 
B,  a  primitive  germ  cell  has  descended  into  the  stroma  of  the  ovarj'  accompanied  by  cells  proliferated 
from  the  germmal  epithelium  which  will  become  the  cells  of  the  membrana  granulosa.  In  C,  the 
oogonia  derived  from  primitive  germ  cells,  and  oocytes  of  the  first  order  produced  by  division  of  the 
oogonia,  are  seen.    (After  Btihler.) 

the  zona  pellucida,  or  zona  striata.     The  protoplasm  is  filled  with  large 
fatty  and  albuminous  granules  {yolk  spherules),  except  in  the  part 


836 


THE   REPKODUCTIVE   ORGANS 


[CH.  LVIII. 


around  the  nucleus,  which  is  comparatively  free  from  them.  It  con- 
tains a  nucleus,  and  usually  one  very  well-marked  nucleolus.  The 
nucleus  and  nucleolus  are  still  often  called  by  their  old  names, 
germinal  vesicle  and  germinal  spot  respectively.  An  attraction 
sphere,  not  shown  in  the  figure,  is  also  present,  and  a  fine  mem- 
brane, the  vitelline  membrane,  is  said  to  lie  between  the  protoplasm 
and  the  zona  pellucida. 

The  oocytes  are  developed  from  the  primitive  germ  cells  which 
in  the  earliest  stages  are  interspersed  amid  other  cells  of  the  germinal 
epithelium.  The  primitive  germ  cells  divide  and  produce  oogonia ; 
and  by  the  division  of  the  oogonia,  oocytes  are  formed  (fig.  618). 
The  oogonia  and  oocytes  sink  into  the  stroma,  surrounded  by  cells, 
produced  by  the  proliferation  of  the  germinal  epithelium,  which  are 
destined  to  form  the  membrana  granulosa  and  the  discus  proligerus. 


Fig.  619. — Section  of  the  lining  membrane  of  a  Imman  uterus  at  the  period  of  commencing  pregnancy, 
showing  the  arrangement  of  the  glands,  d,  d,  d,  with  their  orifices,  a,  a,  a,  on  the  internal  surface 
of  the  organ.     Twice,  the  natural  size. 

The  Fallopian  tubes  have  externally  a  serous  coat  from  the 
peritoneum,  then  a  muscular  coat  (longitudinal  fibres  outside,  circular 
inside),  and  most  internally  a  vascular  mucous  membrane  thrown 
into  longitudinal  folds,  and  covered  with  ciliated  epithelium. 

The  uterus  consists  of  the  same  three  layers.  The  muscular 
coat  is,  however,  very  thick  and  is  made  up  of  two  strata  imperfectly 
separated  by  connective  tissue  and  blood-vessels.  Of  these  the 
thinner  outer  division  is  the  true  muscular  coat,  the  fibres  of  which 
are  arranged  partly  longitudinally,  partly  circularly.  The  inner 
division  is  very  thick,  its  fibres  run  chiefly  in  a  circular  direction  ; 
the  extremities  of  the  uterine  glands  extend  into  its  internal  surface. 
It  is  in  fact  a  much  hypertrophied  muscularis  mucosae.  The 
mucous  membrane  is  thick  and  consists  of  a  corium  of  soft  con- 
nective tissue,  lined  with  ciliated  epithelium ;  this  is  continued  down 
into  long  tubular  glands  which  liave,  as  a  rule,  a  convoluted  course. 
In  the  cervix  the  glands  are  shorter.  Near  the  os  uteri  the  epi- 
thelium becomes  stratified ;  stratified  epithelium  also  lines  the 
vagina. 


CII    LVIII.]  MENSTRUATION  837 

At  each  menstrual  period  the  uterus  becomes  congested,  and 
some  of  the  blood-vessels  of  the  mucous  membrane  are  ruptured ; 
the  blood,  together  with  the  secretion  of  the  glands  and  some 
epithelial  cLfbris  from  the  surface,  constitutes  the  menstrual  flow, 
which  usually  lasts  two  or  three  days.  The  amount  of  destruction 
of  the  surface  epithelium  is  not,  however,  a  marked  phenomenon ; 
still  less  is  there  any  disintegration  of  the  deeper  parts  of  the 
mucous  membrane. 


CHAPTEE  LIX 

DEVELOPMENT 

The  description  of  the  origin  and  formation  of  the  tissues  and  organs 
constitutes  the  portion  of  biological  science  known  as  embryology. 
In  a  physiological  text-book  it  is  only  possible  to  deal  with  the 
merest  outlines  of  the  principal  facts  of  development. 

The  following  descriptions  are  based,  as  far  as  possible,  upon 
observations  which  have  been  made  on  the  development  of 
mammals,  but  many  of  the  phenomena  of  development  have  only 
been  seen  in  lower  forms,  and  their  occurrence  in  mammals  (includ- 
ing man)  is  a  matter  of  inference. 

Interest  is  added  to  the  subject,  however,  by  the  consideration 
of  phenomena  which  occur  in  lower  animals ;  for  the  scientific  dis- 
cussion of  embryology  must  always  start  from  a  wide  survey  of 
the  whole  animal  kingdom,  because  tlie  changes  which  occur  in  the 
embryological  history  of  the  highest  animals,  form  a  compressed, 
though  in  many  cases  a  modified  picture  of  the  changes  which  have 
taken  place  in  their  historical  development  from  lower  types. 

The  Ovum. 

The  human  ovum  is  like  that  of  other  mammals,  a  small  cell 
about  jl^  to  y-l-o   inch  in  diameter. 

The  changes  by  which  the  ovum,  or  a  portion  of  the  ovum,  is 
transformed  into  the  young  animal  may  take  place  either  inside  or 
outside  the  body  of  the  parent.  If  they  take  place  inside  the  parent, 
as  in  mammals,  including  the  human  subject,  the  ovum  is  small,  and 
the  nutriment  necessary  for  its  growth  and  development  is  derived 
from  the  surrounding  tissues  and  fluids  of  the  mother.  If  the 
development  takes  place  outside  the  parent's  body,  as  in  birds,  the 
egg  is  larger;  it  contains  a  large  amount  of  nutritive  material 
called  the  yolk,  and  it  may,  in  addition,  be  surrounded  by  sheaths  of 
nutritive  substance.  Thus,  in  the  hen's  egg,  the  yellow  part  alone  is 
comparable  with  the  mammalian  ovum,  and  the  larger  part  of  that 


CII    LIX.]  MATURATION   OF   THE   OVUM  839 

is  merely  nutritive  substance.  Upon  the  yolk  is  a  whitish  speck,  the 
cicatricula,  which  is  a  small  mass  of  protoplasm,  about  l  of  an  inch 
in  iliameter.  In  the  cicatricula  lies  the  nucleus  or  germinal  vesicle, 
and  it  is  this  small  mass  of  protoplasmic  substance  which  divides 
and  grows  to  produce  the  chick ;  the  yolk  and  the  surrounding  white 
being  used  as  food. 

Ova  like  the  hen's,  in  which  only  a  small  part,  the  cicatricula, 
divides  and  grows,  are  called  meroblastic.  Small  ova,  with  little  food 
yolk,  such  as  the  human  ovum,  divide  completely  during  develop- 
ment, and  are  called  holoblastic,  but  numerous  gradations  occur 
between  the  two  extreme  types. 

The  structure  of  the  ovarian  ovum  in  mammals  and  its  mode  of 
formation  have  already  been  considered  (p.  835),  but  before  such  an 
ovum  can  develop  it  must  first  become  mature,  and  then  it  must  be 
impregnated  by  the  entrance  of  a  spermatozoon. 

Maturation  of  the  Ovum. 

It  will  be  remembered  that  the  germ  cells  which  form  the  ova 
are  at  first  embedded  in  the  germinal  epithelium,  from  which  they 
pass  into  the  stroma  of  the  ovary,  and  then  by  division  and  growth 
they  form  oogonia ;  from  the  oogonia,  oocytes  of  the  first  order  are 
developed,  and  the  oocytes  of  the  first  order  become  enclosed  in 
Graafian  follicles.  It  is  the  process  by  which  the  oocytes  of  the  first 
order  become  converted  into  mature  ova,  which  is  known  as  matura- 
tion, and  it  consists  essentially  of  a  double  mitotic  division  of  the 
oocyte,  each  division  producing  two  unequal  parts.  The  first  division 
produces  an  oocyte  of  the  second  order  and  the  first  polar  body,  and 
the  second,  which  takes  place  without  any  resting-stage,  results  in 
the  formation  of  the  mature  ovum  and  the  second  polar  body.  Thus, 
when  the  two  divisions  are  completed,  the  mature  ovum  and  two 
polar  bodies  lie  inside  the  zona  pellucida.  In  some  cn^en,  only  one 
polar  body  is  formed,  that  is,  only  one  division  occurs. 

The  unequal  division  is  naturally  associated  with  an  eccentric 
position  of  the  spindle.  At  each  division  one  end  of  the  spindle 
projects  on  the  surface  with  a  little  surrounding  protoplasm,  and  it 
is  the  small  process  which  becomes  the  polar  body  (see  fig.  620). 

One  of  the  essential  features  of  maturation  is  the  reduction  of 
the  number  of  chromosomes  in  the  nucleus.  It  is  well  known  that 
the  nuclei  of  all  animal  cells,  including  germ  cells  and  oogonia,  con- 
tain a  definite  number  of  chromosomes.  When  maturation  com- 
mences in  the  oocytes  of  the  first  order,  an  achromatic  spindle  is 
formed  in  the  usual  way;  but  instead  of  the  ordinary  number  of 
chromosomes  appearing  at  its  equator,  only  half  that  number  are 
seen :  for  example,  if  eight  be  the  normal  number  of  chromosomes. 


840 


DEVELOPMENT 


[CH.  LIX, 


only  four  appear.    Farther,  each  chromosome  is  not  a  slender  V-shaped 
loop,  but  a  short,  thick  rod,  or  ring,  or  group  of  four  particles.    Neither 


B 


Pio.  620.— Diagram  showing  the  formation  of  the  polar  bodies  (maturation  of  the  ovum).  A,  B,  and  C 
show  stages  in  the  formation  of  tlie  first  polar  body  by  heterotype  mitosis.  A  is  the  oocyte  of  the 
first  order  at  the  commencement  of  mitosis,  when  only  hfilf  the  usual  number  of  chromosomes 
appear.  C  is  the  oocyte  of  the  second  order ;  it  has  no  distinct  nucleus,  because  no  restiug-stage 
occurs  ;  after  the  separation  of  the  first  polar  body,  the  chromosomes  which  remam  in  the  oocyte 
of  the  second  order  at  once  rearrange  tliemselves  on  a  new  spindle.  D  is  the  mature  ovum,  with 
the  female  pronucleus  and  the  two  polar  bodies.  1,  First  polar  bud  ;  2,  first  polar  body  ;  3,  second 
polar  body ;  4,  chromosomes  on  spindle  of  oocyte  of  first  order ;  5,  zona  striata  ;  6,  vitelline 
membrane;  7,  daughter  chromosomes  in  first  polar  bud  ;  8,  female  pronucleus. 

does  it  split  longitudinally  in  the  usual  way,  but  transversely ;  and  at 
the  end  of  the  process  the  oocyte  of  the  second  order  and  the  first 


-2a2 


Fio.  621. — Diagram  showing  the  stages  in  the  maturation  of  the  ovum  when  the  first  polar  body 
divides.  A  similar  diagram  would  represent  the  formation  of  spermatids  from  a  spermatocyst  of 
the  first  order.  1,  Oocyte  of  the  first  order  ;  2,  oocyte  of  the  second  order  ;  2o,  first  polar  body  ;  3, 
mature  ovum  ;  3«,  second  polar  body  ;  2al,  and  2ci2,  daughter  cells  of  the  first  polar  body.  All  the 
last  generation  in  the  male  would  be  spermatids  of  equal  value. 


polar  body  both  contain  four  chromosomes.     This  form  of  mitosis  is 


CH.  LIX.] 


IMPREGNATION 


841 


known  as  heterotype,  whilst  the  ordinary  form  is  called  homotype. 
The  second  division  which  produces  the  mature  ovum  and  the  second 
polar  body  is  of  the  homotype  form,  and  the  final  result  is  that  each 
of  the  segments  into  which  the  oocyte  of  the  first  order  has  divided 
— the  mature  ovum  and  the  two  polar  bodies — contains  half  the 
number  of  chromosomes  present  in  the  parent  germinal  cell.  In 
some  cases  the  first  polar  body  divides  at  the  same  time  that  the 
second  polar  body  is  formed,  and  the  process  may  be  represented  by 
the  schema  in  fig.  621. 

The  nucleus  of  the  mature  ovum  is  known  as  the  female  pro- 
nucleus. 

Impregnation. 

By  impregnation  is  meant  the  union  of  a  spermatozoon  with  a 
mature  ovum.  The  spermatozoon,  moving  by  the  flagellar  movement 
of  its  tail,  meets  the  mature  ovum 


ZONA       PELLUCIOA 


./  POLAR 

Lglobules 


Fig.  G22. — The  fertilised  ovum  or  blastosphere, 
showing  its  new  nucleus  and  attraction 
spheres  ;  the  yolk  granules  have  been  omitted. 


in  the  upper  part  of  the  Fallopian 
tube,  and  by  means  of  its  sharp 
head  cap  it  pierces  the  zona  pel- 
lucida,  and  the  head,  neck,  and 
possibly  part  of  the  body,  enter 
the  substance  of  the  ovum, 
where  they  undergo  transforma- 
tion, and  are  converted  into  a 
malepronucleus  with  an  attendant 
attraction  sphere  and  its  centro- 
some.  The  male  pronucleus  con- 
tains the  same  number  of  chromo- 
somes as  the  female  pronucleus, 
for  the  mitosis  which  occurs  when  the  spermatocyst  of  the  first  order 
divides  to  form  the  two  spermatocysts  of  the  second  order,  is  a 
heterotype  mitosis,  in  which  only  half  the  usual  number  of  chromo- 
somes appear;  and  consequently  the  spermatocysts  of  the  second 
order,  and  their  descendants  the  spermatids,  also  contain  only  half 
the  typical  number  of  chromosomes.  These  are  retained  in  the 
spermatozoa,  which  are  produced  by  modification  of  the  spermatid, 
and  they  reappear  in  the  male  pronucleus. 

After  the  male  pronucleus  has  formed  in  the  substance  of  the 
mature  ovum,  it  approaches  the  female  pronucleus,  and  when  the 
two  pronuclei  fuse,  fertilisation  is  completed.  The  nucleus  which 
results  from  the  fusion — the  first  segmentation  nucleus — contains 
the  typical  number  of  chromosomes,  half  being  derived  from  the  female 
and  half  from  the  male  germinal  element.  When  the  fertihsation  is 
completed,  the  segmentation  nucleus  is  accompanied  by  two  attrac- 
tion spheres  with  their  centrosomes  (see  fig.  622) ;  one  of  these  spheres 


842 


DEVELOPMENT 


[CH.  LIX. 


is  that  associated  with  the  male  pronucleus,  but  the  origin  of  the  other 
is  uncertain.  It  may  l)elong  to  the  ovum,  though  it  was  not  apparent 
during  the  maturation,  or  it  may  have  been  produced  by  the  division 
of  the  centrosome  and  attraction  sphere  which  accompany  the  male 
pronucleus. 

Segmentation. 

After  fertilisation  is  completed,  the  ovum  divides  into  two  parts ; 
each  of  these  again  divides,  and  so  on  till  a  mulberry-shaped  mass — 
the  morula — is  formed.  It  consists  of  a  large  number  of  small  cells, 
and  it  is  enclosed  together  with  the  polar 
bodies,  in  the  zona  pellucida.  The  polar 
Ijodies  soon  disappear ;  indeed  in  many  cases 
they  have  vanished  long  before  the  morula 
is  completed.  A  cavity  soon  appears  in  the 
morula,  which  thus  becomes  converted  into 
a  blastula  or  blastocyst.  The  cells  which 
form  the  peripheral  wall  of  the  blastula 
assume  a  more  or  less  cubical  form,  whilst 
those  which  lie  in  the  interior  and  form  the 
inner  cell  mass  are  irregular  in  outline,  and 
they  are  grouped  together  at  one  pole  of  the 
blastula.  At  this  period  the  blastula  is 
unilaminar,  except  at  the  region  where  the 
inner  cell  mass  is  situated ;  but  soon  the 
cells  of  the  inner  mass  extend  round  the 
cavity  and  the  wall  of  the  cyst  becomes 
bilaminar,  the  outer  layer  being  called 
cinhlast  and  the  inner  liypoblast.  In 
amphioxus  and  in  many  invertebrates  the 
blastula  is  at  first  entirely  unilaminar,  no 
inner  cell  mass  being  present.  In  these  cases 
the  inner  layer  is  formed  by  the  invagination 
of  a  part  of  the  wall  of  the  vesicle,  and  the 
opening  at  which  the  invagination  occurs  is 
known  as  the  blastopore  or  primitive  mouth. 
If  the  surface  of  a  bilaminar  mammalian 
blastoderm  is  examined,  an  area  is  found 
which  is  darker  or  more  opaque  than  the 
rest;  this  is  the  area  where  the  embryo 
will  be  formed,  and  it  is  known  as  the  germinal  or  embryonic 
area  (fig.  624).  It  corresponds  with  the  region  where  the  inner 
mass  is  adherent  to  the  outer  layer,  and  in  it  the  epiblast  cells 
are  of  cubical  or  columnar  form,  whilst  over  the  remainder  of  the 
wall    of   the   vesicle    they   have    been    transformed    into   flattened 


Fio.  (328.  —  Diagrams  of 
various  stages  of  cleava; 
the  ovum.    (Dalton.) 


CII.  LIX.] 


THE    I'ltlMITIVE    STKEAK    AND    CROOVE 


843 


plates  (tig.  625).  At  first  the  gerniiiial  area  is  circular,  then  it 
becomes  ovoid,  and  ultimately  pear-shaped,  the  narrow  part  of 
the  pear-shaped  area  indicating  the  region  of  the  posterior  end  of 


Fki.  C24. — Dianrani  of  a  surface 
view  of  a  young  maninialian 
blastula.  1,  Germinal  area. 
A,  line  of  section  reiiresented 
in  fig.  62.0. 


Fig.  625.  —  Diagram  of  a 
section  of  the  mammalian 
blastula  shown  in  tig.  024 
along  the  line  A.  1,  Ger- 
minal area  ;  2,  epiblast ; 
3,  inner  cell  mass. 


the  body  of  the  future  embryo  (fig.  626).  A  linear  streak — the 
primitive  streak — quickly  appears  in  the  narrow  part  of  the  area, 
and  after  a  time,  a  groove — the  primitive  groove — appears  on  its 
surface.  In  the  meantime,  a  second  groove  has  appeared  on  the 
surface  of  the  ovum  in  front  of  the  primitive  streak.  This  is  the 
neural  groove  or  rudiment  of  the  central  canal  of  the  brain  and  spinal 
cord.  It  is  bounded  by  two  folds — 
the  neural  folds,  which  are  united 
together  at  their  anterior  ends,  but 
their  posterior  ends,  which  embrace 
the  anterior  end  of  the  primitive 
streak,  do  not  unite  until  after  the 
appearance  of  the  opening  at  the 
anterior  end  of  the  primitive  streak. 
This  opening,  therefore,  connects  the 
neural  groove  with  the  cavity  in  the 
interior  of  the  blastodermic  vesicle, 
which  is  called  the  archenteric  cavity, 
and  through  it  the  epiblast  be- 
comes continuous  with  the  hypoblast. 
Therefore  it  evidently  represents  a 
part    of    the    blastopore    of    more 

primitive  forms,  and  it  is  called  the  neurenteric  canal, 
closes,  and  all  traces  of  it  are  lost. 

The  primitive  streak  itself  is  due  to  a  down-growth  of  a  linear 
ridge  of  epiblastic  cells,  and  soon  after  its  formation  a  layer  of  cells, 
the  mesohlast  or  third  layer  of  the  blastoderm,  grows  out  from 
its  sides  and  posterior  end,  and  extends  between  the  epiblast  and 
hypoblast  over  the  whole  area  of  the  vesicle. 

That  portion  of  the  mesoblast  which  lies  immediately  at  the  sides 


Fif!.  626. — Diagram  ol  a  surface  view  of  a 
mammalian  blastoderm  after  the  formation 
of  the  neural  groove.  1,  Germinal  area  ;  2, 
neural  ridge  ;  3,  neural  groove ;  4,  neuren- 
teric canal  (part  of  blastopore)  ;  5,  primitive 
groove  and  streak.  A,  line  of  section  shown 
in  tig.  627 ;  B,  line  of  section  shown  in 
tig.  628. 


It  soon 


844 


DEVELOPMENT 


[CH.  LIX. 


of  the  neural  groove  becomes  partially  separated  from  the  rest,  and 
at  the  same  time  divided  into  cuboidal  blocks,  the  protovertebrge  or 
mesoblastic  somites.  The  more  laterally  situated  part  of  the  meso- 
blast  constitutes  the  lateral  plates,  and  the  narrow  strand  of  meso- 
blastic cells  which  connects  the  lateral  plate  on  each  side  with  the 
protovertebral  somites  is  the  intermediate  cell  mass.  Soon  after  its 
formation  the  lateral  mesoblast  is  cleft  into  two  layers,  and  the  space 
which  appears  between  the  two  layers  is  called  the  ccelom  (figs.  627, 
628).     The  outer  or  somatic  layer  of  the  mesoblast  adheres  to  the 


Fio.  627. — Diagram  of  a  transverse  section 
through  a  mammalian  blastoderm  along 
line  A  in  tig.  62C.  1,  primitive  groove  ;  2, 
primitive  streak  ;  3,  epiblast ;  4,  mesoblast ; 
5,  hypoblast ;  6,  cn-lom  ;  7,  archfnteron. 


Fig.  628. — Diagram  of  a  transverse  section 
through  a  mammalian  blastoderm  along 
line  B  in  tig.  626.  1,  neural  groove  ;  2, 
neural  ridge ;  3,  epiblast ;  4,  somatic 
mesoblast ;  5,  splanchnic  mesoblast ;  6, 
hypoblast ;  7,  somatopleur ;  8,  splanch- 
nopleur  ;  9,  notochord  ;  10,  ccelom  ;  11, 
archenteron. 


epiblast;  the  two  together  form  the  somatopleur.  The  inner  or 
splanchnic  layer  fuses  with  the  hypoblast  to  form  the  splanchnopleur. 
Cavities  also  appear  in  the  mesoblastic  somites. 

Whilst  the  mesoblast  is  extending  and  cleaving,  the  neural  folds 
gradually  grow  in  height,  and  their  free  margins  turn  inwards  and 
fuse  together.  This  fusion  commences  in  the  cervical  region,  and 
extends  forwards  and  backwards,  and  when  it  is  completed  the  neural 
groove  is  converted  into  a  closed  tube,  the  neural  tube,  and  the  original 
groove  is  now  the  central  canal  of  the  nervous  system.  In  the  ovum 
at  this  period  there  are,  therefore,  three  cavities :  (1)  The  neural  or 
central  canal  confined  to  the  embryonic  region ;  (2)  The  ccelom  or 
space  in  the  mesoblast;  (3)  The  archenteron  within  the  hypoblast. 
The  embryonic  area  is  still  outspread  on  the  surface  of  the  ovum. 
When  the  changes  to  which  reference  has  been  made  are  well 
advanced,  and  in  many  cases  before  the  neural  groove  is  closed,  the 
embryonic  area  begins  to  fold  off  from  the  rest  of  the  ovum.  A 
sulcus  appears  all  round  the  margins  of  the  area,  and  over  this  sulcus 
the  area  bends  forwards,  backwards,  and  laterally.  It  looks  as  if 
some  constricting  agent  had  been  placed  round  the  margin  of  the 
area,  and  that  afterwards  the  area  above  the  constriction,  and  the 
area  below  had  gone  on  growing  rapidly.  In  this  way,  the  ovum  is 
clearly  separated  into  two  parts,  an  upper,  the  embryo,  and  a  lower, 
which  becomes  the  appendages  of   the  embryo.     The  anterior  part 


CH.  LIX.] 


THE   EMBRYONIC    FOLDS 


845 


of  tlio  folded  eiuln-yoiiic  area  is  known  as  the  head  fold,  the  posterior 
as  the  tail  fold,  and  the  two  are  connected  together  on  each  side  by 
the  lateral  folds.  As  the  constriction 
between  the  embryonic  and  non-embryonic 
parts  affects  the  interior  as  well  as  the 
exterior  of  the  ovum,  it  follows  that  three 
cavities  are  present  in  the  embryo.  (1)  The 
central  canal  of  the  neural  tube,  which  is 
of  course  lined  by  epiblast,  (2)  A  por- 
tion of  the  archenteron  lined  by  hypo- 
blast. (3)  A  portion  of  the  coelom  or 
cavity  of  the  mesoblast  (fig.  630). 

The  central  canal  of  the  neural  tube,  as 
before  stated,  becomes  the  cavity  of  the 
permanent  central  nervous  system,  and  it 
forms  the  central  canal  of  the  spinal  cord, 
the  lateral,  third  and  fourth  ventricles,  and 
the  aqueduct  of  Sylvius  which  connects 
the  third  and  fourth  ventricles  together. 

The  portion  of  the  archenteron  en- 
closed in  the  embryo  forms  the  primitive 
gut.  The  part  contained  in  the  head  fold 
is  the  fore-gut,  that  in  the  tail  fold  is  the 
hind-gut,  and  the  remainder  is  the  mid- 
gut  (fig.  631). 

The  constriction  where  the  body  of  the 
embryo  becomes  continuous  with  the  re- 
mainder of  the  ovum,  is  known  ultimately 
as  the  umbilicus.  It  remains  pervious  till 
birth,  when  the  embryo  is  separated  from 
the  rest  of  the  ovum,  and  through  it  the 
mid-gut  is  connected  with  the  remainder 
of  the  archenteron  (which  is  henceforth 
called  the  yolk  sac)  by  a  narrow  hypoblastic 
tube,  the  vitello -intestinal  duct  (fig.   630, 

The  portion  of  the  mesoblastic  cavity 
enclosed  in  the  embryo  is  called  the  body 
cavity.  It  gradually  differentiates  into  the 
pericardial,  pleural  and  peritoneal  cavities, 
which  are  eventually  entirely  separated 
from  each  other. 

In  the  early  stages  the  gut  is  close  to 
the  posterior  w^all  of  the  body,  but  after  a  time  it  advances  into  the 
body  cavity ;  it  remains  connected,  however,  with  the  dorsal  wall  by 


Fio.  62y.— Embryo  chick  (36  hours), 
viewed  from  beneath  as  a  trans- 
parent object  (magnified),  pi,  Out- 
line of  pellucid  area  ;  fiJ,  fore-brain, 
or  first  cerebral  vesicle  :  from  its 
sides  project  op,  the  optic  vesicles  ; 
SO,  backward  limit  of  somatopleur 
fold,  "tucked  in"  under  head; 
o,  head-fold  of  true  amnion  ;  a',  re- 
flected layer  of  amnion,  sometimes 
termed  "  false  amnion  "  ;  sp,  back- 
ward limit  of  splanchnopleur  folds, 
along  which  run  the  omphalo- 
mesenteric veins  uniting  to  form 
h ,  the  heart,  which  is  continued 
forwards  into  ba,  the  bulbus  arte- 
riosus ;  d,  the  fore-gut,  lying  behind 
the  heart,  and  having  a  wide  cres- 
centic  opening  between  the  splanch- 
nopleur folds  ;  JJH,  hind-brain  ; 
MB,  mid-brain  ;  pv,  protovertebra; 
lying  behind  the  fore-gut ;  mc,  line 
of  junction  of  medullary  folds  and 
of  notochord  ;  ch,  front  end  of  noto- 
chord  ;  vpl,  vertebral  plates  ;  pr, 
the  primitive  groove  at  its  caudal 
end.    (Foster  and  Balfour.) 


846 


DEVELOPMENT 


[CH.  LIX. 


a  fold  of  the  splanchniu  portion  of  the  incsoblast,  which  is  called  the 
dorsal  mesentery.  A  similar  mesentery  is  found  connecting  the 
ventral  wall  of  that  portion,  fore-gut,  which  becomes  stomach  and 
duodenum,  with  the  ventral  wall  of  the  body. 

Before  the  neural  groove  is  closed  and  becomes  the  neural  canal, 
the  hypoblast  beneath  the  middle  of  the  groove  becomes  thickened  to 
form  a  longitudinal  ridge  (fig.  628).  This  ridge  is  the  notochord  or 
primitive  skeletal  axis.  It  soon  separates  from  the  remainder  of  the 
hypoblast,  and  forms  a  round  cord,  which  lies  at  first  immediately 


5  14     7      15 


Fig.  630. — Diagram  of  a  transverse  section 
through  a  mammalian  ovum  at  the  period 
when  the  folding  otf  of  tlie  embryo  has 
commenced.  1,  Neural  tube  ;  2,  proto- 
vertebral  somite  ;  3,  epiblast ;  4,  somatic 
mesoblast ;  5,  splanchnic  mesoblast ;  (i, 
hypoblast ;  7,  notochord  ;  8,  primitive 
alimentary  canal  ;  0,  ca?lom ;  10,  vitello- 
intestinal  duct ;  11,  yolk  sac  ;  V2,  lateral 
fold  of  amnion. 


Fig.  631. — Diagram  of  a  longitudinal  section  of  a 
mammalian  ovum  at  the  period  when  the  folding  oil 
of  the  embryo  has  commenced.  1,  Xeural  tube; 
2,  epiblast ;  3,  notochord  ;  4,  stomadceai  space  ;  5, 
head  fold  of  amnion  ;  6,  tail  fold  of  amnion  ;  7, 
hypoblast ;  8,  somatic  mesoblast ;  9,  splanchnic 
mesoblast ;  10,  yolk  sac  ;  11,  ccelom  ;  12,  allantois  ; 
13,  hind-gut;  14,  mid-gut ;  15,  fore-gut;  16,  peri- 
cardium. 


beneath  the  neural  groove,  and  afterwards  beneath  the  neural  tube, 
extending  from  the  anterior  end  of  the  primitive  gut,  which  lies 
beneath  that  region  of  the  neural  tube  which  afterwards  becomes 
the  mid-brain,  to  the  caudal  end  of  the  embryo  (figs.  630,  631). 

It  follows  from  what  has  already  been  stated,  that  the  embryo 
attains  its  distinct  form  by  a  process  of  folding ;  but  for  some  time 
after  it  is  separated  off  from  the  remainder  of  the  ovum  (except  at  the 
margins  of  the  umbilical  orifice),  it  has  no  limbs.  After  a  time  a  ridge 
appears  on  each  side  of  the  body,  along  the  line  of  the  intermediate 
cell  mass  in  the  interior ;  this  is  the  Wolffian  ridge,  and  from  its 
anterior  and  posterior  parts,  the  limbs  grow  out  as  small  horizontal 
ledges. 

The  differentiated  embryo  contains  parts  of  all  the  layers  of  the 


CH.  LIX.]  THE   DECIDUA  847 

blastoilerm,  and   from  each  of  these  certain    nvoans  are  formed  as 
indicated  in  the  following  list: — 

1.  From  Epiblast.— a.  The  epidermis  and  its  appendages. 

b.  The  nervuns  .system,  both  central  and  peripheral. 

c.  The  epithelial  structures  of  the  sense-organs. 

(/.  The  ei)itholium  of  the  mouth,  and  the  enamel  of  the  teeth. 
c.  The  epithelium  of  the  nasal  passages. 

/.  The  epithelium  of  the  glands  opening  on  the  skin  and  into  the 
vestibule  of  the  moutii,  and  nasal  passages. 
ij.  The  muscular  fibres  of  the  sweat-glands. 

2.  From  Mesoblast. — a.  The  skeleton  and  all  the  connective 
tissues  of  the  body. 

b.  All  the  muscles  of  the  Ijody. 

c.  The  vascular  system,  including  the  lymphatics,  serous  mem- 
branes, and  spleen. 

d.  The  urinary  and  generative  organs,  except  the  epithelium  of 
the  bladder  and  urethra. 

The  Somatic  mesohlast  forms  the  osseous,  fil)rous,  and  muscular 
tissues  of  the  body-wall,  including  the  true  skin. 

The  Splanchnic  mesohlast  forms  the  fibrous  and  muscular  wall  of 
the  alimentary  canal,  the  vascular  system,  and  the  urino-genital 
organs. 

3.  Prom  Hypoblast. — a.  The  epithelium  of  the  alimentary  canal 
from  the  inner  sides  of  the  teeth  to  the  anus,  and  that  of  all  the 
glands  (including  liver  and  pancreas)  which  open  into  this  part  of 
the  alimentary  tube. 

b.  The  epithelium  of  the  respiratory  cavity. 

c.  The  epithelium  of  the  Eustachian  tube  and  tympanum. 

d.  The  epithelium  lining  the  vesicles  of  the  thyroid. 
c.  The  epithelial  nests  of  the  thymus. 

/.   The  epithelium  of  the  bladder  and  urethra. 

The  Decidua  and  the  Foetal  Membranes. 

When  the  uterus  is  ready  for  the  reception  of  an  ovum  it  is  lined 
by  a  greatly  hypertrophied  mucous  membrane,  called  the  decidua, 
because,  after  the  delivery  of  the  child,  a  portion  of  it  comes  away 
from  the  uterus  with  the  other  membranes. 

When  the  ovum,  which  has  been  fertilised  in  the  upper  part  of  the 
Fallopian  tube,  reaches  the  uterine  cavity,  it  is  usually  in  the  stage  of 
a  morula  or  blastula.  It  rapidly  eats  its  way  into  the  substance  of 
the  decidua  which  closes  over  it,  obliterating  the  opening  tlirough 
which  it  passed,  and  thus  the  ovum  becomes  embedded  in  the 
membrane,  which  thereupon  becomes  separable  into  three  parts. 
1.  The  part  between  the  uvum  and  the  muscular  wall  of  the  uterus. 


848 


DEVELOPMENT 


[CH.  LIX. 


Fio.  632. — Diagram  representing  the  relation  of 
the  fieveloping  ovum  to  the  decidua  at  a  vprj- 
early  stage.  1,  Uterine  muscle;  2,  epiblast 
of  ovum  ;  3,  inner  cell  mass  of  ovum  (hypo- 
blast and  embrj-onic  (•[jiblast) ;  4,  decidua 
basalis  ;  5,  decidua  cap.sularis  ;  6,  decidua 
vera  ;   7,  cavity  of  uterus. 


the  decidua  basalis.     2.  The  part  between  the  ovum  and  the  uterine 
4-  cavity,  the   decidua  capsularis  or 

reflexa.  3.  The  remaining  part  is 
called  the  decidua  vera.  Between 
the  decidua  capsularis  and  the 
decidua  basalis  lies  the  ovum, 
wdiich  speedily  becomes  differen- 
tiated into  embryo  membranes, 
and  appendages.  The  outermost 
of  the  foetal  membranes  is  the 
chorion ;  this  is  covered  with  vas- 
cular villi,  which  dip  into  the 
decidua  capsularis  and  basalis. 
Inside  the  chorion  is  the  amnion, 
a  closed  sac,  which  surrounds  the 
embryo  and  is  attached  to  its 
ventral  wall  at  the  umbilicus. 
The  amnion  is  filled  with  fluid, 
the  amniotic  fluid  in  which  the 
foetus  floats,  and  it  forms  a 
sheath  for  the  umbilical  cord  by 
which  after  a  certain  time,  the  embryo  is  attached  to  the  inner  surface 
of  the  chorion,  or  outer  wall  of  the  ovum.  The  umbilical  cord  con- 
tains not  only  the  blood- 
vessels which  pass  between 
a  specialised  portion  of  the 
chorion,  which  forms  the 
foetal  part  of  the  placenta, 
and  the  embryo,  but  also 
the  remains  of  the  yolk-sac, 
and  the  duct  by  which  it  is 
connected  with  the  intestine 
of  the  embryo. 

As  the  ovum  grows,  the 
decidua  capsularis  is  ex- 
panded over  its  surface,  and 
as  the  growth  continues  the 
uterine  cavity  is  gradually 
obliterated,  and  the  decidua 
capsularis  is  forced  into  con- 
tact with  the  decidua  vera, 
with  which  it  fuses. 

As  the  decidua  is  merely 
thickened   mucous   membrane, 
become  enlarged  as  the  decidua  thickens.     It  was  believed,  at  one 


;.  033.— Diagram  representing  a  later  stage  of  develop- 
ment than  that  shown  in  fig.  632.  1,  Uterine  muscle  ; 
2,  villi  of  chorion  of  ovum ;  3,  coelom ;  4,  decidua 
basalis  ;  b,  decidua  capsularis ;  6,  decidua  vera ;  7,  cavity 
of  uterus  ;  8,  allantois  ;  0,  amnion  cavity  ;  10,  primitive 
intestine;  11,  yolk-sac. 

it    naturally   contains   glands   which 


CH.  LIX.] 


THE   FCETAL   MEMBRANES 


849 


bime,  that  the  villi  of  the  chorion  entered  the  glands,  but  this  is  now 
known  to  be  incorrect.  The  villi  enter  the  interglandular  substance, 
and,  in  the  human  subject,  the  glands  of  the  decidua  capsularis  eventu- 
ally disappear  entirely.  In  the  decidua  basalis  and  the  decidua  vera 
the  superficial  portions  of  the  glands  also  disappear ;  their  deep  por- 
tions remain   in  an   almost   unchanged   condition,  and    furnish    the 


Fio.  034.— Diagrammatic  view  of  a  vertical  transverse  section  of  the  uterus  at  the  seventh  or  eighth 
weeli  of  pregnancy,  c,  c,  c',  cavity  of  uterus,  which  becomes  the  cavity  of  the  decidua,  opening  at 
c,  c,  the  comua,  into  the  Fallopian  tubes,  and  at  c'  into  the  cavity  of  the  cervix,  which  is  closed  by 
a  plug  of  mucus;  dv,  decidua  vera;  dr,  decidua  reflexa,  with  the  sparser  villi  embedded  in  its 
substance;  ds,  decidua  basalis  or  serotina,  involving  the  more  developed  chorionic  villi  of  the 
commencing  placenta.  The  foetus  is  seen  lying  in  the  amniotic  sac  ;  passing  up  from  the  umbilicus 
is  seen  the  umbilical  cord  and  its  vessels  passing  to  their  distribution  in  the  villi  of  the  chorion  ; 
also  the  pedicle  of  the  yolk-sac,  which  lies  in  the  cavity  between  the  amnion  and  chorion.  (Allen 
Thomson.) 

epithelium  for  the  regeneration  of  the  glands  and  the  lining  of  the 
uterine  cavity  after  parturition.  The  intermediate  parts  of  the 
glands  in  the  decidua  vera  and  the  decidua  basalis  become  very  much 
enlarged,  and  form  a  stratum  of  the  decidua  called  the  spongy  layer, 
and  ultimately  this  layer  is  converted  into  a  series  of  clefts,  and  it 
is  along  the  line  of  these  clefts  that  the  decidua  is  separated  at  birth. 
In  some  mammals  in  which  the  connection  between  the  chorion 
and   the  decidua  is  less  intimate  than  in  the  human  subject,  the 

3  H 


850 


DEVELOPMENT 


[CH.  LIX. 


glands  persist  to  a  greater  or  less  extent,  and  secrete  a  fluid  called 

uterine  milk,  which  is  absorbed  by  the  chorion. 

The  portion  of  the  decidua  which  undergoes  the  greatest  change  is 

the  decidua  basalis,  formerly  called  the  decidua  serotina.     In  it  a 

number  of  large  blood  spaces  are  formed,  and  these  are  separated  into 

masses  or  cotyledons  by  fibrous  strands.     The  cotyledons  are  penetrated 

by  chorionic  villi,  and  it  is  this  conjunction  of  chorionic  villi  and 

decidua  basalis  which  produces  the  placenta. 

The  placenta  is  the  organ  of  fcetal  nutrition  and  excretion,  and  at 

full  term  it  is  seven  or  eight  inches  across  and  weighs  nearly  a  pound. 

Its  blood  sinuses  are  filled 
with  maternal  blood,  which 
is  carried  to  them  by  the 
uterine  arteries  and  away 
from  them  by  the  uterine 
veins.  Into  these  blood- 
filled  spaces  the  vascular 
foetal  villi  project;  hence 
it  is  easy  for  exchanges  to 
take  place  between  the 
foetal  and  the  maternal 
blood,  though  the  two 
blood-streams  never  mix  to- 
gether. Oxygen  and  nutri- 
ment pass  from  the  maternal 
blood  through  the  coverings 
of  the  foetal  vessels  into  the 
foetal  blood,  and  carbonic 
acid,  urea,  and  other  waste 
products  pass  in  the  con- 
trary direction.  The  foetal 
blood  is  carried  to  the 
placenta   by  the  umbilical 

arteries,  which  are  the  terminal  branches  of  the  aorta  of  the  foetus ; 

these  pass  to  the  placenta  by  the  umbilical  cord,  and  the  blood  is 

returned,  through  the  cord,  by  the  umbilical  vein. 


Fig.  035.— Diagram  representing  a  later  stage  of  develop- 
ment of  membranes  and  placenta  than  that  shown  in 
fig.  633.  1,  Uterine  muscle  ;  2,  placenta  ;  3,  yollc-sac  ; 
4,  fused  decidua  vera  and  capsularis  ;  5,  primitive  blood- 
vessel of  embryo  ;  6,  amnion  cavity  (outer  surface  of 
amnion  is  fused  with  inner  surface  of  chorion) ;  V,  um- 
bilical cord  ;  S,  fo;tal  villus  in  placenta.  For  blood- 
vessels see  subsequent  figures. 


Development  of  the  Foetal  Appendages  and  Membranes. 

The  manner  in  which  the  primitive  intestinal  canal  is  separated 
from  the  yolk-sac  during  the  folding  off  of  the  embryo  from  the 
ovum,  has  already  been  considered  (p.  845). 

In  birds  the  yolk-sac  affords  nutriment  till  the  end  of  incubation, 
and  the  omphalo-mesenteric  blood-vessels  which  convey  the  nutriment 
to  the  embryo,  are  correspondingly  well  developed.     In  mammalia, 


CH.  LIX.] 


THE   AMNION 


851 


tlie  office  of  the  umlHlical  vesicle  ceases  at  an  early  period,  for  the 
(piantity  of  yolk  is  small,  and  the  embryo  soon  becomes  independent 
of  it,  on  account  of  the  intimate  relations  established  with  the 
maternal  blood  in  the  placenta.  In  birds,  moreover,  as  the  yolk-sac 
empties,  it  is  gradually  withdrawn  into  the  abdomen  of  the  chick 
through  the  umbilical  opening  which  then  closes  over  it.  In  mammals 
it  remains  outside  the  embryo,  and  in  man  its  remnants,  in  a  con- 
tracted and  shrivelled  condition,  are  found  in  the  umbilical  cord.  In 
some  mammals,  however,  it  plays  a  much  more  important  part  than  it 
does  in  man,  and  the  time  and  mode  of  its  disappearance  differ  in 
different  orders  of  mammals. 

At  an  early  stage,  and  whilst  the  changes  to  which  reference  has 
been  made  are  proceeding,  three  important  structures,  the  amnion, 
the  chorion,  and  the  allantois,  are  developed. 

Amnion. — As  the  embryo  is  differentiated,  the  surface  of  the 
ovum   beyond    its    margins,   formed    by    somatopleur,   is   gradually 


Fig.  636. — Diagram  of  a  longitudinal  section  of  an  ovum  showing  mode  of  formation  of  amnion,  allantois, 
and  the  primitive  blood-vessels.  1,  Amnion  cavity  ;  2,  villi  on  placental  part  of  chorion  ;  3,  allan- 
tois ;  4,  epiblast  of  chorion  ;  j,  somatic  mesoblast ;  6,  splanchnic  mesoblast ;  ",  yolk-sac ;  S,  ccelom  ; 
9,  vascular  area  on  yolk-sac  ;  10.  pericardium  ;  11,  heart ;  12,  allantois  diverticulum  from  cloaca  ; 
13,  chorion. 

raised  as  a  circular  fold  wliich  is  looked  upon  as  consisting  of  head, 
tail,  and  lateral  portions.     The  various  parts  of  the  fold  rise  quickly 


852 


DEVELOPMENT 


[CH.  LIX. 


and  converge  over  the  embryo,  which,  at  the  same  time,  passes 
towards  the  interior  of  the  ovum.  Finally,  the  folds  meet  and  fuse 
together  at  a  point  which  is  called  the  amnion  navel.  As  soon  as  the 
folds  fuse,  the  inner  parts  separate  from  the  outer  and  form  a  closed  sac 
(figs.  630  to  639).  The  inner  wall  of  the  sac  is  formed  by  epiblast,  the 
outer  by  mesoblast,  and  both  are  continuous  with  the  same  layers  of 
the  embryo  at  the  umbilical  orifice.      At  first  the  amnion   closely 


Pro.  637.— Diagram  of  a  longitudinal  section  of  an  ovum,  showing  later  stage  of  formation,  amnion 
and  foetal  part  of  placenta  than  that  shown  in  fig.  636. 

1.  Amnion   cavity  almost  completely    3.  Allantoic  diverticulum  from  cloaca.  7.  Yollv  sac. 

closed  in.  4.  Epiblast  of  chorion  |  g    Somatonleur         S.  Coelom. 

2.  Placental  villi  of  chorion.  5.  Somatic  mesoblast  J     "  '        '      10.  Pericardium. 


invests  the  embryo,  but  soon  the  space  between  the  two,  the  amniotic 
cavity,  becomes  filled  with  fluid,  and  this  increases  in  amount,  till  at 
the  end  of  pregnancy  it  is  present  in  very  considerable  quantity. 

The  amniotic  fluid  consists  of  water  containing  small  quantities  of 
albumin,  urea,  and  salts.  It  is  an  exudation  from  the  foetal  and  the 
maternal  blood,  and  the  urea  in  it  comes  from  the  foetal  urine  which  is 
passed  into  the  amniotic  cavity  in  the  later  part  of  pregnancy. 

The  function  of  the  fluid  appears  to  be  purely  mechanical.  It 
supports  the  embryo  on  all  sides,  and  protects  it  from  blows  and  other 


CH.  LIX.]  THE  AMNION  853 

injuries  to  the  abdumen  of  the  mother,  and  from  sudden  irregular 
contractions  of  the  abdominal  walls. 

The  preceding  account  of  amnion  formation  is  based  upon  the 
phenomena  observed  in  the  majority  of  amniotic  vertebrates,  but  the 


Fig.  640. 

Figs.  638,  639,  and  640  are  (iia<;ranimatic  representations  of  three  stages  in  the  development  of  the 
ovum  in  certain  inammals.  They  show  the  metliod  of  amnion  formation  and  mesodermal  extension 
iu  monkeys  and  probably  also  in  the  human  subject.  A,  Allantoic  mesoblast;  AC,  Ammon 
Cavity;  BC,  Blastula  Cavity  ;  C,  Ciriom  ;  CV,  Chorionic  Villi ;  E,  Rudiment  of  bpiblast;Ii  A, 
Epiblast  of  Amnion  ;  EC,  Epiblast  of  Chorion  ;  EE,  Epibla.-,t  of  Embryo  ;  G,  Gut ;  H,  HypobJast ; 
SMA,  Somatic  Mesoblast  on  Amnion;  SMC,  Somatic  Mesoblast  on  Chorion;  SpMi,  Splanchnic 
Mesoblast  on  Yolk-sac  ;  YS,  Y'olk-sac. 

process  is  considerably  modified  in  many  rodents,  cheiroptera, 
monkeys,  and  probably  also  in  man.  In  the  animals  in  which  such 
modifications  occur  the  inner  cell  mass  which  becqpies  distinct 
as  the  blastula  condition  is  attained  (p.  8-42),  contains  not  only  the 
rudiments  of  the  hypoblast  but  also  the  rudiments  of  the  epiblast  of 


854  DEVELOPMENT  [CH.  LIX. 

the  embryo  and  the  amnion  and  the  rudiments  of  the  mesoblast, 
whilst  the  outer  wall  of  the  blastula  consists  of  chorionic  epiblast 
alone.  As  the  epiblastic  and  hypoblastic  parts  of  the  inner  mass  begin 
to  differentiate  from  each  other  a  cavity  appears  in  each  (fig.  639). 
The  cavity  in  the  hypoblast  is  the  yolk-sac  cavity,  a  part  of  which 
is  afterwards  enclosed  in  the  embryo  to  form  the  primitive  ali- 
mentary canal.  The  cavity  formed  in  the  epiblast  is  the  amnion 
cavity,  and  that  portion  of  its  epiblastic  wall  which  lies  in  contact 
with  the  hypoblast  becomes  the  epiblast  of  the  embryo,  and  the 
remainder  the  epiblast  of  the  amnion.  The  mesoblast  springs  in  the 
usual  way  from  the  primitive  streak,  which  forms  in  the  usual  way 
in  the  posterior  part  of  the  embryonic  area  (see  p.  843),  and  it  spreads 
over  the  yolk-sac,  the  amnion,  and  the  chorion,  reaching  the  latter 
from  the  amnion  before  the  two  have  been  distinctly  separated  from 
each  other. 

Chorion. — The  chorion  is  that  portion  of  the  surface  of  the  ovum 
wliich  does  not  enter  into  the  formation  of  the  embryo  or  of  the 
amnion,  and  after  the  separation  of  the  amnion,  it  forms  the  whole  of 
the  outer  surface  of  the  ovum,  completely  surrounding  the  embryo, 
the  amnion,  and  the  allantois. 

At  a  very  early  period  its  surface  is  set  with  fine  processes,  the 
chorionic  villi,  which  at  first  consist  of  epiblastic  cells,  alone,  but  very 
soon  they  acquire  cores  of  somatic  mesoblast,  which  becomes  vascu- 
larised  by  the  allantoic  vessels  which  rapidly  extend  throughout 
the  whole  of  the  chorionic  mesoblast. 

The  young  villi  are  small,  but  grow  rapidly  and  branch  repeatedly, 
as  they  project  into  the  decidua  capsularis  and  decidua  basalis. 
Their  function  is  to  obtain  nutriment  from  the  uterine  tissues.  In 
the  higher  mammals,  including  man,  they  destroy  and  eat  up  many 
of  the  cells  of  the  decidua,  and  gases  and  fluids  pass  through  them 
from  the  maternal  to  the  foetal  blood,  and  vice  versa.  In  some 
mammals,  however,  they  do  not  destroy  the  uterine  tissues,  and  in 
those  cases  they  absorb  the  uterine  milk,  which  is  secreted  by  the 
enlarged  uterine  glands. 

The  chorionic  villi  wliich  penetrate  the  decidua  capsularis  gradu- 
ally disappear  as  the  capsularis  fuses  with  the  vera,  and  is  reduced  to 
a  thin  membrane ;  but  the  villi  which  enter  the  decidua  basalis 
increase  enormously  in  size  and  complexity,  to  form  the  foetal  part  of 
the  placenta,  and  their  branches  hang  free  in  the  interiors  of  large 
blood  sinuses  which  are  filled  with  maternal  blood  (fig.  634). 

Allantois, — The  allantois  is  an  outgrowth  from  the  ventral  portion 
of  the  posterior  part  of  the  primitive  alimentary  canal,  and  it  consists 
of  a  hollow  process  of  h}^oblast  covered  with  mesoblast  (fig,  631,  12). 
In  the  human  embryo  it  appears  at  a  very  early  period,  before  the 
amnion  has  separated  from  the  chorion,  and  it  conveys  the  allantoic 


CII.  UX.]  THE    ALLANTOIS  855 

arteries  fr(»in  the  ciuhryo  to  the  chorion,  and  the  allantoic  vein  fnmi 
llie  cliorion  to  the  embryo.  As  development  proceeds,  and  that  part 
nf  the  ch(»ri()n  in  contact  with  the  decidua  basahs  is  converted  into 
the  foetal  part  of  the  placenta  (figs.  634  to  637),  the  allantoic  blood- 
vessels in  the  chorion  gradually  disappear,  except  in  the  placental  area, 
where  they  grow  larger  till  birth. 

At  first  the  allantois  is  very  sh(jrt,  but,  as  the  amnion  distends  and 
the  embryo  passes  further  and  further  into  the  interior  of  the  enlarg- 
ing ovum,  it  is  elongated  into  a  cord  which,  together  with  the  remains 
of  the  yolk-sac,  is  surrounded  and  ensheathed  by  the  amnion  ;  this 
cord  is  called  the  umbilical  cord  (fig.  634). 

In  the  human  subject  that  portion  of  the  allantois  which  lies  in 
the  umbilical  cord  consists  entirely  of  vascular  meso blast,  for  the 
hollow  pouch  of  hypoblast  ends  near  the  umbilicus ;  but  in  some 
mammals  the  hypoblastic  diverticulum  is  prolonged  to  the  inner  surface 
of  the  chorion.  In  man,  therefore,  the  umbilical  cord  consists  of — 
1,  An  outer  covering  of  amnion ;  2,  a  core  of  modified  mesoblast 
derived  from  the  mesoblast  of  the  allantois  and  the  wall  of  the  yolk- 
sac  ;  3,  the  remains  of  the  hypoblastic  portion  of  the  yolk-sac,  and 
4,  the  two  allantoic  arteries  and  the  allantoic  vein. 

In  the  early  stages  immediately  after  the  separation  of  the  amnion 
from  the  chorion,  the  embryo  and  its  amnion  are  attached  to  the 
chorion  by  the  allantois,  and  they  are  situated  in  a  space  which  is 
part  of  the  original  coelomic  space  between  the  somatic  and  splanchnic 
mesoblast  (figs.  635  to  637).  This  space  is  continuous  with  the  coelom 
in  the  embryo  at  the  umbDical  orifice.  In  the  later  periods  it  is  entirely 
obliterated,  for  the  amnion  is  distended  till  its  outer  surface  fuses 
with  the  inner  surface  of  the  chorion ;  and  at  the  same  time  the 
umbilical  cord  is  differentiated  as  the  distending  amnion  surrounds 
and  presses  together  the  allantoic  stalk  and  the  remains  of  the  yolk- 
sac  (fig.  634). 

At  birth,  on  account  of  the  contraction  of  the  walls  of  the  uterus 
and  the  pressure  of  the  surrounding  muscles,  the  liquor  amnii  forces 
part  of  the  membrane  formed  by  the  fused  amnion  and  chorion 
through  the  cervix  uteri,  which  is  gradually  distended.  When  the 
distension  is  sufficient,  the  membrane  ruptures,  the  liquor  amnii 
escapes,  and  afterwards  the  child  is  forced  out.  It  still  remains  con- 
nected with  the  placenta  by  the  umbilical  cord  which  is  about  20 
inches  long,  and  this  connection  should  not  be  severed  for  a  few 
minutes,  in  order  that  as  much  blood  as  possible  may  be  aspirated 
from  the  foetal  part  of  the  placenta  into  the  child  as  breathing 
connnences. 

After  the  child  is  expelled  the  contraction  of  the  uterine  wall  con- 
tinues and  the  placenta  is  separated  and  forced  out.  The  separation 
gradually  extends  through  the  decidua,  along  the  line  of  the  stratum 


856 


DEVELOPMENT 


[CH.  LIX. 


spongiosum,  aud  the  fused  chorion,  amnion  and  decidua  turned  inside 
out,  follow  the  placenta  to  wliich  they  are  attached,  constituting,  with 
the  placenta,  the  after-birth. 

After  the  umbihcal  cord  is  tied  and  separated,  the  umbilical 
arteries  inside  the  child  become  filled  with  blood-clot,  and  ultimately 
they  are  converted  into  fibrous  cords,  the  so-called  obhterated  hypo- 
gastric arteries,  and  at  the  same  time  the  allantois  is  also  converted 
into  a  fibrous  strand,  the  urachus,  which  extends  from  the  apex  of  the 
bladder  to  the  umbilicus. 

Development  of  the  Frame-work  of  the  Body. 

In  the  early  stages  of  development,  the  only  indication  of  a  frame- 
work or  skeleton  is  the  notochordal  rod  of  hypoblastic  cells,  which 


Fig.  611. — Diagram  of  a  transverse  section  of  an  ovum  showing  differentiatiou  of  protovertebrte  an<i 
formation  of  amnion  folds,  primitive  intestine,  and  yolk-sac. 


1.  Spinal  cord. 

2.  Notochord. 

3.  Amnion  cavity. 

4.  Epiblast 


9.  Somatopleur. 


5.  Somatic    mesoblast  / 

7.  ntpoS  ""°''"*}  ''■  «l'lanchnopleur. 

S.  Yolk-sac. 


10.  Primitive  intestine. 

11.  CiBlom  (extra-embryonic). 

12.  Ccelom  (intra-embryonic). 

14.  Primitive  dorsal  blood-vessel. 

15.  Scleratogenous  part  of  protovertebra. 
1(5.  Muscle  plate  part  of  protovertebra. 
17.  Cutaneous  lamella  of  protovertebra. 
IS.  Amnion  folds. 


extends  along  the  whole  length  of  the  dorsal  wall  of  the  primitive 
intestine  beneath  the  neural   tube,  its  anterior    end  being  situated 


CH.  LIX.]  THE   I'ROTO VERTEBRA  857 

iniiuediatcly  beliiiid  the  position  where  the  pituitary  body  is  after- 
wards formed.  In  mammals  the  uotochord  disappears,  except  in  the 
centres  of  the  intervertebral  discs,  but  in  amphioxus  and  lampreys  it 
persists  as  a  permanent  skeletal  support,  and  in  these  cases  it  closely 
resembles  cellular  cartilage  enclosed  in  a  fdjrous  sheath.  It  is  com- 
posed of  a  very  insoluble  protein-like  substance,  which,  however,  is 
not  collagen.  Collagen  and  gelatin  (which  is  formed  from  collagen 
by  boiling),  are  characteristic  of  true  connective  tissues  which  are 
formed  from  mesoblast;  the  notochord  is  hypoblastic.  The  noto- 
chord  contains  also,  like  all  embryonic  tissues,  a  large  quantity  of 
glycogen. 

The  rudiments  from  which  the  axial  skeleton  of  the  body  is 
formed  are  the  pro  to  vertebrae  or  mesoblastic  somites  (see  p.  844). 
Each  protovertebra  separates  into  three  parts: — 1.  An  outer,  the 
cutaneous  lamella,  from  which  the  deeper  parts  of  the  skin  and  the 
subcutaneous  tissues  of  the  body  are  developed.  2.  A  middle  portion, 
the  muscle  plate.  From  the  muscle  plates  all  the  striped  muscles  of 
the  body,  with  the  exception  of  those  of  the  heart,  are  formed. 
3.  A  scleratogenous  segment.  The  scleratogenous  segments  fuse 
together  round  the  neural  tube  and  the  notochord,  and  in  this  way  a 
continuous  membranous  vertebral  column  is  formed.  This  is  cleft  on 
each  side  in  every  segment,  for  the  passage  of  the  nerve-roots  and  the 
accompanying  blood-vessels.  Part  of  the  membranous  column  is 
converted  first  into  cartilaginous  and  afterwards  into  bony  vertebrae  ; 
other  parts  are  transformed  into  intervertebral  discs  and  ligaments, 
and  the  remainder  forms  the  membranes  which  line  the  spinal  canal 
and  surround  the  spinal  cord.  From  the  sides  of  the  vertebrae  the 
ribs  grow  outwards  and  forwards  in  the  thoracic  region,  and  some  of 
them  meet  together  in  front,  and  enter  into  the  formation  of  the 
sternum  or  breast-bone. 

The  Limbs. — At  first  there  are  no  limbs,  and  then  they  jut  out  as 
buds  from  the  sides  of  the  body.  Each  consists  of  an  epiblastic 
covering  and  a  core  of  mesoblast.  The  central  part  of  the  mesoblast 
condenses  and  forms  the  cartilaginous  rudiments  of  the  bones  which 
afterwards  become  ossified,  and  it  also  forms  the  ligaments  wliich 
connect  the  bones  together.  Buds  from  the  muscle  plates,  oppo- 
site the  limbs,  grow  into  them  to  form  the  muscles,  and  nerves 
from  the  corresponding  segments  of  the  spinal  cord  enter  the  buds 
(fig.  642).  Blood-vessels  connected  with  the  vessels  of  the  body  also 
appear. 

The  Head. — In  the  early  stages  the  head  is  merely  a  rounded 
projection  developed  in  the  head  fold  of  the  embryo.  Its  anterior  part 
is  bent  sharply  downwards  in  front  of  the  anterior  end  of  the  body  in 
which  the  pericardium  has  been  formed,  and  the  cleft  between  the 
front  of  the  head  and  the  pericardium  is  the   stomadaeal  space    or 


858 


DEVELOPMENT 


[CH.  LIX. 


primitive  mouth  cavity  (figs.  643,  644,  645).     At  this  time  there  is 
no  neck,  but  from  the  posterior  part  of  the  head  to  the  side  of  the 


Fig.  642.— Diagram  of  a  transverse  section  of  embryo  and  amnion,  showing  extension  of  muscle  plate.s, 
rudimentary  limbs,  and  membranous  vertebral  column.  1,  Spinal  cord  with  nerve-roots  ;  2, 
membranous  vertebral  column,  formed  from  fused  scleratogenous  segments  of  protovertebrie  ;  3, 
descending  aorta  ;  4,  cadom  ;  5,  amnion  cavity  ;  6,  primitive  intestine ;  7,  muscle  plate  extending 
into  body  wall ;  8,  bud  of  muscle  plate  into  limb  ;  9,  muscle  plate. 

pericardium,  a  series  of  five  visceral  arches,  with  four  intermediate 
clefts,  extend  round  the  sides  of  the  foregut.  As  the  neck  forms,  the 
visceral  arches  move  forward  with  the  head,  and  their  lower  ends  meet 
in  the  middle  line  of  the  neck  in  front  of  the 
anterior  end  of  the  body ;  thus  it  comes 
about  that  the  stomadseal  space  is  now 
bounded  laterally  and  below  by  the  first  or 
mandibular  arches,  and  above  by  the  anterior 
part  of  the  head  which  is  called  the  fronto- 
nasal process.  The  back  of  the  space  is 
bounded  for  a  time  by  a  thin  membrane 
which  separates  the  foregut  from  the  stoma- 
dseum.  Just  in  front  of  the  upper  end  of 
this  meml:)rane  a  diverticulum  projects  from 
the  stomadseum  towards  the  brain — this  is 
Eathke's  pouch ;  it  meets  a  downgrowth  from 
the  brain  called  the  hypophysis,  and  the  two  structures  unite  to  form 
the  two  lobes  of  the  pituitary  body.  The  membrane  soon  disappears, 
and  the  primitive  mouth  and  the  foregut  form  a  continuous  cavity. 
In  the  meantime  two  olfactory  pits  have  appeared  on  the  under 
surface  of  the  fronto-nasal  process,  and  they  grow  back  into  the  roof 
of  the  stomadaeum.  These  pits  cut  the  fronto-nasal  process  into 
three  parts,  the  mesial  nasal  process  between  them,  and  the  lateral 


Fiu.  643. — Diagram  representing 
front  view  of  anterior  part  of 
a  very  young  embryo.  1, 
Fronto-nasal  process  of  head  ; 
2,  olfactory  pit ;  3,  stoma- 
dieum  ;  4,  umbilical  orilice  ;  5, 
pericardium ;  6,  mandibular 
arch  ;   7,  eye. 


CH.  LIX.] 


FORMATION   OF   THE    FACE 


859 


nasal  processes  at  the  sides.  Mureover,  two  little  projections,  the 
globular  processes,  grow  down  on  each  side  of  the  middle  line  from 
the  mesial  nasal  process.  At  this  period  the  upper  ])oundary  of 
the  orifice  of  the  stomadaeum  is  formed  by  the  two  globular  pro- 
cesses separated  by  a  small  cleft,  and  the  two  lateral  nasal  processes 
separated  from  the  globular  processes  by  the  olfactory  pits,  and  the 
sides  and  the  lower  boundary  of  the  orifice  are  formed  by  the  first  or 
mandibular  arches.  From  the  upper  ends  of  the  mandibular  arches 
the  maxillary  processes  grow  forwards  immediately  beneath  the 
eyeballs  (which  have  appeared  on  the  sides  of  the  head),  and  as  they 


Fig.  644  — Diagram  of  anterior 
view  of  an  embryo  older  than 
that  shown  in  "tig.  640.  1, 
Mid-brain  ;  2,  fore-brain  ;  3, 
eye ;  4,  olfactory  pit ;  5, 
stomada-um;  6,  pericardium; 
7,  umbilical  orilice ;  S,  third 
visceral  arch ;  9,  second 
visceral  arch ;  10,  first  or 
mandibular  arch  ;  11,  max- 
illary process  of  mandibular 
arch  ;  12,  globular  process  ; 
13,  mesial  nasal  process  ;  14, 
lateral  nasal  process. 


Fig.  645. — Diagram  representing  a 
later  stage  of  development  of  the 
face  than  that  shown  in  fig.  641. 
1,  Mid-brain  ;  2,  fore-brain  ;  3,  eye  ; 

4,  anterior  nasal  orifice  ;  0,  globular 
process  ;  6,  mouth  ;  7,  pericardium; 

5,  second  visceral  arch ;  0,  first 
visceral  arch  ;  10,  maxillary  pro- 
cess of  first  arch  ;  11,  lateral  nasal 
process. 


grow  they  pass  beneath,  the  lateral  nasal  processes,  and  beneath  the 
anterior  ends  of  the  olfactory  depressions,  and  fuse  with  the  globular 
processes  which  also  fuse  together.  Thus  the  orifice  of  the  stomadseal 
space  is  cut  into  three  parts,  the  two  nasal  orifices  and  the  mouth. 
The  upper  lip  is  formed  by  the  fused  globular  and  maxillary  processes, 
and  contains  three  lines  of  fusion — one  in  the  middle  line  between 
the  globular  processes,  and  two  more  laterally  placed  between  the 
maxillary  processes  and  the  globular  processes.  In  certain  cases  the 
fusions  do  not  take,  and  then  clefts  are  left  in  the  upper  lip,  and 
constitute  the  various  forms  of  harelip.  From  the  inner  parts  of  the 
maxillary  processes  of  opposite  sides,  palatal  ledges  grow  across  the 
stomadseal  space ;  and  meeting  in  the  middle  line,  they  fuse  together 


860 


DEVELOPMENT 


[CH.  LIX. 


disappear  at  an  early  period. 


and  separate  the  space  into  an  upper  or  nasal  and  a  lower  or  buccal 
space.  If  the  palatal  ledges  fail  to  meet,  cleft  palate  results.  A  cleft 
may  also  appear  between  the  nasal  orifice  and  the  conjunctival  sac,  as 
a  result  of  the  absence  of  fusion  between  the  maxillary  process  and 
the  lateral  nasal  process.  The  lower  boundary  of  the  mouth  orifice  is 
formed  by  the  mandibular  arches. 

Both  the  tissues  of  the  fronto-nasal  process  and  those  of  the 
mandibular  arches  take  part  in  the  formation  of  the  skeleton  of  the 
head.  The  notochord  extends  forwards  as  far  as  the  pituitary  body  in 
all  vertebrates,  and  in  some,  protovertebral  somites  can  be  traced 
forwards  to  a  similar  point ;  but  in  mammals  they  are  only  distinct 
behind  the  ear  in  the  occipital  region,  and  even  there  they  enth'ely 

In  the  lower  vertebrates  a  bar  of 
cartilage  appears  at  each  side  of  the 
notochord  in  the  head ;  these  are 
the  parachordal  cartilages,  and  they 
soon  fuse  to  form  a  basilar  plate  in 
which  the  notochord  is  embedded. 
It  becomes  the  basi-occipital  and 
basi-sphenoid  bones.  In  mammals, 
the  parachordal  stage  is  eliminated, 
and  a  basilar  plate  is  formed  at 
once.  In  front  of  the  basilar  plate 
two  trabecule  cranii  embrace  the 
pituitary  body  and  extend  forward 
into  the  fronto-nasal  process,  where 
they  blend  together  to  form  an 
ethmo vomerine  plate ;  and  from  this 
processes  extend  down  on  each  side, 
the  nasal  part  of  the  stomadseal 
space  forming  the  rudiments  of  the  ethmoid  and  inferior  turbinal 
bones,  and  a  mesial  process  descends  into  a  septum  which  has  grown 
down  from  the  under  surface  of  the  fronto-nasal  process  and  united 
with  the  palate,  dividing  the  nasal  chamber  into  right  and  left  halves. 
In  tliis  the  vertical  plate  of  the  ethmoid  and  the  vomer  are  ossified. 
The  posterior  parts  of  the  trabeculae  fuse  with  the  basilar  plate  and 
form  the  rudiment  of  the  presphenoid.  Posteriorly,  and  at  the  sides, 
cartilaginous  plates  grow  over  the  cerebral  vesicles ;  but  in  mammals 
the  occipital  region  alone  is  roofed  in  by  cartilage;  the  rest  of  the 
cranial  vault  being  formed  of  membrane  bones. 

From  the  sides  of  the  presphenoid,  the  lesser  wings  or  orbito- 
sphenoids  containing  the  optic  foramina  are  developed,  and  from  the 
sides  of  the  basi-sphenoid  the  greater  wings  or  alisphenoids.  A 
cartilaginous  capsule  invests  the  auditory  vesicle,  and  becomes  con- 
nected to  the  parachordal  cartilage  on  each  side.     It  is  called  the 


-Diagrams  of  the  cartilaginous 
cranium. 

A,  first  stage.  Cli,  Notochord ;  Tr,  trabeculae 
cranii ;  P. cA.,  parachordal  cartilages ;  P,  situa- 
tion of  pituitary  body ;  .Y,  E,  0,  situations  of 
olfactory,  visual,  and  auditory  organs. 

B,  later  stage.  B,  Basilar  cartilages ;  S,  nasal 
septum  and  ethmoidal  cartilages;  Eth,  Eth' , 
prolongations  of  ethmoid  around  olfactory 
organ,  completing  the  nasal  capsule  ;  N,  E,  0, 
Ch,  Tr,  P,  as  before.    (After  Wiedersheim.) 


CH.  LIX.]  DEVELOPMENT  OF  THE  VASCULAR   SYSTEM  861 

periotic  capsule ;  it  is  replaced  by  bone,  which  constitutes  the  petrous 
and  mastoid  portions  of  the  temporal  bone. 

Cartilaginous  l)ars  appear  in  the  visceral  arches,  and  from  that  in 
the  mandibular  arch  on  each  side — Meckel's  cartilage; — the  symphysis 
of  the  jaw,  the  malleus,  and  possibly  the  incus  are  formed.  The 
stapes  is  the  result  of  a  separate  ossification  round  the  stapedial 
artery.  The  remainder  of  the  mandible  is  ossified  in  the  membrane 
around  the  mandibular  cartilage. 

From  the  second  bars  the  anterior  part  of  the  body  of  the  hyoid 
bone,  its  small  cornua,  the  stylo-hyoid  ligaments,  and  the  styloid  pro- 
cesses are  developed.  The  cartilages  of  the  third  arches  give  rise  to 
the  posterior  part  of  the  body  of  the  hyoid,  and  its  great  cornua; 
the  cartilages  of  the  remaining  arches  take  part  in  the  formation  of 
the  cartilages  of  the  larynx. 

In  mammals  the  clefts  between  the  arches  are  merely  grooves 
which  do  not  communicate  with  the  cavity  of  the  foregut,  as  they  do 
in  fishes  and  amphibians.  The  outer  depression  of  the  first  cleft  forms 
the  external  auditory  meatus,  and  the  inner  depression  is  converted 
into  the  tympanic  cavity  and  the  Eustachian  tube.  The  remaining 
clefts  disappear. 

The  cranial  nerves  are  also  associated  with  the  arches  and  clefts. 
The  third  division  of  the  fifth  is  distributed  to  the  mandibular  arch, 
its  second  division  goes  to  the  maxillary  process,  and  its  first  division 
to  the  fronto-nasal  process.  The  seventh  is  the  nerve  of  the  second 
arch,  the  ninth  belongs  to  the  third  arch,  and  the  remaining  arches 
are  associated  with  the  tenth  nerve. 


Development  of  the  Vascular  System. 

We  have  already  seen  that  at  an  early  stage  of  development,  blood- 
vessels begin  to  form  in  the  splanchnic  mesoblast  on  the  wall  of  the 
yolk-sac,  outside  the  embryo,  in  an  area  called  the  area  vasculosa. 
From  the  cephalic  end  of  this  area  two  longitudinal  vessels  run  back- 
wards through  the  embryonic  region,  and  they  terminate  posteriorly  in 
the  caudal  part  of  the  area  vasculosa  (fig.  647).  As  they  run  through  the 
embryonic  region,  which  is  still  outspread  on  the  surface  of  the  ovum, 
they  pass  beneath  the  pericardium,  and  then  beneath  the  inner  parts 
of  the  protovertebrae,  not  far  from  the  sides  of  the  notochord.  As  the 
head  and  the  tail  folds  of  the  embryo  form,  these  longitudinal 
vascular  tubes  are  bent,  both  in  front  and  behind,  and,  after  the 
bending,  each  consists  of  five  parts.  A  dorsal  part  which  extends 
along  the  dorsal  wall  of  the  alimentary  canal ;  two  ventral  parts,  one 
in  front  of  the  umbilicus  and  one  behind  that  orifice,  and  two  arches,  a 
cephalic  and  a  caudal,  connecting  the  dorsal  portion  of  each  vessel  with 
the  anterior  and  posterior  ventral  portions  respectively  (figs.  636, 637,  and 


862 


DEVELOPMENT 


[CH.  LIX. 


648).  The  blood  flows  from  the  anterior  part  of  the  yolk-sac  wall  into 
the  anterior  ventral  parts  of  these  primitive  embryonic  vessels  by  two 
channels,  which  are  called  the  omphalo-mesenterie  veins.  The  anterior 
ventral  vessels  into  which  the  omphalo-mesenterie  veins  pass,  lie,  now 


Fio.  047. — Diagram  representing  the  arrangement  of  the  primitive  blood-vessels  before  the  embrj-o  is 
folded  off  from  the  ovum.  1,  Primitive  vessel  of  left  side  ;  2,  protovertebra  ;  3,  primitive  streak  ; 
4,  vascular  area  of  yolk-sac  ;  5,  non-vascular  area  of  yolk-sac  ;  6,  splanchnic  mesoblast ;  V,  somatic 
mesoblast ;  8,  epiblast ;  9,  pericardium. 

that  the  folding  of  the  embryo  has  taken  place,  in  the  dorsal  wall  of 
the  pericardium  and  on  the  ventral  wall  of  the  foregut ;  they  are  the 
primitive  heart  tubes,  and  their  anterior  ends  run  into  the  first 
cephalic  aortic  arches,  which  pass  round  the  sides  of  the  anterior  end 
of  the  foregut  into  the  primitive  dorsal  vessels.  A  little  later  the 
parts  of  the  anterior  ventral  vessels  in  front  of  the  heart  are  con- 
nected with  the  dorsal  vessels  by  four  additional  arches,  one  in  each 
visceral  arch — that  is,  there  are  now  five  aortic  arches  on  each  side 
connecting  the  anterior  parts  of  the  ventral  with  the  anterior  parts  of 
the  dorsal  vessels.  The  portions  of  the  ventral  vessels  which  lie  behind 
the  arches  in  the  dorsal  wall  of  the  pericardium  rapidly  enlarge,  and 
they  fuse  together  to  form  the  single  heart,  which  is  thus  for  a  time 
a  single  longitudinal  vessel.  The  parts  of  the  ventral  and  dorsal 
vessels  immediately  behind  each  arch  are  called  the  roots  of  the  arch. 

In  mammals,  the  first  and  second  arches  disappear,  and  their 
ventral  roots  become  the  external  carotid  artery.  The  third  arches 
and  the  dorsal  roots  of  the  first  and  second  arches  form  the  internal 
carotids.  The  dorsal  root  of  the  third  arch  disappears  on  each  side, 
and  the  ventral  root  forms  the  common  carotid  artery.     The  ventral 


uir.  ux.] 


THE   AORTIC   ARCHES 


863 


root  of  the  right  fourth  arch  becomes  the  innominate  artery,  and 
the  arch  itself  takes  part  in  the  formation  of  the  right  subclavian 
artery.  The  dorsal  roots  of  the  right  fourth  and  fifth  arches  and  the 
dorsal  part  of  the  fifth  arch  itself  disappear,  and  the  ventral  part 
of  the  fifth  arch  becomes  the  riglit  pulmonary  artery.  The  left  fourth 
arch,  with  its  dorsal  and  ventral  roots, 
and  the  dorsal  root  of  the  left  fifth 
arch,  take  part  in  the  formation  of  the 
arch  of  the  aorta.  The  left  fifth  arch 
persists  till  birth,  then  its  dorsal  part 
becomes  a  fibrous  cord,  the  Ugamentum 
arteriosum,  and  its  ventral  part  forms 
the  left  pulmonary  artery  (fig.  650). 

The  five  aortic  arches  correspond 
with  the  gill  arteries  of  fishes,  but  in 
mammals  they  never  break  up  into 
capillaries,  as  in  the  fishes'  gills.  In 
ampliibia  three  pairs  persist  throughout 
life.  In  reptiles  the  fourth  pair  re- 
mains throughout  life  as  the  permanent 
right  and  left  aortae.  In  birds  the 
right  fourth  remains  as  the  permanent 
aorta,  curving  over  the  right  bronchus, 
whereas  in  mammals,  the  left  fourth 
arch  becomes  the  permanent  aorta, 
curving  over  the  left  bronchus. 

Behind  the  dorsal  roots  of  the  fifth 
arches  the  dorsal  longitudinal  vessels 
fuse  together,  as  far  back  as  the  lumbar 
region,  to  form  the  descending  aorta, 
and  the  lower  or  posterior  end  of  this 
vessel  is  continued  at  first  through  the  caudal  arches  into  the  pos- 
terior ventral  portions  of  the  longitudinal  vessels  which  end  on  the 
yolk-sac  (fig.  649).  As  soon  as  the  allantois  forms,  each  of  the 
posterior  ventral  vessels  gives  off  a  large  branch  to  it,  and  in  front 
of  the  origin  of  this  vessel  it  atrophies,  so  that  now  the  dorsal  vessels 
are  continued  through  the  caudal  arches  into  the  allantoic  or  umbilical 
arteries,  which  carry  blood  to  the  placenta,  and  new  vessels  of  small 
size  are  given  off  from  the  descending  aorta  to  the  yolk-sac.  A  little 
later  the  primary  caudal  arches,  which  lie  inside  the  posterior  ends 
of  the  Wolffian  ducts,  are  replaced  by  new  arches,  which  pass  out- 
side the  ducts,  and  connect  the  posterior  ends  of  the  dorsal  longi- 
tuLhnal  vessels  with  the  allantoic  arteries.  At  the  same  time  the 
hind  limbs  appear,  and  each  receives  a  branch  from  the  corresponding 
dorsal  vessel ;  this  is  the  external  iliac  artery.     After  its  appearance 


Fio.  64S. — Diagram  representing  the 
primitive  blood-vessels  of  the  embryo. 
1,  First  cephalic  aortic  arch  ;  2,  anterior 
ventral  part  of  primitive  vessel ;  3, 
dorsal  part  of  primitive  vessel ;  4, 
vascular  area  of  yolk-sac  ;  5,  posterior 
ventral  part  of  primitive  vessel ;  6, 
caudal  aortic  arch  ;  7,  allantoic  or 
umbilical  branch ;  S,  umbilical  or 
allantoic  vein  ;  1),  placenta. 


864 


DEVELOPMENT 


[CII.  LIX. 


the  part  of  the  dorsal  vessel  between  it  and  the  aorta  is  the  common 
iliac  artery,  and  the  portion  of  the  dorsal  vessel  behind  it,  together 
with  the  caudal  arch,  becomes  the  internal  iliac  or  hypogastric  artery. 


Fio.  649.— Diagram  representing  arrangement  of  primitive  blood-vessels  of  left  side  of  embryo.  1,  Left 
primitive  jugular  vein;  2,  left  duct  of  Cuvier  ;  3,  left  cardinal  vein  ;  4,  protovertebra  ;  ,^,  primitive 
intestine  ;  6,  caudal  aortic  arch  ;  7,  allantoic  or  umbilical  artery  ;  8,  placenta  ;  9,  atrophied 
posterior  ventral  part  of  primitive  vessel ;  10,  yolk-sac  artery  ;  11,  yolk-sac  ;  12,  \ascular  area  on 
yolk-sac  ;  13,  pericardium  ;  14,  heart ;  15,  cephalic  aortic  arch  ;  16,  brain. 

This  is  continued  in  the  embryo  along  the  ventral  wall  of  the  body  as 
an  umbilical  artery  to  the  placenta. 

The  Heart. — The  simple  longitudinal  heart  soon  becomes  separ- 
ated by  three  transverse  constrictions  into  four  chambers,  which  are, 
from  behind  forwards,  the  sinus  venosus,  the  auricle,  the  ventricle,  and 
the  aortic  bulb  (figs.  651  and  652).  The  sinus  venosus  receives  the 
omphalo-mesenteric  and  other  .veins,  and  the  aortic  bulb  terminates 
in  the  fifth  arches  and  the  ventral  roots  of  the  fourth  arches.  The 
sinus  venosus  is  gradually  absorbed  into  the.  auricle,  and  at  the  same 
time  the  heart  tube  bends  so  that  the  auricle  is  placed  behmd  the 
ventricle  and  the  aortic  bulb — that  is,  between  them  and  the  wall 
of  the  foregut  (figs.  653  and  654).  As  soon  as  the  bending  is  com- 
pleted each  chamber  is  divided  by  septa  into  right  and  left  halves, 
but  an  opening,  the  foramen  ovale,  remains  in  the  interauricular 
septum  till  after  birth.  The  aortic  bulb  is  also  divided  into  two 
parts :  one  of  these  is  connected  above  with  the  fifth  arches,  which 
become  the  pulmonary  arteries,  and  below  with  the  right  ventricle ; 
it  becomes,  therefore,  the  stem  of  the  pulmonary  artery.     The  other 


ClI.  LIX.] 


DEVELOPMENT   OF   THE   VEINS 


865 


part,  which  is  connected  with  the  roots  of  the  fourtli  arches  above 
and  the  left  ventricle  below,  forms  the  asceiKhiig  [)art  (jf  tlie  aorta. 


Fig.  650. — Diagram  of  the  aortic  arches  in  a  mammal,  showing  transformations  which  give  rise  to  the 
permanent  arterial  vessels.  A,  Primitive  arterial  stem  or  aortic  bulb,  now  divided  into  A,  the 
ascending  part  of  the  aortic  arch,  and  p,  the  pulmonary;  a  a',  right  ami  left  aortic  roots; 
A',  descending  aorta;  1,  2,  3,  4,  5,  the  five  primitive  aortic  or  branchial  arches;  /,  //,  ///,  IV,  the 
four  branchial  clefts  which,  for  the  sake  of  clearness,  have  been  omitted  on  the  right  side.  The 
permanent  systemic  vessels  are  deeply,  the  pulmonary  arteries  lightly,  shaded ;  the  parts  of  the 
primitive  arches  which  are  transitory  are  simply  outlined ;  c,  placed  between  the  permanent 
common  carotid  arteries;  ce,  external  carotid  arteries;  ci,  intemat  carotid  arteries;  s,  right 
subclavian,  rising  from  the  right  aortic  root  beyond  the  fifth  arch ;  v,  right  vertebral  from  the 
same,  opposite  the  fourth  arch;  v'  s',  left  vertebral  and  subclavian  arteries  rising  together  from 
the  left,  or  permanent  aortic  root,  opposite  the  fourth  arch  ;  p,  pulmonary  arteries  rising  together 
from  the  left  fifth  arch ;  d,  outer  or  back  part  of  left  fifth  arch,  forming  ductus  arteriosus ;  p  n, 
pn',  right  and  left  pneumogastric  nerves  descending  in  front  of  aortic  arch,  with  their  recurrent 
branches  represented  diagraramatically  as  passing  behind,  to  illustrate  the  relations  of  these  nerves 
respectively  to  the  right  subclavian  artery  (4)  and  the  arch  of  the  aorta  and  ductus  arteriosus  (d), 
(Allen  Thomson,  after  Rathke.) 

The  Veins. — The  veins  of  the  embryo  are: — 1.  The  omphalo- 
mesenteric, wliich  carry  blood  from  the  yolk-sac  to  the  heart. 
2.  The  umbilical  or  allantoic,  bearing  oxygenated  blood  from  the 
placenta  to  the  heart.  3.  The  primitive  jugular  veins,  one  on  each 
side  returning  blood  from  the  head,  neck,  and  upper  extremities. 
4.  The  cardinal  veins  returning  blood  from  the  body  walls,  the 
Wolffian  bodies,  and  the  hind  limbs.  5.  The  ducts  of  Cuvier,  each  of 
which  receives  a  primitive  jugular  and  a  cardinal  vein.  Thus  six  veins 
terminate  in  the  sinus  venosus,  and  the  blood  passes  through  into 
the  auricle  (fig.  651).  Both  ducts  of  Cuvier  retain  their  connection 
with  the  auricle,  the  right  forming  the  lower  part  of  the  superior 
vena  cava,  and  the  left  the  oblique  vein  of  Marshall  in  man,  and  the 
lower  part  of  the  left  superior  cava  in  some  mammals. 

The  upper  part  of  the  primitive  jugular  vein  on  each  side  becomes 
the  internal  jugular.     The  lower  part  on  the  right  side  becomes  the 

3  I 


866 


DEVELOPMENT 


[oil  LIX. 


right  innominate  vein,  and  the  upper  portion  of  the  superior  vena 


Fio.  651. — Diagram  representing  an 
anterior  view  of  the  primitive 
heart,  aortic  arches,  and  their 
roots.  1,  Bulbus  arteriosus;  2, 
ventricle ;  3,  auricle ;  4,  sinus 
venosus ;  5,  desceniling  aorta  ;  6, 
omphalo-meseuteric  vein ;  7,  um- 
bilical vein  ;  8,  duct  of  Cuvier  ; 

9,  dorsal  roots  of  aortic  arches  ; 

10,  ventral  roots  of  aortic  arches. 


Fig.  652.— Diagram  representing  a  side  view  of  the 
primitive  heart  with  the  cephalic  aortic  arches 
and  their  roots.  1,  First  cephalic  aortic  arch  ;  '2, 
second  cephalic  aortic  arch ;  3,  third  cephalic 
aortic  arch  ;  4,  fourth  cephalic  aortic  arch  ;  5, 
fifth  cephalic  aortic  arch ;  6,  bulbus  arteriosus ; 
7,  ventricle  ;  8,  auricle ;  9,  sinus  venosus  ;  10, 
omphalo-mesenteric  vein  (left);  11,  ventral  roots 
of  aortic  arches  ;  1'2,  dorsal  roots  of  aortic  arches ; 
18,  descending  aorta. 


cava.     On  the  left  side  the  lower  part  helps  to  form  the  left  superior 
mtercostal  vein. 


Fig.  653. — Diagram  representing  a  side  view  of 
heart  after  it  has  folded  on  itself.  4,  Ventral 
root  of  fourth  aortic  arch ;  5,  fifth  aortic 
arch  ;  6,  bulbus  arteriosus  ;  7,  ventricle  ;  S, 
auricle ;  9,  sinus  venosus  ;  10,  left  omphalo- 
mesenteric vein. 


Fig.  654. — Diagram  representing 
an  anterior  view  of  the  heart 
after  it  has  folded  on  itself. 
4,  Ventral  root  of  fourth 
aortic  arch ;  5,  fifth  aortic 
arch  ;  6,  bulbus  arteriosus  ; 
7,  ventricle  ;  8,  auricle. 


The  left  innominate  vein  is  a  transverse  anastomosis  betvv^een  the 
primitive  jugular   veins.      The  subclavian   veins   and    the   external 


CH.  LTX.] 


DEVELOPMENT  OF  THE   VEINS 


867 


jugular   veins   are  new  formations,  the   former   being   developed   in 
association  with  the  growth  of  the  upper  limbs. 

The  cardinal  veins  receive  the  intercostal  and  lumbar  veins  from 
the  walls  of  the  body,  and  the 
veins  from  the  Wolffian  bodies 
and  kidneys.  Below  the  point  of 
union  with  the  external  iliac  vein 
from  the  hind  limb  the  cardinal 
vein  becomes  the  internal  iliac 
vein.  Above  the  external  iliac 
vein  the  right  cardinal  vein  forms 
the  right  common  iliac  vein,  and 
the  lower  part  of  the  inferior 
vena  cava  below  the  right  renal 
vein.  Above  the  right  renal  vein 
it  becomes  the  vena  azygos  major. 
The  parts  of  the  left  cardinal 
between  the  left  lumbar  veins 
disappear,  and  blood  from  the 
left  lumbar  veins  and  the  left 
common  iliac  vein  is  carried 
across  to  the  right  cardinal,  and 
subsequently  to  the  inferior  vena 
cava  by  a  series  of  transverse 
anastomosing  channels,  of  which 
the  lowest  becomes  the  left  com- 
mon iliac  vein.  The  upper  part 
of  the  left  cardinal  vein  is  also 
broken  up,  and  its  remains  form 
the  vertical  parts  of  the  minor 
azygos  veins  and  lower  part  of 
the  left  superior  intercostal  vein. 
The  transverse  parts  of  the  minor 
azygos  veins  are  also  developed 
from  transverse  anastomosing 
channels  (fig.  655). 

In  the  early  stages  both  the 
omphalo-mesenteric  and  the  right 
and  left  terminal  branches  of  the 
umbilical  vein  end  in  the  heart. 
When  the  liver  forms,  the  om- 
phalo-mesenteric veins  end  in 
venae    advehentes,    which    break 

up  into  capillaries  in  the  liver,  and  the  capillaries  end  in  vense  reve- 
hentes,  which  become  the  hepatic  veins  (fig.  656).     The  left  hepatic 


Fig.  655. — The  dark  are  the  primitive,  the  light 
the  secondary  veins,  with  the  exception  of  the 
external  and  internal  jugular  veins.  The  dark 
portions  entering  the  auricles  are  the  remains 
of  the  primitive  ducts  of  Cuvier.  The  dark 
portion  above  each  duct  of  Cuvier,  as  far  as 
the  external  and  internal  jugular  veins,  is  the 
primitive  jugular  vein,  and  the  dark  portion 
below  the  duct  of  Cuvier  is  the  cardinal  vein. 
],  External  jugular  vein;  2,  internal  jugular 
vein ;  3,  subclavian  vein ;  4,  right  innominate 
vein  ;  5,  superior  vena  cava  ;  6,  right  superior 
intercostal  vein  ;  V,  vena  azygos  major ;  S,  right 
hepatic  vein  ;  9,  upper  part  of  inferior  vena 
cava;  10,  renal  vein;  11,  right  common  iliac 
vein;  12,  right  external  iliac  vein;  13,  right 
internal  iliac  vein ;  14,  left  innominate  vein  ; 
15,  left  superior  intercostal  vein  ;  1(3,  oblique 
vein  of  Marshall  ;  17,  vena  azygos  minor 
superior;  18,  vena  azygos  minor  inferior; 
19,  atrophied  part  of  left  cardinal  vein  ;  20,  left 
common  iliac  vein;  21,  auricle;  22,  duct  of 
Cuvier. 


868 


DEVELOPMENT 


[cn.  Lix. 


vein  joins  the  right  hepatic  vein  to  f(jnn  a  common  trunk,  which 
becomes  the  upper  end  of  the  inferior  vena  cava,  and  this  is  prolonged 
down  to  unite  with  the  right  cardinal  at  the  level  of  the  right  renal 
vein ;  but  before  joining  the  right  cardinal  it  gives  off  a  branch  to  join 
the  left  cardinal  at  the  level  of  the  left  renal  vein,  and  thus  the  blood 


Fig.  656.— Diagram  showing  the  arrangement  and  transformation  of  some  of  the  primitive  veins.  A, 
Early  stage  ;  B,  later  stage.  1,  Primitive  jugular  vein  ;  2,  duct  of  Cuvier;  3,  cardinal  vein  ;  4, 
right  umbilical  vein  ;  5,  right  omphalo-mesenteric  vein  ;  6,  common  umbilical  vein  ;  ",  sinus 
venosus  ;  8,  liver  ;  9,  left  umbilical  vein  ;  10,  right  vena  revehens  ;  11,  left  vena  revehens  ;  12,  right 
vena  advehens  ;  13,  left  vena  advehens. 


from  both  kidneys  enters  the  inferior  vena  cava.  In  the  meantmie 
two  transverse  anastomoses  have  formed  between  the  omphalo- 
mesenteric veins  below  the  liver,  and  still  lower  the  two  veins  fuse 
together;  thus  two  loops  are  formed  through  which  the  duodenum 
passes.  The  veins  from  the  intestine  open  into  the  fused  trunks,  and 
the  splenic  vein  enters  the  left  vein  at  the  level  of  the  lower  transverse 
anastomosis.  Subsequently  the  left  side  of  the  upper  and  the  right 
side  of  the  lower  loop  cUsappear,  and  the  portal  vein  is  produced  from 
the  remains.  In  the  meantime  the  right  umbilical  vein  has  disappeared, 
and  the  left  has  united  with  the  left  omphalo-mesenteric  vein  at  the 
point  where  the  latter  ends  in  the  left  vena  advehens.  From  this 
point  a  direct  channel  opens  up  beneath  the  liver  to  the  upj^er  part  of 
the  inferior  vena  cava ;  tliis  is  the  ductus  venosus,  and  it  conducts  the 
greater  part  of  the  oxygenated  blood  from  the  umbilical  vein  directly 
to  the  inferior  vena  cava,  and  so  to  the  right  auricle ;  but  part  of  the 
umbilical  blood  passes  into  the  liver  with  the  omphalo-mesenteric 
blood. 

A  pulmonary  vein  forms  and  carries  blood  from  the  lungs  to  the 


en.  MX.] 


THE   PffiTAL  CIRCULATION 


869 


left  auricle.     It  is  subsequently  replaced  first  by  two  veins,  one  from 
each  lung,  and  afterwards  four  veins,  two  from  each  lung. 


ff — ' 

It — — 6 


Fig.  657. — Diat,Tani  representing  a  later  stage  in  the  development  of  the  veins  than  that  shown  in  Jig. 
656.  1,  Primitive  jugular  vein  ;  2,  duct  of  Cuvier  ;  3,  upper  part  of  cardinal  vein,  novi'  vena  azygos 
major ;  5,  remains  of  light  lower  limb  of  loop  formed  by  fusion  of  omphalo-mesenteric  veins ;  6, 
common  umbilical  vein  ;  7,  sinus  venosus  ;  S,  liver  ;  9,  left  branch  of  umbilical  vein  ;  10,  right 
hepatic  vein  ;  11,  left  hepatic  vein  ;  12,  right  vena  advehens  ;  13,  left  vena  advehens  ;  14,  upper 
part  of  inferior  vena  cava  ;  15,  right  renal  vein  ;  16,  lower  part  of  inferior  vena  cava  (cardinal  vein) ; 
17,  fused  part  of  omphalo-mesenteric  vein  ;  IS,  vein  from  alimentary  canal  ;  19,  splenic  vein  ;  20, 
remains  of  left  upper  limb  of  looij  formed  by  fusion  of  omi)halo-mesenteric  veins ;  21,  ductus 
venosus. 


ClECULATION   OF   BlOOD   IN   THE   FCETUS 

The  circulation  of  blood  in  the  foetus  differs  considerably  from 
that  of  the  adult.  It  will  be  well,  perhaps,  to  begin  its  description 
by  tracing  the  course  of  the  blood,  which,  after  being  carried  to  the 
placenta  by  the  two  umbilical  arteries,  has  returned,  oxygenated  and 
replenished,  to  the  foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and  there 
the  stream  is  divided, — a  part  of  the  blood  passing  straight  on  to  the 
inferior  vena  cava,  through  a  venous  canal  called  the  dudics  venosits, 
while  the  remainder  passes  into  the  portal  vein,  and  reaches  the 
inferior  vena  cava  after  circulating  through  the  liver.  Whether, 
however,  by  the  direct  route  through  the  ductus  venosus  or  by  the 
roundabout  way  through  the  liver, — all  the  blood  which  is  returned 


870 


DEVELOPMENT 


[CH.  LIX. 


from  the  placenta  by  the  umbilical  vein  reaches  the  inferior  vena 
cava  at  last,  and  is  carried  by  it  (together  with  the  blood  from  the 
lower  part  of  the  body  and  lower  limbs)  to  the  right  auricle  of  the 
heart,  into  which  cavity  is  also  pouring  the  blood  that  has  circulated  in 


Ji  C'cm.CuioUdL  , 

L  Cow:  CaiW'J. 


a      i.,?«w« 


•<^-.s-~.:\\--Aor}K 


/':■■    --,   ll|K/7      ,-f  \       A    -      .\ 


^.■'■-\'---'A-Ventrid'\\ 


X  -cm^ 


•'      jTtia/'t 
'<■  VVe'iii-ruU 


m-yr''--'--- 


Fig.  G5S. Diagram  of  tlie  Fcetal  Circulation. 

the  head  and  neck  and  arms,  and  has  been  brought  to  the  auricle  by  the 
superior  vena  cava.  It  might  be  naturally  expected  that  the  two 
streams  of  blood  would  be  mingled  in  the  right  auricle,  but  such  is 
not  the  case,  or  only  to  a  slight  extent.  The  blood  from  the  superior 
vena  cava — the  less  pure  fluid  of  the  two — passes  almost  exclusively 
into  the  right  ventricle,  through  the  auriculo-ventricular  opening,  just 


en.  LIX.]  DKVELOrMENT   OF   THE   NEKVOUS    SYSTEM  871 

as  it  does  in  the  adult ;  while  the  blood  of  the  inferior  vena  cava  is 
directed  by  the  fold  of  the  lining  membrane  of  the  heart,  called  the 
Etistachian  valve,  through  the  foramen  ovale  into  the  left  auricle, 
whence  it  passes  into  the  left  ventricle,  and  out  of  this  into  the  aorta, 
and  thence  to  all  the  body,  but  chiefly  to  the  head  and  neck.  The 
blood  of  the  superior  vena  cava,  which,  as  before  said,  passes  into  the 
right  ventricle,  is  sent  out  from  there  in  small  amount  through  the 
pulmonary  artery  to  the  lungs,  and  thence  to  the  left  auricle,  by  the 
pulmonary  veins,  as  in  the  adult.  The  greater  part,  however,  does 
not  go  to  the  lungs,  but  instead,  passes  through  a  canal,  the  ductus 
arteriosus,  leading  from  the  pulmonary  artery  into  the  aorta  just  below 
the  origin  of  the  three  great  vessels  which  supply  the  upper  parts  of 
the  body ;  and  there  meeting  that  part  of  the  blood  of  the  inferior 
vena  cava  which  has  not  gone  into  these  large  vessels,  it  is  distributed 
with  it  to  the  trunk  and  other  parts — a  portion  passing  out  by  way 
of  the  two  umbilical  arteries  to  the  placenta.  From  the  placenta  it 
is  returned  by  the  umbilical  vein  to  the  under  surface  of  the  liver, 
from  which  the  description  started. 

Changes  after  Birth. — Immediately  after  birth  the  foramen  ovale 
begins  to  close,  and  so  do  the  ductus  arteriosus  and  ductus  venosus, 
as  well  as  the  umbilical  vessels ;  the  closure  is  completed  in  a  few- 
days,  so  that  the  circulation  then  takes  the  course  it  traverses  for 
the  rest  of  life. 

Development  of  the  Nervous  System. 

The  nervous  system  originates  from  the  thickened  walls  of  the 
medullary  groove,  which  by  the  meeting  of  the  dorsal  ridges  is  con- 
verted into  the  medullary  canal.  These  walls  are  composed  entirely 
of  epiblast.  The  anterior  part  of  this  mass  becomes  the  brain,  the 
rest  of  it  the  spinal  cord ;  the  canal  itself  is  seen  in  the  adult  as  the 
ventricles  of  the  brain  and  central  canal  of  the  spinal  cord.  The 
nerves  are  formed  of  epiblast  too ;  they  are  outgrowths  from  masses 
of  cells  called  neuroblasts,  the  primitive  nerve-cells.  In  the  case, 
however,  of  the  olfactory  and  optic  nerves  we  have  not  to  deal  with 
solid  outgrowths,  but  with  hollow  protrusions  from  the  brain,  which 
become  solid  at  a  later  stage. 

The  Spinal  Cord. — The  cavity  formed  by  the  closure  of  the 
neural  canal  soon  becomes  a  cleft  running  from  before  backwards.  It 
is  bounded  at  first  by  columnar  epithelium ;  these  cells  afterwards 
become  ciliated ;  on  their  exterior  is  a  homogeneous  basement  mem- 
brane. The  wall  soon  becomes  thicker,  and  the  basement  membrane 
is  thus  separated  further  and  further  from  the  central  canal.  This 
increase  in  thickness  is  due  in  part  to  the  increase  in  length  of  the 
columnar  cells  which  are  called  spongioblasts :  in  part  to  the  appear- 
ance of  new  cells.     The  inner  part  of  the  columnar  lining  retains 


872 


DEVELOPMENT 


[CH.  LIX. 


Fio.  659. — Inner  ends  of  spongio- 
blasts (S),  with  germinal  cells 
(G)  between  them.  NN,  neuro- 
blasts which  have  resulted  from 
the  division  of  a  germinal  cell ; 
M,  myelospongium  formed  by 
the  branching  outer  ends  of  the 
spongioblasts.    (After  His.) 


its  palisade-like  character,  and  forms  ultimately  the  lining  epithelium 
of  the  central  canal.  The  external  ends  of  the  cells  break  up  into 
a  reticulum  called  the  myelospongium,  and  this  is  limited  externally 

by  the  basement  membrane  at  the  circum- 
ference. The  myelospongium  forms  the 
neuroglia. 

Between  the  inner  ends  of  the  spongio- 
blasts (fig.  659,  S)  numerous  rounded  cells 
called  germmal  cells  (G)  next  appear.  These 
rapidly  divide,  and  so  form  neuroblasts  (N). 
The  neuroblasts  are  the  primitive  nerve-cells. 
They  are  pear-shaped ;  each  has  a  large  oval 
nucleus,  and  its  tapering  stalk  becomes 
the  axis  cylinder  process  of  the  adult 
nerve-cell.  At  a  later  period  other  pro- 
cesses, the  dendrites,  grow  out  from  the 
cell-body.  The  nerve  sheaths  are  formed 
later. 

The  neuroblasts  collect  into  groups,  one 
of  which,  especially  large,  is  at  the  situation  of  the  future  anterior 
horn ;  the  processes  of  the  primitive  nerve-cells  pass  out  of  the  cord 
as  the  beginnings  of  the  anterior  roots  (fig.  660).  The  somewhat 
oblique  coursing  of  these  fibres  before  they  leave  the  cord  forms 
the  beginning  of  the  anterior  white  column.  The  posterior  white 
columns  simultaneously  begin  to  apjDear  on  each  side  of  the  narrow 
dorsal  part  of  the  canal.  They  are  formed  by  the  posterior  roots 
entering  the  cord. 

As  the  cornua  of  grey  matter  grow  out  from  the  central  mass,  the 
anterior  fissure  and  the  posterior  septum  of  the  cord  begin  to  appear. 
The  anterior  or  ventral  fissure  is  simply  a  cleft  between  the  enlarg- 
ing lateral  halves  of  the  cord.  The  posterior  septum  is  formed  by  a 
condensation  of  the  neuroglia  in  the  dorsal  wall  of  the  neural  canal. 
The  lateral  columns  are  formed  by  the  processes  from  the  cells  of 
the  cord  and  processes  from  neuroblasts  in  the  brain  which  grow 
down  in  the  sides  of  the  cord,  and  become  medullated  at  a  later 
period.  The  membranes  and  blood-vessels  are  formed  from  mesoblast. 
Up  to  the  fourth  month  the  cord  and  vertebral  canal  increase  in 
length  pari  passu,  but  after  that,  the  vertebral  canal  grows  faster,  so 
that  at  birth  the  coccygeal  end  of  the  cord  is  opposite  the  third 
lumbar,  and  in  the  adult  opposite  the  first  lumbar  vertebra.  This 
gives  an  obliquity  to  the  lower  nerve  roots,  which,  together  with  the 
filum  terminale,  form  the  cauda  equina. 

The  Nerves. — Some  fibres  grow  from  the  spinal  cord  and  form 
the  anterior  roots  (p.  873,  fig.  660).  The  posterior  roots  are  formed 
in  the  following  way : — 


ClI.  LIX.] 


DEVELOPMENT   OF   THE   NEIiVES 


87J 


Along  the  dorsal  aspect  of  the  pnmitive  cord  a  crest  of  epiblast 
appears,  the  neural  crest.     Enlargements  of  this  appear  opposite  the 


Fio.  6tj0. — Section  of  spinal  cord  of  a  four  weeks  human  enibiyo.  Tlie  posterior  roots  are  continued 
within  the  cord  into  a  small  longitudinal  bundle,  which  is  the  rudiment  of  the  posterior  white 
column.  The  anterior  roots  are  formed  by  the  convergence  of  the  processes  of  the  neuroblasts. 
The  latter,  along  with  the  elongated  cells  of  the  myelospongium,  compose  the  grey  matter.    (His.) 

middle  of  each  pair  of  protovertebrse ;  they  grow  downwards  on  each 
side,  and  losing  their  attachment  to  the  cord,  they  become  isolated 


Fio.  601.— a.  Bipolar  cell  from  spinal  ganglion  of  a  4i  weeks  embryo  (after  His).  7),  Nucleus;  the 
arrows  indicate  the  direction  in  which  the  nerve  processes  grow,  one  to  the  spinal  cord,  the  other  to 
the  peripliery.  B,  a  cell  from  a  spinal  ganglion  of  the  adult ;  the  two  processes  have  coalesced  to 
form  a  T-shaped  junction.    (Diagrammatic.) 


874 


DEVELOPMENT 


[CH.  LIX. 


islands  of  epiblast,  each  of  which  contains  numerous  neuroblasts ;  each 
island  forms  a  spinal  ganglion,  and  the  neuroblasts  within  it  become 
the  cells  of  that  ganglion.  Two  processes  grow  from  each  cell ;  one 
directed  towards  the  spinal  cord,  where  it  contributes  to  the  forma- 
tion of  the  posterior  white  column,  and  ultimately  arborises  around 
the  cells  of  the  grey  matter  at  a  higher  level.  The  other  grows  to 
the  periphery.  The  two  processes  become  blended  in  the  first  part 
of  their  course,  and  so  the  T-shaped  junction  is  formed  (fig.  661). 
Small  portions  segmented  off  from  the  spinal  ganglia  form  the 
sympathetic  ganglia. 

The  Brain. — The  histological  details  of  the  formation  of  the 
epithelium  of  the  ventricles  from  spongioblasts,  of  neuroglia  from 
the  myelospongium,  of  nerve-cells  from  neuroblasts,  and  of  the 
nerve-fibres   of   the   white   matter  and   of  the  nerves   as   the  out- 


h      ^ 


Fig.  662. — Early  stages  in  development  of  human  brain  (magnified).  1,  2,  3,  are  from  an  embryo  about 
seven  weeks  old ;  4,  about  three  months  old.  m,  Middle  cerebral  vesicle  (mesencephalon)  ;  c,  cere- 
bellum ;  m  0,  medulla  oblongata ;  i  (in  fig.  3),  diencephalon  ;  7i,  telencephalon  ;  i',  infundibulum ; 
fig.  3  shows  the  several  curves  which  occur  in  the  course  of  development ;  fig.  4  is  a  lateral  view, 
showing  the  great  enlargement  of  the  cerebral  hemispheres  which  have  covered  in  the  thalami, 
leaving  the  optic  lobes,  m,  uncovered.    (KciUiker.) 

A'.B. — In  fig.  2  the  line  i  terminates  in  the  right  hemisphere ;  it  ought  to  be  continued  into  the 
diencephalon. 

growths  from  the  neuroblasts,  are  all  essentially  the  same,  as  already 
described  in  connection  with  the  spinal  cord.  But  the  grosser 
anatomical  details  differ. 

The  front  portion  of  the  medullary  canal  is  almost  from  the  first 


CH.  LIX.]  DEVELOPMENT   OF   THE   BRAIN  875 

widened  out  and  divided  into  three  vesicles.  From  the  anterior 
vesicle  the  two  primary  optic  vesicles  are  budded  off  laterally :  their 
further  history  will  be  traced  in  the  next  section.  Somewhat  later 
the  same  vesicle  divides  into  two,  and  thus  the  telencephalon  and 
diencephalon  are  formed. 

In  the  dorsal  wall  of  the  posterior  (third)  cerebral  vesicle,  a 
thickening  appears  (rudimentary  cerebellum)  which  becomes  separated 
from  the  rest  of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (fig.  662). 
(1.)  A  sharp  bend  of  the  whole  cerebral  mass  downwards  round  the 
end  of  the  notochord,  by  which  the  anterior  vesicle,  which  was  the 
highest  of  the  three,  is  bent  downwards,  and  the  middle  one  comes 
to  occupy  the  highest  position.  (2.)  A  sharp  bend,  with  the 
convexity  forwards,  which  runs  in  beneath  the  rudimentary  cere- 
bellum separating  it  from  the  medulla. 

Thus,  five  fundamental  parts  of  the  fcEtal  brain  may  be  distin- 
guished, which,  together  with  the  parts  developed  from  them,  may 
be  presented  in  the  following  tabular  view : — 

Table  of  Pauts  deaeloped  fhom  Flndamental  Parts  of  Braix. 

,^ Anterior  end  of  third  ventricle, 

^.    .    c,         J  ir    •  1  foramen  of  Monro,  lateral  ven- 

First    Secondary    Vesicle,        ^^^.^^        cerebral    hemispheres. 

Telencephalon,  or  Fore-       corpora  striata,  corpus  callosum, 

I.  Anterior  brain.  f^^^-      ,^^^^.^1  ventricles,  olfac- 

P"™Y-^'  I      torybulb. 

vesicle.  ,r    .  ,     ,  Thalami  optici,  pineal  gland,  part 

Second  Secondary  Vesicle,        ^^   pituitary   body,   third   ven- 

Dienc-ephalon,  or  Twixt-      ^^^f^^  ^p^^  ^^^^'^  ^^^  ^^^j^^^ 

°^^^^-  [     infundibulum. 

IL  Middle   phird   Secondary  Vesicle,  I  (.^  quadrigemina,      crura 

vS7     i     ^5.2^"'^^?^^^°°'°'^  ^^''^- I      cerebri,  aqueduct  of  Sylvius. 

TTT   T3    f    •      r  Fourth  Secondary  Vesicle,!  Fourth  ven- /Cerebellum       and 
ill.  rostenor|      or  Metencephalon.             /      tricle.  \     Pons. 

rriEaar>       ,  pifth    Secondary   Vesicle,!  Fourth  ven-fMeduUa        oblon- 
vesicie.       I      ^j.  Myelencephalon.           I     tricle.  \     gata. 

The  cerebral  hemispheres  formed  by  the  bifurcation  of  the 
telencephalon  grow  rapidly  upwards  and  backwards,  while  from 
their  inferior  surfaces  the  olfactory  bulbs  bud  out.  The  middle 
cerebral  vesicle  (mesencephalon)  for  some  time  is  the  most  pro- 
minent part  of  the  foetal  brain,  and  in  fishes,  amphibia,  and  reptiles, 
it  remains  uncovered  through  life  as  the  optic  lobes.  But  in  birds 
the  growing  cerebral  hemispheres  thrust  the  optic  lobes  down 
laterally,  and  in  mammalia  completely  overlap  them. 

In  the  lower  mammalia  the  backward  growth  of  the  hemispheres 
ceases  in  front  of  the  cerebellum,  but  in  the  higher  groups,  such  as  the 


876 


DEVELOPMENT 


[CH.  LIX. 


monkeys  and  man,  they  grow  still  further  back,  until  they  completely 
cover  in  the  cerebellum,  so  that  on  looking  down  on  the  brain  from 

above,  the  cerebellum  is  quite  con- 
cealed from  view.  The  surface  of 
the  hemispheres  is  at  first  quite 
smooth,  but  as  early  as  the  third 
month  the  great  Sylvian  fissure 
begins  to  be  formed  (fig.  663). 

The  next  to  appear  is  the 
parieto  -  occipital  fissure  ;  these 
two  great  fissures,  unlike  the  rest 
of  the  sulci,  are  formed  by  a 
curving  round  of  the  whole  cere- 
bral  mass. 

In  the  fifth  month  the  fissure 
of  Eolando  appears :  from  this 
time  till  the  end  of  foetal  life  the 
brain  grows  rapidly  in  size,  and 
the  convolutions  appear  in  quick  succession ;  first  the  great  primary 
ones  are  sketched  out,  then  the  secondary  ones.  The  commissures 
of  the  brain,  and  the  corpus  callosum,  are  developed  by  the  growth 
of  fibres  across  the  middle  line. 

The  Hippocampus  major  is  formed  by  the  folding  in  of  the  grey 
matter  from  the  exterior  into  the  lateral  ventricles. 

The  Eye. — Soon  after  the  first  three  cerebral  vesicles  have 
become  distinct  from  each  other,  the  anterior  one  sends  out  a  lateral 
vesicle  from  each  side  (primary  optic  vesicle),  which  grows  out 
towards  the  free  surface,  its  cavity  communicating  with  that  of  the 


Fio.  663 — Side  view  of  fielal  braiu  at  six  months, 
showing  commencement  of  formation  of  the 
principal  Assures  and  convolutions.  F,  Frontal 
lobe;  F,  parietal;  0,  occipital;  T,  temporal; 
o  a  a,  commencing  frontal  convolutions ; 
s,  Sylvian  fissure ;  s',  its  anterior  division ; 
c,  within  it  the  central  lobe  or  island  of  Keil ; 
r,  fissure  of  Rolando;  p,  parieto-occipital  fis- 
sure.    (R.  Wagner.) 


,i 


Fig.  664.— Longitudinal  section  of  tlie  primary  optic  vesicle  in  the  cliiclv,  magnified  (from  Remak).— A, 
from  an  embryo  of  sixty-five  hours ;  B,  a  few  hours  lat*r ;  C,  of  the  fourth  day  ;  c,  the  corneous 
layer  or  epidermis,  presenting  in  A  the  open  depression  for  the  lens,  which  is  closed  in  B  and  C ; 
I,  the  lens  follicle  and  lens;  pr,  the  primary  optic  vesicle;  in  A  and  B,  the  pedicle  which  forms 
the  optic  nerve  is  shown  ;  in  C,  the  section  being  to  the  side  of  the  pedicle,  the  latter  is  not  shown ; 
V,  the  secondary  optic  vesicle  and  vitreous  humour. 

cerebral  vesicle  through  the  canal  in  its  pedicle.  It  remains  con- 
nected to  the  diencephalon.  It  is  soon  met  and  invaginated  by 
an  ingrowing  process  from  the  epiblast  of  the  surface  (fig.   664). 


CH.  LIX.] 


DEVELOPMENT   OF   TITE   EYE 


877 


This  process  of  the  epiblast  is  at  first  a  depression,  which  ultimately 
becomes  closed  in  at  the  edges  so  as  to  produce  a  hollow  ball,  which 
is  thus  completely  severed  from  the  epidermis  with  which  it  was 
originally  continuous.  From  this  hollow  ball  the  crystalline  lens  is 
developed.  The  way  in  which  this  occurs  has  been  described  in  a 
previous  chapter  (see  p.  782).  As  the  lens  grows  inwards,  the  anterior 
wall  of  the  primary  optic  vesicle  is  forced  back  nearly  into  contact  with 
the  posterior,  and  thus  the  primary  optic  vesicle  is  almost  obliterated. 
The  cells  in  the  anterior  wall  of  the  optic  vesicle  are  much  longer 


Fio.  665.— Diagrammatic  sketch  of  a  vertical 
longitudinal  section  through  the  eyeball  of  a 
human  fcetus  of  four  weeks.  The  section  is  a 
little  to  the  side,  so  as  to  avoid  passing 
through  the  ocular  cleft ;  c,  the  cuticle  where 
it  becomes  later  the  corneal  epithelium ;  I, 
the  lens ;  op,  optic  nerve  formed  by  the 
pedicle  of  the  primary  optic  vesicle;  vp, 
primary  medullary  cavity  or  optic  vesicle  ;  p, 
the  pigment  layer  of  the  retina  ;  r,  the  inner 
wall  forming  the  remaining  layers  of  the 
retina  ;  vs,  secondary  optic  vesicle  containing 
the  rudiment  of  the  vitreous  humour,  x  100. 
(Kolliker.) 


Fig.  666. — Transverse  vertical  section  of 
the  eyeball  of  a  human  embryo  of 
four  weeks.  The  anterior  half  of 
the  section  is  represented  :  pr,  the 
remains  of  the  cavity  of  the  primary 
optic  vesicle ;  p,  the  inner  part  of  the 
outer  layer  forming  the  retinal  ijig- 
ment ;  r,  the  thickened  inner  part 
giving  rise  to  the  other  structures  of 
the  retina  ;  v,  the  commencing  vitre- 
ous humour  within  the  secondary 
optic  vesicle ;  v',  the  ocular  cleft 
through  which  the  loop  of  the  central 
blood-vessel,  a,  projects  from  below ; 
I,  the  lens  with  a  central  cavity,  x 
100.    (Kolliker.) 


than  those  of  the  posterior  wall ;  from  the  former  all  the  layers  of 
the  retina  are  developed,  except  the  layer  of  pigment  cells  which  is 
formed  from  the  latter. 

The  cup-shaped  hollow  in  which  the  lens  is  now  lodged  is  termed 
the  secondary  optic  vesicle;  its  walls  are  complete  except  below 
where  a  slit  exists,  known  as  the  choroidal  fissure. 

The  cavity  of  the  secondary  optic  cup  is  filled  by  processes  of  the 
neuroglia  cells  of  the  retina.  Amidst  these  a  process  of  vascular 
mesoblast  projects  through  the  choroidal  fissure,  and  by  the  union  of 
the  two  the  vitreous  humour,  the  lens  capsule,  and  the  capsulo-pupillary 
membrane  are  formed.  In  mammals  the  mesoblastic  process  projects, 
not  only  into  the  secondary  optic  vesicle,  but  also  into  the  pedicle  of 
the  primary  optic  vesicle,  invaginating  it  for  some  distance  from 


878  DEVELOPMENT  [CH.  LIX. 

beneath,  and  thus  carrying  up  the  arteria  centralis  retince  into  its 
permanent  position  in  the  centre  of  the  optic  nerve. 

This  invagination  of  the  optic  nerve  does  not  occur  in  birds,  and 
consequently  no  arteria  centralis  retinae  exists  in  them.  But  they 
possess  an  important  permanent  relic  of  the  original  protrusion  of 
the  mesoblast  through  the  choroidal  fissure,  in  the  peden,  while  a 
remnant  of  the  same  fissure  sometimes  occurs  in  man  under  the  name 
coloboma  iridis.  The  cavity  of  the  primary  optic  vesicle  becomes 
completely  obliterated,  and  the  rods  and  cones  get  into  apposition 
with  the  pigment  layer  of  the  retina.  The  inner  segments  of  the  rods 
are  the  first  formed,  then  the  outer.  The  cavity  of  the  pedicle  dis- 
appears and  the  solid  optic  nerve  is  formed.  Meanwhile  the  cavity  in 
the  centre  of  the  primitive  lens  becomes  filled  up  by  the  growth  of 
fibres  from  its  posterior  wall.  The  epithelium  of  the  cornea  is 
developed  from  the  epiblast,  while  the  corneal  tissue  proper  is  derived 
from  the  mesoblast  which  intervenes  between  the  epiblast  and  the 
primitive  lens  which  was  originally  continuous  with  it.  The  sclerotic 
coat  is  developed  round  the  eyeball  from  the  general  mesoblast  in 
which  it  is  imbedded.  The  choroid  is  developed  from  the  mesoblast 
on  the  outside  of  the  optic  cup,  and  the  iris  by  the  growing  forwards 
of  the  anterior  edge  of  the  optic  cup.  The  ciliary  processes  arise  from 
the  hypertrophy  of  the  edge  oi  the  optic  cup,  which  forms  folds  into 
which  the  choroidal  mesoblast  grows,  and  in  which  blood-vessels  and 
pigment-cells  develop. 

The  iris  is  completed  rather  late.  It  is  formed  by  the  anterior 
part  of  the  optic  cup,  accompanied  by  a  layer  of  mesoblast  from  the 
anterior  part  of  the  choroid,  projecting  inwards  between  the  lens 
and  the  cornea.  In  the  eye  of  a  mammalian  foetus,  the  pupil  is 
closed  by  a  delicate  membrane,  the  menibrana  pupillaris,  which 
forms  the  front  portion  of  a  highly  vascular  membrane  that 
surrounds  the  lens,  and  is  named  the  memhrana  capsulo-pupillaris. 
It  is  supplied  with  blood  by  a  branch  of  the  arteria  centralis 
retince,  which  passes  forwards  to  the  back  of  the  lens,  and  there 
subdivides.  This  branch  of  the  arteria  centralis  is  obliterated  in  the 
adult,  and  is  then  called  the  canal  of  Stilling.  The  membrana  capsulo- 
pupillaris  disappears  in  the  human  subject  a  short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals,  like 
those  of  birds,  are  first  developed  in  the  form  of  folds.  They 
extend  over  the  globe  of  the  eye  until  they  meet  and  become  firmly 
agglutinated  to  each  other.  But  before  birth,  or  in  the  carnivora 
after  birth,  they  separate. 

The  Ear. — Very  early  in  the  development  of  the  embryo  a 
depression  or  ingrowth  of  the  epiblast  occurs  on  each  side  of  the  head, 
which  deepens  and  soon  becomes  a  closed  follicle.  This  primary 
otic  vesicle  sinks  down  to  the  side  of  the  hind-brain ;  from  it  are 


CH.  LIX.]  DEVELOPMENT   OF   THE   ALIMENTARY   CANAL  879 

developed  the  epithelial  lining  of  the  memhranous  labyrinth  of 
the  internal  ear,  consisting  of  the  utricle,  saccule,  the  semicircular 
canals  and  the  scala  media  of  the  cochlea.  The  surrounding 
niesoblast  gives  rise  to  the  various  fibrous  bony  and  cartilaginous 
parts  which  complete  and  enclose  this  membranous  labyrinth,  the 
bony  semicircular  canals,  the  walls  of  the  cochlea  with  its  scala  vesti- 
buli  and  scala  tympani. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the 
external  auditory  passage,  are  the  remains  of  the  first  or  hyo- 
mandibular  cleft.  The  membrana  tympani  divides  the  cavity  of  this 
cleft  into  the  tympanum,  and  the  external  meatus.  The  mucous 
membrane  of  the  pharynx,  which  is  prolonged  in  the  form  of  a  diver- 
ticulum through  the  Eustachian  tube  into  the  tympanum,  and  the 
external  cutaneous  system  come  into  relation  with  each  other  at  this 
point;  the  two  structures  are  separated  only  by  the  membrane  of 
the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of  integu- 
ment in  the  neighbourhood  of  the  first  and  second  visceral  arches, 
and  probably  corresponds  to  the  gill-cover  (operculum)  in  fishes. 

The  Nose. — The  nose  originates,  like  the  eye  and  ear,  in  a  depres- 
sion of  the  superficial  epiblast  at  each  side  of  the  fronto-nasal  process 
(primary  olfactory  pit),  which  is  at  first  in  front  of  the  cavity  of  the 
primitive  mouth,  and  gradually  extends  backwards  into  its  roof 
(p.  859). 

The  olfactory  bulbs  of  the  brain  lie  in  close  relation  with  the 
roofs  of  the  olfactory  pits,  and  the  olfactory  nerves  are  out- 
growths from  special  bipolar  nerve-cells  imbedded  in  the  epithelium 
of  the  pit  (see  p.  748). 

Development  of  the  Alimentary  Canal. 

The  alimentary  canal  in  the  earliest  stages  of  its  development 
consists  of  three  parts — the  fore-  and  hind-gut  ending  blindly  at  each 
end  of  the  body,  and  a  middle  segment  which  communicates  freely 
on  its  ventral  surface  with  the  cavity  of  the  yolk-sac  through  the 
vitelline  or  omphalo-mesenteric  duct. 

From  the  fore-gut  are  formed  the  lower  and  back  part  of  the 
mouth,  the  pharynx,  oesophagus,  stomach,  and  first  and  second  parts 
of  the  duodenum ;  from  the  hind-gut,  the  lower  end  of  the  colon,  the 
rectum,  the  bladder,  the  urethra  in  the  female,  and  part  of  the 
urethra  in  the  male.  The  upper  and  front  part  of  the  mouth, 
and  the  nasal  chambers  are  developed  from  the  stomadaeal  space 
(p.  859). 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed  by 
a  circular  elevation  of  the  surface  tissues  and  the  breaking  down  of 


880 


DEVELOPMENT 


[CH.  LIX. 


the  septum  which  separates  the  posterior  eud  of  the  hind-gut  from 
the  exterior.  When  the  septum  does  not  break  down,  or  v.hen 
the  posterior  part  of  the  hind-gut  is  abnormally  obliterated,  the 
condition  known  as  imperforate  anus  results. 

The  middle  portion  of  the  digestive  canal  becomes  more  and  more 
closed  in,  till  its  wide  communication  with  the  yolk-sac  becomes 
narrowed  down  to  a  small  duct  (vitelline).  This  duct  usually  com- 
pletely disappears  in  the  adult,  but  occasionally  the  proximal  portion 
remains  as  a  diverticulum  from  the  intestine,  Meckel's  diverticulum. 
Sometimes  a  remnant  of  the  diverticulum  forms  a  fibrous  cord 
which  connects  a  part  of  the  intestine  to  the  umbilicus.  Such  a 
cord  has  been  known  to  cause,  in  after-life,  strangulation  of  the 
bowel  and  death. 

The  primitive  alimentary  canal  lies  in  the  form  of  a  straight  tube 
close  beneath  the  vertebral  column,  but  it  gradually  becomes  long, 
convoluted,  and  divided  into  its  special  parts,  stomach,  small  intestine, 
and  large  intestine  (fig.  667),  and  at  the  same  time  comes  to  be 


Fio.  667.— Outlines  of  the  form  and  position  of  the  alimentary  canal  in  successive  stages  of  its  develop- 
ment. A,  Alimentary  canal,  etc.,  in  an  embryo  of  four  weeks  ;  B,  at  six  weeks  ;  C,  at  eight  weeks  ; 
J,  the  primitive  lungs  connected  with  the  pharynx;  s,  the  stomach;  d,  duodenum;  i,  the  small 
intestine;  i',  the  large  intestine;  c,  the  caecum  and  vermiform  appendage;  r,  the  rectum;  cl,  in 
A,  the  cloaca ;  a,  in  B,  the  anus  distinct  from  si,  the  sinus  uro-genitalis ;  v,  the  yolk-sac ,  vi,  the 
vitello-intestinal  duct;  u,  the  urinary  bladder  and  urachus  leading  to  the  allautois;  g,  genital 
ducts.    (Allen  Thomson.) 


suspended  in  the  abdominal  cavity  by  means  of  a  lengthening 
mesentery,  formed  from  the  splanchnopleur,  which  attaches  it  to  the 
vertebral  column.  The  stomach  originally  has  the  same  direction  as 
the  rest  of  the  canal ;  its  cardiac  extremity  being  superior,  its  pylorus 
inferior.     The  changes   of  position  which  succeed  may  be  readily 


CH.  LIX.]  DEVELOPMENT   OF   THE   DIGESTIVE   GLANDS 


881 


understood  from  the  accompanying  figure  (fig.  667).  The  principal 
glands  in  connection  with  the  intestinal  canal  are  the  salivary 
glands,  pancreas,  and  the  liver. 

Salivary  Glands. — In  mammalia,  each  salivary  gland  first 
appears  as  a  bud-like  process  of  epithelium  lying  in  a  mass  of 
mesoblast,  and  continuous  with  the  epithelium  of  the  mouth.  As 
the  development  of  the  gland  advances,  the  bud  grows,  ramifies, 
and  becomes  hollow.  The  submaxillary  and  sublingual  glands  are 
developed  exactly  in  the  same  way,  and  their  cells  are  derived  from 
the  hypoblast  lining  the  fore-gut,  while  those  of  the  parotid  glands 
are  formed  from  the  epiblast  lining  the  stomadaeum.  In  all  cases 
the  blood-vessels  and  connective  tissues  are  formed  from  the 
mesoblast  into  which  the  glandular  structure  grows. 

The  Liver  and  Pancreas. — The  secreting  portions  of  the  liver 
and  pancreas  are  also  developed  as  diverticula  from  the  alimentary 
canal,  and  they  are  essentially  similar  to  the  diverticula  which  form 


Fig.  G6S.— a,  B,  C,  D,  Schematic  representations  of  four  stages  in  the  development  of  the  liver  and 
pancreas.  E  (after  Stoss,  modified),  diagram  of  a  transverse  section  through  the  fore-gut  in  the 
region  of  the  hepato-pancreatic  diverticulum. 
A  (in  diagram  B),  Aorta,  dp,  Dorsal  pancreatic  diverticulum,  ds,  Duct  of  Santorini.  dw, 
Duct  of  Wirsung.  o,  Gall  bladder,  i,  Intestine,  l,  Rudiment  of  liver,  lpd,  Hepato-pancreatic 
diverticulum,  n,  Xotochord.  p,  Pleuro-peritoneal  cavity,  s,  Stomach,  sp,  Spinal  cord,  vp. 
Ventral  pancreatic  diverticulum. 

the  secreting  parts  of  the  salivary  glands,  but  there  are  special  points 
about  the  development  of  the  two  abdominal  glands  which  require 
particular  consideration.  The  liver  is  formed  by  a  primarily  single 
diverticulum  from  the  ventral  wall  of  the  posterior  part  of  the  fore- 

^  K 


882  DEVELOPMENT  [CH.  LIX. 

gut,  and  the  pancreas  by  two  diverticula,  a  dorsal  which  springs 
from  the  dorsal  wall  of  the  gut  opposite  the  liver  diverticulum, 
and  a  ventral  which  springs  from  the  right  side  of  the  liver 
diverticulum. 

The  body  of  the  ventral  hepato-pancreatic  diverticulum  separates 
into  an  anterior  and  a  posterior  part.  The  former  becomes  the 
common  hepatic  duct,  and  from  its  anterior  end  two  buds  grow  out 
which  become  the  right  and  left  hepatic  ducts ;  the  branches  of  these 
grow  into  the  ventral  mesentery  and  into  a  mass  of  mesoblast  called 
the  septum  transversum,  and  they  form,  with  the  surrounding 
mesoblast,  the  liver  substance.  The  posterior  segment  of  the  ventral 
diverticulum  is  the  rudiment  of  the  gall  bladder  and  the  cystic  duct, 
whilst  the  root  of  the  diverticulum  is  converted  into  the  common 
bile  duct,  and  the  ampulla  of  Vater  which  lies  in  the  substance  of 
the  wall  of  the  duodenum  and  opens  into  its  cavity. 

The  dorsal  pancreatic  diverticulum  grows  into  the  dorsal 
mesentery  and  forms  with  the  surrounding  mesoblast  a  portion  of 
the  head,  and  the  body  and  tail  of  the  pancreas.  Two  ventral 
pancreatic  diverticula  spring  from  the  root  of  the  common  ventral 
evagination,  but  the  left  soon  disappears  and  the  right  grows  round 
the  side  of  the  gut  into  the  dorsal  mesentery  where  it  takes  part  in 
the  formation  of  the  head  of  the  pancreas.  In  man  the  stem  of  the 
ventral  diverticulum  fuses  with  the  stem  of  the  dorsal  diverticulum 
which  thereafter  loses  its  connection  with  the  gut,  and  as  a  result 
the  duct  of  the  adult  pancreas  or  duct  of  Wirsung  consists  of  the 
stem  of  the  ventral  diverticulum  and  the  stem  of  the  dorsal  diverti- 
culum beyond  the  point  of  fusion  of  the  two.  The  remainder  of  the 
dorsal  diverticulum  is  the  duct  of  Santorini.  In  some  animals  both 
dorsal  and  the  ventral  diverticula  retain  their  connection  with  the 
duodenum,  and  the  pancreas  has  two  ducts.  This  condition  is  not 
uncommonly  present  in  man  also. 

The  spleen  and  lymphatic  glands  are  developed  from  the  meso- 
blast :  the  thyroid  originates  from  the  hypoblast ;  it  grows  as  a  median 
diverticulum  from  the  floor  of  the  fore-gut,  opposite  the  first  clefts, 
and  by  two  diverticula  from  the  fourth  visceral  clefts.  The  hypo- 
blastic  cells  form  the  lining  epithelium  of  the  vesicles ;  the  stroma  of 
the  gland  is  formed  by  the  surrounding  mesoblast.  The  thymus  is 
formed  in  a  similar  way  from  the  third  visceral  clefts,  and  its  hypo- 
blastic  cells  form  the  corpuscles  of  Hassall ;  the  lymphoid  tissue  by 
which  they  are  invaded  and  ultimately  surrounded  is  mesoblastic. 

Development  of  the  Respiratory  Apparatus. 

The  rudiment  of  the  larynx,  trachea,  bronchi,  and  lungs  appears 
as  a  small  longitudinal  groove  in  the  ventral  wall  of  the  fore -gut. 


CH.  LIX.] 


DEVELOPMENT   OF  THE   LUNGS 


883 


This  groove  bifurcates  behind  and  is  gradually  separated  off'  from 
the  rest  of  the  fore-gut  except  at  its  anterior  end,  which  remains  as 
the  aperture  of  the  larynx.     The  diverticula  at  its  posterior  end 
are  the  germs  of  the  bronchi. 
When  the  groove  is  converted 
into  a  tube  it  forms  the  trachea 
and  larynx,  and  the  dorsal  part 
of  the  fore-gut  in  the  region 
from  which   the   rudiment  of 
the  respiratory  system  is  sepa- 
rated becomes  the  oesophagus. 

The  bronchial  diverticula 
grow  out  into  the  surrounding 
mesoblast  to  form  the  air  tubes 
and  alveoli  of  the  lungs,  and 
with  the  surrounding  meso- 
blast they  constitute  the  lung 
substance;  therefore  the  lining 
epithelium  is  hypoblastic  and 
the  surrounding  tissue  meso- 
blast. As  the  lungs  grow,  each 
projects  into  a  corresponding 
anterior  prolongation  of  the 
body  cavity,  which  becomes 
the  pleural  sac,  as  soon  as  it 
is  cut  off"  from  the  peritoneal 
portion  of  that  cavity  by  the 
formation  of  the  diaphragm. 

The  diaphragm  is  early 
developed  as  a  partition  of 
mesoblast  dividing  the  original 
pleuro-peritoneal  cavity  into 
thoracic  and  abdominal  serous 
cavities. 


ML- 


Fig.  (3(39.— a,  Anterior  view  of  ventral  protrusion  of 
fore-gut  whicli  forms  the  rudiment  of  the  respiratory 
apparatus.  B,  Transverse  section  through  lore-gut 
in  region  of  posterior  part  of  respiratoiy  protrusion 
along  line  1,  fig.  A,  showing  bifurcation  of  the 
posterior  part  of  respiratory  diverticulum  to  form 
the  bronchi. 

Fig.  670. — C,  Anterior  view  of  lungs  of  a  young  human 
embryo,  showing  bifurcation  of  each  main  bronchus 
into  two  primary  parts  (after  His,  modified). 

Fig.  671. — D,  Anterior  view  of  the  lungs  of  an  older 
human  embryo,  showing  further  divisions  of  bronchi 
(after  His,  modified). 

KG,  Fore-gut.  il,  Bronchus  of  inferior  lobe,  ml. 
Bronchus  of  middle  lobe  on  right  side,  o,  Oesopha- 
gus. RD,  Respiratory  diverticulum,  sl,  Bronchus 
of  superior  lobe,  sml,  Bronchial  rudiment  on  right 
side  which  divides  into  bronchi  of  middle  and  superior 
lobes  (SL  and  ml). 


Development  of  the  Genito- 
urinary Apparatus. 

The  rudiments  of  the  secre- 
ting parts  of  the  genito-urinar}' 
system  are  found  in,  and  in  association  with,  the  intermediate  cell 
strand  of  mesoblast  which  connects  the  protovertebral  somites  with 
the  lateral  plates,  p.  857.  In  lower  animals  it  is  probable  that  three 
sets  of  tubules  appear  at  different  times  in  the  intermediate  cell  mass 
of  almost  every  segment  of  the  body.  These  tubules  are  known,  in 
accordance  with  the  relative  time  of  their  appearance,  as  pro-,  meso- 


884 


DEVELOPMENT 


[CH.  LIX. 


SNR 


and  metanephric  tubules,  and  their  function  is  to  remove  from  the 
body  certain  waste  products  and  the  genital  elements.  In  mammals, 
however,  the  three  sets  of  tubules  appear  not  only  at  different  times, 
but  also  in  different  segments  of  the  body ;  in  the  rabbit,  for 
instance,  the  pronephric  tubules  are  formed  in  the  fourth  to  the 
eleventh  segments,  the  mesonephric  tubules  in  segments  thirteen  to 
thirty,  and  the  metanephric  tubules  in  a  small  but  indefinite  number 
of  the  still  more  posterior  segments. 

The  nephric  tubules  of  vertebrates  are  homologous  with  the  seg- 
mental tubules  or  nephridia  found  in  worms  and  other  invertebrata. 

In  these  invertebrates,  the 
tubes  extend  from  the  body 
cavity  internally  to  the 
exterior.  In  the  verte- 
brates, however,  this  primi- 
tive communication  with 
the  exterior  is  lost  and  the 
tubules  open  into  a  com- 
mon channel,  the  primitive 
ureter,  pronephric  or  Wolf- 
fian duct  (fig.  672),  by 
which  the  secretion  from 
the  tubules  is  carried  at 
first  into  a  cloacal  chamber, 
developed  at  the  posterior 
end  of  the  hind-gut,  and 
afterwards  into  a  genito- 
urinary chamber  which  is 
separated  off  from  the 
cloaca.  In  the  higher 
forms  also,  the  communi- 
cations of  the  nephric 
tubules  with  the  body 
cavity  are  either  quite 
transitory  or  do  not  exist, 
and  each  tubule  commences  in  a  blind  invaginated  extremity  which 
embraces  a  mass  of  small  blood-vessels,  and  with  the  vessels  con- 
stitutes a  glomerulus  (figs.  672  and  673). 

The  pronephric  duct  commences  in  mammals  by  the  fusion  of 
the  outer  ends  of  the  pronephric  tubules,  and  is  therefore  at  its 
commencement  of  mesoblastic  origin.  As  it  passes  backwards, _  it 
separates  from  the  mesoblast  and  becomes  closely  associated  with 
the  epiblast,  but  it  is  a  matter  of  doubt  whether  its  further  increase 
is  due  to  the  addition  of  epiblastic  cells,  or  to  the  proliferation  of  its 
mesoblastic  elements. 


Fio.  672.— Diagram  of  half  of  a  transverse  section  througli 
the  body  of  a  young  embryo,  showing  the  relations  of  the 
Wolffian  body,  tlie  Wolffian  duct,  and  the  mesonephric 
tubules.  A,  Aorta.  AC,  Alimentary  canal.  AV,  Afterent 
blood-vessels  to  glomerulus.  CV,  Cardinal  vein.  .G,  Glom- 
erulus. GR,  Genital  ridge.  M,  Mesentery  of  gut.  N,  Note- 
chord.  XS,  Mouth  of  mpsonephric  tube  =  Nephrostome. 
PC,  Peritoneal  cavity.  SC,  Spinal  cord.  SXR,  Spinal 
nerve  roots.  WB,  Wolffian  body.  WU,  Wolffian  duct. 
WT,  Wolffian  tube. 


CH.  LIX.] 


DEVELOPMENT   OF   THE   KIDNEYS 


885 


The  pronopliros  has  practically  no  function  in  man  and  soon  dis- 
appoars.  The  mesonephric  tubides,  on  the  other  hand,  grow  rapidly. 
They  open  into  the  Wolffian  duct,  and  together,  with  the  surrounding 
mesoblast,  they  form  a  large  mass,  the  Wolffian  body  or  primitive 
kidney,  which  projects  into  the  peritoneal  cavity  (figs.  672,  673). 
After  a  time  (the  second  month  in 
man),  the  Wolffian  body  undergoes 
atrophy  and  the  majority  of  the 
mesonephric  tubules  disappear. 
Remnants  of  them  are  found  in  the 
female  in  the  broad  ligament  of  the 
uterus  as  the  vertical  tubules  of  the 
ep-  and  parovarium  (fig.  675).  In 
the  male  some  of  them  attain  con- 
nection with  the  germinal  epithe- 
lium (fig.  675),  and  then  become 
the  seminal  tubules  of  the  testicle, 
the  rete  testis,  and  the  vasa  effer- 
entia  (fig.  675),  wliilst  others  persist 
in  the  vasa  aberrantia  and  the 
organ  of  Giraldes,  both  of  which 
are  merely  fostal  remnants.  In  the 
male  the  Wolffian  duct  persists  and 
becomes  the  convoluted  tube  of  the 
epididymis,  the  vas  deferens,  and 
the  common  ejaculatory  duct,  the 
seminal  vesicle  being  merely  a 
diverticulum  from  its  lower  end. 
In  the  female  the  greater  part  of 
the  Wolffian  duct  disappears  and 
the  portions  of  it  which  persist  form 
the  horizontal  tubes  of  the  ep-  and 
parovarium  and  the  occasionally 
present  Gartner's  duct  (figs.  674 
and  675). 

Before  the  above  changes  have  taken  place,  indeed  before  the 
atrophy  of  the  Wolffian  body  or  mesonephros  has  commenced,  a 
diverticulum  grows  from  the  posterior  part  of  the  AVolffian  duct  into 
the  metanephric  mesoderm  posterior  to  the  Wolffian  body.  This 
diverticulum  is  the  permanent  ureter  (fig.  674  B).  Its  lower  end 
soon  separates  from  the  Wolffian  duct  and,  mo\'ing  forwards,  reaches  to 
and  opens  into  the  anterior  or  bladder  section  of  the  cloaca  (fig.  674  C). 
Its  dorsal  or  upper  end  grows  backwards  into  the  metanephric 
mesoblast  where  it  forms  the  pelvis  of  the  ureter  and  the  collecting 
tubules  of  the  kidney.     The  latter  fuse  with  the  metanephric  tubules 


'iG  673.— Diagram  of  half  of  a  transverse  sec- 
tion through  the  body  of  an  embrj'O,  showing 
a  more  advanced  stage  of  development  than 
tliat  represented  in  fig.  672.  A,  Aorta.  AC, 
Alimentary  canal.  AV,  Aflerent  vessel  to 
nephric  glomerulus.  CV,  Cardinal  vein.  EV, 
EBerent  vessel  from  nephric  glomerulus  to 
cardinal  vein.  G,  Glomerulus.  GR,  Genital 
ridge.  M,  Mesentery  of  gut.  MD,  Mullerian 
duct.  N,  Xotochord.  PC,  Peritoneal  cavity. 
PE,  Peritoneal  epithelium.  SO,  Spinal  cord. 
WB,  Wolffian  body.  WD,  Wolffian  duct. 
WT,  Wolffian  tube. 


886  DEVELOPMENT  [CH.  LIX. 

which  are  developed  independently  in  the  metanephric  mesoblast. 
The  collecting  tubules,  the  metanephric  tubules,  and  the  surrounding 
mesoblast  form,  collectively,  the  metanephros  or  permanent  kidney. 
The  secreting  parts  of  the  kidney  are  the  metanephric  tubules,  each 


Fir..  674. — A,  B,  C,  Diagram  representing  three  stages  in  the  development  of  the  genito-urinary  system. 

A,  Early  stage  in  whicli  the  cloaca  is  still  undivided,  and  receives  ventrally  the  Miillerian  and 

Wolffian  ducts. 

B,  Later  stage.     The  cloaca   is   separating  into  a  genito-urinary  and  a  rectal  section,   and  the 

permanent  ureter  has  api)eared  as  an  outgrowth  from  the  Wolffian  duct. 

C,  The  cloaca  has  separated  into  rectal  and  genito-urinaiy  parts,  and  the  latter  is  differentiated 

into  bladder  and  genito-urinary  canal.  The  permanent  ureter  now  opens  into  the  bladder, 
and  metanephric  tubules  are  present. 
A,  Allantoic  diverticulum,  u,  Bladder,  c,  Cloaca,  ct,  Collecting  tubes  of  kidney  developed  as 
outgrowths  from  permanent  ureter,  gk,  Genital  eminence,  gg,  Genital  gland,  guc,  Genito- 
urinary canal,  ourn,  Genito-urinary  chamber.  ho,  Hind-gut.  md,  Miillerian  duct.  mt, 
Metanephric  tubules,  pu,  Permanent  ureter,  pt,  Pronephric  tubules,  wd,  Wolffian  duct. 
WT,  Wolffian  or  mesonephric  tubules. 

of  which  becomes  expanded  at  one  end  to  form  a  glomerular  chamber 
which  is  invaginated  by  a  mass  of  fine  arteries,  the  arteries  and  the 
invaginated  chamber  forming  together  a  kidney  glomerulus. 

The  Bladder  and  Urethra. — It  has  already  been  stated  that  the 
posterior  end  of  the  hind-gut  dilates  and  forms  for  a  time-  a  cloacal 
chamber.  Into  the  ventral  part  of  this  chamber  the  urinary  and 
genital  ducts  open,  and  from  its  anterior  end  the  allantoic  diverticu- 
lum is  given  off  (p.  854).  After  a  time  the  ventral  part  of  the  cloaca 
is  separated  from  the  dorsal,  the  latter  becoming  the  rectum,  whilst 
the  former  is  the  genito-urinary  chamber,  and  each  section  of  the 
divided  cloaca  attains  a  separate  opening  to  the  exterior  (fig.  674  C). 
The  genito-urinary  chamber  is  differentiated  into  two  sections,  an 


CH.  LIX.]  DEVELOPMENT   OF    BLADDKR    AND    T'ltKTFIRA 


88' 


anterior  the  bladder,  and  a  posterior  the  genito-urinary  canal 
(fig.  675).  In  both  sexes  the  genito-urinary  canal  opens  on  the 
surface  in  the  posterior  end  of  a  groove,  and  the  groove  extends 
forwards  on  the  under  surface  of  a  superficial  eminence,  the  genital 
eminence,  which  is  the  rudiment  of  the  clitoris  or  penis.     In  the 


Fio.  675. — A  and  B,  Diagrams  representing  fully  developed  periud  of  genito-uiiiiarj-  .system.  A, 
Female.  B,  Male. 
A,  Allantois.  b,  Bladder,  bg,  Bartolin's  gland,  co,  Cowper's  gland,  cl,  Clitoris,  e,  Tube  of 
epididymis,  eg,  Epovarium.  kt,  Fallopian  tube,  gd,  Gartner's  duct  (sometimes  present  as  a 
variation),  k,  Kidney,  nc,  Nephrostomal  canal,  occasionally  present  and  connecting  one  of  the 
vasa-efferentia  of  testicle  with  cavity  of  tunica  vaginalis,  o,  Ovary,  oo,  Organ  of  Giraldes.  p, 
Penis.  PH,  Pedunculated  liydatid,  sometimes  attached  to  upper  end  of  testicle,  developed  from 
a  Wolffian  tubule.  I'o,  Parovarium  corresponding  with  organ  of  Giraldes  of  male.  i'R,  Prostatic 
diverticulum,  vu,  Permanent  ureter,  r,  Rectum,  sh,  Sessile  hydatid  attached  to  top  of  testicle 
is  the  remnant  of  the  orilice  of  Miiller's  duct,  sv,  Seminal  vesicle,  t,  Testicle,  te,  Tubo- 
epoophoron  canal  of  female,  or  tubo-epididymal  canal  of  male,  sometimes  present,  possibly  a 
remnant  of  pronephric  duct,  u,  Urethra,  cm,  Uterus  masculinus,  represents  lower  ends  of  fused 
Miillerian  ducts,     va,  Vasa  aberrantia.    vd,  Yas  deferens,     ve,  Vasa  ett'erentia. 

female  the  margins  of  this  groove  remain  separate  and  form  the 
labia  minora,  whilst  the  genito-urinary  canal  shortens  till  the  vagina, 
formed  by  the  fusion  of  the  genital  canals,  is  brought  to  the  surface 
between  the  labia  minora.  When  this  has  occurred  the  remainder 
of  the  genito-urinary  canal  becomes  the  urethra  (fig.  675  A).     In 


888  DEVELOPMENT  [CH.  LIX. 

the  male,  on  the  other  hand,  the  genito-urinary  canal  is  lengthened, 
the  lips  of  the  groove  into  which  the  primitive  genito-urinary  canal 
opens  fuse  together,  thus  converting  the  groove  into  a  tube,  and  in 
this  manner  the  canal  is  prolonged  to  the  end  of  the  penis  (fig. 
675  B).  It  follows  from  what  has  been  said  that  the  bladder  and 
the  whole  of  the  urethra  of  the  female  are  lined  by  hypoblastic 
epithelium,  whilst  in  the  male  only  that  part  of  the  urethra  which 
extends  from  the  bladder  to  the  openings  of  the  genital  ducts  is 
lined  by  hypoblast,  and  the  remainder  by  epiblastic  cells. 

The  Genital  Glands. — As  soon  as  the  Wolffian  body  becomes 
distinct,  the  epithelium  on  its  inner  side  thickens  and  forms  the 
germinal  ridge  (figs.  672,  673).  The  thickened  epithelium  consists 
partly  of  enlarged  mesoblastic  cells  and  partly  of  germ  cells  which 
have  wandered  to  the  germinal  ridge  from  the  wall  of  the  yolk-sac 
where  they  first  become  distinct.  In  the  male  the  germinal  ridge 
becomes  the  testicle ;  its  germinal  cells  proliferate  and  form  cords ; 
these  are  gradually  enclosed  in  outgrowths  of  the  mesonephric 
tubules  which  then  assume  the  functions  of  seminal  tubes  and 
convey  the  descendants  of  the  germinal  cells  to  the  modified 
Wolffian  duct,  which  is  now  transformed  into  the  tube  of  the 
epididymis  and  the  vas  deferens  (fig.  675  B).  In  the  female  the 
germinal  ridge  becomes  the  ovary  from  which  the  descendants  of 
the  germ  cells,  the  immature  ova,  are  cast  out  into  the  peritoneal 
cavity,  whence  they  are  conveyed  to  the  exterior  through  the 
Fallopian  tubes,  the  uterus,  and  the  vagina  (fig.  675  A). 

Both  the  ovary  and  the  testicle  are  developed  from  the  germinal 
ridcre  in  the  lumbar  region,  and  each  is  connected  with  the  skin  of 
the  perineo-inguinal  region  and  the  front  of  the  symphysis  pubis 
by  a  fibrous  cord.  This  is  called  the  gubernacular  cord;  it 
descends  from  the  gland  and  passes  through  the  inguinal  canal.  In 
the  male  this  cord  contracts  till  the  testicle  is  pulled  down  into  the 
fold  of  skin  which  forms  the  scrotimi,  and  in  its  descent  it  passes 
through  the  inguinal  canal  in  the  seventh  and  eighth  months  of 
foetal  life  and  is  preceded  by  a  pouch  of  peritoneum  destined  to 
become  the  tunica  vaginalis;  this  is  cut  off  from  the  peritoneum 
immediately  before  or  after  birth.  The  gubernacular  cord  of  the 
ovary  does  not  shorten  to  so  great  an  extent  as  that  of  the  testicle, 
and  the  ovary  is  merely  drawn  down  into  the  pelvis  to  the  back 
of  the  broad  ligament  when  the  gubernacular  cord  is  converted 
into  the  ligament  of  the  ovary  and  the  round  ligament  of  the 
uterus.  The  blood  -  vessels,  lymphatics,  and  nerves  of  the 
ovary  and  testicle  are  formed  in  the  lumbar  region  and  are 
carried  down  with  the  organs  to  which  they  belong,  hence  it  is 
that  they  rise  in  the  adult  so  far  from  the  organ  to  which  they 
are  distributed, 


CH.  LIX.] 


THE    Mt'LLRKIAN   DUCTS 


889 


Tho  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed 
from  a  pair  of  ducts  called  the  Midlerian  ducts. 

In  elasmobranch  fishes  the  Miillerian  ducts  are  split  off  from  the 
pronephric  ducts,  the  anterior  ends  and  ventral  parts  of  the  latter 
becoming  the  Miillerian  ducts  and  the  dorsal  parts  the  Wolffian 
ducts,  but  in  man  and  other  mammals  the  Miillerian  ducts  are 
developed  quite  independently  of  the  pronephric  ducts,  and  each 
commences  as  three  thickenings  of  the  peritoneal  epithelium  on  the 
lower  and  outer  side  of  the  Wolffian  body  just  beneath  the  Wolffian  duct 
(figs.  673,  674,  and  676).  The  deeper  ends  of  the  three  thickenings 
unite  to  form  a  cord  of  cells  which  grows  backwards  to  the  cloaca 
and  becomes  hollow.  In  the  meantime,  however,  two  of  the  three 
primitive  thickenings  have  disappeared  but  the  anterior  remains  and 
forms  the  dilated  anterior  extremity  of  the  duct.     The  margin  of  the 


Fig.  676. — A,  B,  C,  Three  diagrams  representing  stages  in  the  development  of  tlie  Miillerian  ducts 
In  A  they  have  formed  as  solid  cords  of  cells  proliferated  from  three  thickenings  of  peritoneal 
epithelium,  and  they  have  not  yet  reached  the  cloaca.  In  B  they  have  become  hollow  tubes, 
communicating  at  opposite  extremities  with  the  peritoneal  cavity  and  the  cloaca  (c).  In  0  they 
have  partly  fused  to  form  the  uterus  and  vagina. 

dilated  extremity  is  subsequently  cleft  into  a  number  of  processes  or 
fimbriae,  and  by  means  of  one  of  these  the  open  end  of  the  duct 
gains  attachment  to  the  ovary  (fig.  675  A). 

As  the  two  Miillerian  ducts  approach  the  cloaca  they  pass 
between  the  Wolffian  ducts  and  are  bound  with  them  into  a  common 
cord,  the  genital  cord,  and  after  they  have  opened  into  the  cloaca 
their  lower  parts  fuse  together.  In  the  female  the  lowermost  part  of 
the  fused  tubes  form  the  vagina,  that  next  adjacent  the  uterus,  and 
the  highest  parts,  which  remain  separate,  become  the  Fallopian  tubes 
(fig.  676  C).  It  is  obvious  that  if  the  fusion  which  should  occur 
is  incomplete,  the  vagina  or  the  uterus  may  be  double,  in  part  or  the 
whole  of  its  extent,  or  its  cavity  may  be  more  or  less  completely 
divided  by  a  septum,  and  all  of  these  abnormal  conditions  are 
occasionally  met  with.  In  the  male  the  greater  part  of  each 
Miillerian  duct  disappears,  but  the  upper  end  remains  in  a  modified 


890 


DEVELOPMENT 


[CH.  LIX. 


form  and  is  attached  to  the  upper  end  of  the  testicle,  where  it  forms 
the  sessile  hydatid  of  Morgagni;  and  the  fused  lower  ends  are 
embedded  in  the  prostate,  where  they  form  the  sinus  pocularis  or 
uterus  masculinus,  which  opens  into  the  urethra  between  the  mouths 
of  the  common  ejaculatory  ducts  (fig.  675  B). 

The  external  parts  of  generation  are  at  first  the  same  in  both 
sexes.  The  opening  of  the  genito-urinary  apparatus  is,  in  both  sexes, 
bounded  by  two  folds  of  skin,  the  external  genital  folds,  whilst  in 
front  of  it  there  is  formed  a  penis-hke  body  surmounted  by  the 
glans,  with  a  cleft  or  furrow  along  its  under  surface.  The  borders 
of  the  furrows  diverge  posteriorly,  running  at  the  sides  of  the 
genito-urinary  orifice  internal  to  the  cutaneous  folds  just  mentioned  ; 
they  form  the  internal  genital  folds.     In  the   female,  the  genital 


Fig.  677. — A,  B,  C,  Three  diagrams  representing  the  development  of  the  external  genital  organs.  A  is 
the  indill'erent  stage.  B  is  the  female  condition,  the  internal  and  external  genital  folds  remain 
distinct.  C  is  the  male  condition,  the  internal  folds  have  united  to  form  the  floor  of  an  elongated 
urethra  (comp.  tig.  675),  the  line  of  fusion  being  indicated  by  a  dotted  line  on  the  body  of  the  penis. 
The  external  folds  have  united  below  the  posterior  part  of  the  penis  to  form  the  scrotnm,  the  line 
of  union  being  indicated  on  the  scrotum  by  a  dotted  line. 

eminence  forms  the  clitoris,  and  the  margins  of  the  furrow  on 
its  under  surface  are  converted  into  the  nymphae,  or  labise  minora, 
the  labia  majora  pudendae  being  constituted  by  the  external  genital 
folds  (fig.  677).  In  the  male  foetus,  the  margins  of  the  furrow  at 
the  under  surface  of  the  penis  unite  at  about  the  fourteenth  week, 
and  form  that  part  of  the  urethra  which  is  included  in  the  penis. 
The  large  cutaneous  folds  form  the  scrotum,  and  later  receive  the 
testicles.  Sometimes  the  urethra  is  not  closed,  and  the  deformity 
called  hypospadias  then  results.  The  appearance  of  hermaphroditism 
may,  in  these  cases,  be  increased  by  the  retention  of  the  testes 
within  the  abdomen. 

The  supra-renal  capsules  originate  partly  from  the  mesoblast  and 
partly  from  certain  special  cells  of  the  sympathetic  ganglia,  called 
chromaffine  cells,  on  account  of  the  yellow  colour  they  acquire  when 
hardened  with  chromic  salts.  The  chi-omaffine  cells  form  the 
medullary  parts  of  the  suprareaial  bodies,  and  the  cortex  is  de- 
veloped from  buds  of  mesoblastic  cells  separated  from  the  peri- 
toneum on  the  inner  sides  of  the  germinal  ridges. 


INDEX 


A. 

Abderlialden's  experiments,  531 
Abdominal  muscles,  action  in  respiration,  352 
Abdominal  retiex,  682 
Abducens  nerve,  640,  652 

centre,  652 
Aberration, 

chromatic,  708 

spherical,  798 
Abrin,  453 
Absorption 

of  carbohydrates,  529 
fats,  532 
food,  529  et  seq. 
proteins,  530 

by  the  skin,  590 
Accelerator  nerves,  162 

urinse,  501 
Accessory  auditory  nucleus,  054 
Accommodation  of  eye,  788,  792 

defects  of,  790 

mechanism  of,  793 
Beer's  experiments,  796 
Acetonemia,  528,  001 
Acetyl,  398 
Achromatin,  11 
Achromatopsia,  814 
Achroo-dextrin,  390,  401 
Acids  in  gastric  juice,  490 
Acid-albumin,  414,  499 
Acini  of  secreting  glands,  483,  485 
Acoustic  tubercle,  654 
Acrolein,  398 
Acromegaly,  341 
Acrylic  series,  398 
Adamantoblasts,  73 
Adamkiewicz  reaction,  403,  407 
Adaptation  in  sensations,  741 
Adenase,  574 
Adenine,  335,  573 
Adenoid  or  lymphoid  tissue,  47 

in  intestines,  469 
Adipose  tissue,  43.    See  Fat. 

development,  44 

situations  of,  ib. 

structure,  ib. 

uses,  46 

vessels  and  nerves,  ib. 
Adrenaline,  340 

administration  of,  528 
Adsorption,  327  ti. 
Aerotonometer,  381 
^stheslometers,  739 
Affenspalte  (ape's  split),  727 
Afferent  nerves,  90, 162 

nerve-ceUs,  203 
After-birth,  856 


Aminq.caproic  Acid. 

After-images,  811,  814 
Agglutinin,  454 
Agraphia,  '775 
Air, 

atmospheric,  composition  of,  374 

breathing,  350 

changes  by  breathing,  374 

complemental,  357 

quantity  breathed,  357 

reserve,  ib. 

residual,  ib. 

tidal,  ib. 

transmission  of  sonorous  vibrations  through, 
759 

undulations    of,   conducted    by  external    ear, 
760 
Air-calorimeters,  013 
Air-pumps,  384,  385 
Air-sacs,  349 
Air-tubes.    See  Bronchi. 
Alanine,  400,401,  402 
Albumin,  406,  409 

absence  of  glycine  from,  404 

acid,  414 

alkali,  414 

egg,  414 

of  blood,  428 
Albuminates,  414 
Albuminoids,  410 
Albuminometer,  Esbach's,  581 
Albuminous  alveoli,  4S6 
Albuminous  substances,  7 

action  of  gastric  fluid  on,  504 
Albumins,  406,  400 
Alcapton,  583 
Alcaptonuria,  583 

Alcohol  as  an  accessory  to  food,  480 
Alcohols,  nionatomic,  392 
Aldehyde,  391 
Aldoses,  391 
Alimentary  canal,  457  et  seq. 

development  of,  879 

nerves  of,  540 
Alisphenoids,  860 
Alkali-albumin,  414 

properties  of,  414 
Allantoic  diverticulum,  886 
Allantoic  veins,  865 
Allantoin,  572 

Allantois,  development  of,  854 
Alloxan,  572 

Alloxuric  or  purine  bases,  413 
Allyl  alcohol,  398 
Amacrine  cells,  785 
Amino-aciJs,  400,  402,  414 
Amino-caproic  acid,  401,  511 


892 


INDEX 


Ammonia. 

Ammonia,  403,  569,  570 

cyanate  of,  isomeric  with  urea,  504 
Amnesia,  775 
Amnion,  848 

development  of,  851 
Amniotic  cavity,  852 

fluid,  848,  852 
Amcebse,  6 

Amoeboid  movements,  12  et  seq.,  433 
cells,  6 

colourless  corpuscles,  432 
cornea-cells,  779 
protoplasm,  12,  100 
Tradescantia,  14,  326 
Amyloids  or  starches,  396 
action  of  pancreas  and  intestinal  glands,  504 
of  saliva  on,  491 
Amylolytic  ferments,  417 
Amylopstn,  action  of,  504 
Amyloses,  393 
Anabolic  nerve  groups,  301 
Anabolic  phenomena,  594 
Anacrotic  pulse,  290 
Anelectrotonus,  183 
Angio-neuroses,  310 
Angular  convolution,  670 
Angulus  opticus  seu  visorius,  791 
Animal  cell,  structure  of,  8  ft  seq. 
Animal  heat.    See  Heat  and  Temperature. 
Anions,  321 
Ankle-clonus,  683 
Anosmatic  animals,  750 
Ano-spinal  centre,  544 
Antagonistic  muscles, 

reciprocal  action  of,  684 
Antero-lateral  ascending  tract,  630 
Antero-lateral  descending  tract,  628 
Antilytic  secretion,  488 
Antithrombin,  423,  425 
Antitoxin,  452,  453 
Anus,  the,  469,  879 
Aortic  arches,  802 
Aortic  bulb,  864 
Aphasia,  702,  775 
Aphemia,  774 
Apnoea,  origin  of,  362 
Apoplexy,  660 
Appendices  epiploicse,  469 
Appendix  vermiformis,  ib. 
Aquaductus  cochlese,  756 
Aqueduct  of  Sylvius,  635,  640,  649,  876 
Aqueductus  Fallopii,  754 
Aqueous  humour,  778 
Arachnoid  membrane,  618 
Arbor  vitte,  600 
Archenteron,  844  et  seq. 
Arches,  visceral,  858 

aortic,  863 
Archipallium,  677 
Area  cheiro-kinaesthetlc,  709 
germinal,  or  embryonic,  842 
glosso-kinsesthetic,  709 
vasculosa,  861 
Areas,  of  Cohnheim,  81 
intermediate,  709-711 
primary,  709,  710 
terminal,  709-711 
Areolar  tissue,  30 

development  of,  40 
Arginase,  56S,  574 
Arginine,  401,  402,  568 
Aromatic  amino-acids,  402 
Arteria  centralis  retinae,  783,  788,  878 
Arterial  blood,   carbonic  oxide  method  of  esti- 
mating the  oxygen  tension  of,  383 
Arterial  tension  in  asphyxia,  373 


Basilar  Memeraxe. 

Arteries,  214 

allantoic,  865 

bronchial,  350 

circulation  in,  velocity  of,  278 

coronary,  237 

development  of,  861 

distribution,  214 

elasticity,  262 

hypogastric,  864 

muscularity,  263 

nerves  of,  210 

nervous  system,  influence  of,  307 

pressure  of  blood  In  asphyxia,  373 

pulse,  2S7  et  seq. 

renal,  ligature  of,  560 

rhythmic  contraction,  263  et  seq. 

structure,  215  et  seq. 

umbilical,  850,  864,  865 

velocity  of  blood-flow  in,  278 
Arterioles,  260 
Articulate  sounds,  classification  of,  773 

vowels  and  consonants,  773,  774 
Articulation  positions,  774 
Artifacts,  9 
Arytenoid  cartilages,  765 

etfect  of  approximation,  767 

movements  of,  ib. 
Arytenoid  muscle,  768 
Ascending  tubule  of  Henle,  546 
Aspergillus  niger,  531 
Asphyxia,  370  et  seq. 

causes  of  death  in,  371 

conditions  of  the  vascular  system  in,  371 

symptoms,  370 
Assimilation,  6,  529 
Association  centres,  707 

fibres,  670,  705,  707 
Astigmatism,  798 
Atmospheric  air,  373.    See  Air, 
composition  of,  374 

pressure  in  relation  to  respiration,  373 
Atropine,  effect  of, 
on  heart,  250 
on  salivarj'  secretion,  488 
Attraction  sphere,  12,  841 
Auditory  area,  703 
Auditorj'  nerve,  640,  654,  756 
distribution,  757 
origin,  654 

word  ci-ntre,  70S,  775 
Auerbach's  plexus,  97,  464 
Auricles  of  heart.    See  Heart. 
Auricular  diastole,  231 

systole,  232 
Auriculo-ventricular  valves.    See  Heart  valves. 
Auto-intoxication  theory  of  the  ductless  glands, 

329 
Avogadro's  law,  325,  375 
Axial  skeleton,  844 
Axipetal  conduction,  law  of,  204 
Axis-cylinder  of  nerve-fibre,  92 
Azygos  veins,  867 


B. 


Bacterial  action  in  intestinal  digestion,  510 

Bacterio-lysin,  451-453 

Bacterium  lactis,  395 

Baillarger,  line  of,  669 

Barcroft's  apparatus  fur  blood  gas  analysis,  386 

Barnard's  cardiometer,  246 

Bartolin's  gland,  887 

Basal  ganglia,  664 

Basement-membrane,  47,  467 

Basilar  membrane  of  ear,  756,  757 


INDEX 


893 


Basilar  Plate. 

Basilar  plate,  800 
Basi-occi[)ital  bones,  800 

sphenoid  bones,  t(). 
Basopliile  cells,  433 
Batteries  and  keys,  lOS 
DanieU  ceU,  107, 108 
Bayliss,  observations  on  vaso-dilator  nerves  of 
dogs,  302 
on  adsorption,  3'27  n. 
on  pancreatic  secretion,  505 
Becliterew,  nucleus  of,  655 
Beckmann's  diflerential  thermometer,  325 
Bed  sores,  825 

Beef-tea,  the  making  of,  479 
Beer's   experiments   on  accommodation    of   the 

eye,  796 
Bernard's  discovery  in  the  liver,  524 
experiment  on    independent    muscular    irrita- 
bility, 102,  305 
on  pancreatic  secretion,  508 
Betz  cells,  009 
Bezold's  ganglion,  253 
Bicuspid  valve,  211 
Bidder's  ganglion,  253 
Biedermann's  fluid,  101  n. 
BUaminar  blastoderm,  842 
Bile,  513,  618 
absorption  by  lymph,  523 
analyses  of  human,  520 
capillaries,  510 
characters  of,  519 
constituents  of,  ib. 
digestive  properties,  509 
doubtful  antiseptic  power,  522 
influence  of,  on  fat  absorption,  532 
mixture  with  chyme,  522 
mucin,  520 
pigments,  521 
process  of  secretion,  518 
quantity  secreted,  619 
salts,  520 

secretion  and  flow,  518,  519 
specific  gravity,  519 
uses,  522 
Bile-expelling  mechanism,  523 
BUlrubin,  443,  521 
BUiverdin,  521 

Binocular  colour-mixture,  813 
Binocular  vision,  822,  823 
Bipolar  nerve-cells,  193,  750 
Birth,  changes  after,  871 
Biuret  test,  407 
"  Black-water  fever,"  584 
Bladder  reflexes,  091 
Bladder,  urinary.    Sec  Urinary  bladder. 
Blastocyst,  blastoderm,  blastula,  bilaminar,  842 
Blastopore,  842 
Blastosphere,  841 
"  Blaze  current,"  815 
Blind  spot,  S02,  814 
Blocking,  254 
Blood,  76,  419 
agglutiuatiui;  action  of,  454 
amino-acids  in,  530 

arterial  and  venous,  difference  between,  214 
bactericidal  power  of,  451 
buffy  coat,  422 

carbonic  acid  in,  378,  379,  382 
circulation  of,  226  d  scq. 
in  the  foetus,  870 
local  peculiarities,  Sll 
schema  of,  228 
coagulation,  76,  421  et  seq. 
colour,  76,  419 
colouring  matter,  489 
relation  to  that  of  bile,  443 


Blood-vessels. 

Blood — continued 

corpuscles    or    cells    of,    70,    419.    Sec    Blood- 
corpuscles, 
red,  429 

corpuscles,  white,  432 

crystals,  440  ct  seq. 

extractive  matters,  429 

fatty  matters,  429 

fibrin,  76,  422 
separation  of,  423 

gases  of,  377,  380  rt  seq. 
method  of  analysing,  380 

globulicidal  power  of,  452 

hemoglobin,  420,  429,  440  ct  seq. 
photographic  spectrum  of,  446 

nitrogen  in,  377 

odour  or  halitus  of,  419 

oxalated,  424 

oxygen  in,  377 

oxyhaemoglobin,  440  ct  scq. 
photographic  spectrum  of,  446,  447 

plasma,  419,  420 

proteins  of,  428 

quantity,  420 
Haldane's  and  Lorrain  Smith's  experiments , 
420 

reaction,  419 

salts,  429 

serum  of,  421,  426 

specific  gravity,  419 

splenic,  332 

structural  composition,  430 

taste,  419 

temperature,  419 

tests  for,  450 

transfusion  of,  318 

venous,  214 
Blood-corpuscles,  red,  76,  419,  429 

action  of  reagents  on,  481  et  scq. 

chemistry  of,  439 

composition  of,  429 

development,  436,  437,  438 
intracellular,  438 

disintegration  and  removal,  331,  332 

methods  of  counting,  434 

rouleaux,  430 

specific  gravity,  429 

stroma,  429 

tendency  to  adhere,  430 

varieties,  429 

vertebrate,  various,  430 
Blood-corpuscles,  white,  76,  432 

action  of  reagents  on,  434 

amoeboid  movements  of,  483 

chemistry  of,  439 

composition  of,  439 

emigration  of,  295 

formation  in  spleen,  331 

locomotion,  434 

origin  of,  423,  439 

varieties,  432 
Blood-crystals,  440  ct  seq. 
Blood-platelets,  419,  434 
Blood-pressure,  263  ct  scq. 

in  capillaries,  272 

in  veins,  271 
action  of  respiratory  movements  on,  297 

measurement  in  man,  292  et  seq. 

schema  to  illustrate,  265-267 
Blood-vessels, 

circulation  in,  259 
effect  of  gravity,  276 

elasticity  of,  201 

of  eyeball,  788 

in  intestines,  465 

Of  kidney,  548 


894 


INDEX 


Blood-Vessels. 

Blood-veiSBls— continued 

of  muscle,  86 

of  stomach,  403 

influence  of  nervous  system  on,  297 

primitive,  802,  803 
Body-cavity,  845 

Body,  development  of  framework  of,  856 
Body,  the  chemical  composition  of,  390  et  seq. 
Boiler-maliers'  disease,  703 
Bone,  54 

canaliculi,  56 

cancellous,  64 

chemical  composition,  ib. 

compact,  ib. 
lamellas  of,  67 

development,  59  et  seq. 

growth,  64 

Haversian  canals,  56 

lacunae,  57 

marrow,  54 

medullary  canal,  ib. 

microscopic  structure,  55 

ossification  in  cartilage,  60 

ossification  in  membrane,  09 

periosteum  and  nutrient  blood-vessels,  55 

structure,  54  et  seq. 
Bowman, 

on  muscle,  81 

on  urine,  555 
Bowman's  capsule,  546 

glands,  748 

lamina,  779 
Boyle-Mariotte's  law  for  gases,  324 
Brain.  See  Bulb,  Cerebellum,  Cerebrum,  Pons,  etc. 

capUlaries  of,  311 

child's,  673 

circulation  of  blood  in,  311  et  seq. ' 

commissures,  870 

comparative  physiology  of,  724  et  seq. 

convolutions,  673 

development,  874  et  seq. 

dog's,  698 

extirpation  of,  in  mammals,  093 

fissures,  673 

in  foetus,  630,  875 

grey  matter,  191 

lobes,  673  et  ieq. 

lunatic's,  718 

membranes  of,  618 

monkey's,  673 

motor  areas,  700 

orang's,  674 

quantity  of  blood  In,  311,  312 

sensori-motor  area,  '704 

sensory  areas,  703 

structure,  634 

ventricles,  635 

vertebrate  (section),  637 

vesicles,  875 

white  matter,  191 
Bread  as  food,  479 
Breathing.    See  Respiration. 
Bright's  disease,  581,  583 
Broca's  convolution,  702 
Brodie,  on  splenic  nerve,  151 

his  bellows-recorder,  161,  310 

on  heat  rigor,  157 
Bronchi,  arrangement  and  structure  of,  343,  882 
Bronchial  arteries  and  veins,  350 
Brownian  movement,  100 
Bruch,  membrane  of,  780,  781 
Briicke  on  the  self-steering  action  of  the  heart,  237 
Brunner's  glands,  467 
Brunton,    after    Gaskell,  tracing   of  actions  of 

vagus  on  the  heart,  248 
Buffy  coat,  formation  of,  422 


Carbamide. 

Bulb,  pons  and  mid-brain,  638  et  seq. 

anterior  aspect,  638 

internal  structure,  640  et  seq. 

posterior  aspect,  639 

tracts  of,  651 
Bulbus  arteriosus,  866 
Bundle  of  Helweg,  629 

of  Monakow,  629,  651 

of  von  Gudden,  651 
Burch's  experiments  on  colour  vision,  811 
Burdach's  column,  623  et  seq. 
Burdon-Sanderson's  stethograph,  354 
Bursas,  synovial,  482 
Butyric  acid,  395,  510 


c. 


Cachexia  strumlpriva,  337 
Csecum,  tlie,  468 
Caffeine,  480 
Caisson  disease,  378 
Cajal,  law  of  axipetal  conduction,  204 
Cajal's  descending  cerebellar  bundle,  662 
Calcarine  an'a,  727 
Calcarine  fissure,  677 
Calcification  of  bone,  61 
Calcium  carbonate,  54 
in  urine,  680 

fluoride,  54 

oxalate  in  urine,  679 

phosphate,  64 
Calcium  salts,  the  action  of,  424 
Calleja,  islands  of,  653 
Callosal  convolution,  676 
Calloso-marginal  fissure,  676 
Calorimeters,  612,  613 
Calyces  of  the  kidneys,  646 
Canal,  alimentary.    .See  Stomach,  Intestines,  etc. 

external  auditory,  752 
function  of,  759 

spiral,  of  cochlea,  757 
Canal  of  Schlemm,  782 

of  Petit,  788 
Canaliculi  of  bone,  56 
Canalis  cochle;f,  750,  757 
Canals,  semicircular,  of  ear,  755 

development  of,  866 
Cancellous  tissue  of  bone,  64 
Cane  sugar,  394 
Cannon,  shadow  photographs  of  the   stomach, 

showing  peristaltic  movements,  539 
Capacity  of  chest,  vital,  357 
CapUlaries,  219 

bUe,  516 

circulation  in,  2S0,  293 
velocity  of,  280 

development,  863 

diameter,  219 

form,  ib. 

Influence  on  circulation,  294 

network  of,  219,  220 

number,  221 

passage  of  corpuscles  through  walls  of,  295 

pressure  in,  272  et  seq. 

resistance  to  flow  of  blood  In,  294 

still  layer  in,  ib. 

size,  219 

structure  of,  ib. 
Capsule  of  Bowman,  646 

external  and  internal,  666 

of  Glisson,  514 

of  Tenon, 779 
Capsules,  Malpighian,  546 
Carbamide.    See  Urea 


INDEX 


895 


Carbohydrates. 

Carbohydrates,  890  et  seq. 
absorption  of,  529 
iiieUibulisin  of,  69(5 
Carbouates  in  urine,  57G 
Carbonic  acid  in  atmosphere,  374,  375 
in  blood,  377,  378 

etfect  of,  379 
increase  in  breathed  air,  374 
influence  of,  on  nerve,  171,  172 
in  lungs,  377 
Carbonic  oxide  haemoglobin,  448 
Carbonic  oxide,  poisonous  action  of,  373 
Cardiac  cycle,  231 
Cardiac  glands,  461 

Cardiac  orifice  of  stomach,  action  of,  539 
sphincter  of,  540 
relaxation  in  vomiting,  ib. 
Cardiac  sympathetic,  249 
Cardinal  veins,  865 
Cardiogram  from  human  heart,  239 
Cardiograph,  237  ct  scq. 
Cardiometer,  Barnard's,  246 

Roy's,  ib. 
Carotid  artery,  802 
Carotid  gland,  342 
Cartilage,  49 
articular,  50 
cellular,  53 

chondrin  obtained  from,  51 
classification,  49 
costal,  50 
development,  52 
elastic,  49,  52 

fibrous,  51,  52.     Sec  Fibro-cartUage. 
hyaline,  50 
matrix,  ib. 
Meckel's,  S'^1 
ossification  in,  60 
parachordal,  860 
perichondrium  of,  51 
structure,  49 
temporary,  50 
transitional,  ib. 
varieties,  49 
Cartilages  of  larynx,  764 
Cartilaginous  cranium,  860 

bars,  861 
Casern,  411,  473.    Hee  Milk. 
Caseinogen,  411,  473,  474 
Cauda  equina,  620,  872 
Caudal  arch,  Sol 
Caudate  nucleus,  665 
Cavity  of  reserve,  75 
Cell  di\'i3ion,  16 
Cells,  4,  5 
amceboid,  6 

blood.    Ste  Blood-corpuscles, 
bone,  57 

cartilage,  49  et  seq. 
central,  401,  494 
characteristics  of,  12 
chromafine,  890 
ciliated,  27 
connective  tissue,  36 
definition  of,  6 

epithelium,  25.    See  Epithelium, 
fission,  16 
germinal,  872 
gustatory,  745 
hepatic,  514 
nerve,  192 
olfactorial,  748 
parietal,  402,  494 
pigment,  100 
structure,  8  ct  scq. 
varieties,  22  et  seq. 


Cheynk-Stokes'  Respiration. 

Cells — continued 
vegetable,  6,  13 
distinctions  from  animal  cells,  6  et  teq. 
Cells  of  Deiters,  759 

of  Purklnje,  197,  GOO  it  seq. 
Cellular  cartilage,  53.    ^e  Cartilage. 
Cellulose,  390 
Cement  of  teeth,  69,  71,  74 
Central  cells,  461,  494 
Centres,  nervous,  etc.    See  Nerve-centres. 

of  ossification,  59 
Centrifugal  machine,  427 

nerve-fibres,  161 
Centripetal  nerve-fibres,  162 
Centro-acinar  cells,  502 
Centrosome,  8,  12,  17,  830 
Cephalic  aortic  arches,  862 
Cephalic  arch,  861 
Cerebellar  ataxy,  718 
Cerebellum,  059 
effects  of  removal  or  disease,  718 
equilibration,  ib. 
functions  of,  710  et  seq, 
grey  matter,  197,  630,  659 
heml-extirpation,  results  of,  724 
impulses,  718,  719 
peduncles  of,  002,  717 
semicircular  canals,  719,  722 
extirpation  of,  717,  721,  723 
sensory  impulses,  718 
stimulation,  717,  718,  723 
structure,  659 
Cerebral  cortex,  664,  607,  669 
grey  matter  of,  073 
histological  structure,  607 
pyramidal  cells,  073 
Cerebral  hemispheres.    See  Cerebrum. 
Cerebral  nerves,  origin  of,  640  et  seq. 

See  under  names  of  nerves. 
Cerebrins  or  cerebrcsides,  176 
Cerebro-spinal  axis,  191,  619 
Cerebro-spinal  fluid,  178,  620,  635 
Cerebro-spinal  nervous  system,  191,  618 

See  Brain,  Spmal  cord,  etc. 
Cerebrum,  603 
convolutions  of,  673  et  scq. 
crura  of,  635 
degeneration   tracts    after  Injury  of  Rolandic 

area,  6':i6 
development,  874 
effects  of  injury,  690 
removal,  0'j2,  695 
external  capsule,  666 
functions  of,  0;i2  et  seq. 

early  notions,  692 
grey  matter,  197,  664 
hemispheres,  003,  673,  675,  875 
internal  capsule,  660 
localisation  of  functions,  693 
motor  areas,  695 
relation  to  speech,  774 
sensory  areas,  696 
extirpation,  ib. 
stimulation,  ib. 
structure,  663  et  seq. 
white  matter,  600 
Ceruminous  glands  of  ear,  590 
Chambers  of  the  eye,  788 
Charcot's  disease,  824,  826 
Chauveau's  dromograph,  284 
Cheiro-klnEBSthetic  area,  709 
Chemical    composition    of    the    human    body, 

390  et  scq. 
Chest,  expansion  In  inspiration,  851 
Chest-voice,  772 
Cheyne-Stokes'  respiration,  365 


896 


INDEX 


Chimpanzees  Beain. 

Chimpanzee's  brain,  700 
Chittenden  diet,  471,  472,  605 

important  character  of  his  work,  604 
Chlorides  in  urine,  675 
Cholagogues,  523 
Cholalic  acid,  520 
Cholesterin,  9,  92,  176,  399,  521 
Choletelin,  521 
Choline,  171, 178,  399 
Chondrin,  51,  411 
Chorda  secretion,  489 
Chorda  tympani,  487 

effects  of  stimulation  of  divided,  488 
Chord®  tendlnese.    See  Heart. 
Chorion,  848,  849,  854 
Chorionic  epiblast,  854 
Chorionic  villi,  854 
Choroid  coat  of  eye,  777,  780 

blood-vessels,  780 

development,  878 

stmcture,  780 
Choroidal  fissure,  878 
Chromafine  cells,  890 
Chromatic  aberration,  798 
Chromatin,  11 
Chromatolysis,  202 
Chromatoplasm,  201 
Chromogen,  339 
Chromophanes,  818 
Chromoplasm,  10 
Chrome-proteins,  412 
Chromosomes,  17,  839,  840 
Chyle,  223,  315,  532 

molecular  basis  of,  315 
Chyme,  519 
Cicatricula,  839 
Cilia,  28 
Ciliary  epithelium,  27 

function  of,  28 
Ciliary  motion,  29 

nature  of,  ib. 
Ciliary  muscles,  781 

action  of,  in  adaptation  to  distances,  792,  793 
Ciliary  processes,  7S0 
Cilio-spinal  centre,  690 
Circulation  of  blood,  206,  226  ct  seq. 

action  of  heart,  206 

in  brain,  311 

capillaries,  294 

course  of,  213  et  scq. 

erectile  structures,  312 

in  fcetus,  870 

iniiuence  of  respiration  on,  366 
of  gravity,  276 

peculiarities  of,  In  different  parts,  311 

portal,  214 

pulmonary,  ib. 

renal,  ib. 

systemic,  ib. 

in  veins,  216 
velocity  of,  278 
Circulatory  system,  206  et  seq, 
Circumvaliate  papillae  of  the  tongue,  743 
Clarke's  column,  622,  625,  032,  672 
Claustrum,  665,  669 
Cleft-palate,  cause  of,  860 
Clefts,  visceral,  858 
Clerk-Maxwell's  experiment,  808 
aitorls,  313 

development  of,  887,  890 
Cloaca,  886 
Clonus,  121 

Clot  or  coagulum  of  blood.    Sec  Coagulation. 
Clupeine,  409 

Coagulation  of  blood,  76,  421  et  seq. 
conditions  affecting,  422 


CORNKA. 

Coagulation  of  blood — continued 
theories  of,  423 

of  milk,  473 
Coagulative  ferments,  417 
Cocaine,  480 
Coccygeal  gland,  342 
Cochlea  of  the  ear,  755 

theories  In  connection  with,  762,  763 
Cochlear  nerve,  640 
Coelom,  844 
Cohnhelm,  areas  of,  81 
Cohnheim's  experiment,  294 

with  succus  entericus,  509 
Cold  areas,  740 
Collagen,  37,  54,  411 
Collateral  fissure,  676 
Colloids,  323,  406 
Colon,  the,  46S,  879 
Colostrum,  472 

corpuscles,  473,  476 
Colour-blindness,  810 
Colour-perception,  80S 
Colour  sensations,  80S 

Burch's  experiments,  811 

theories  of,  S09-S11 
Colours,  optical  phenomena,  808  et  seq. 
Columnar  epithelium,  25 
Combination-tones,  762 
Comma  tract,  624,  626 
Commissural  iibres,  670 

nucleus,  657 
Common  path,  principle  of,  686 
Common  sensations,  741 
Complemental  air,  357 
Complementary  colours,  809 
Compound  tubular  glands,  483 

racemose  glands,  483,  484 
Conception,  729 
Concha,  752 

Condiments  as  accessories  to  food,  480 
Conductmg  paths  in  cord,  678  et  scq. 
Conduction,  law  of  axipetal,  204 
Conductivity,  172 
Cones  and  rods,  785,  786 

movement  of,  814 
Conical  and  filiform  papillse  of  tongue,  744 
Coni  vasculosi,  830 

Conjugate  deviation  of  head  and  eyes,  703,  717 
Conjugated  proteins,  411 
Conjunctiva,  776 
Conjunctival  reflex,  683 
Connective  tissues,  35 

classification,  ib. 

corpuscles,  38 

elastic,  43 

fibrous,  41 

general  structure  of,  36 

jelly-like,  48 

retiform,  46 

varieties,  35 
Conservation  of  energy,  law  of,  614 
Consonants,  774 
Contractility  of  muscle,  99 
Contraction  of  pupil,  796 
Contrast  of  colour,  812 
Convergence  of  eye,  796 
Convolutions,  cerebral,  673  et  seq. 
Cooking,  effect  of,  479 
Co-ordijQation  of  muscular  movements,  124 
Copper  sulphate,  or  Piotrowski's  test,  407 
Cord,  spinal.    Sec  Spinal  cord. 
Corlum,  459 
Cornea,  779 

corpuscles,  779,  780 

nerves,  779 

structure,  779 


INDEX 


897 


CORNEO-SlXKRAL  JUNCTION. 

Corneoscleral  junction,  782 
Coronary  arteries,  237 
Corona  radiata,  OOO 
Corpora  caveniosa,  31'2,  830 

quadrigemina,  040,  050 
Corpus  Arantli,  213 

callosum,  003,  670,  876 

dentatum 

of  cerebellum,  660 
of  olivary  body,  ib. 

Hlgbmorianum,  828 

luteum,  834 
of  human  female,  ih. 
of   menstruation  and   pregnancy  compared, 

834 
sponKlosum,  312,  830 
striatum,  604 
Corpusclea  of  blood,  76, 419.    See  Blood-corpuscles. 
Corpuscles,  Malpighian,  546 
Corpuscles,  of  Grandry,  735 

of  Herbst,  733 

of  Meissner,  734 
Corti,  organ  of,  654,  655,  758 
Cortico-pontine  fibres,  647 
Cortico-spinal  fibres,  047,  670 
Corti 's  rods,  758  et  seq. 

office  of,  702 
Cotyledons,  850 
Coughing,  mechanism  of,  364 
Cowper's  glands,  552,  SS7 
Cranial  nerves,  I'JO,  640  ct  seq.,  861 

nuclei  of,  641,  042,  044,  647 

origin  and  functions  of,  652  et  seq. 
Creatine,  401 
Creatinine,  401,  570 
Cremasteric  retlex,  682 
Crescents  of  Gianuzzi,  486 
Cretinism,  cause  of,  336 
Crlco-arytenoid  muscles,  766,  767 
Cricoid  cartilage,  765 
Crico-thyroid  muscle,  766 
Crista  acoustica,  721 
Crossed  hemiplegia,  697 
Crossed  pyramidal  tract,  627 
Crosses  of  Ranvier,  93 
Crowbar  accident,  705 
Crura  cere  belli,  639 

cerebri,  635,  651,  666 
grey  matter  of,  636 
Crusta, 650 

petrosa,  71,  74 
Crypts  of  Lieberkuhn,  466 
Crystallin,  782 
CrysUlline  lens,  778,  788 
Crystallisable  proteins,  406 
Crystalloids,  406 
Cubical  epithelium,  25 
Cuneus  or  cuneate  lobule,  677 
Cupula,  721 

Curative  inoculation,  451 
Curdling  ferments,  473 
Currents  of  action, 

constant,  108 

induced,  109 

nerve,  103 
Cutaneous  sensations,  733  et  seq. 
Cuticle.    See  Epidermis,  Epithelium. 
Cutis  vera,  585 
Cuvier,  ducts  of,  805 
Cybnlslci's  haematachometer,  283 
Cyclopterine,  409 
Cystic  duct,  613 
Cystine  in  urine,  579 
Cystine,  403 
Cytosine,  403 


DEVBLOrMLNT. 


D. 


Daniell's  battery,  107,  108 

Dark-adaptation  of  eye,  814 
Deaf-mutes  and  equilibrium,  728 
Decldua,  847,  849 

basalis,  848,  849,  850 

development  of,  848 

menstrual  is,  837 

reflexa,  or  capsularis,  848 

serotina,  850 

vera,  848 
Decussation  of  fibres  in  medulla  oblongata,  044, 

64G 

In  spinal  cord,  679 

of  optic  nerves,  819 
Deep  sensibility,  741 
Defalcation,  mechanism  of,  543,  091 

centre,  690 

influence  of  spinal  cord  on,  544 
Degeneration  method,  164,  169,  307,  623  et  seq. 
Deglutition.    See  Swallowing. 
Deiters,  cells  of,  759 

nucleus,  648,  655 
Demilunes  of  Gianuzzi,  486 
Demoor's  sleep  theory,  712 
Dendrites,  872 
Dental  germ,  72 

papilla,  ib. 
Dentine,  69 

formation  of,  73 

structure,  09 
Depressor  nerve,  305 
Dermis,  585,  587 
Descemet's  membrane,  779 
Descending  tubule  of  Henle,  546 
Deutero-albumose,  499 
Development,  838  et  seq. 

adipose  tissue,  44 

alimentary  canal,  879 

allantola,  854 

amnion,  851 

anus,  879 

arteries,  862 

blood-corpuscles,  436 

blood-vessels,  436,  862 

bone,  59  ct  seq. 

brain,  874 

decldua,  847 

diaphragm,  883 

ear,  878 

extremities,  857 

eye,  876 

eyelids,  878 

face,  859 

Fallopian  tubes,  887 

foetal  membranes,  847 

framework  of  body,  856 

genital  glands,  S8S 

genito-urinary  apparatus,  883  et  seq. 

head,  857 

heart,  864 

Intestines,  880 

iris,  878 

limbs,  857 

liver,  881 

lungs,  882 

lymphatic  glands,  882 

medulla  oblongata,  874 

mouth,  879 

muscle,  88 

nasal  chambers,  879 

nerve-fibres,  96 

nervous  system,  871,  872,  873 

nose,  879 

oesophagus,  ib. 

3  L 


898 


INDEX 


Development. 

Development — contiwued 

optic  nerve,  877 

organs  of  sense,  878 

ovary,  S3S,  SSS 

0%-um,  83S 

pancreas,  881 

pharynx,  879 

respiratory  apparatus,  882 

salivarj-  glands,  SSI 

spinal  cord,  S71 

spleen,  SS2 

stomach,  879 

teeth,  71 

testicle,  888 

thymus,  882 

thyroid  glands,  88'2 

urethra,  879 

vagina,  887 

vascular  system,  861 

veins,  86.t 

vertebrae,  857 

visceral  arches  and  clefts,  858  et  seq. 

Wolffian  bodies,  urinary  apparatus,  and  sexual 
organs,  8S4  et  seq. 
Dextrin,  396 
Dextrose,  391,  303 

in  urine,  582 

tests  for  determining,  393,  582 
Diabetes,  526 

artificial  production  in  animals,  526,  527 
Dialvser,  a,  406 
Dialysis,  323,  406 
Diamino-aci'ls,  401 
Diapedesis  of  blood-corpuscles,  294 
Diaphragm.    Sec  Inspiration,  etc. 

development,  883 
Diastase  of  liver,  525 
Diastole  of  heart,  231 
Diastolic  pressure,  292 
Dicrotic  pulse,  291 
Diencephalon,  S36,  875 
Diet,  595  et  seq. 

a  healthy,  470 

Chittenden's,  471,  472 

nutritive  value,  470  ct  seq. 

tables,  471,  473,  595  et  seq. 

Voit's,  471 
Difference-tones,  762 

Diffusion  and  osmosis,  distinguished,  322,  406 
Digestion, 

in  the  intestines,  502  et  seq. 
duration  of,  543 

mechanical  processes,  535  et  seq. 
See  Gastric  fluid.  Food,  Stomach. 
Dilator  pupillse,  781 
Dilemma,  689 
Dipeptides,  405 
Diphtheria  toxin,  452 
Diplopia,  816 
Direct  cerebellar  tract,  630 

pyramidal  tract,  627 
Disaccharides,  392,  393 
Discus  proligerus,  833 
Disease,  "  germ  theory  "  of,  416 
Distributing  nerve-cells,  204 
Disuse  atrophy,  203,  704 
Diuretics,  559 

Diverticulum,  Meckel's,  880 
Dobie's  line,  82 
Dog,  "  scratch  "  reflex  of,  687 
Dog's  brain,  698 
Dorsal  mesentery,  846 
ridges,  871 

vessels,  862 
Dorsal  pancreatic  diverticulum,  882 
Double  vision,  816 


End-bclbs. 

Dromograph,  Chauveau's,  284 
Drugs,  action  of,  543,  742 

on  the  eye,  801 

on  the  heart,  250 

on  perspiration,  592 
Duct  of  Gartner,  S85 
Ductless  glands,  328  et  seq. 

theories  of  secretion,  329 
Ducts  of  Bellini,  547,  548 

of  Cuvier,  865 

of  Gartner,  885 

of  Santorini,  882 

of  Wirsung,  882 
Ductus  arteriosus,  865,  871 
closure  of,  871 

venosus,  869 
closure  of,  871 
Dudgeon's  sphygmograph,  289 
Dulong's  calorimeter,  612 
Duodenum,  463,  S79 
Dupr^'s  urea  apparatus,  506 
Dura  mater,  618 
Dyne,  264 
Dyspnoea,  359,  371 


Ear,  752 

bones  or  ossicles  of,  753 
function  of,  760 

ceruminous  glands  of,  590 

development,  878 

external,  752 
function  of,  759 

internal  or  labyrinth,  754,  879 
function  of,  760 

middle,  752 
function  of,  760 
Ectopia  vesicff,  561 
Efferent  nerves,  90, 161 

nerve-cells,  203 
Eggs  as  food,  470,  476 

Ehrlich's  experiments  with  methylene  blue,  878 
695 

side-chain  theory,  453 
Elastic  cartilage,  49,  52 

fibres,  41 

tissue,  43 
Elastln,  38,  411 
Electrical  currents  of  retina,  815 

nerves,  162 

phenomena  of  muscle,  133  et  seq.,  186 

variation  in  central  nervous  system,  711 
in  glands,  484 
Electricity, 

in  muscle,  141  et  seq.,  187 

nerve,  187 
Electrodes,  non-polarisable,  135 
Electrometer,  Lippmann's  capillary,  138 
Electrotonus,  179 
Eleidin,  586 

Elementary  substances  in  the  human  body,  390 
Embryo,  838  et  seq.    See  Development. 
Embryological  method,  623 
Embryonic  area,  842,  844 

heart  and  blood-vessels,  862-865 
Emetics,  541 
Bminentia  teres,  640 
Emmetropic  eye,  796 
Emotions,  729i 
Emulsification,  399,  505 
Enamel  of  teeth,  70 

formation  of,  73 
Enamel  organ,  ib. 
Enchylema,  9 
End-bulbs,  734 


INDEX 


899 


Endoob.nous  Protein  Mktabolism. 

Knilu^enous  protein  rnotabolisiii,  (iO-t 
End-plates,  motorial,  8(5,  9^< 
Endocaniiac  prossure,  240  ct  seij. 
EudocarJiuni,  'JOT 
Endogenous  libres,  700 
Endolymph,  720,  755,  759 
Endoinysium,  79 
Endoneurium,  94 
Endothelium,  24 

distinctive  characters,  ih. 

gerrainatlnt;,  il>. 
BnertO'i  law  of  conservation  of,  014 
Englobulins,  581 
Entero-kinaso,  508 
EosinophiJe  colls,  433 
Epiblast,  21,  842  I «  scq. 

organs  formed  from,  847 
Epicardium,  200 
Epicritic  sensibility,  741 
Epidermis,  585 
Epididymis,  828,  830 
Epigastric  reflex,  682 
Epiglottis,  769,  770 
Epimysium,  79 
Epineurium,  94 
Epithelium,  22 

chemistry  of,  33 

ciliated,  27,  836 

cogged,  82 

columnar,  25 

compound,  22 

cubical,  25 

germinal,  832,  SSS 

goblet-shaped,  26 

nutrition  of,  33 

pavement,  22 

renal,  546 

simple,  22 

spheroidal,  25 

stratified,  31 

transitional,  30 
Erectile  structures,  circulation  in,  312 
Erection,  313,  091 

cause  of,  ib, 

centre,  090 

influence  of  muscular  tissue  in,  313 
Erepsin,  509 
Erg,  264 

Ergograph,  Mosso's,  150 
Erythroblasts,  439 
Erythro-dextrin,  396,  491 
Esbach's  albuminometer,  581 
Ethmoid,  860 

Ethmo-vomerine  plate,  860 
Eustachian  tube,  056,  752,  760,  879 

function  of,  701 

valve,  871 
Ewald,  "  sound  picture  "  theories  of,  703 
Excitability  of  nerves,  172 

of  tissues,  99 
Exercise,    effects   on   temperature    of   body, 

610 
Exogenous  fibres,  706 
Exogenous  protein  metabolism,  604 
Expiration,  352 

force  of  expiratory  act,  359 

influence  on  circulation,  350,  359 

mechanism  of,  353 

muscles  concerned  in,  ih. 

relative  duration  of,  355 
External  auditory  meatus,  752 
External  capsule,  600 
External  parieto-occipital  fissure,  674 
External  respiration,  374 

sphincter  muscle,  542 
Extraventricular  nucleus,  665 


FinitKS   OF   Mi'LLER. 

Extremities,  development  of,  857 
Eye,  770 

action  of  drugs  on  pupil,  800 

adaptation  of  vision  at  ditlierent  distances,  792 

H  s.q. 

blood-vessels,  788 

causes  of  dilatation  an<l  contraction  of  puiiil, 
801 

chambers  of,  788 

develoiimont,  876 

focus,  789 

optical  ajjparatus  of,  788 
defects  in,  790 

principal  point,  789 

refractive  media  of,  788,  789 

resemblance  to  camera,  788 
Eyeball,  777 

blood-vessels  of,  788 

electrical  currents  of,  815 

muscles  influencing  movement,  815 

point  of  rotation,  816 

transverse  and  visual  axis,  816 

various  positions  of,  816 
Eyelids,  770 

development  of,  876 
Eyes,  simultaneous  action  in  vision,  816 


Face,  development  of,  859 
Facial  nerve,  640,  653 

effects  of  paralysis  of,  653 

origin,  654 

relation  of,  to  expression,  ib. 
Fajces,  composition  of,  534 

quantity  passed,  ib. 
Fallopian  tubes,  880 

development  of,  889 
Falsetto  voice,  772 
Faradisation,  121 
Far-point,  796 
Fasciculus  retroflexus,  651 
Fasciculus  solitarius,  642,  658 
Fat.    i>ce  Adipose  tissue. 

action  of  bile  on,  522 
of  pancreatic  secretion,  508 

metabolism  of,  598 

situations  where  found,  43,  44 

uses  of,  46 
Fatigue,  711 

in  nerves,  151 
Fats, 

absorption  of,  582 

acids  of,  897 

action  of  pancreatic  juice  on,  504 

chemical  constitution,  397 

decomposition  products,  398 

emulsification,  399 

of  mUk,  474 

saponification,  399 
Patty  acids,  397 
Fehling's  solution,  582 
Female  generative  organs,  832 

pronucleus,  841 
Fenestrated  membrane  of  Henle,  216 
Fenestra  ovalis,  752,  755 

rotunda,  752,  756,  761,  762 
action  of,  762 
Ferment  coagulation,  410 

Ferments,  415.    See  also  Blood,  Milk,  Digestive 
juices. 

classification  of,  417 
Fertilisation,  841 
Fibres  of  Muller,  772 

of  Remak,  95 


900 


INDEX 


Fibrils  of  Muscle. 

Fibrils  of  mascle,  81 

of  nerve,  92 
Fibrin,  i-2-2,  423 

ferment,  423,  428,  429 

formation.  422 
Fibrinogen,  76,  423,  428 
Fibro-cartilage,  51 

classification,  ib. 

development,  52 

white,  51 

yellow,  52 
Fibrous  tissue,  41 

white,  ib. 

yellow,  43 
Pick's  spring  kymograph,  272,  273 
Fifth  cranial  nerve,  640,  653 
Filiform  papillae  of  tongue,  744 
Fillet,  645,  649 
Filtration,  318,  319,  328 
FUum  terminale,  620,  872 
Fischer's  laboratory,  the  work  in,  404 
Fishes,  circulatory  system  in,  229 
Fistula,  intestinal,  508 
Flechsig's  method,  705 
Fleischl's  haemoglobinometer,  449,  450 
Flesh  of  animals,  470 
Flicker,  803,  S20 
Flour  as  food,  478 
Flourens'  experiment,  722 
Fluids,  swallo^vlng,  537 
Fluids,  tension  of, 

gases  in,  380  et  s^q. 
Fluoride  of  calcium,  54 
Focal  distance,  792 
Fatal  membranes,  847 

development  of,  850 
Fcetus, 

circulation  in,  869 

communication  with  mother,  850 
Follicles,  Graafian.    See  Graafian  foUicles. 
Food,  470  ,:t  .^c■^ 

absorption  of,  529  et  seq. 

accessories  to,  480 

chemical  compounds  of,  470 

cooking,  479 

digestibility  of  articles  of,  470 
value  dependent  on,  ib. 

heat-value  of,  610 

of  man,  470 

proximate  principles  in,  470 

vegetable,  ib.,  479 
Foramen  ovale,  864- 

of  Magendie,  635 

of  Munro,  r>C5 
Fore-brain,  875 
Fore-gut,  846,  883 
Formatio  reticularis,  645 
Formic  acid,  397 
Fornix,  665 

Fourth  cranial  nerve,  640 
Fovea  centralis,  783,  787,  805 
Fovea  hemieUiptica  et  hemispherica,  756 
Frogs, 

circulatory  system  in,  229 

corpuscles  of,  430 

reflexes  in,  680  et  fcq. 
Fromann's  lines,  93 
Frontal  lobe,  675 
Fronto-cerebellar  fibres,  65 
Fronto-nasal  process,  859 
Fundus  glands,  461,  493 
Fundus  of  eye,  804 

of  urinary  bladder,  551 
Fungiform  papiUse  of  the  tongue,  744 
Funiculus  cuneatus,  639,  644 
Funiculus  gracilis,  639,  644 


Glosso-pharvxgeal  Nerve. 

Funiculus  solitarius,  647,  657 
Furfuraldehyde,  521 
Furth,  on  muscle  proteins,  156, 160 
Fuscin  granules,  814 

G. 

Galactose,  394 
GaU-bladder,  51S 

development  of,  882 

structure,  518 
Galvanism,  133 
Galvanometer,  134 
Gamgee,  photographic  spectrum  of  haemoglobin 

and  its  derivatives,  447,  44S 
Ganglia.    Sec  Xen-e-centres. 

sympathetic,  functions  of,  299,  300,  489 
Ganglion  cells,  layer  of,  784 
Ganglion  spirale,  759 
Gartner's  duct,  S5>5 
Gases, 

extraction  from  blood,  377 

in  blood,  ib. 

in  the  lungs,  376 

of  plasma  and  serum,  428 
Gastric  glands,  493 

innervation  of,  496 
Gastric  juice,  493 

acids  in,  494,  496 
test  for,  496 

action  on  bacteria,  510 

action  on  food,  498  (see  538) 

artificial,  493 

composition  of,  495 

pepsin  of,  493,  496 

secretion  of,  495,  496 
influence  of  nervous  svstem  on,  496,  497 
Gastrin,  507 

Gay-Lussac's  law  for  gases,  325 
Gehuchten,  von,  law  of  axipetal  conduction,  204 
Gelatin,  37,  411 

as  a  constituent  of  food,  477 
Generative  organs  of  the  female,  832 

of  the  male,  827 
Genital  cord,  888 

ducts,  886 

glands,  SSS 
Genito-urinary  apparatus,  development  of,  833  et 

seq. 
Gennari,  line  of,  670,  703,  727 
Genu  of  internal  capsule.  667 
Gerlach's  network,  622 
Germinal  area,  842 

cells,  872,  888 

epithelium,  832,  8S8 

ridge,  888 

spot,  20,  836 

vesicle,  20,  836 
Giant  cells,  55 
Gilbert's  experiments,  715 
Giraldes,  organ  of,  885 
Glands.    See  names  of  different. 
Glisson's  capsule,  514 
Globin,  409,  441 
Globular  processes,  859 
Globulins,  176,  406,  408,  410,  581 

distinctions  from  albumin,  406 
Glomeruli,  550 

activity  of,  557 

olfactory,  750 
Glosso-ktnsesthetic  area,  70S,  709 
Glosso-pharyngeal  nerve,  641,  656 

communications  of,  656 

functions,  ib. 

motor  filaments,  657 

a  nerve  of  common  sensation  and  of  taste,  ib. 


INDEX 


901 


Glottis,  Movbments  of. 

Qlottls,  movements  of,  770  771 
Gluco-proteins,  412 
Glucosamine,  412 
Glucose, 

In  liver,  524 

test  for,  890 
Gluteal  rellex,  082 
Glycerides,  397 
Glycerin  or  Glycerol,  39S 
Glycine,  401,  508 
Glycocholic  acid,  520 
Glycogen,  391,  396,  524,  525 

characters,  390 

destination  of,  525 

preparation,  ih. 

quantity  formed,  ih. 

source  of,  524 

variation  with  diet,  525 
Glycosuria,  526 

Glycuronic  acid  and  sugar,  527 
Glyoxylic  acid,  impurity  of,  407 
Gmelin's  test,  521 
Goblet  ceUs,  20,  732 
Golgi's  method,  517,  G22,  609,  704,  713 
Goll's  column,  623,  626,  629,  639, 644 
Goltz,  experiments  on  the  cerebrum,  72() 
Gotch,  experiments  on  nerves,  153, 171 
Gowers'  hemacytometer,  434,  435 

hsemoglobinometer,  449 
Gowers-IIaldaue  h;emoglobinometer,  420 
Graafian  follicles,  832,  839 

formation  and  development  of,  ib.  et  seq 

relation  of  ovum  to,  S33 

rupture  of,  changes  following,  884  et  seq. 
Gradient,  pressure,  281,  307 
Gramme-molecular  solutions,  322 
Grandry,  corpuscles  of,  735 
Granular  layers  of  retina,  7S5 
Grape-sugar.    See  Dextrose. 
Gravity,  intluence  of,  on  circulation,  270 
Grehant,  output  of  the  heart,  246 
Grey  matter  of  cerebellum,  191,  630,  660 

of  cerebrum,  197,  004 

of  crura  cerebri,  030 

of  medulla  oblongata,  631,  644,  645,  648 

of  pons  Varolii,  648 

of  spinal  cord,  191,  622 
Groove,  primitive,  842 
Grossmann,  on  the  course  of  the  inhibitory  fibres 

in  mammals,  250 
Growth  of  bone,  64 
Guanase,  574 
Guanine,  573 
Gubemacular  cord,  888 
Gudden,  von,  bundle  of,  651 
Gullet,  458.    See  (Esophagus. 
Gunsberg's  reagent,  496 
Gustatory  cells,  745 
Gyrus  fornicatus,  676 


H. 

Haemacytometers,  434,  435,  436 
Haemadromometer,  Volkmann's,  278 
Hamatachometer,  Cybulski's,  283 

Vierordt's,  ib. 
Haematin,  441 
Hsemato blasts,  332,  430 
Hiematogens  of  cells,  413 
Haematoidin,  443 
Haematoporphyrin,  442,  447 
Htftmatoscope,  Herrmann's,  445 
Haem-autograph,  292 
Haemin,  442 
Hsemochromogen,  442 


Haemoglobin,  76,  406,  429,  440  et  seq. 
analysis  of,  441 
compounds  of,  443 
crystalllsable,  400 
distribution,  440 
estimation  of,  449 
I)hotographic  spectrum  of,  440 
Hiemoglobinometers,  420,  449 
Hicmoglobinuria,  paroxysmal,  583 
Iltemolymph  glands,  333 
Htemolysins,  453 
Hair-cells,  721,  759 
Hair-follicles,  588 
Hairs,  588 

structure  of,  ib. 
Haldane's  apparatus  for  estimating  the  carbonic 
acid  and  aqueous  vapour  given   off  by  an 
animal,  875 
carbonic  oxide  method  of  estimating  oxygen 
tension  of  arterial  blood,  383 
Haldane  and  Priestley's  method  in  dealing  with 

respiration,  302 
Haldane's  measurement  of  air  breathed,  350 
Haldane's  modification  of  Gowers'  haemoglobino- 

meter,  449 
Hamburger's  experiments  with  Succus  entericus, 

508 
Hamulus,  757 

Hardy,  microscopic  structure  of  cells,  9 
Hare-lip,  cause  of,  850 
Hassall,  concentric  corpuscles  of,  334,  882 
Haversian  canals,  50 
Head,  development  of,  857 
Head  and  tail  folds,  845,  861 
Head's  study  of  nerve  regeneration,  741 
Hearing,  anatomy  of  organ  of,  752  et  seq. 
influence  of  external  ear  on,  759 

of  middle  ear,  ib. 
physiology  of,  759 
range  of,  702 
See  Sound,  Vibrations,  etc. 
Heart,  206  et  seq. 
action  of, 
accelerated,  249 
auricle,  864 
force  of,  244 
frequency,  ib. 
inhibited,  249,  252 
self-steering,  237 
auricles  of,  207,  231 
chambers,  207 

capacity  of,  210 
chordae  tendinese  of,  212 
columnae  cameae  of,  ib. 
conduction  in  the,  253 
course  of  blood  in,  213 
cycle,  231 
development,  804 
endocardiac  pressure,  240 
endocardium,  207,  211 
foetal,  862 
force,  244 
frog's,  229,  230 
instruments  for  studying,  256 
nerves  of,  250 
ganglia  of,  253 

gaseous  exchanges  during  inhibition,  252 
influence  of  drugs,  ib. 
of  pneumogastric  nerve,  247 
of  sympathetic  nerve,  249 
innervation,  247 
Intracardiac  nerves,  252 

pressure,  240 
Investing  sac,  206 
muscular  fibres  of,  86 
musculi  papillares,  212 


902 


INDEX 


Heart. 

Heart — continued 

nervous  system,  influence  on,  247 

output  of,  245 

pericardium,  206 

physiology,  231  et  seq. 

reflex  Inhibition,  251 

situation,  206 

size  and  weight,  210 

sounds  of,  234 
causes,  235 

structure  of,  210 

valves,  211 
auriculo-ventricular,  210 

function  of,  233 
semilunar,  212 

function  of,  234 
structure,  211 

ventricles,  their  action,  207,  210,  864 

work  of,  244,  245 
Heat,  animal.    See  Temperature, 
influence  of  nervous  system,  665 

of  various  circumstances  on,  014  et  seq. 
losses  by  radiation,  etc.,  611 
regulation  of,  615 
variations  of,  609 
Heat  areas,  740 
Heat  coagulation,  405 
Heat-rigor  of  muscle,  157 

of  nerve,  178 
Heat-value  of  food,  610 
Heidenhain's  researches,  556 
Held,  experiments  on  myelination,  706 
Helicine  arteries,  830 
Helicotrema,  757 
Heller's  nitric-acid  test,  581 
Helmholtz's  induction  coil.  111 

myograph,  112 

phakoscope,  793,  794 

resonance  theory,  763 
Helweg's  bundle,  629 
Hemianopsia,  703,  819 
Hemiplegia,  660,  697 
Hemisection  of  spinal  cord,  631 
Hemispheres,  cerebral.    See  Cerebrum. 
Henla,  sheath  of,  94 

tubule  of,  546 
Henry-Dalton  law  for  gases,  325 
Hensen's  line  or  disc,  82 
Hepatic  artery,  513,  516 
Hepatic  cells,  514 

colic,  523 

duct,  513,  516 

glycogen,  597 

veins,  513,  516 
Herbst,  corpuscles  of,  733 
Hering's  theory  of  colour,  810 
Hermaphroditism.  890 
Herpes,  825 

Herrmann's  hwmatoscope,  445 
Hetero-albumose,  499 
Heterotype  mitosis,  841 
Hexatomic  alcohols,  392 
Hexone  bases,  402 
Hexoses,  392 

Hiccough,  mechanism  of,  365 
Hill  (Croft)  on  inverting  ferments,  418 
HiU  (Leonard)  on  the  circulation  of  Kood  in  the 
brain,  312  et  seq. 

on  the  influence  of  gravity  on  the  circulation, 
277 

on  alterations  in  atmospheric  pressure,  373 
Hind-gut,  845 

Hippocampal  convolution,  676 
Hippocampus  major,  676,  876 
Hippuric  acid,  574 
Histidine,  402 


Intercostal  Muscles. 

Histone,  409 
Iloloblastic  ova,  839 
Homotype  mitosis,  841 
Hopkins'  test  for  lactic  acid,  496 

for  uric  acid,  573 
Hormone,  506 
Horopter,  818,  819 

Hurst,  "  sound-picture"  theories  of.  703 
Hurthle's  manometer,  242,  273,  310 

differential  manometer,  243 
Hyaline  cartilage,  50 

corpuscle,  433 
Hyaloplasm,  9 
Hydrobilirubln,  521 
Hydro-kinetic  force,  281 

-static  force,  281 
Hydrolysis,  400 
Hyo-mandibular  cleft,  879 
Ilypermetropia,  797 
Hyperpnoea,  371 
Hypertonic  solutions,  326 
Hypoblast,  21,  842,  847 

organs  formed  from,  847 
Hypogastric  artery,  8^4 
Hypoglossal  nerve",  641 

distribution,  658 

origin,  ib. 
Hypo.spadias,  890 
Hypotonic  solutions,  326 
Hypoxanthine,  335,  573 

presence  in  the  spleen,  332 
Hysteria,  774 

I. 

Idiosorae,  830 

Ileo-csecal  valve,  463,  467,  468,  469 

Ileum,  463,  467 

Iliac  artery,  804 

Image,  formation  on  retina,  792 

Immunity,  451  et  si,/. 

Impregnation  of  ovum,  841 

Inanition  or  starvation,  603,  607 

Incus,  753,  754 

development  of,  801 
Indican,  576 
Indigo,  ib. 
Induction  coil,  109  et  seq. 

current,  109 
Infantile  paralysis,  737 
Infundibulum,'349 
Inhibition,  vagus,  247,  252 
Inhibitory  centre  for  heart,  effect  of  venous  blood 

on,  373 
Inhibitory  influence  of  pneumogastric  nerve,  247 
Inhibitory'  nerves,  102 
Inoculation,  curative,  451 

protective,  ib. 
Inogen, 155 
Inorganic  compounds  in  body,  390 

salts  in  protoplasm,  10 
Inosite,  397 
Insalivation,  535 
Inspiration,  851 

elastic  resistance  overcome  by,  352 

expansion  of  chest  In,  ib. 

extraordinary,  ib. 

force  employed  in,  ib. 

mechanism  of,  351  et  seq. 
Instruments  for  demonstrating  muscular  action, 

107  ct  seq. 
Intercellular  material,  5,  36 

passage,  349 
Intercentral  nerves,  103 
Intercostal  muscles,  action  in  tn3piration,352  et  seq. 

action  in  expiration,  353 


INDEX 


90J 


lNTERCaOS3IMO    PlBRK3   OF   SlIVRPEV. 

lutercrosslng  fibres  of  Sharpey,  58,  59 
Intermediary  nerve-cells,  203 
Iiiternu'iliate  areas,  709 
Intermittent  i)ul3e,  28S 
Internal  capsule,  Oi'iO 

tmi)ortance  of,  000 

respiration,  374 
Internal  secretion  theory  of  the  ductless  glands 

3'JS,  3'.'9 
Internal  sphincter  muscle,  409 
Interstitial  cells,  830 
Intestinal  juice,  503  ct  scq. 
Intestinal  oncometer,  543 
Intestines,  403 

action  of  drugs,  543 

digestion  In,  502  ct  seq. 
duration  of,  543 

development,  880 

large,  408 
coats  of,  409 
glands,  409 
structure,  ih. 

movements,  541 

mucous  membrane  of,  469 

nervous  mechanism,  541,  544 

small,  403 
coats  of,  ib. 
glands,  400,  407 
structure,  407 
Intracardiac  nerves,  252 

pressure,  240 
Intraventricular  nucleus,  605 
Inversion,  394,  507 
Inversive  ferments,  417 
Invertln,  507 
Involuntary  muscles,  78  {see  158  et  seq.) 

structure  of,  78 
lodo-thyrin,  337 
Iris,  778,  781,  788 

angle  of,  782 

development  of,  878 

functions,  799 

retlex  actions,  801 
Irradiation,  799 
IiTitabllity  of  tissues,  99 
Island  of  Heil,  665,  669,  675,  676 
Islands  of  Calleja,  053 
Islets  of  Langerhans,  502,  512 
Iso-cholesterln,  522 
Iso-maltose,  395 
Isometric  contraction,  132 
Isotonic  contraction,  ib. 

solutions,  320 

J. 

Jacksonian  epilepsy,  697 
Jacobsen's  nerve,  656 
Jaundice,  523 
Jecorin,  339 
Jejimum,  403 
Jelly  of  Wharton,  40 
Jelly-like  connective  tissue,  48 
Jugular  ganglia,  057 
Juice,  gastric,  493 
pancreatic,  583 

K. 

Kaiser's  views  on  muscular  contraction,  132 
Karyokinesis,  16  et  seq. 

phases  of,  20 
Katabollc  nerve  groups,  301 
Katabollc  phenomena,  594 
Katelectrotonus,  183 
Rations ,  321 


Lateral  Sclerosis. 

Kennedy,  experiment  on  nerve  crossing,  174 

Kephalin,  176 

Keratin,  33,  411,  586,592 

Ketone,  391 

Ketoses,  392 

Key,  Du  I3ois  Reymond's,  108 

Kidney  oncometer,  the,  554 

Kidneys,  545 

blood-vessels  of,  how  distributed,  548 

calyces,  546 

capillaries  of,  550 

development  of,  885 

diseases  of,  effect  on  the  skin,  593 

extirpation  of,  500 

function,  5')3.    See  Urine. 

hilus  of,  545 

Malpighlan  corpuscles  of ,  546,  553 

nerves,  553 

pelvis  of,  546 

structure,  545 

tubules  of,  546  et  seq. 

weight,  545 

work  done  by,  559 
Kinsesthetic  area,  695,  704 

sense,  742 
Kinetoplasm,  201 

Kjeldahl's  method  of  estimating  urea,  500 
Klein  on  the  stages  of  karyokinesis,  17 
Knee-jerk,  683,  085 
Konig's  apparatus  for  obtaining  flame-pictures  of 

musical  notes,  778 
Kossel  on  protamines,  409 
Krause's  membrane,  82-87 
Kronecker's  perfusion  cannula,  257 
Kiihne's  gracilis  experiment,  173  (see  302) 

muscle  plasma  experiment,  156 
Kymograph,  Pick's  spring,  272,  373 

Ludwig's,  270 

tracings,  272,  274 
Kymoscope,  Anderson  Stuart's,  268 


Labia  externa  and  interna,  development  of,  890 

Labyrinth  of  the  ear.    Hee  Ear. 

Lacrimal  gland,  776 

Lact-albumtn,  473 

Lacteals,  223,  465,  466,  532 

Lactic  aciil,  tests  for,  496 

fermentation,  395 
Lactiferous  ducts,  475 
Lactose,  391,  394,  474,  582 
Lamina  crlbrosa,  783 

spiralis,  750,  757 

supra-choroldea,  780 
Lamina  fusca,  779 
Lamina  of  Bowman,  779 
Langerhans,  islets  of,  502,  512 
Langley's    experiment    on    vagus    and    cervical 
sympathetic  nerve,  174, 175  (see  732) 

ganglion,  487 

nicotine  method,  301,  489 
Lanoline,  522 

Large  intestine.    See  Intestines. 
Laryngoscope,  768 
Larynx,  anatomy  of,  704 

cartilages  of,  ib. 

mucous  membrane,  766 

muscles  of,  766  et  seq. 

nerves  of,  768 

rudiment,  882 

vocal  cords,  764 
movements  of,  770 
Lateral  nasal  process,  859 
Lateral  sclerosis,  682 


904 


INDEX 


IjATKRAL,  Ventricle. 

Lateral  ventricle,  664 

Lateritious  deposit,  572 

Lawes'  and  Gilberts'  experiments,  599 

Lecithin,  9,  92,  176,  399 

Lee's  experiments,  722 

Lens,  crystalline,  781,  782 

Lenticular  nucleus,  665 

Le  Page's  investigations  into  pancreatic  secre. 

tion,  505 
Lepine's  theory  of  the  ferment  of  the  pancreatic 

internal  secretion,  527 
Leucine,  335,  401,  511,  508 
Leucocytes.    See  Blood-corpuscles  (white). 
Levator  palpebral  superioris,  770 
LcTOlose,  392,  394 
Lems,  on  h»moIymph  glands,  333 
Lleberktihn's  glands,  4(j6 

jelly,  414 
Liebermann's  reaction,  522 
Ligamentum  pectinatum  iridis,  782 

arteriosum,  863 
Limbic  lobe,  676 
Limbs,  development  of,  857 
Line  of  Baillarger,  669 

of  Gennari,  670,  703 
Lipase,  699 

Lippmann'3  capillary  electrometer,  138 
Liquor  sanguinis,  or  plasma,  76,  419 
Lissauer,  tract  of,  626 
Liver,  513 

blood-vessels,  514 

capillaries,  516 

cells  of,  513 

cirrhosis  of,  567 

circulation  in,  516 

diastase,  525 

development  of,  867,  881 

extirpation  in  mammals,  526 

formation  of  urea  by,  518 

functions,  51S 

glycogenic  function  of,  524 

nerves  of,  528 

secretion  of.     See  Bile. 

structure,  514 

sugar  formed  by,  524,  525 

supply  of  blood  to,  513 
•'  Living  test-tube  "  experiment,  427 
Local  sign,  73S 

Localisation  of  tactile  sensations,  737 
Locomotor  ataxy,  673,  679,  685,  719 
Loewenthal's  tracts,  628 
Loewy's  aerotonometer,  381 
Loop  of  Henle,  546 
Lortet  on  the  carotid  flow,  285 
Loudness  of  voice,  772 
Ludwig's  kymograph,  270 

Stromuhr,  279 
Lugaro's  sleep  theory,  712 
Lunatic's  brain,  718 
Lungs,  347 

air-sacs  of,  349 

blood-supply,  350 

capillaries  of,  349 

changes  of  air  in,  374 

circulation  in,  350 

coverings  of,  347 

development  of,  SS2 

diffusion  of  gases  within,  376 

lobes  of,  348 

lobules  of,  ib. 

lymphatics,  350 

muscular  tissue  of,  348 

nerves,  351 

nutrition  of,  350 

position  of,  348 

structure,  347 


Medulla  Oblongata. 

Lymph,  221,  314 

composition  of,  314 

current  of,  317 

formation  of,  318 
Lymph  capillaries,  222 

origin  of,  223 

structure,  225 
Lymph-hearts,  structure  and  action  of,  317 

relation  to  spinal  cord,  318 
Lymphagogues,  319 
Lymphatic  glands,  223,  315,  462 

development,  8S2 
Lymphatic  vessels,  221 

of  arteries  and  veins,  218 

communication  with  blood-vessels,  221 

structure  of,  222 
Lymphocytes,  331,  433 
Lymphoid  or  retiform  tissue,   47.    See  Adenoid 

tissue. 
Lysine,  401 

M. 

Macallum's  reagent,  178 

MacMunn,  use  of  the  term  myo-haematin,  156 

Macrosmatic  animals,  750 

Macula,  721 

lutea,  703,  783,  784,  787 
Magnesium  phosphate,  54 
Male  organs  of  generation,  827,  828 

pronucleus,  841 

sexual  functions,  830 
Malleus,  753,  745,  861 

Malpighian  bodies  or  corpuscles  of  kidney,  546. 
See  Kidney. 

corpuscles  of  spleen,  331 
Malpigliian  layer,  585,  586 
Maltase,  418 
Maltose,  895,  491 
Mammal,  nerves  of,  251 
Mammalian  ovum,  84i'i 
Mammary  glands,  47"i 

evolution,  476 

involution,  ib. 

lactation,  ib. 

structure,  475 
Mandibular  arch,  859 
Mannite,  892 
Mannose,  892 
Manometer,  Hiirthle's,  242,  278 

Martin's,  872 
Marchi  reaction,  177 
Marey's  sphygmograph,  287 

tambour,  122,  239,  310 
Marginal  convolution,  676 
Marrow,  54 

Martin's  sphygmometer,  292,  293 
Mastication,  535 
Mastoid  cells,  752 
Maturation  of  the  ovum,  839 
Maxillary  process,  859 
Maximal  pulsation,  292 
May,  Page,  reaction  of  degeneration,  189 
Meat  as  food,  477 
Meatus  of  ear,  756 
Meckel's  cartilage,  861 

diverticulum,  8S0 
Meckel's  ganglion,  656 
Meconium,  584 
Mediastinum  testis,  828 
Medulla  oblongata,  190,  635,  638  ct  seq. 

columns  of,  639 

decussation  of  fibres,  644-646 

development,  875 

dorsal  aspect,  643 


INDEX 


905 


Medulla  Ohi.onqata. 

Mflilulla  oblongata — continued 

libres  of,  how  distributed,  639 

urey  matter  in,  081 

pjTamldB,  anterior,  638 
posterior,  039 

structure  of,  640 
Medullary  f;roove,  871 
Meibomian  follicles,  483,  770 
Meissner  and  Biittner's  experiments,  825 
Meissner's  corpuscles,  734 

plexus,  404 
Melanin  f;ranules,  814 
Jlembrana  eapsulo-puplllarls,  878 

cliorio-capUlaris,  780 

decidua,  847 

granulosa,  833 
development  Into  corpus  luteum,  834 

liyaloidoa,  788 

limitans  externa,  785,  787 
interna,  7S3 

propria  or  basement  membrane.    See  Basement- 
membrane. 

pupUlaris,  878 

tectoria,  750 
action  of,  762 

tympani,  752,  753,  700,  879 
Membrane,  vitelline,  836 
Membranes  of  the  brain  and  spinal  cord,  190 
Membranes,  mucous.    Sec  Mucous  membranes. 

semipermeable,  323 
Membranous  labyrinth,  755,  756,  879.    See  Ear. 
Mendel  and  Rockwood's  experiments,  531 
Meniere's  disease,  722 
Menstruation,  834 

coincident  with  discharge  of  ova,  834 

corpus  luteum  of,  834 
Mercurial  air-pumps,  384,  3S5 
Mercurial  kymograph,  209,  271 
Meroblastic  ova,  839 
Mesencephalon,  636,  875 
Mesentery,  dorsal,  846 
Mesial  nasal  process,  858 
Mesoblast,  21,  843 

organs  formed  from,  847 
Mesoblastic  somites,  844,  854,  857 
Mesoneplirie  tubules,  885 
Mesonephros,  885 

Metabolic  balance-sheets,  595  et'.seq. 
Metabolism,  7,  824 

general,  694  et  scq. 
Metanephric  tubules,  883  ct  seq, 
Metanephros,  886 
Meta-proteins,  414 
Meteucephalon,  036,  875 
Methsemoglobin,  447,  448 

photographic  spectrum  of,  ib. 
Mett's  tubes,  500 

Meyer,  "sound  picture"  theories  of,  763 
Meynert's  fountain  decussation,  650 
Micrococcus  ureae,  580 
Microcytes,  430 
Micro-organisms,  types  of,  416 
Microsmatic  animals,  750 
Micro-spectroscope,  445 
Micturition,  561 

centre,  561,090 
Mid-brain,  035,  875 

anterior  aspect,  638 

posterior  aspect,  639 

structure  of,  038  et  seq. 

tracts  of,  651 
Middle  ear.    See  Tympanum. 
Mid-gut,  846 
Milk,  as  food,  470,  472 

alcoholic  fermentation  of,  474 

chemical  composition,  473 


MuREXiDE  Test. 

Milk — eontinued 

coagulation  of,  ib. 

fats  of,  474 
chemical  composition,  ih. 

proteins  of,  473 

reaction  and  specific  gravity,  473 

salts  of,  476 

secretion  of,  472 

souring  of,  474  (sec  410) 

uterine,  850 
Milk-curdling  ferment,  505 
Milk-globules,  470 
Milk-sugar,  394,  474 

properties  of,  396 
Milk-teeth,  05  et  scq. 
MUlon's  reagent  and  test,  407 
Mitochondrial  sheath,  831 

Mitosis,  10,  840,  841  • 

Mitral  cells,  750 
Modiolus,  756 
Molars.    See  Teeth. 
Molecular  layers,  668 
Momentum,  204 

Monakow's  bundle,  029,  649,  051 
Monaster  stage  of  karyokinesls,  17 
Monatomic  alcohols,  392 
Monkey's  brain,  099 
Mono-amino-acids,  401 
Monoplegia,  697 
Monosaccharides,  392 
Monro-Kellie  doctrine,  311 
Moore  and  Rockwood's  experiments,  533 
Moore's  test  for  sugar,  393 
Morgagni,  sessile  hydatid  of,  890 
Momer  and  Sjoquist's  method  of  estimating  urea, 

566 
Morphological  development,  20 
Morula,  847 
Mosso's  ergograph,  150 

experiments  on  the  effects  of  fatigue,  151 
Motor  areas  of  cerebrum,  696,  699 

impulses,  transmission  in  cord,  680 

nerve-fibres,  91 
Motor  nerves,  161 
Motor  oculi  nerve,  640 

origin  of,  652 
Motorial  sense,  742 
Mott  and  Halliburton,  on  degenerated  nerve,  167, 

177 
Mountain  sickness,  373 
Mouth,  457 
Movements  of  protoplasm,  12,  100 

peristaltic,  of  intestines,  541 
of  involuntary  muscle,  158 
of  stomach,  539 
Mucic  acid,  394 

Mucigen  or  Mucinogen,  20,  33,  486 
Mucin,  20,  33,  412 
Mucoids,  48,  412 
Mucous  membrane,  464,  482 

digestive  tract,  ib. 

epithelium-cells  of,  482.    See  Epithelium. 

gastro-pulmonary  tract,  482 

genito-urinary  tract,  ib. 

gland-ceUs  of,  ib. 

of  intestines,  469 

respiratory  tract,  482 

of  stomach,  4G0 

of  uterus,  changes  in  pregnancy,  836 
MiUlerian  duct,  887,  889 
Miiller's  fibres,  783 

Midler's  law  of  specific  nerve  energy,  732 
Miiller's  muscle,  781 
Munk's  experiments,  533,  703 
Multipolar  nerve-cells,  194 
Muiexlde  test,  672 

O     1.    Z 


906 


INDEX 


Muscarine. 

Muscarine,  action  of,  on  the  heart,  250 
Muscle,  105 

blood-vessels  of,  86 

cardiac,  87 

changes  iu  form,  when  it  contracts,  107  et  seq. 

chemical  changes  in,  149 
composition  of,  154 

clot,  ib. 

columns,  81 

contractility,  99 

curves,  113,  116-118,  132 

development,  88 

dynamometer,  131 

elasticity,  125 

electrical  phenomena  of,  133  et  seq.,  186 

extensibility  of,  125  et  seq. 

fatigue,  effect  of,  117,  150 
•    curves,  117 

Hensen's  line,  82 

involimtary,  79  (see  158  et  seq.) 

irritability,  99 
evidence  of,  ib. 

nerves  of,  86 

plain,  87 

plasma,  154,  156 

proteins,  166 

red,  87 

response  to  stimuli,  102  et  seq.,  186 

rigor,  153,  160 

sarcolemma,  SO 

sensory  nerve-endings  in,  736 

serum,  154 

shape,  changes  in,  121 

skeletal,  79 

sound,  developed  in  contraction  of,  122 

spindle,  86,  684.    See  Neuro-muscular  spindle. 

stimuli,  102 

striated,  structure  of,  81  et  seq. 

tetanus,  121 
negative  variation  of,  140 

thermal  changes  in,  147 

tonus,  130,  160 

twitch,  116  (see  141) 

voluntary,  79  (see  158  et  seq.) 

wave,  118, 141 

work  of,  130 
Muscles,  reciprocal  action  of  antagonistic,  687 
Muscular  action,  conditions  of,  131 
Muscular  contraction,  106,  116 

effect  of  two  successive  stimuli,  119 
of  more  than  two  stimuli,  120 

voluntary  tetanus,  121 
Muscular  fibres, 

development,  88 

plain,  78 

transversely  striated,  ib. 
Muscular  force,  130 

irritability,  99 

tissue,  78  et  seq. 
composition  of,  155 
Muscularis  mucosa;,  345, 459, 460, 464,  466, 467, 469 
Musical  sounds,  772 
Mydriatics,  800 
Myelencephalon,  636,  875 
Myelination,  705 
Myelocytes,  439 
Myeloplaxes,  55 
Myelospongium,  872 
Myogen-fibrin,  156 
Myoglobulin,  156 
Myohsematin,  156 
Myograph,  107 

Helmholtz's,  112 

pendulum,  114 

spring,  ib. 

transmission,  122  (see  172) 


Nervks. 

Myopia,  or  short-sight,  796 
Myosin,  154,  156,  157 
Myosin-tibrin,  156 
Myosinogen,  155-157 
Myotics,  800 
Myxoedema,  336  (see  341) 


N. 

NaUs,  588 

Nasal  cavities  In  relation  to  smell,  748  et  seq. 

Nasmj'th's  membrane,  69,  74 

Near  puint,  795 

Neopallium,  677 

Nephric  tubules,  884 

Nerve-cells,  classification  of,  203 

structure  of,  192  et  seq. 
Nerve-centres,  190  et  seq.    See  Cerebellum,  Cere- 
brum,  etc. 

ano-sptnal,  544 

cOio-spinal,  690 

defaecation,  543 

deglutition,  537 

erection,  690 

micturition,  561 

parturition,  690 

respiratory,  359 

secretion  of  saliva,  487 

speech, 702 

vaso-motor,  297,  685 
Nerve-corpuscles,  192  et  seq. 

bipolar,  193 

unipolar,  ib. 
Nerve  epithelium,  730 
Nerve-tibres,  cardio-inhibltory,  247 

intercentral,  163 
Nerve-impulse,  velocity  of,  172 
Nerves,  90 

accelerator,  162 

action  of  stimuli  on,  102,  561 

afferent,  90,  162 

axis-cylinder  of,  92 

cells,  91,  192 

centrifugal,  161 

centripetal,  162 

cerebro-spinal,  191,  618 

changes  in,  during  activity,  171 

classification,  161 

conductivity  of,  181,  189 

cranial,  191,  640  et  seq.,  848 

development  of,  S72 

degeneration,  164,  200 
chemistry  of,  177 
reaction  of,  188 

direction  of  a  nerve  impulse,  173 

efferent,  90, 161 

electrical,  162 
stimulation  of,  186 

excitability  of,  172 

fibres,  91 
development  of,  96 

functions  of,  164 

funiculi  of,  94 

grey  matter,  91 

inhibitory,  162 

intracardiac,  252 

irritability  of,  99 

laws  of  conduction,  162  et  seq. 

medullary  sheath,  92 

meduUated,  91 

motor,  161 
termination  of,  95 

nodes  of  Ranvier,  92 

non-medullated,  91 

olfactory,  640,  749 


INDEX 


907 


Nkrvks. 

Nerves— CO  n<inwed 
physlolot;y  of,  1(51  ct  scq. 

pilo-niotor,  580 

plexuses  of,  DO 

rellex  actions,  103,  198 

secretory,  102 

section  of,  104,  487 

size  of,  94 

spinal.    Sec  Spinal  nerves. 

splanchnic,  stimulation  of,  300 

stimulation  of  cut,  104,  300 

structure,  91 

gympatliotic,  influence  on  heart,  249 

taste,  74;) 

terminations  of, 
m  corpuscles  of  Golgi,  730 
in  corpuscles  of  Grandry,  735 
in  corpuscles  of  llerbst,  733 
in  enil-bulbs,  734 
in  motorial  eml-plates,  95 
in  networks  or  plexuses,  737 
in  Pacinian  corpuscles,  733 
in  touch-corpuscles,  734 

trophic,  102,  S24 
Nervous  circles,  073,  085 
Nervous  system, 

cerebro-spinal,  191,  018  et  seq. 

development,  811  et  seq. 

electrical  variation  in  central,  711 

influence  on  the  heart,  370 

sympathetic,  249 

vaso-motor,  297  et  seq. 
Nervous  tissues,  chemistry  of,  175 

potassium  salts  in,  178 
Neural  crest,  873 
Neurenteric  canal,  843 
Neuroblasts,  872 
Neurot;lia,  191,  021 
Neurokeratin,  92,  192,  411 
Neuro-muscular  spindles,  80,  730 
Neutral  sulphur,  570 
Nicotine,  action  of,  301,  340,  489 
Nissl's  granules,  195  ct  seq.,  714 

signilicance  of,  200 
Nitric  oxide  haemoglobin,  448 
Nitrogen  in  the  blood,  377 

eliminated  in  the  form  of  urea,  470 
Nodal  point,  789 
Nodes  of  Ranvier,  92 
Normoblasts,  439 
Nose.    Hee  Smell. 

development  of,  879 
Notochord,  840,  857,  S()0 
Nuclear  layers,  785 

sap  or  matrix,  10 
Nuclease,  574 
Nucleic  acid,  412,  413 
Nuclein,  11,  412 
Nuclei  pontis,  047 
Nucleoli,  10 

Nucleo-proteins,  9,  412,  413 
Nucleus  of  animal  cell,  5,  6,  10  et  seq. 

chemical  composition,  11 

division,  10 

staining  of,  11 

structure,  ib. 
Nucleus  ambiguus,  047,  057 
Nucleus  cuneatus,  044,  047,  072 

gracilis,  ih. 
Nucleus  of  Bechterew,  055 

of  Deiters,  055 
Nyctalopia,  814 
Nymph:v,  890 
Nystagmus,  814 


o. 

Oblique  vein  of  Marshall,  805 
Occipital  convolutions,  070 
Occipital  lube,  (;75 
Odontoblasts,  08,  70,  72,  73 
Odontogon,  73 
Odours,  751.    See  Smell. 
(JOsophagus,  development,  879 

structure  of,  458 
Oleaginous  principles,  397 
Oleic  acid,  398 
Olein,  44,  397 
Olfactory  bulb,  740,  879 

cells,  748 

depression,  859 

glomeruli,  750 

nerves,  040,  750 

tract,  740 

"  roots  "  of,  ill. 
Olivary  body,  038,  040 
Oliver's  hasmacytometer,  430 

his  method  of  estimating  hn?moglobin,  450 
Omphalo-mesenteric  veins,  850,  802,  805,  807 
Oncograph,  Roy's,  309 
Oncometer,  309,  554 

Intestinal,  543 

Roy's,  309,  333 
Oocytes,  832,  835,  830,  839,  840 
Oogonia,  830,  839 
Ophthalmoscope,  804  et  seq. 
Opsonins,  455 
Optic  disc,  783 
Optic  nerve,  040,  783 

decussation  of  fibres  in,  819 

development  of,  877 

fibres,  784 

nervous  paths  in,  819 
Optic  thalamus,  005 

vesicle,  primary,  870 
Optical  angle,  791 

apparatus  of  eye,  789 

axis,  791 
defects  in,  790 
Optogram,  813 

Ora  sen-ata  of  retina,  782,  783,  787 
Orang's  brain,  074 
Orbicularis  muscle,  770 
Orbital  sulcus,  077 
Orbito-sphenoids,  800 
Organ  of  Corti,  054,  055 

of  Giraldi!;3,  885 
Organic  compounds  in  body,  390  et  seq. 
Organised  ferments,  415,  410 
Ornithine,  401,  508 
Osazone,  305 
Osmosis,  322 

distinguished  from  diffusion,  400 
Osmotic  pressure,  method  of  estimating,  321,  323- 
327 

calculation  of,  325 

determination  of,  ib, 

of  proteins,  320 

phenomena,  321  et  seq. 

physiological  applications,  320 
Os  orbiculare,  754 
Osseous  labyrinth,  755.    See  Bar. 
Ossicles  of  the  ear,  753 

action  of,  700 
Ossification,  stages  of,  59  et  seq. 
Osteoblasts,  59,  03 
Osteoclasts,  03 
Osteogen,  59 

Otic  vesicle,  primary,  878 
Otoliths,  721 
Ovary,  827,  832 


908 


INDEX 


Ov&Ty— continued 

development  of,  838,  888 

Qraalian  follicles  In,  832 
Oviduct,  or  Fallopian  tube,  827 
Ovo-mucold,  412 
Ovum,  20,  833,  838 

action  of  seminal  lluid  on,  839  et  seq. 

changes  in  ovary,  838 
previous  to  fecundation,  839 

cleaving  of  yolk,  842 

development,  838 

fertilised,  841,847 

formation  of,  835 

germinal  vesicle  and  spot  of,  836  et  seq. 

impregnation  of,  841 

maturation,  839 

segmentation,  842 

structure  of,  838 
in  mammals,  835 

subsequent  to  cleavage,  842  et  seq. 
Oxidases,  417,  574 
Oxygen  in  the  blood,  377,  390 
OxyhEemoglobin,  77,  440  et  seq.,  443 

spectrum  of,  446,  447  (sec  coloured  plate) 
Oxyntic  cells,  462,  493,  494 
Oxyntic  glands,  493 


Pacchionian  bodies,  618 
Pacinian  corpuscles,  733 
Pain,  730 

Pain  spots,  739,  740 
Palmitic  acid,  393 
Palmltin,  44,  397 
l^ancreas,  502 

adaptation  of,  507 

development  of,  881 

extirpation  of,  511 
diabetic  condition  produced  in  animals  by, 
512,  526 

functions  of,  512 

so-called  peripheral  reflex,  SBcretion  of,  505 

structure,  502 
Pancreatic  juice,  603 

action  on  fats,  504 

composition  and  action,  503 

ferments  in,  ib. 
Panoramic  vision,  727 
PapiUa;, 
.  of  the  kidney,  546 

of  skin,  distribution  of,  587 

of  tongue,  743 
Parachordal  cartilages,  860 
Paradoxical  contraction,  182 
Parallel  puzzle,  823 
Paralytic  secretion,  488 
Paramyosinogen,  156 
Parathyroids,  337 
Parietal  ceUs,  462,  404 
Parietal  lobe,  675 
Parietal  lobule,  676 
Parieto-occipital  fissure,  G77,  876 
Parotid  gland,  490 

alveoli  of,  487 
Parovarium,  885 
Pars  ciliaris  retinte,  788 
Parturition  centre,  690 
Par  vagum.    See  Pneumogastric  nerve. 
Pathological  urine,  581 
Patrick's  experiments,  715 
Pavy's   views  as  to   the  liver  being   a   sugar- 
forming  organ,  526 


Pawlow's  method  for  obtaining  pure  gastric  juice, 

495,  506,  507,  508 
his  observations  on  the  salivary  glands,  490 
Peduu('l(;s,  sujierior  cerpbellar,  662 
Pelvis  of  the  kidney,  546 
Pendulum  myograph,  114 
Penis,  830,  887,  890 

structure,  ib. 
Pepsin,  493,  494,  496 
Pepsinogen,  494 
Pepsin-hydrochloric  acid,  496 
Peptides,  405 
Peptogens,  498 
Peptones,  400,  414,  499 

characters  of,  498,  499 
Peptonuria,  581 
Perception,  729 
Perforated  spots,  066 
Perforating  fibres  of  Sharpey,  58 
Perfusion  cannula,  Kronecker's,  257 
Pericardium,  206 
Perichondrium  of  cartilage,  51 
Perichoroidal  space,  778 

Perilymph,  or  fluid  of  labyrinth  of  ear,  720,  755 
Perimeter,  806 
Perimysium,  79 
Perineurium,  94 
Periotic  capsule,  861 
Peripheral  resistance,  260 
Peristaltic  movements  of  intestines,  541,  542 
of  Involuntary  muscle,  158,  159  {see  537) 
of  stomach,  ri38 
Perivitelline  fluid,  841 
Permanent  teeth.    See  Teeth. 
Perspiration,  cutaneous,  590 
insensible  and  sensible,  591 
ordinary  constituents  of,  592 
Petrosal  ganglia,  657 
Pettenkofer's  reaction,  520 
Peyer's  patches,  466,  467,  469 
Pfluger's  law  of  contraction,  184, 189 

his  method  in  dealing  with  respiration,  363 
Phagocytes,  295,  434,  451 
Phakoscope,  Helmholtz's,  794 
Pharynx,  457 
action  in  swallowing,  ib. 
development,  879 
Phenyl-alanine,  402 
Phenyl  hydrazine  test,  395  (see  583) 
Pliloridzin-dia betes,  527 
Phosphates  in  urine,  577,  579 
Phospho-proteiiis,  411 
Photo-chromatic  interval,  814 
Photographic  spectra  of  haemoglobin,  oxyh.tmc- 

globin,  and  methaemoglobin,  447 
Photophobia,  814 
Phrenograpli,  355 
Physiological  methods,  3 
pit,  805 

rheoscope,  145, 159 
zero,  747 
Pia  mater,  618 
Picric  acid  test,  582 
Pigment  cells  of  retina,  100,  786 

movement  of,  814 
Pilo-motor  nerves,  5S9 
Pineal  gland,  341 
Pinna,  752,  87'.t 
Piotrowski's  reaction,  407 
Piperidine,  action  of,  340 
Pitch  of  voice,  759,  772 
Pitot's  tube,  283 
Pituitary  body,  341 
development,  854 
effects  of  removal,  341 
Placenta,  maternal,  850 


INDEX 


909 


Placbnta. 

Flacenta— continued 

foeUl,  850 
Plantar  ri'tlfx,  682 
Plasma  of  blood,  76,  419,  426 

gases  or,  428 
Plelhysmograph,  307 

Sch.ifer's,  258 
Pleura,  347 
Plexus,  terminal,  737 

of  Auerbach,  97,  404 
Pllinmer,  experiments  by,  507 
Fneumogastric  nerve,  641,  667 

distribution  of,  657 

functions,  641,  657 

Influence  on 
deglutition,  537 
gastric  digestion,  540 

secretion,  497 
heart,  247 
lungs  (trophic),  825 
muscles  of  stomach,  540 
pancreatic  secretion,  505 
respiration,  361 
vomiting,  541 

mixed  function  of,  657 

origin,  ib. 
Poggendorf's  rheochord,  ISO 
Pohl's  commutator.  179 
Polar  globules,  840,  841 
Polarimeter,  415 
Poly morpho-nncl ear  cells,  432 
Polymorphic  laver,  669 
Polypeptides,  400,  405,  414 
Polysaccharides,  393 
Pons  Varolii,  635,  637 

grey  matter  iii,  636 
Popielslii's  investigations  into  pancreatic  secre- 
tion, 505 
Portal  canals,  514 

circulation,  214 

vein,  513,  514.    See  Liver. 
Porus  opticus,  783 
Postero-lateral  column,  630 
Post-ganglionic  fibres,  301 
Potassium  salts,  in  nervous  tissues,  178 
Precipitin,  455 

Precuneus  or  quadrilateral  lobule,  677 
Preganglionic  fibres,  301 
Pregnancy, 

corpus  luteum  of,  834 
Prepyramidal  tract,  629 
Presbyopia,  79'J 
Presphenoid,  860 
Pressor  nerves,  303 
Pressure  gradient,  281,  367 
Pressure  head,  282 
Pressure-measurers,  264 
Primary  areas,  707 
Primary  responses  of  eye,  814 
Primitive  groove,  843 

germ  cells,  832 

jugular  veins,  865 

mouth  cavity,  SoS 

nerve-sheath,  or  Schwann's  sheath,  92 

streak,  843 
Processus  gracilis,  753 

vaginalis,  SSS 
Projection  fibres,  670 
Pronephric  tubules  and  ducts,  883,  SS4 
Pronephros,  SS5 
Pronucleus,  female,  840,  841 

male,  841 
Propeptone,  499 
Prosecretin,  500 
Prosencephalon,  636 
Prostate  gland,  552 


Rathke's  Pourii. 

Protamines,  409 
Protective  inoculation,  451 
Protein-hydrolysis,  414 
Protein  metabolism,  7,  399,  602 
Proteins,  7,  399 

absorption  of,  530 

action  on  polarised  light,  407 

of  blood,  428 

classification,  408 

cleavage  products,  399 

coagulated,  408 

colloidal  solution,  405 

colour  reactions,  407 

composition,  399,  400 

conjugated,  411 

crystallisation,  406 

ferment  coagulation,  408 

heat  coagulation,  405,  408 

indifl'usibility  of,  400,  406 

osmotic  pressure  of,  326 

precipitants  of,  407,  408 

simple,  399 

solubilities,  400,  405 
Proteolytic  ferments,  417 
Proteoses,  400,  414,  499 

characters  of,  499 
Prothrombin,  424 
Proto-albumose,  499 
Protones,  409 

Protopathic  sensations,  741 
Protoplasm,  5,  6,  8 

chemical  structure,  9 

irritability,  15 

movements,  12  et  scq.,  100 
Proto-vertebrffi,  S44,  807 
Protrusion  of  eyeball,  815 
Pseudopodia,  13,  15 
Pseudoscope,  822 
Pseudo-stomata,  219 
Ptosis,  810 
Ptyalin,  480,  491 
Ptyalinogen,  487 
Pulmonary  artery,  863 
Pulsation,  maximal,  292 
Pulse,  anacrotic,  290 

arterial,  287  et  seq. 

dicrotic,  291 

velocity,  281 

venous,  294,  290 
Purine  bases,  413,  573 
Purkinje's  cells,  197,  660 

fibres,  89 

figures,  802 
Pyloric  glands,  462,  493 

orifice,  539 
Pyramidal  tracts,  627,  651,  670  et  seq. 
Pyramids,  layer  of,  009 
Pyramids  of  medulla  oblongata,  638 

of  kidney.    See  Kidney. 
Pj-rimidine  bases,  403 
Pyrrolodine  derivatives,  403 
Pzibram,  Hans,  theory  of  classification  by  muscle 
proteids,  157 

Q. 


Quinquand,  output  of  the  heart,  246 


R. 


Racemose  glands,  484 
Kanke's  diet.  Oil 
Rathke's  pouch,  858 


910 


INDEX 


Raynaud's  Disease. 

Raynaud's  disease,  311 
Reaction  time  in  man,  689 
Rectum,  the,  468,  879 
Red  nucleus,  649 
Reduced  eye,  790 
Reflex  arc,  682 

actions,  678  et  seq. 

inhibition  of,  6S1,  687 

in  frog,  680 

in  man,  082 
superficial,  ib. 
tendon,  683 

of  dog,  687 

of  nerves,  163,  198 

of  spinal  cord,  680  ct  seq. 

"scratch,"  687,  6S8 

time,  6S2 
Reflex  secretion,  490 
Reflexes, 

cumulation  of,  681 

inhibition  of,  ib. 

spreading  of,  to. 

uterine,  691 
Refraction,  laws  of,  789 
Refractive  media  of  eye,  ib. 
Reil,  island  of,  005,  669,  675,  076 
Reissner's  membrane,  758 
Remak,  fibres  of,  95 

ganglion  of,  253 
Renal  circulation,  214 

epithelium,  activity  of,  555 

oncometer,  554 
Rennet,  473 

Reproductive  organs,  827  et  seq. 
Requisites  of  diet,  595 
Reserve  air,  357 
Residual  air,  ib. 
Resistance,  peripheral,  260 
Respiration,  343 

abdominal  type,  353 

alteration  in  atmospheric  pressure,  373 

breathing  or  tidal  air,  356 

chemical  cause  of,  362 

chemistry  of,  374 

effect  on  circulation,  366 

gases  in  relation  to,  373,  377,  388 

influence  of  nervous  system,  369 

mechanism  of,  351  et  seq. 

movements,  353 

nervous  mechanism  of,  359 
of  vocal  cords  in,  770 

quantity  of  air  changed,  356 

tissue,  384,  387,  388 
Respirations,  number  of,  in  healthy  person,  357 
Respiratory  acts,  special,  364 

apparatus,  343 
development  of,  882 

capacity  of  chest,  357 

movements  of  glottis,  350 
methods  of  recording,  353 

muscles,  351  et  seq. 

muscular  force  of,  358 

nerve-centre,  359 

rate,  358 
relation  to  pulse-rate,  ib. 
size  of  animal,  ib. 

relation  to  will,  360  et  seq. 

rhythm,  352,  368 

sounds,  355 
Restiform  bodies,  647,  652  et  seq. 
Rete  testis,  830 
Reticulum,  9 
Retiform  tissue,  46 
Retina,  777,  782 

blind  spot,  802,  814 

blood-vessels,  788 


Salivarv  Glands. 

Retina — continued 

changes  in,  during  activity,  813 

duration  of  impression  on,   803 
of  after-sensations,  811,  812 

electrical  variations  in,  815 

excitation  of,  802 

focal  distance  of,  792 

fovea  centralis,  783,  805 

functions  of,  801 

identical  points  of,  818 

image  on,  how  formed  distinctly,  791 

layers,  783 

ora  serrata,  ib. 

pigment-cells,  100,  7S6 
movement  of,  814 

pigments  of,  814 

in  relation  to  single  vision,  816 

structure  of,  782,  783 

visual  purple,  785,  813,  814 
Retinitis  pigmentosa,  814 
Retraction  of  eyeball,  815 
Retractor  lentis  muscle,  796 
Reymond,  Du  Bois,  711 
Rheochord,  180 

Poggendorfs,  ib. 
Rheoscope,  physiological,  145,  159 
Rheoscopic  frog,  145 
Rheotome,  138 

Rhodopsin  or  visual  purple,  813 
Rhythmicality  of  movement,  101, 158 
Ricin,  453 
Rigor  mortis,  153,  154,  156 

affects  all  classes  of  muscles,  153,  154 

phenomena  and  causes  of,  154 

physical  basis  of,  149 
Rima  glottidis,  706 
Ringed  amino-acids,  402,  403 
Ritter's  tetanus,  186 
Rocci,  Riva,  his  sphygmometer,  292 
Rods  and  cones,  785,  814 
Rolandic  area,  609,  671,  695,  699,  701,  704 

injury  of,  690 
Rolando,  fissure  of,  674,  699,  876 
RoUett's  view  of  the  red  corpuscles,  429 
Rose's  test,  407 
Roy's  cardiometer,  246 

oncograph,  309 

oncometer,  309,  333 

tonometer,  257 
Rubner,  law  of  conservation  of  energy,  615 
Rumination,  535 
Rutherford's  "sound-picture"  theories,  763 


Saccharic  acid,  394 

Saccharoses,  393 

St  Martin,  Alexis,  case  of,  481,  530 

Saccule,  756 

Salathe,  effect  of  gravity  on  the  circulation,  27C 

Saliva,  485,  490 

action  of,  491 

composition,  491 

process  of  secretion,  ib. 

reflex  secretion,  490 

secretion  following  stimulation  of  nerves,  487 
et  seq. 
Salivary  glands,  485 

development  of,  881 

digestion,  492 

extirpation  of,  490 

influence  of  nervous  system,  487,  488 
effect  of  section  of,  487 


INDEX 


911 


Salivary  Glands. 

Salivary  g\tn:\(\s— continued 

structure,  4S5 
Salkowski's  reaction,  522 

Salniiue,  40'.' 

Sanderson's  cardioj^raph,  239 

Sanson's  images,  7'.'3 

Santorini's  liuct,  SS2 

Saponification,  S'J'J,  505 

Sarcolemma,  80 

Sarcomeres,  S3 

Sarcoplasni,  81 

Sarcosine,  571 

Sarcostylos,  81 

Scala  media,  757 

Scala  tynipani,  757,  762 

Scala  vestlbuli,  757,  7e2 

Scarpa,  ganglion  of,  655 

Scliafor,  heart  pletbysmograph,  258 

experiments  with  liver  cells,  517 

researches  on  the  structure  of  a  sarcostyle,  83 

views  regarding  the  function  of  the  Rolandic 
area,  704 
Scheiner's  experiment,  795 
Schematic  eye,  790 
Sclienk  on  muscular  contraction,  132 
Schiff's  clip  test,  704 
Schlemm,  canal  of,  782 
Schroder's  experiment,  508 
Schiitz'  law,  501 

Schwann,  white  substance  of,  170 
Scleratogenous  segment,  857 
Sclero-proteins,  410 
Sclerotic,  777,  778 

development  of,  878 
Scotoma,  814 
Scratch  reflex,  087,  088 
Scrotum,  890 
Sebaceous  glands,  589 
Sebum,  589,  590 
Secretin,  500 
Secreting  glands,  481  et  seq. 

classification  of,  483 
Secreting  membranes.    Si-e  Mucous    and   Serous 

membranes. 
Secretion,  internal,  328 

of  kidney,  500 
pancreas,  505 

reflex,  490 

suprarenal,  339 

thyroid,  330 
Secretory  nerves,  102 

of  pancreas,  600 

of  salivary  glands,  487 
efl'ect  of  section  of,  487 

of  stomach,  490 

of  sweat  glands,  591 
Segmentation  of  cells,  842* 

in  chick,  845 

nucleus,  S41 
ovum,  842 
Semen,  830 

spermatozoa,  830 
Semicircular  canals  of  ear,  755 

development  of,  879 

structure,  719  ct  seq. 
Semilunar  valves.    Sec  Heart  valves. 
Seminiferous  tubules,  828  et  seq. 
Semipermeable  membranes,  323 
Sensation,  728  it  seq. 

conception,  729 

homologous  stimuli,  731 

nerves  of,  102 

pain,  730 

perception,  729 

subjective,  731 

tactile,  718 


Sound. 

Sense,  organs  of,  development,  878,  879 
Sensori-motor  area,  095,  704 
Sensory  areas  in  cerebral  cortex,  090 
Sensory    imjires^ions,  conduction    of,   by   spinal 
cord,  078 

in  brain,  703  et  seq. 
Sensory  nerve-endings  in  muscle,  730  ;  in  skin,  733 
Serous  alveoli,  480 
Serous  membranes,  206 
Serum, 

albumin,  410,  428 

of  blood,  421,  420,428 

globulin,  410,  428 
Seventh  cerebral  nerve,  040,  653 
Sexual  organs  in  the  female,  832 

in  the  male,  827,  828 
Sherrington, 

observations  on  binocular  flicker,  820 

principal  of  the  common  path,  080 

reciprocal  action  of  antagonistic  muscles,  684 
Shingles,  825 
Side-chain  theory,  453 
Sighing,  mechanism  of,  305 
Sight.    See  Vision. 
Silver  nitrate  reaction  of  cementing  substance, 

34 
Simple  tubular  glands,  483 
Sinus  venosus,  804 
Sinuses  of  Valsalva,  213 
Sixth  cerebral  nerve,  040,  652 
Skeletal  muscles.  79 
Skin,  585 

absorption  by,  590 

dermis,  587 

diseases,  593 

epidermis  of,  585 

functions  of,  590 

nerve  endings  in,  733 

papillae  of,  587 

respiration,  590 

rete  mucosum  of,  585 

sebaceous  glands  of,  589 

secretions,  590 

sensory  nerves  of,  360 

sweat,  590,  592 

sweat-glands,  589 

varnishing  the,  593 
Sleep,  711 

SmaU  intestine,  403  et  siq.    See  Intestines. 
Smell,  sense  of,  743  (see  703) 

anatomy  of  regions,  748 

delicacy  of  sense  of,  751 

tests  for,  750 

varies  in  difi'erent  animals,  748 
Smith,  Lorrain,  carbonic  oxide  method   of  esti- 
mating oxygen  tension  of  arterial  blood,  383 
experiments  on  quantity  of  the  blood ,  420 
Smith's  perimeter.  Priestly,  800 
Sneezing,  mechanism  of,  304 
Snoring,  mechanism  of,  365 
Soap, 399 
Sobbing,  365 

Sodium  chloride  method,  413 
Solitary  glands.    See  Peyer's  patches. 
Solutions,  gramme-molecular,  322 
Somatic  mesoblast,  847 
Somatopleur,  844,  851 
Somites,  mesoblastic,  844,  854,  857 
Sonorous  vibrations,  how  communicated  in  ear, 
759  et  seq. 

in  air  and  in  water,  760.    See  Sound. 
Sorbite,  392 
Soret's  band,  447 
Sound, 

conduction  by  ear,  759 

heart,  234 


912 


INDEX 


Sound. 

Sound — continued 

production  of,  771 
Soup,  value  as  food,  480 
Spaces  of  Fontana,  782 
Speaking,  mechanism  of,  773 
Special  senses,  733  et  seq. 
Hpecitic  nerve  energy,  law  of,  732 
Spectroscope,  444  et  seq. 
Speech,  764  et  seq.,  773 

centre,  702 

defects  of,  774 
Spermatids,  829 
Spermatocysts,  829,  841 
Spermatogonia,  829 
Spermatozoa,  827,  830,  831 

form  and  structure  of,  831 
Spheno-palatine  ganglion,  050 
Spherical  aberration,  798 

correction  of,  ib. 
Sphincter  anl.    See  Defsecation. 

pupillae,  781 
Sphygmographs,  288,  289 

tracings,  289  et  seq. 
Sphygmometers,  292 
Spinal  accessory  nerve,  641,  657 

functions  of,  658 

origin,  ib. 
Spinal  cord,  620 

association  fibres  in,  630 

canal  of,  020 

centres  in,  690 

columns  of,  621 

commissures  of,  620 

conduction  of  impressions  by,  678  et  seq. 

course  of  fibres  in,  625 

development  of,  871 

fissures  and  furrows  of,  620 

functions  of,  678  et  seq. 
of  columns,  627 

grey  matter,  191,  622,  631 
cells  in,  622 

hemisection,  631,  678 

inj\iries  of,  678,  681 

membranes  of,  618 

morbid  irritability  of,  084 

nerves  of,  625 

reflex  action  of,  680  et  seq. 
inhibition  of,  681 
in  frog,  680 
in  man,  682 
superficial,  ib. 

regions  of,  631 

special  centres  in,  690 

structure  of,  620  et  seq.,  871 

tracts,  611,  627,  678 

transverse  section  of,  631 

white  matter,  191,  621 
tracts  in,  623 
Spinal  nerves,  168 

functions  of  roots  of,  168 

origin  of,  108  et  seq. 

physiology  of,  168 
Spinal  visceral  reflexes,  690 
Spiral  canal  of  ear,  756 
Spiral  ganglion,  759 
Spiral  ligament  of  ear,  757 
Spirem,  17 
Spirometer,  357 
Splanchnic  mesoblast,  846,  847 
Splanchnopleur,  844 
Spleen,  329 

apparatus  for  splenic  curves,  152 

development,  882 

functions,  331 

Influence  of  nervous  system  upon,  332 

Malpighian  corpuscles  of,  331 


Submaxillary  Glands. 

Spleen — continued 

pulp,  330 

structure  of,  329 

trabeculse  of,  ib. 
Spongioblasts,  784,  871 
Spongioplasm,  9 
Spongy  layer,  «49 
Spot,  germinal,  836 
Spring  myograph,  114 
Staircase  phenomenon,  117,  159,  255 
Stannius'  experiment,  255 
Stapedius  muscle,  754,  761 
Stapes,  753,  754,  761 

development  of,  861 
Starch,  396 

Starling,  on  swaying  or  pendulum  movement  of 
intestines,  543 

on  pancreatic  .secretion,  505,  506 

on  tendon  phenomena,  685 
Starvation,  603,  607 

effects  of,  604,  607 
Steapsin,  503 
Stearic  acid,  398 
Stearin,  44,  397 
Steatolytic  ferments,  417 
Stercobilin,  521 
Stereoscopic  vision,  727,  822 
Stethographs,  353,  354 
Stewart's 

experiments  on  the  circulation  of  the  blood, 
286 
on  muscle  proteins,  160 
on  the  output  of  the  heart,  246 
Steyrer  on  paramyosinogen,  157 
Stimulants  as  accessories  to  food,  480 
Stimulation  fatigue,  153 
Stimuli,  varieties  of,  15,  102 
Stokes'  reagent,  444 
Stolnikow,  measurement  of  the  heart's  output, 

245 
Stomach,  460 

blood-vessels,  463 

development,  879 

digestion  in,  509,  543 

glands,  461 

lymphatics,  463 

movetnents,  538 
influence  of  nervous  system  on,  540 

mucous  membrane,  460 

muscular  coat,  ib. 

nerves,  463 

peritoneal  coat,  460 

secretion  of.    See  Gastric  juice. 

shadow  photographs  of,  539 

submucous  coat,  460 

structure,  ib. 
Stomad<eum,  858 
Stomata,  25 
Stratum  granulosum,  586 

Intermedium  of  Haimover,  73 

lucidum,  586 
Stria'  acoustica;,  640,  655 
Striated  border,  465  {see  25-27) 
Striated  muscle,  81  et  seq.    See  Muscle. 
Striate  area,  72'r 
Stroma,  429 
Stromuhr,  Ludwig's,  279 

Tigerstedt's,  280,  281 
Structure  of  cells,  9  et  seq. 
Stuart's  kymoscope,  268 
Sturine,  409 

Stylo-hyoid  ligaments,  861 
Stylo-pharyngeus,  656 
Submaxillary  gland  of  dog,  480 
Submaxillary  and    sublingual   glands,   484,    487, 
881 


INDEX 


913 


Submaxillary  Ganolion. 

iSubmaxillary  g.ii\glion,  4S7 

Substantia  gelatinosa  of  Uolaiido,  622,  044,  646 

nit;ra,  050,  051 
Subthalamic  area,  666 
Succagojiues,  498 
Succus  ontericus,  507,  508,  509 

functions  of,  507 
Sucroses,  393 

Sugar.    See  Dextrose,  Lactoso,  etc. 
Sulci,  073-075 
Sulphates  in  urine,  575 
Summation-tones,  702 
Superlicial  reflexes,  082 

Superior  laryngeal  nerve,  etl'ects  of  stimulation 
of  cut,  300 

olivary  nucleus,  647 

parietal  convolution,  670 
Supra-renal  capsules,  338 

development,  890  (sec  340) 

function,  339 

structure,  338 
Swallowing,  536 

centre,  537 

fluids,  ib. 

nerves  engaged,  ib. 
Sweat-glands.    See  Skin. 
Swim-bladder  of  fishes,  380 
Sylvius,  fissure  of,  074,  87<i 
Sympathetic  secretion,  489 
Symphysis  of  jaw,  801 
Synovial  HuiH,  secretion  of,  482 

membranes,  ib. 
Syntonin,  414 
Syringomyelia,  079 

Systemic  circulation,  214.    See  Circulation. 
Systole  of  heart,  231 
Systolic  pressure,  292 


Tache  cerebrale,  310 
Tactile  end-organs,  733 

discs,  737 

senslbUlty,  704,  737 
variations  in,  789 
Talbot's  law,  804 
Tapetum  lucidum,  804 
Tarsus,  770 
Taste,  sense  of  (see  703) 

classification  of,  746 

connection  with  smell,  743 

delicacy  of,  747 

nerves  of,  745 
Taste-buds,  ib. 
Taurine,  520 
Taurocholic  acid,  ib. 
Taxis,  positive  and  negative,  10 
Teeth,  64 

development,  71 

eruption,  times  of,  66 

structure,  67  et  seq. 

temporary  and  permanent,  66  et  seq. 
Tegmental  nucleus,  649 
Tegmentum,  649,  650 
Telencephalon,  636,  875 
Temperature,  609 

average  of  body,  ib. 

changes  of,  effects,  009  et  seq. 

circumstances  modifying,  614 

efTect  on  muscular  contraction,  118 

of   cold-blooded   and    warm-blooded    animals, 
009 

in  disease,  610 


Trachea. 

Temperature — continued 
loss  of,  614,  615 
maintenance  of,  609 
of  Mammalia,  birds,  etc.,  ib. 
regulation  of,  615  cl  seq. 
sensation  of  variation  of,  739.    See  Heat. 
Temporo-occipital  corebellar  fibres,  650 
Teraporo-spheiioidal  lobe,  675 
Tendon-rellexes,  083,  684 
Tension,  arterial,  in  asphyxia,  383 
Tensor  palati  muscle,  700 
tympani  muscle,  754,  701 
action  of,  700 
Terminal  areas,  709,  710 
Testicle,  827,  828 

development,  888 

descent  of,  ib. 

structure,  827  et  seq. 
Tetanus,  121  (see  141) 

Hitter's,  180 

voluntary,  122,  159 
Thalamencephalon,  636 
Thalami  optici,  665 
Theine,  480 
Theobromine,  ib. 

Thoma-Zeiss  hsemacytometer,  435,  436 
Thoracic  duct,  77,  223 

innervation  of,  318 
Throat  deafness,  760 

ventricle,  700 
Thrombin,  423 
Thrombogen,  424 
Thrombokinase,  424 
Thymine,  403 
Thymus  gland,  334 

development,  882 

effects  of  removal,  335 

function,  ib. 

structure,  334 
Thyro-arytenoid  muscle,  767 
Thyro-epiglottidean  muscle,  707 
Thyroid  cartilage,  764 
Thyroid  gland,  335 

development,  882 

function,  336 

structure,  335 
Thyro-iodin,  337 

effect  of  intravenous   injection  of,  on    blood- 
pressure,  337,  341 
Tigerstedt,  measurement  of  the  heart's  output, 
245 

Stromuhr,  280,  281 
Timbre  of  voice,  759,  772 
Tissue-erepsin,  531,  574 
Tissue-respiration,  374,  384 
Tongue,  743 

action  in  deglutition,  536 

epithelium  of,  745 

muscles  of,  743 

papillae  of,  743 

parts  most  sensitive  to  taste,  745 

structure  of,  743 
Tonometer,  Boy's,  257 
TonsUs,  458 
Tonus,  130,  160,  684 
Tfipfer's  test,  496 
Touch,  733  et  seq. 

muscular  sense,  742 

sense  of  locality,  737 
of  pressure,  739 
of  temperature,  739 

tactile  end  organs,  733 
Touch-corpuscles,  734 
Toxin,  452 

Trabecule  cranii,  860 
Trachea,  343,  882 


914 


INDEX 


Tract  ok  Flechsio. 

Tract  of  Plechsig,  630 

of  Gowers,  630 

of  Lissauer,  626,  630 

of  Loewenthal,  628 
Tracts     in     the     spinal     cord,     623,    627,     678, 
679 

of  bulb,  pona,  and  mid-brain,  651  et  seq. 
Transfusion  of  blood,  818 
Transmission  myograph,  122  (see  172) 
Transverse  axis  of  eyeball,  816 
Trapezium,  the,  647 
Traube-IIering  curves,  303,  304,  555 
Triacetin,  398 
Tricuspid  valve,  211 
Trigeminal  nerve,  640,  653 

function,  653 

origin  of,  ib. 
Trochlear  nerve,  640,  652 

origin  of,  652 
Trommer's  test,  393 
Trophic  nerves,  162 

intluence  of,  824 
Tropoeolin  test,  496 
Ti-ypsin,  action  of,  504 
Trypsinogen,  502 
Tryptophane,  403 
Tschistovitch's  test,  455 
Tubercle  of  Rolando,  644 
Tubular  glands,  469 
Tubuli  seminiferi,  827,  828,  830 

uriniferi,  546  et  seq. 
Tubulo  •  racemose    or    tubulo  -  acinous    glands, 

484 
Tunica  albuginea  of  testicle,  828 

dartos,  88 

propria,  720 

vaginalis,  828,  888 

vasculosa,  780 
Turck's  column,  627 
Tympanum  or  middle  ear,  752 

development,  879 

membrane  of,  752,  753 

muscles  of,  754 

structure,  753 
Tyrosine,  403,  511 


u. 


UmbUical  arteries,  850,  862,  865 

cord,  848,  855 

vesicle,  848 
Umbilicus,  845 
Uncinate  convolution,  676 
Unicellular  organisms,  6 
Unilaminar  blastoderm,  842 
Unipolar  nerve-cells,  193 
Unorganised  ferments,  417 
Urtemia,  569 
Urate  of  sodium,  579 
Urates,  deposit  of,  579 
Urea,  564 

apparatus  for  estimating  quantity,  566 

chemical  composition  of,  5G4 

difficulty  of  tracing,  557 

formation  of,  by  liver,  514,  567 

isomeric  with  ammonium  cyanate,  564 

quantity,  567 
Ureters,  545,  550,  885 
Urethra,  545,  551,  879,  886 
Uric  acid,  571 

condition  in  which  it  exists  in  urine,  574 

deposit  of,  578 

forms  in  which  it  is  deposited,  571,  578 


Vagus  Escape. 

Uric  &cid— continued 

origin  of,  564,  573 

presence  in  tlie  spleen,  332 

proportionate  quantity  of,  573 

tests,  571 
Uricolytiu  ferment,  574 
Urina  potus,  504 
Urinary  apparatus,  545  et  seq. 
Urinary  bladder,  551 

development,  879,  886 

nerves,  551 

structure,  ih. 
Urinary  deposits,  578  et  seq. 
Urine,  563  et  seq. 

analysis  of,  564 

bile  in,  583 

blood  in,  ih. 

chemical  sediments  in,  580 

colour,  563 

composition,  564 

cystine  in,  579 

expulsion,  561 

flow  into  bladder,  561 

hippuric  acid  in,  574 

inorganic  constituents,  575 

mineral  salts  in,  575,  576 

mucus  in,  577 

pathological,  581 

phosphates  in,  577,  579 

physical  characters,  563 

pigments,  ib. 

proteins,  581 

pus  in,  584 

quantity,  563 
varies  with  blood-pressure,  554,  555 

reaction  of,  563 
in  different  animals,  564 
made  alkaline  by  diet,  ib. 

.saline  matter,  564,  569 

solids,  503 

specific  gravity  of,  564 
variations  of,  ib. 

sugar  in,  582  et  seq. 
tests  for  estimating,  582 

tests  for  inorganic  salts  of,  578 

urates,  579 

urea,  564 

uric  acid  in,  571 
UrobUin,  521,  563 
UrobUinogen,  563 
Urochrome,  563 
Uro-erythrin,  579 
Uterine  milk,  850 

reflexes,  691 
Uterus,  827,  836 

change  of  mucous  membrane  of,  836 

development  in  pregnancy,  ib. 

follicular  glands  of,  ib. 

round  ligament  of,  888 

structure,  836 
Uterus  masculinus,  887 
Utricle,  756 
Uvea,  781 


V. 


Vaccination,  451 

Vagina,  827 

Vagina,  development  of,  887 

Vago-sympathetic  of  frog,  248 

Vagus  escape,  249 

nerve.    See  Pneumogastric. 

pneumonia,  360,  825 


INDEX 


915 


Valsalva's  Expkriment. 

Valsalva's  experiment,  S70 

Valves  of  heart,  211.    Sec  Heart. 

Valvulie  coniiiventes,  404 

Vasa  aberraiitia,  885 

Vas  deferens,  82S.  830 

Vasa  etlerentia  of  testicle,  8'28,  830 

Vasa  vasorum,  216 

Vascular  system,  ilevelopment  of,  iOl 

in  asphyxia,  370 
Vaso-constrictor  nerves,  299 
Vaao-dilator  nerves,  300,  306,  488 
Vaao-motor  nerves, 

distribution  of,  298 

effect  of  section,  298  et  scq. 

experiments  on,  305 

inltuence  upon  blood-pressure,  303 

of  the  liver,  528 

stimulation  fatigue,  153 
Vaso-motor  nerve-centres,  297,  690 

nervous  system,  297  et  seq. 

reflex  action,  303 
Vegetables  as  food,  470,  479,  480 
Vegetable  cells,  5,  6 

protoplasmic  movement  in,  13,  14 
Veins,  216 

allantoic,  865 

azygos,  867 

cardinal,  865 

circulation  in,  295  et  seq, 
velocity  of,  285 

collateral  circulation  in,  217 

development,  865 

distribution,  216 

hepatic,  867 

iliac,  805,  867 

innominate,  866 

intercostal,  867 

jugular,  865,  866 

lumbar,  867 

omphalo-mesenteric,  850,  802,  865,  867 

pulmonary,  868 

pressure  in,  273 

rhythmical  action  in,  296 

structure  of,  217 

subclavian,  S66 

umbilical,  850,  865 

valves  of,  218  et  seq. 
Velocity  head,  282 

pulse,  281 
Velocity  of  blood  in  arteries,  278 
in  capillaries,  280 
In  veins,  ib. 

of  circulation,  ib. 

of  ferment  action,  500,  501,  504 

of  nervous  impulse,  172 
Vena  azygos,  S67 
Vena  cava,  S07,  868 
Venae  advehentes,  867 

revehentes,  S07 
VentUation,  389 
Ventral  cerebellar  tract,  630 
Ventral  hepato-pancreatic  diverticulum,  882 
Ventral  vessels,  862 
Ventricles  of  heart.    See  Heart. 
Ventricular  diastole,  232 

systole,  ib. 
Veratrine,  effect  of,    on    muscular    contraction, 

118 
Vermicular  movement  of  intestines,  541 
Vernon,  heat  rigor  experiment,  157 

on  tissue-erepsin,  531 

pancreatic  secretion,  507,  508 
Vertebrae,  development  of,  856 
Verwom,  Max,  strychnine  and  fatigue,  153 
Vesicle,  germmal,  20,  825 
Vesiculae  semlnales,  830 


Wallerian  Deokneration  Method. 

Vestibular  nerve,  040 

Vestibule  of  osseous  internal  ear,  755 

Vibrations,  conveyance  of,  to  auditory  nerve,  759 

(t  seq. 
Vierordt's  ha;matachometer,  283 
VUli  in  chorion,  function  of,  84S,  849,  854 

of  intestines,  405 
Vincent,  Swale,  muscle  jiroteins,  100 
Visceral  clefts  and  arches,  development  of,  858 
et  seq. 
connection  with  cranial  nerves,  801 
Visceral  mesoblast,  843 

pain,  741,  742 
Vision,  770 
angle  of,  791 
at  different  distances,  adaptation  of  eye  to,  792 

et  seq. 
correction  of  aberration,  798  et  seq. 

of  inversion  of  image,  820 
defects  of,  796  et  xcq. 
distinctness,  how  secured,  822  el  seq. 
duration  of  sensation  in,  803 
estimation  of  the  size  and  form  of  objects,  820- 

822 
focal  distance  of,  792 
impaired  by  lesion  of  fifth  nerve,  824 
range,  795 

relation  of  nerve-cells  and  fibres,  820 
single,  with  two  eyes,  816  et  seq. 
Visual  area,  703 
axis,  791,  816 
judgments,  820  et  seq. 
plane,  817 
purple,  785,  813,  814 
sensations,  808 
word-centre,  708 
Visuo-psychic  region,  703 
Visuo-sensory  cortex,  703 
Vital  action,  326 
Vitellin,  411 
Vitelline  duct,  880 
membrane,  20,  836 
spheres,  S36 
Vitello-intestinal  duct,  846 
Vitreous  humour,  778,  788 
Vocal  cords,  76-1,  769 
action  in  respiratory  actions,  770 
approximation    of,  effect   on   height    of  note, 

771 
vibrations  of,  cause  voice,  771,  772 
Voice,  764  et  seq.,  771 

range  of,  772 
Volt's  diet,  471,  603,  604 
Volition,  729 

Volkmann's  haemadromometer,  278 
Voluntary  muscle,  79  et  seq. 

nerves  of,  86 
Voluntary  tetanus,' 122, 159 
Vomer,  860 
Vomiting,  540 
action  of  stomach  in,  ib. 
centre,  541 
nerve  actions  in,  ib. 
voluntary  and  acquired,  ib. 
Vowels  and  consonants,  773,  774 


w. 


Waldeyer,  stages  of  karyoklnesis,  17  el  seq. 
Wallerian  degeneration  method,  164, 169, 623,  714, 
824,  820 


916 


I>."DEX 


Waller. 

Waller, 

fatigue  theory,  151-153 

on  the  electrical  currents  of  the  eyeball,  815 

"  sound-ijicture  "  tlieories  of,  7G3 

variation  in  nerv-e  action,  171 
Water-hammer  pulse,  288 
Wave  of  blood  causing  the  pulse,  ib. 

velocity  of,  ih. 
Weber-Fechner  law,  730 
Weber's  paradox,  129 
Weigert's  method,  705 

Wertheimer's  investigations  into  jjancreatic  secre- 
tion, 505 
Whey  protein,  473 

White  corpuscles.    See  Blood-corpuscles,  white ; 
and  Lymph-corpuscles. 

emigration  of,  295 
White  fibro-cartilage,  51 

fibrous  tissue,  41 

spot,  783 
Widal's  reaction,  454 
Wirsung's  duct,  8S2 
Wolffian  bodies,  865,  884  et  seq. 

duct,  863,  884 

ridge,  846 
Wooldridge's  method  of  preparing  tissue-fibrino- 

gen,  413 
Word-centres,  775 
Worms,  circulatory  system  in,  229 
Wright,  Hamilton,  sleep  theory,  713 
Wrisberg,  cartilages  of,  765 


ZVJIOLVSIS. 

X. 


Xanthine,  332,  335,  573 

presence  in  the  spleen,  332 
Xantho-proteic  reaction,  407 


Yawning,  mechanism  of,  365 

Yeast  plant,  cells  of,  in  process  of  budding,  410 

Yellow  elastic  fibre,  37,  43 

fibro-cartUage,  52 

spot  of  Sommering,  783,  805 
Yolk-sac,  845,  850,  851 
Yolk-spherules,  835 
Young-Helmholtz  theory,  809 


Zona  peUucida,  or  striata,  20,  835 

Zonule  of  Zinn,  788 

Zuntz,  output  of  the  heart,  246 

on  muscle  respiration,  388 
Zymogen,  424,  487,  494 
Zymolysis,  reversible,  596 


Pkinted  by  Oliver  and  Boyd,  Edinburgh. 


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